Soybean Rust work group
meeting held on Friday 25 May 2001 at 09h00, Potchefstroom
Welcome and purpose
The chairperson, Dr J Purchase extended a warm welcome to all present.
Dr Purchase presented a short summary with regard to the discovery and occurrence of soybean rust. He also mentioned that the disease is highly virulent and poses a great threat to the soybean industry. During the Soybean Rust Workshop held on 22 March 2001, the establishment of a task team was suggested and seconded. The broadened aim of the meeting is to develop a management strategy which will consist of short, medium and long term objectives, in order to ensure the competitiveness of the industry.
Matters identified as urgent, are as follows: i) identify research priorities, ii) coordinate research activities, iii) ensure that good science is practiced in the projects that emanate from the discussions, iv) ..... solid proposals and v) deliver on the objectives as stipulated/indicated in the proposals.
Even though constructive contributions will come forth from all the participants, the Chairperson indicated that should the meeting feel that only limited expertise is available, outside expertise may be coopted – function of the Task Team is not exclusive.
Attendance and apologies
Dr JL Purchase ARC-Grain Crops Institute Dr NW McLaren ARC-Grain Crops Institute Dr AJ Liebenberg ARC-Grain Crops Institute Dr MA Smit ARC-Grain Crops Institute Mr AJ de Lange ARC-Grain Crops Institute Mr N J Mbhamali ARC-Grain Crops Institute Mr KE Mokgothu ARC-Grain Crops Institute Mr NJ Vermaak Grain South Africa / Oil Seeds Advisory Committee Mr J Middel Grain South Africa Ms ED du Preez Dept. of Agriculture KwaZulu-Natal Mr N van Rij Dept. of Agriculture KwaZulu-Natal Dr J de Kock Protein Research Trust Prof ZA Pretorius Dept. of Plant Pathology UOFS Mr A Jarvie SANSOR Mr ID Lamprecht Dept. of Agriculture Mpumalanga Mr A de Klerk AVCASA Ms P Kruger Secretary
Dr AH McDonald ARC-Grain Crops Institute
Prof Pretorius mentioned that according to the symptoms of the disease, spore dimension and morphology, it looks like Phakopsora pachyrhizi. However, samples of various specimens, were sent to Dr Frederick from the USDA who has developed DNA markers for both the Phakopsora species – still awaiting a reply.
Dr Purchase enquired as to whether any other aspects, such as races, are being dealt with.
Prof Pretorius explained that they do molecular typing of isolates – he is not sure what it means in terms of pathogenicity, but explained that they like to classify items in terms of DNA sequences. The relevant parties will be notified in writing as to the results of the testing, as well as to confirm the correctness of the identification.
Dr De Kock enquired as to whether the soybean rust disease found in South Africa is homogeneous to the disease found in Zimbabwe. Prof Pretorius mentioned that samples from Clive Levy (Zimbabwe) have been received and that the results from the various tests will enable them to determine whether similarities exist.
Crop specialization (formis specialis)
Dr McLaren informed the meeting that according to existing literature, reports on crops other than soybean do exist. When looking at the survival of organisms and alternate hosts in the production areas of South Africa, we need to distinguish between soybean rust and the same species restricted to other hosts, and not necessarily on soybeans – in some way distinguishing between formis specialis or host specificity, i.e. for example you will find it on cowpeas in Nigeria but not on the adjacent soybean.
Prof Pretorius concurred that host specificity should definitely be looked at. We need to determine which hosts support this fungus as this could have a significance in determining survival and reoccurrence of the disease. This aspect falls within studies on "pathogen variation" and "survival".
Dr De Kock enquired firstly as to whether there is any connection between the rust on maize and the rust on soybeans in order to rule out any confusion that might arise amongst producers and, secondly, whether further work on markers is a necessity.
Prof Pretorius informed the meeting that the rust on maize and the rust on soybeans are completely unrelated.
Race(s), differentials, markers
Dr Purchase mentioned that according to the minutes of the Soybean Rust Workshop held on 22 March 2001 (attachment 1), Rex Tattersfield specifically mentioned that there is no set of differentials available.
Prof Pretorius stated that he is not sure about what is available and what not, but that according to Proceedings on Soybean Rust Workshop over the past ten years, you will find information on short term differential sets and race types. However, material is available and should be obtained as soon as possible.
Dr Purchase indicated that a critical element in research will be to establish whether we are working with one race or more than one.
Prof Pretorius mentioned that when breeding for resistance, it will be most efficient if you know what variation there is in the pathogen. Thus there is sense in determining races of the pathogen but he indicate that he was uncertain as to what differentials sets were available.
Dr Smit informed the meeting that four differentials have already been described in the Proceedings of the workshop held in 1998 when Dr Sundar visited South Africa and that four races were specifically noted.
Dr McLaren commented that if only four races exist, resistance would theoretically be easy, but from the literature, one gets the impression that almost as soon as resistance has been developed it is overcome. This would indicate that more than four races are involved.
Dr Pretorius mentioned that the races are only a proportion of the differentials used – making use of more differentials will result in more variation being identified. The idea is not to determine the exact number of races, but to ensure that when working with breeding material, the whole spectrum is covered. The principle is to look into the nature of pathogens in order to compile a base from which breeders can work.
Pathogen morphology (urediospores, teliospores, pycnia, aecia) and whether autoecious / dioecious
Dr McLaren commented that pycnia and aecia are unknown for this fungus. If one considers the rate at which resistance supposedly breaks down, this indicates that sexual recombination is taking place. The rate of change in the pathogen would not be as high if there was no sexual recombination.
Prof Pretorius indicated that to find an alternate host and thus the sexual structures of the fungus could be like looking for a needle in a hay stack since one has no idea on which hosts to start looking. The best place to start looking would be in the immediate vicinity of the disease and if one notes material there this would be worth further study. He indicated that too little is known about the mechanisms of variation and indicated that mechanisms such a somatic recombination ie pseudo-sexual stage could also be involved.
Dr McLaren indicated that he does regard such studies as a very high priority but feels that it is something that we need to be aware of.
Influence of weather conditions
Survival of propagules (frost)
Dr McLaren informed the meeting that the disease is very weather dependant – weather affects various components of the epidemic and one needs to note issues such as i) the survival of the propagules, ii) the effect of frost, iii) the effect of temperature, humidity, leaf wetness and iv) effect on sporulation. He also mentioned that the disease occurred on seedlings in a greenhouse, whilst Zimbabwe claim that the disease is host age related (physiological stage of the host) – it could be that in Zimbabwe weather conditions probably just happen to be ideal for rust development at that specific stage of the host. Environmental conditions are an important aspect that need to be looked at in order to determine the development and spread of the disease.
Dr Smit commented that USDA and AVRDC did an extensive study on environmental conditions (i.e. humidity, temperature, etc., the so-called "relative soybean life time"), and found that growth stages as well as the cultivar, have an influence on infection.
Prof Pretorius stated that he agrees with Dr Smit's comment and said that there is merit in analysing weather data, determining when in the season there is dew, when maximum and minimum temperatures are conducive for disease development and which areas and growth stages synchronize with these, etc.
Dr Purchase mentioned that many interactions exist, and the development of the disease remains very complex. It is important that the publication mentioned by Dr Smit and the effects of the environmental conditions, be used as a basis for the gathering of further information and for the determining of low, medium and high risk areas in South Africa, in order to assist the producers and the industry effectively.
Dr McLaren indicated that even though rapid germination of spores may occur, the development of disease may be slow, i.e. a slow rust cultivar – this is why the interactions are of greater importance than the components.
Mr De Lange enquired as to the spread of the disease – the disease starts at the bottom of the plant and works its way up the canopy, whereas with spread via the wind, the disease starts at the top and works its way downwards. This implies two different ways of spreading.
Dr Smit explained that the disease will start at the bottom due to the micro-climate being more favourable and the need for high disease pressure to move upwards. Due to the micro-climate, leaf wetness will occur for longer on the bottom leaves than on the top leaves. Favourable environmental conditions will cause the disease to develop faster. Unfavourable environmental conditions, such as too low or too high temperatures or drought stress, will cause the disease to develop slower.
Mr Middel suggested that production practices will also have to be investigated seeing that producers tend to have narrower rows in order to increase the plant density.
Dr Purchase mentioned that production practices were investigated by the Zimbabweans and it was found that, i) production practices had a limited influence and ii) no differences were detected in the development of the disease with different row widths.
Dr McLaren explained that when referring to environmental conditions, we are not only referring to the micro-climate but also to the broader environment.
Dr Smit quoted from the Epidemiology of Soybean Rust and Breeding for Host Resistance by Wang and Hartman (Attachment 2, p44): "Temperatures of < 15ºC and/or > 30ºC along with dry conditions retarded the development of rust, and prolonged temperatures above 27ºC inhibited the fungus even when leaf surface wetness was adequate". Even though information is available in the literature, a huge gap in terms of the description of risk and high risk areas still exists.
Prof Pretorius commented that the issue of temperature-humidity relationships and the entire modelling, epidemiology and risk area aspects are very important and require thorough research.
Disease spread (sporulation and wind)
Already discussed under item 3.2.1
Germination and disease development (temperature, humidity, leaf wetness)
Already discussed under item 3.2.1
Physiological age of host vs influence of weather condition
Already discussed under item 3.2.1
Overwintering / alternate hosts / survival
Hosts (species and distribution)
Dr McLaren explained that according to the literature, the organism is frost susceptible which means that theoretically it is not suppose to survive in many of our production areas. Due to the disease not having an overwintering phase or an alternative host, it is forced to survive on a living host, i.e. it has to move from soybeans onto an alternative host during the winter and then back to soybeans. The idea is to determine alternative hosts and their distribution. Theoretically this will be in the Lowveld or in the Natal coastal area. If we know the distribution of these hosts we can get an idea of where the disease is coming from and also how long it will take to reach certain critical production areas.
Dr Purchase referred to forest legumes that have been identified in Zimbabwe and these may initially be worth looking at. He also expressed concern about how long the spores can survive – research has showed that the spores can survive for five to seven days, while certain literature states longer than sixty days.
Dr McLaren also suggested that spore survival may be affected by debris or soil moisture and should spores survive for sixty days, as suggested in the literature, this period may give the pathogen a time frame until a new host is available.
Dr De Kock stated that it essential to determine whether frost or dry conditions do in fact kill spores since, if they remain in soil or debris, they could remain dormant until a new host and favourable conditions become available.
Mr Middel suggested that "frost" needs to be defined as the degrees of frost can vary. Thus temperatures associated with frost and spore survival need to be quantified.
Dr Smit explains that the new compendium in contrast to the old compendium, does not indicate the survival period of the spores. According to Dr Sundar and other literature sources, the spores have a short survival period and not sixty days as previously mentioned.
Prof Pretorius suggested that it would be easy to conduct survival studies in the greenhouse but questioned the relationship between this and the field as the latter conditions were very different. He regards this aspect as a very important aspect of the total survival study.
Mr De Lange pointed out that even in areas that frost, one can get isolated gulleys and hollows that remain frost-free and could be areas in which the pathogen survives.
Prof Pretorius suggested that survival on one isolated plant would be sufficient to initiate infection in a specific area.
Mr Middel suggested that one should not only concentrate on farm areas but survival may also occur in towns.
Consensus was reached that aspects such as overwintering on alternative hosts and survival in relation to environmental conditions, should be researched.
Mr Vermaak questioned the value of survival research to the producer.
These studies would indicate the risk of the disease in specific areas and serves as an early warning for initiation of control strategies. The whole aspect regarding the survival and the method of dispersion is of critical importance.
Chemical control (critical timing of sprays, chemical efficacy, rates, economics, trap crops, fungicide resistance, application methods)
Mr De Klerk explained that a preventative program is not cost effective and he doubted whether farmers would follow a preventative program. He suggested that if an early curative strategy is followed then application rate becomes critical. A low a rate is not feasible since companies will have to protect themselves since claims will be directed to the respective companies. Economics is a problem and it appears that, depending on the stage of infestation and environmental conditions, a minimum of two sprays will be required. Companies will now have to look at application rates and do their own development work in preparation of final registration. New products may also become available. They will have to wait and see what happens during the first season before any decisions can be made.
Referring to Mr De Klerk's first statement regarding curative vs preventative control strategies, Dr Purchase commented that the Zimbabweans recommended the use of preventative spraying before flowering.
Mr De Klerk explained that the ideal would be to make use of preventative sprays, but in the case of farmers who are first-timers in terms of using preventative sprays on soybean fungus diseases, it will require an intensive training programme.
Dr Smit emphasised that it is difficult to identify and diagnose the disease before the onset of severe crop damage. The advice for the coming season in the areas where the disease has been detected, should be to make use of preventative sprays.
Mr Middel commented that even though farmers are not used to spraying soybeans, the aspect of preventative sprays is of paramount importance and needs to be emphasised as a critical measure, seeing that by the time the virulent disease is detected, it may already be too late. It is essential that farmers initiate a preventative action.
Consensus was reached that the areas where the disease has already occurred be regarded as high risk areas.
Dr De Kock reiterated the difficulty of disease detection at an early stage, indicating that by the time you see the disease there is already a large cloud of spores and that losses have already occurred. In Natal where farmers sprayed after disease detection, losses were greater than initially anticipated. Thus he regards indicator crops as essential to act as an early warning system for rust and the need for sprays. He stated that we need to determine where and when they will be planted and who will do the identifications. He also wanted to know whether AVCASA would be overseeing the testing of chemicals in the immediate future and how, where and when these test will be done, bearing in mind that the disease may not yet be endemic. He feels that the Task Team should be aware of these activities. He pointed out that the current rates are an estimate and not based on the Zimbabwean rates.
Mr De Klerk stated that each company is responsible for their own research and those companies who currently have emergency registrations will have to provide data to ensure continued registration. He also pointed out that it would have been irresponsible for a company to register marginal rates initially since any claims for poor efficacy would be directed to the responsible company.
Dr Purchase enquired as to whether artificial inoculation of trials should be allowed or not.
Dr McLaren explained that currently the disease may not be endemic and by making use of artificial inoculation, you could create an epidemic. It was decided that no artificial inoculations will be made whatsoever by all cooperating institutions.
Mr Vermaak suggested that an extension programme be implemented with updated information on how to control the disease. He also requested that a subcommittee of the Task Team should be formed to communicate with AVCASA regarding chemical control. Although he appreciates the concern of companies commencing at too low a rate, he is also concerned that rates may be such that producers cannot afford to control the disease. He suggests that the parties can meet midway on this issue.
Dr Purchase commented that the implementation of an extension programme will be discussed in detail under "Extension / Information Services". Dr Purchase pointed out that the question of correct dosage remains contentious and will play an important role in the effective control of the disease.
Dr Liebenberg mentioned that by advancing the planting date or planting early maturing varieties at a sufficient number of localities, one can ensure that the disease is picked up early and can serve as a warning of the need for preventative sprays.
Consensus were reached that when chemicals are to be applied, producers preferably make use of preventative sprays, especially in the areas where the disease was detected this past season.
Dr Purchase enquired as to dosage rates that should be recommended to the producer – dosages as recommended by the chemical companies or a lower dosage as used in Zimbabwe.
Mr De Klerk emphasised that according to the law, nobody can recommend any dosage rate unless it has been registered. This rule also applies to emergency registrations. The chemical companies will have a wide spectrum of chemicals available for further development – it will take a season or two's data to reach a point where exact data can be made available.
Dr De Kock enquired as to whether the chemical companies are liable for the chemicals being recommended. In Zimbabwe the researchers / organizations make recommendations according to their experiences and, the chemical companies supply the chemicals to the farmers via an agent (this implies that farmers receive no cover from the chemical companies for damages).
Mr Van Rij asked how one would know whether the disease had become endemic. He also commented that the registration authorities in Zimbabwe go for the lowest effective rate as a rule and questioned whether they gave any thought to the issue of fungicide resistance. Triazoles are the only effective chemicals against soybean rust and resistance to these could be a serious threat to rust control.
Prof Pretorius commented that a disease is regarded as endemic when it occurs year after year. He also indicated that according to Gorter (1980) the disease was recorded in South Africa in 1934 and then disappeared.
Mr Middel suggested that whilst risk areas in South Africa still need to be identified, the opportunity exist in Zimbabwe to test different rates. He indicated that soybean production does not allow for a big profit margin and if producers have to spray up to three times at the currently registered rates, this will kill the industry. At a lower rate, chemical control may still be a viable proposition. He also indicated that he was fairly certain that rust would occur again in the high risk areas and questioned waiting before commencing with artificially inoculated trials which ensure a sufficiently high inoculum pressure.
Dr Purchase suggested that artificial inoculation should be avoided for a minimum period of at least one to two years and confirmed that the trials being planted in the coming season need to rely on natural inoculum.
Dr De Kock explained that the dosage rate, by law, will have to be tested in South Africa under South African conditions.
Dr Liebenberg suggested that areas where commercial soybeans have been planted, should be investigated as potential trial sites.
Dr Purchase emphasised that the areas where the disease was detected, should be where the disease will occur again. Thus, the best place to plant a trial will be in the area where it was initially detected. Having such trials will eliminate the need to make use of any Zimbabwean sites and will limit the risk of spreading the disease in South Africa.
Mr De Klerk explained that the Registration Act stipulates that the tests must be conducted in the area where the disease was detected. Even if tests were to be conducted in Zimbabwe, the results can not be presented for local registration purposes due to the fact that the tests need to be conducted under South African / local conditions.
Dr Smit pointed out the possibility that an indicator trial might not become infected and that the local inoculum might build up to slowly to conduct effective research. Even if we do have perfect indicator trials, the only information to be generated from these will be whether the inoculum is present or not and not how a later planting date will influence the infestation rate.
Dr Purchase agreed with Dr Smit's statement, but suggested that such indicator trials can be used as an early warning system. If the disease does not occur, producers do not have to spray.
Mr Van Rij suggested that if rust occurs in the indicator crop or earlier planted crop, this could serve as an indicator that it is safe enough to artificially inoculate trials in the immediate vicinity. The meeting agreed to this.
Prof Pretorius commented that should sufficient indicator strips be planted, it will serve as a spreader of the disease and will ensure the generation of enough data.
Consensus were reached regarding the idea of planting indicator trials for research purposes in order to obtain more data.
Mr Vermaak enquired as to whether the Task Team possesses enough knowledge / information regarding the planting of indicator trials in order to minimize risks and to maximize outputs and whether the idea is practical or not.
Dr Purchase explained that there will be indicator strips and crops and that if the disease is detected, the indicator strips could serve as a spreader and possibly increase the rate of spread somewhat. There was consensus that under these conditions the disease cannot be escaped in any case.
Mr Middel commented that some farmers will plant early in the season and some late and it is essential that research material should be available to assist the farmers. He also mentioned that the farmers desperately need a solution for chemical dosage rates and that he can't understand why the already available Zimbabwean dosage rates can not be used in order to speed up registration processes.
Dr De Kock explained that the chemical companies are prescribed by law as how to conduct evaluations. It is prescribed that such evaluations must be conducted under South African conditions. Climatic conditions can have a definite influence on the outcome.
Mr De Klerk explained that dosage rates are available and that it is not a matter of starting from scratch, but more a case of fine-tuning. He also warned that from a company point of view, it would be dangerous to make use of artificial inoculation – it would have been possible to make use of artificial inoculation if it was an established disease (a disease not making its appearance for the first time). Artificial inoculation to a certain extent can be used by researchers, but under no circumstances are chemical companies allowed to make use of it in the registration process.
Dr Purchase again emphasised that data obtained from Zimbabwe has no relevance to the registration of fungicides locally. He also indicated that the only possible areas for cooperation between Zimbabwe and South Africa would be in the fields of genetics and whether to spray or not.
Mr De Klerk seconded Dr Purchase's statement.
Mr Vermaak commented that he understands the situation regarding the registration of fungicides, as well as the problem with the dosages, but what is of paramount importance is that all issues must be dealt with and when making decisions, consensus must be reached.
Dr Purchase supported Mr Vermaak's comment and added that the members of the Task Team must at all times be well informed. All the aspects regarding the disease must be investigated in order to ensure that all solutions / possibilities are exploited.
- No artificial inoculation may used until the disease has been declared endemic;
- Chemical companies will conduct their registration trials under natural infestation conditions in South Africa;
- AVCASA is to convey the decisions to the different chemical companies.
Mr Vermaak suggested that Dr Purchase as coordinator of the Task Team, should distribute a draft copy of the decisions to AVCASA.
Decisions to be verbally communicated to the chemical companies.
Mr De Klerk
Document regarding the decisions to be drafted and distributed to AVCASA and the technical managers of chemical companies who are involved with the registration process.
Prof Pretorius enquired as to who will be responsible for independant trials in which chemicals will be tested against each other.
Dr Purchase indicated that the companies do their own developing and that the meeting cannot interfere with their normal set procedures. However, tests to compare the chemicals will have to be conducted independently, i.e. critical timing of sprays, chemical efficacy, rates, economics, trap crops, fungicide resistance, application methods, etc. The assigning of research responsibilities will be done under point 5.
The meeting noted that not all crops / soybeans reacted the same towards chemical applications and that such observations usually will form part of the normal observations – thus trials will have to be conducted in the area where the disease was detected.
Mr De Klerk explained that when conducting an experiment, a set standard (the currently registered chemical) is used but currently the chemical companies do not possess a standard chemical against which to make comparisons.
Dr Purchase commented that all emergency-registered chemicals will have to be evaluated first, and one will then have to discuss standards regarding new chemicals with the relevant companies. The detail regarding the dosage rates which may vary from chemical to chemical, will be left to the experts who will be drafting the project proposal.
Mr Van Rij asked about research into application methods, i.e. aerial application compared with ground applications.
Dr Purchase referred to Dr Levy from Zimbabwe and the different rates recommended for aerial application and boomspray application. Even within the latter there are different water rates associated with air-bag applicators compared to other applicators.
Dr McLaren stated that the chemical control programme needs to encompass both application methods, rates, water volumes, penetration of the canopy, etc., and not only the rate.
The meeting noted that the chemical control research group should consult with all the role players to ensure that all the relevant aspects are covered in the research programme.
In response to a question from Dr de Kock regarding efficacy and mechanisms of fungicide activity, Prof. Pretorius indicated that spores do not absorb fungicides but that fungicides protect the leaves from penetration and mycelium development.
Mr De Klerk indicated that fungicides do not move in a dead leaf and indicated that applications need to be made before lesions develop – this is the curative period. On the issue of air-bag applications he stated that it is essential that water volumes are not reduced so as to ensure optimal penetration of the canopy.
Dr Purchase mentioned that the minutes of the Soybean Rust Workshop indicated that most chemicals possess their own wetters and enquired as to whether wetters should be regarded as an important aspect or not – making use of wetters will depend on the formulation of the chemical.
Consensus was reached that the person / institute responsible for the chemical control proposal, will also have to make provision for the use and specifications of wetters.
Mr Middel requested that all chemicals, should specify whether they contain wetters or not.
Mr Van Rij commented that wetners protect the chemicals from evaporation and ensures effective control.
Disease escape (planting dates, maturity groups, localities, genotypes / cultivars)
Dr Purchase enquired as to, even though no resistance currently exists, whether aspects such as planting dates, maturity groups, localities (high / low risk areas), genotype cultivars (slow cultivars), row widths and population could provide some kind of protection or escape.
Mr Jarvie suggested that research institutes in cooperation with farmers, plant a network of indicator crops in order to determine / identify whether the above-mentioned contributes to escape or not.
Dr McLaren commented that indicator crops in various fields will give an idea of the time at which the disease enters and once this knowledge is obtained, it creates a time-frame within which you can work. Working in a time-frame will create an opportunity to look at different maturity groups – indicator crops can be seen as a starting point.
Dr De Kock mentioned the possibility that fast growing cultivars might escape the disease and that planting dates and growth stages are definitely aspects that need to be a priority.
Prof Pretorius agreed that planting dates and maturity are a priority. Indicator crops are to be planted over different time periods to indicate the effect that planting dates have on infection. Indicator crops definitely have to be a research topic on its own – crop stages vs environmental conditions.
Dr De Kock emphasised that the indicator crops are to be planted before the main soybean plantings, preferably two to three weeks before the actual soybean crop for that area is planted.
Dr Smit expressed his concern that relevant parties should always strive to establish and maintain good hygiene conditions – as soon as the desired data is obtained, the trials should be terminated. The inoculum should be kept as low as possible in order to prevent the rate of spread from increasing. Researchers should be careful not to encourage sources of inoculum via indicator crops in strategic areas – unnecessary contamination must be avoided. He also mentioned that with the right climatic conditions, plant population would have a great influence on the infection rate.
Dr Purchase stated that the trials will have to be conducted to the very end in order to ensure that all relevant data is obtained. He referred to the earlier comment that planting dates and maturity difference are more important than plant density and row widths, and enquired as to whether research on plant density and row widths would be worthwhile.
Dr McLaren mentioned that when researching the climatic / environmental conditions (which included micro-climate) to establish conditions favourable for the disease, row widths and density, which forms part the canopy, will automatically be included in the study.
Dr Smit explained that if the micro-climate can be manipulated, the disease can to some extent be controlled.
Consensus was reached that micro climate should be included in the compilation of a research proposal.
Mr Lamprecht enquired as to whether the meeting has enough knowledge to be able to make decisions and also suggested that although data are available from different sources, some kind of literature study should compiled containing all the relevant information, i.e. a condensed overview.
Prof Pretorius seconded Mr Lamprecht's suggestion and commented that information currently known should be compiled into an overview and be placed on the web in order to facilitate access to information.
Dr De Kock emphasised that it is essential that current available information be gathered and compiled into one condensed document and be distributed via all possible means in order to ensure that all relevant parties are reached.
Consensus was reached that a literature study / overview should be compiled and it was suggested that a PhD student would be the perfect candidate to conduct such a study. The outcome of this study / final product should be published or be placed on the web.
Genetic resistance (sources, heritability, stability, races, differentials, tolerance, slow rusting vs resistance, rating system, artificial inoculation, markers)
Dr Purchase commented that although genetic resistance does exist, sources, heritability, stability, races, differentials, tolerance, slow rusting vs resistance, rating systems, artificial inoculation and markers for marker assisted selection are aspects that need to be researched and addressed. The seed companies will have their own specific programmes in terms of genetic resistance, apart from what public institutions will be doing – this will be very important when looking at a long-term strategy for controlling the disease.
Mr Jarvie stated that the public / farmers / role players must be made aware that genetic resistance is a long-term strategy.
Mr Van Rij commented that the different tolerances should be quantified, as well as the effect the disease has on the plant itself.
Dr De Kock suggested that in cooperation with seed companies, both phases of the national cultivar trials be sent to Zimbabwe for evaluation. The trials should include a fourth replicate with a request that one replicate be left unsprayed in order to determine the different reaction types. He suggested that the Phase 1 trial with new entries is the most important.
Mr Jarvie commented that not all South African cultivars are adapted to Zimbabwean conditions and ones assessment of tolerance under these conditions is therefore not accurate. Assessment of resistance or susceptibility can be done in Zimbabwe but tolerance includes the extent to which the cultivar is adapted to the environment.
Dr Purchase suggested that we should consider evaluating tolerance as a part of our local cultivar trials this season in high risk areas. He also expressed concern about only spraying one replicate and suggested that a split plot trial design be used.
Dr de Kock questioned the effect of drift when spraying fungicides in a split plot design.
Dr Purchase commented that it is more important that all data obtained, be scientifically justifiable and not be generated for popular publishing purposes only.
Mr Middel suggested that genes known to provide some kind of resistance, should be incorporated into the breeding programme.
Dr De Kock commented that this would be a long process since the sources of rust resistance are vegetable-type soybeans from Taiwan. He indicated that Seed-Co has crossed these with their local lines and now have F4's available. These will be introduced into the South African market once the problem of phytosanitary regulations has been sorted out. He also explained that Syngenta wants to market Solitaire, which is supposedly a slow rusting cultivar. He expressed his concern that local breeding programs are too far behind the Zimbabwean program and that we should exploit the material available there as opposed to trying to catch up. He also referred to introduced lines from Illinois which showed tolerance to rust in Seed-Co trials and expressed the need to get the names of the material so that they can be evaluated in KwaZulu-Natal and be introduced to the local markets. He therefore questioned whether we should commence a full scale breeding program.
Dr Smit warned participants to be careful not to compare different maturity groups in one trial. There would be a definite physiological response and this needs to be equated with the relative crop duration / soybean lifetime in order to conduct a real comparison between different cultivars.
Dr Purchase enquired as to whether this relates to the before mentioned cultivar trials being sprayed and not being sprayed.
Dr Smit explained that relative crop duration will have be included in such evaluations. Phase one trials have already been sent to Zimbabwe to be scored and to establish whether our cultivars are susceptible or not. Worldwide literature indicates that very little resistance exists. He quoted from the Compendium that only four dominant independent genes for resistance and nine races have been identified. Knowing that all our cultivars to some extent originate from the east or from American germplasm, the chances that we possess unique cultivars / indigenous cultivars are minimal and this indicates / implies that the genetic background of our cultivars has already been evaluated somewhere else. The chance of discovering new resistance genes that have not yet been discovered elsewhere, is very slim. He also mentioned that proper observations cannot be conducted on just one trial replicate.
Dr Purchase enquired as to whether it is worthwhile to even conduct tests regarding maturity / growth differences.
Prof Pretorius stated that we cannot just accept information without conducting trials ourselves. There are methods of evaluation which take growth stage into account when evaluating disease severities. He also indicated that disease rating will have to be taken every 4-5 days to achieve this.
Dr Purchase suggested that the evaluations in Zimbabwe should continue, but also be conducted in Natal for a start. He also mentioned that it would be meaningless to continue with a soybean breeding programme if resistance didn't form part of the programme.
Mr Middel expressed the view that it is of national importance that the genes used in the breeding programmes should be marked.
Dr Purchase enquired as to whether markers are available.
Prof Pretorius indicated that markers are available for the two main pathogens but not the resistance genes.
Dr Smit indicated that in 1998 a proposal was made that markers for the resistance genes be developed at Potchefstroom after the breeding has been done by AVRDC and Dr Sundar gave no indication of markers being available at that stage.
Dr McLaren commented that in Zimbabwe they only conduct research according to symptoms and not on the genes that are involved. He also expressed his concern regarding the fast rate at which the resistance breaks down, and over the four genes and nine races involved.
Prof Pretorius explained that germplasm from other institutions needs to be tested to determine our spectrum of races. Material also needs to be obtained in order to develop molecular markers to ensure the introduction of more than one gene in a cultivar. He pleaded that when conducting these tests, more attention should be given to the genotype characterisation of the population against which markers are developed as it is here that errors can occur very easily.
Mr De Lange stated that he would rather go for tolerance than for resistance, seeing that the resistance will break down faster, while tolerance will last longer.
Prof Pretorius commented that this indicates another aspect, i.e. genetic analysis of the tolerance in cultivars, in other words how many genes are involved. It is assumed that this is polygenic and this will also give an indication of the durability. He also indicated the complexities of such a study and questioned the size of the host population required to identify 5 or 6 so-called minor genes, and suggested that it would be an near impossible task. He also mentioned that a germplasmbank was necessary to maintain everything that can be obtained worldwide.
Dr Smit commented that traditional breeding should be seen as a long-term strategy. Accelerated generation breeding can be conducted once you know what you are breeding for.
Dr Purchase asked whether the 4 resistance genes could not be built into elite material by means of a back-crossing programme.
Prof Pretorius confirmed that this should be a priority and suggested that funding should be made available to a breeder for the sole purpose of obtaining genes from other countries and institutes and to build up personal contacts.
Dr Smit explained that germplasm can be obtained from AVRDC, as well as from Dr Sundar.
Mr Middel enquired as to whether genes responsible for resistance can be used for tolerance when presented in different combinations.
Prof Pretorius explained that tolerance is based on susceptibility, but without yield losses. These other genes provide complete / total resistance. He explained that tolerance is based on physiological characteristics associated with growth rates and grain fill which make plants less sensitive.
Mr De Lange commented that according to different literature sources there are certain production areas in China that are very similar to South Africa. China ought to have some kind of resistance in their cultivars that might be useful and which may also be adapted to our conditions.
Consensus were reached that contact with AVRDC and Dr Sundar should be established as soon as possible to establish what assistance and material they can provide.
Dr Liebenberg emphasised that if the disease becomes endemic, it would be difficult to release a new cultivar if you do not have some kind of resistance.
Dr Purchase quoted from the minutes of the Soybean Rust Workshop that a rust scoring system was used at AVRDC which showed where in the plant the disease was detected and also a severity score showed the intensity of the infection. He also stated that, should material be obtained from AVRDC, it would be logical to make use of their rating system and to ensure uniformity seeing that different standards exist.
Prof Pretorius commented that it makes sense to measure the height and intensity in order to determine the degree of the disease, seeing that the disease starts spreading from the bottom. Whilst these measurements are conducted, the growth stages should also be monitored.
Dr Purchase tasked the Task Team members to individually evaluate the system and to inform the relevant parties as to the working of the system, seeing that a lot of the members will be making use of the system. It is also of paramount importance that everybody work with a uniform system for genetic evaluation or chemical control and that they know how to use the system.
Mr Van Rij commented that the system should be quick and simple, particularly if one is going to rate 40 or 50 cultivars.
Prof Pretorius informed the meeting that the are different ways of measuring a disease. Plant breeders make use of a different method to plant pathologists, i.e. breeders investigate the tissue / texture whereas pathologists the disease. You must have a system that is practical and fulfill1s the specific needs of the task at hand. It is therefore evident that different rating systems will be used for different needs.
Dr Purchase commented that other systems can be exploited and that we should not be limited to AVRDC's system, if it has limitations.
Dr McLaren suggested that the issue of a rating system should be a study on its own as you want to link it up with plant growth stage, yield, economics, etc.
Dr Smit was asked to contact Dr Sundar regarding a rating system. He quoted that a modified Horsfall-Barret system was used.
Prof Pretorius commented that the system has only two classes between 25% and 75% which excludes distinguishing between a whole series of disease levels. The system enables the generation of workable data which can also be converted to percentages for statistical analysis. He however indicated that he does not find the system acceptable.
Mr De Klerk explained that chemical control needs a rough class system, whereas the breeders would be looking at a system that can provide finer detail. It is not inevitable that one system will comply with all the needs.
Dr Purchase expressed his concern that when results are presented they may be misinterpreted by the various parties.
Dr McLaren suggested that for each research situation, the person responsible should specify / indicate the system which was used, as well as why the specific system was used. He also indicated that the development of a unique system can be incorporated into the loss assessment proposal.
Consensus was reached that the researcher should use his / her own discretion and where possible, the AVRDC system should be used. In the case of the mentioned system not being practical for the specific situation, an adopted system which is scientifically justifiable may be used. The meeting also requested that a document containing the AVRDC system, should accompany the minutes as an appendix. Dr Smit was asked to provide the rating system / reference to this (Attachment 3).
Disease severity vs growth stage
Disease severity vs growth stage has already been discussed under rating systems.
Dr McLaren confirmed that the main aspects that need to be looked at are: i) whether to spray or not, ii) whether to spray preventative or curative, iii) spraying at different growth stages and iv) the effect spraying will have on economics and yield losses.
Mr Van Rij commented that it may be worth looking at loss assessment charts of Sentra-oes to get an indication of expected losses with various degrees of leaf loss in relation to growth stage.
Prof Pretorius mentioned that a loss assessment study should be conducted separately from the other studies, not only to study the economics, but also to see whether the disease can cause 70% or more yield losses.
Dr Smit suggested that disease severity vs growth rate should be a priority, but should not be seen as the most important. He again pleaded that the inoculum in South Africa should be limited to the absolute minimum and that the producers should not be encouraged to leave their crops and not to make use of chemical control.
Early warning system
Already discussed in detail previously.
Dr De Kock mentioned that a well planned system indicating precisely who is responsible for what, should be developed and that reporting and coordinating should come from a central point. He also suggested that Dr McLaren and Dr Smit should contact Dr Levy from Zimbabwe in order to establish a good working relationship. He explained that the aim would be to have numerous, but small indicator plantings.
Dr Smit again expressed his pessimism regarding the planting of indicator crops, seeing that the environment as well as the proportionate spread of the disease over an area, plays a vital role, i.e. if overwintering occurs on a specific bush, it could be possible that an adjacent soybean production area becomes infected while the indicator crop situated just a few meters away is not infected due to inoculum distribution, wind direction, etc. This could lead to errors in forecasting and effect the credibility of the rust programme. He also indicated that a large number of indicator crops will have to be planted. Furthermore, the growth stage of the indicator crop relative to the farmers crop, leaf wetness at certain critical stages, etc., may result in different disease severities even at the same locality.
Dr Purchase informed the meeting that Zimbabwe suggested that an indicator network should be developed in order to serve as an early warning system. He also indicated that it is possible that it will fail in some instances, but that we should at least give it a chance to succeed.
Dr McLaren suggested that the indicator trials should be incorporated into another research proposal – two aspects in one.
Dr Smit mentioned that the reason why indicator trials were conducted in Zimbabwe, was to establish whether spores are present in the atmospheric currents coming from the north. Since we know that the spores have arrived in South Africa, he suggested that indicator crop are redundant.
Dr Purchase commented that the dispersion pattern remains unknown and that the indicator trials can be used to establish the dispersion of the spores in the coming season. Aspects to be considered when conducting indicator trials are: i) cultivar, ii) cultivar type, iii) known infected areas, iv) climatic conditions, v) frequency of observations and vi) co-workers, seeing that one person will not be able to attend to all the set requirements. Delegates were requested to nominate co-workers in this regard. Sites identified for indicator plantings should be in the area where the disease was first detected, in order to maximise and secure the chances of infestation.
Weather / disease prediction model
Dr Purchase indicated weather conditions/disease prediction models have already been discussed under point 3.2 (influence of weather conditions). He also emphasised that it is important that a prediction model should be developed.
Prof Pretorius enquired as to what the prevailing wind patterns from the north are during the critical stages. Information regarding atmospheric currents, tropical storms, air moisture content, etc. can be obtained from the Weather Bureau in order to assist in establishing the risk of spread and the development of the prediction model. Should wind patterns be such that an inflow of spores can be expected during certain critical times a warning can be put out to producers.
Dr Purchase mentioned that GCI has a GIS system available with all the relevant variables in the data base. Once the rust variables are known this can be applied to predictions.
Integration of current knowledge
Dr McLaren suggested that as information becomes available, it should be incorporated into an integrated management system. The Task Team is to be responsible to sort out and prioritise the information. All the information should be integrated to ensure the development of an effective working disease model.
Dr Purchase confirmed that the submission of relevant information to a central point is essential. This information should be made available and be incorporated into whatever effort is being conducted, eg whilst developing the prediction model.
The meeting enquired as to whether GCI will be able to fulfill the function as coordinator – consensus was reached and GCI was appointed the coordinating body with Dr Purchase at the helm.
Dr Purchase suggested that meetings should be held on a six monthly or annual basis in order to monitor progress. Once the disease is under control, the Task Team can be considered redundant and will be disbanded.
Extension / information service
- radio reports and press releases;
- pamphlets; and
- farmer's days.
Mr De Klerk enquired as to the procedures that need to be followed when producers suspect a possible rust infestation and are in desperate need to have samples identified.
Dr Smit explained that under no circumstances may any samples from infected areas be transported / taken to disease-free areas. Field officers and producers are requested to: i) report the infestation to ARC-GCI, ii) communicate this warning as a matter of urgency to the news media and iii) have either the field officers to identify the disease or take samples to the University of Natal, Cedara or to PANNAR Greytown, instead of taking the risk of spreading the disease further by sending it to ARC-GCI (Potchefstroom), the University of Pretoria or to the University of the Orange Free State for identification. The aim is to restrict the disease to certain areas and not to spread the disease via artificial means. He also suggested that all chemical representatives and even specialists in the field, should attend a workshop regarding the identification of the disease, as well as to provide efficient advice.
Mr De Klerk commented that most of the chemical representatives undergo training during the winter season to ensure that all representatives are trained and ready by the end of August – June would be a convenient time to schedule such a workshop.
Mr Lamprecht indicated that the main focus should be to provide correct identification of the disease, as it is difficult for farmers to identify.
Prof Pretorius enquired as to the amount of available training material and suggested that visual material can be obtained from Rikus Klopper (PANNAR) in order to compile a training manual to ensure the correct identification of the disease.
Mr Vermaak indicated that GSA-TV and radio, as well as SA Grain be used as ways of releasing information (mentioned media coverage will ensure that a wide spectrum is reached). He also requested that Grain South Africa be granted the opportunity to broadcast any such information first, due to GSA's first priority being to the welfare of grain farmers.
Finalization of research activities and projects
Potential research projects as identified and prioritised by the Task Team are: i) short term strategies (the entire chemical control component), ii) influence of the weather, survival, modelling / epidemiology of the disease and identification of risk areas, iii) breeding (resistance, races, differentials and markers), iv) management practices (planting dates, maturity groups and row widths), v) loss assessment / overwintering, vi) early warning system and vii) a literature study review.
Responsible institutions and scientists
Short term strategy (the entire chemical control component)
Ms Eve du Preez (Provincial Department of Agriculture KwaZulu-Natal) in cooperation with Mr Leon Killian (Protein Research Trust (Cedara)) were tasked with the chemical control component of the disease. Mr Van Rij indicated that KZN has automatic weather stations in various areas which could be used to develop prediction models. Funding would be required to upgrade these stations.
It was indicated that the PDA-KZN do not need to make use of external funding (PRT/OPDT), but they still need to submit a full proposal.
Influence of the weather, survival, modelling / epidemiology of the disease and identification of risk areas
Mr Van Rij (Provincial Department of Agriculture KwaZulu-Natal) in cooperation with Dr Neal McLaren (ARC-GCI). Dr McLaren will lead this aspect.
Breeding (resistance, races, differentials and markers)
Prof Pretorius (UOFS) was tasked to concentrate on the races, differentials and isolates, and Mr De Lange (ARC-GCI) to do the hands-on breeding (back-crossing).
The meeting suggested that breeding should be the responsibility of the companies and that the public breeding programme will be seated at ARC-GCI. It was also indicated that in the back-crossing programme, the services of a plant pathologist will be essential. It was also decided that the genetic resistant material be acquired as soon as possible by sending the relevant person to the USA to physically bring it to South Africa.
Management practices (planting dates, maturity groups and row widths)
Dr Neal McLaren (ARC-GCI) to lead the agronomy and pathology research in cooperation with Mr Van Rij (Provincial Department of Agriculture KwaZulu-Natal) and Mr Leon Killian (Protein Research Trust (Cedara)).
Loss assessment / overwintering
Dr Smit indicated that Prof Mark Lang (Natal University) is already busy with research regarding the overwintering – Dr Purchase to contact Prof Lang and to enquire the extent of his research. Dr Neal McLaren (ARC-GCI) was tasked with the loss assessment.
Early warning system
ARC-GCI will coordinate the early warning system, but all the relevant parties will be involved.
Literature study review
Prof Pretorius (UOFS) to select a student to conduct a literature study.
No further research requirements were identified.
Dr De Kock mentioned that the research proposals as identified, be submitted to the PRT and that the funders (PRT / OPOT) will decide amongst themselves how the funding will be divided. All the research applications will be considered ad hoc proposals. The complete proposals together with budgets, need to be compiled according to the set PRT new application format (format to be attached). Due to the deadline for new PRT projects being set for 1 June 2001, it was decided that the new project applications regarding soybean rust, be submitted to the coordinator of the Task Team before or at the end of June 2001. Dr Purchase will be responsible for submitting these to the PRT / OPDT.
Nothing was submitted under this item.
Date of next meeting
TDr De Kock suggested that a report-back should be done as soon as possible and that the end of August 2001 would be an appropriate time.
The next meeting has been scheduled for Friday 24 August 2001 in the conference room of the JPF Sellschop Building at 09:00.
The meeting adjourned after the Chairperson thanked everyone for their active participation in the discussions.