BSPP News Spring 2001 - Online Edition

The Newsletter of the British Society for Plant Pathology
Number 38, Spring 2001 

Conference and Travel Reports

13th  International Cocoa Research Conference & INCOPED 3rd International Seminar on Cocoa Pests and Diseases
Kota Kinabalu, Malaysia : 9-14 and 16-17 October, 2000

Cultivation of Cocoa (Theobroma cacao L.), 'food of the gods,' is rapidly expanding due to continuous increase in consumption of the product all over the world. Cocoa is, and can, be grown in an environmentally friendly way in many situations. At present, due to low prices, cocoa cultivation is scarcely economic even at the modest level of inputs, which directly leads to deterioration of management of pests and diseases and adversely affects the livelihood of cocoa farmers. The Cocoa Research Conferences were organised by the Malaysian Cocoa Board on behalf of the Cocoa Producers Alliance, to address the challenges of improving profitability of cocoa by increasing productivity and decreasing costs while maintaining farm stability. The major theme of the conferences was effective and optimum promotion of cocoa.

The conference venue, Kota Kinabalu, is located in northern Borneo in the heart of South East Asia.  Apart from exotic flora and fauna,  spectacular beaches and great weather,  a warm welcome and good hospitality from the local people made these conferences a unique experience. The bounty of the tropics, especially the magnificent seafood and succulent tropical fruits make dining in Kota Kinabalu an endlessly delicious experience. The 13th ICRC centered around sustainable cocoa development, while the INCOPED conference concentrated on integrated pest and disease management and regional project proposals.

A special meeting to discuss the concept of a global programme for sustainable cocoa was organized by the Cocoa Producers Alliance. Most participants appreciated that a major weakness in the cocoa community was the lack of co-ordination and exchange of information on common problems between and within regions , and an overall lack of major donor support for cocoa.

Genetics, Breeding and Molecular Markers: The main results in the CFC/ ICCO/ IPGRI project on "Cocoa Germplasm utilization and Conservation", up to July 2000, were summarized by A.B. Eskes, France. The project promotes the selection of better cocoa varieties, reinforcement of population improvement and of characterization and evalution of cocoa germplasm with emphasis on disease and pest resistance. The use of rapid screening methods for resistance to Phytophthora using leaf disc or detached pod inoculations has made it possible to identify interesting clones in local germplasm collections (G. Blaha, PNG, A.D Iwaro and D.R.Butler, Trinidad). 20-30 international clones have been identified and distributed from the Intermediate Quarantine Centers (CIRAD, France and University of Reading, UK) and planted in bud wood gardens in Ecuador, Malaysia and PNG (A.B. Eskes, France). L.A. Motilal, Trinidad constructed a genetic map of cocoa, from F1 progeny of IMC 57 x CATONGO. This map contains 14 putative QTL's for resistance to P.palmivora confirming polygenic mode of inheritance. In the sessions on crop protection, papers were presented on major and emerging diseases: Phytophthora, Crinipellis, Oncobasidium, swollen shoot, Corticium and Moniliophthora, and insect pests (mirids and pod borer).

Phytophthora pod rot:  The presentations by G. Blaha, CIRAD, France and P.Chowdappa, CPCRI, India highlighted the use of molecular criteria for assessing genetic diversity within and genetic relatedness between Phytophthora.   P. Chowdappa demonstrated the use of rDNA-ITS sequences and AFLP fingerprints for characterization of Phytophthora isolates affecting cocoa, coconut, black pepper and bell pepper in palm based cropping systems in India. The AFLP fingerprints of P. palmivora from cocoa and coconut showed similar patterns, in contrast to P. palmivora isolates in Indonesia. This lack of genetic diversity, coupled with morphological and pathological studies, suggest the presence of a clonal population of P. palmivora pathogenic to coconut and cocoa in India and two genetic groups on cocoa that are distinct from isolates on black pepper and bell pepper.

Screening for disease resistance: Amongst several control techniques pursued, host resistance tends to be the most durable and environmentally friendly. Several methods have been used in disease screening programmes. The papers presented in this conference mostly used leaf disc inoculation technique with zoospore suspension. This has been found to be highly correlated with pod infections, suggesting that the method is reliable and can be used as a standard in screening of cocoa germplasm for resistance. Using leaf disc inoculation technique, six accessions have been identified as tolerant to P. palmivora and P. megakarya respectively (A.Appiah, United Kingdom). S Surujdeo-Maharaj, Trinidad presented the results on foliar resistance to 10  isolates of P.palmivora in five cocoa genotypes and indicated no significant genotype x isolate interaction effects, suggesting resistance found using one isolate would be equally valid for other isolates of Phytophthora within the location. A.D Iwaro illustrated the possibility of creating populations from germplasm in the Cocoa Research unit, Trinidad with improved resistance to black pod and witches broom diseases. More than 500 accessions were screened for black pod resistance with detached pod test and 1000 seedlings from crosses among the resistant clones were selected in the nursery with the leaf test. 10% possessed good resistance. These will be made available to national cocoa breeding programmes for the development of high-yielding resistant cultivars  A method using peeled cocoa seeds coated with P. palmivora inoculum, to select resistant rootstock against Phytophthora disease was presented by Ahmad Kamil, Malaysia. The germinated seedlings were re-inoculated by wounding the stem of the seedlings after three months of germination. Using this method, several lines were identified as resistant to P. palmivora.

Biological control:  Dr Sharifuddin, Malaysia identified nine potential antagonistic bacteria against P. palmivora and P. nicotianae from cocoa rhizo-sphere   based on in-vitro screening with dual culture technique. They are Enterobacter sp; Pseudomonas aeruginosa, Serratia marescens, Burkholderia cepacia and five isolates of Bacillus spp. The efficacy of Trichoderma, Gliocladium virens and an entomopathogen Beauveria bassiana, insecticide (deltamethrin) and a fungicide (metalaxyl + copper) were evaluated alone and in combinations for control of black pod and cocoa pod borer (C.L. Bong, Malaysia). Efficacy of fungicides or G. virens was apparently reduced when mixed with insecticide while that of Trichoderma spp apparently enhanced control of black pod. Gliocladium roseum, a native mycoparasitive, has been found to be highly promising for simultaneous biological control of three major pod diseases of cocoa: frosty pod (Moniliophthora roreri), witches broom (Crinipellis perniciosa) and black pod (Phytophthora spp) in Peru (U. Krauss). In India, T. harizianum has been found to be a potential biocontrol agent as one of the components in integrated disease management (P. Chowdappa)

Chemical control:  A field trial, for four years in Trinidad, indicated that a single application of copper fungicide at the rate of 15g ai/tree/year was highly effective in controlling black pod. The benefit–cost ratio (3.7) indicated the profitability of the treatment (C. Shripat, Trinidad).

 Vascular Streak die-back (Oncobasidium theobromae): The variations in peroxidase, polyphenol oxidase, chitanase and beta-1, 3-glucanase activities in leaves of cocoa clones and their relationships to vascular streak die-back disease susceptibility was presented by Rosmin Kasran, Malaysia. Polyphenol oxidase and chitinase enzyme activities were significantly higher in resistant clones than in susceptible clones, suggesting these enzymes as useful markers to determine the resistance or susceptibility of cocoa clones to VSD.

Cocoa Swollen Shoot: L.A. Ollennu, Ghana demonstrated that Amazon Amelonadu hybrids are useful in the re-planting of swollen shoot disease outbreaks until higher sources of resistance found.

Pink disease: I.Y. Opoku, Ghana reported severe outbreaks caused by Corticium salmonicolor for the first time in the Eastern region of Ghana. The disease is controlled by removal and burning of all infected branches followed by spraying with either Ridomil MZ-72 plus or Kocide 101.

Mycotoxins: Ochratoxin, produced by Aspergillus alutaceus and Penicillium verrucosum are widely distributed toxins, which are suspected to cause cancer and kidney damage. Pioneering work by Dr Reinhard Matissek, LCT, Germany showed that mycotoxin occurs frequently and in broad concentration ranges in cocoa and products containing cocoa. Fermentation and drying is of greater importance in this aspect than transport, storage and processing.

Cocoa pod borer: Cocoa pod borer (Conopomorpha cramerella) has become a major production-limiting factor in Malaysia, Indonesia and Philippines. Chemical sprays (Cypermethrin, Nurelle, a formulation of Cypermethrin and Chloropyriphos) have become ineffective against C.cramerella after continuous usage. Most papers highlighted the use of integrated pest management, which consists of cultural and biological control methods and planting of resistant clones for managing this pest. In Malaysia, cocoa black ant (Dolichoderus thoracciuss (Y.F. Wong and I. Azar) and egg parasitoid,  (Tricho-grammatoidea bacterial fumata) have been found to be potential bio-control agents in limiting cocoa pod borer infestation. Integration of weekly harvesting and spraying of Beauveria bassiana every two weeks was the most effective method to control CPB infestation in Indonesia (S. Wiryadiputra). Pod sleeving with plastic bags have been able to control CPB in smallholders garden but not in larger plantations. Some of the clones have conferred resistance against the CPB in Malaysia but they may not have good agronomic traits, thus requiring further cross breeding with the agronomically good clones.

Mirids: Cocoa mirids,  (Distantiella theobromae (Dist) and Sahlbergella singularis (Hagl)) are the most important pests in West Africa and crop losses may rise to as high as 75% if affected gardens are neglected. Due to ineffectiveness of existing chemical practices, coupled with environmental concerns, the Cocoa Research Institute of Ghana initiated programmes since 1995 in collaboration with international organisations to develop environmentally safer methods in the context of an IPM programme (B.Padi, GRIG, Ghana). Use of sex pheromones and analogues of host plant origin, biological control agents (Beauveria bassiana), neem based pesticides and host plant resistance have been encouraging.

Rodents: H.C. Lee showed that rats could be controlled effectively by establishing barn owl nesting boxes in cocoa gardens in Malaysia. Owl colonization was noticed in 2-16 weeks, with consequent reduction of rat population and crop losses in cocoa gardens. Chemical disease control in cocoa has been unsatisfactory and the main method available to the resource-poor farmer is phytosanitation. Breeding for resistance and development of bio-control formulations will be the most economical in years to come. It was clear from these conferences that biological control strategies have been highly useful for effective management of major cocoa pest and diseases. Perhaps it would be a rewarding exercise to organize a conference exclusively on biological control of cocoa pests and diseases.

P.Chowdappa
Central Plantation Crops Research Institute, Vittal, India


The BCPC Conference - Pests & Diseases
Brighton : 13-16 November  2000

The November 2000 trek to Brighton for the biennial BCPC Pests & Diseases Conference was complicated by the effects of flooding and the efforts of Railtrack, but eventually most of the 1,400 registered delegates (and some unregistered ones) reached the Metropole.

Monday's pre-Conference Symposium on 'Human Exposure to Pesticide Residues, Natural Toxins and GMOs: real and perceived risks', chaired by Sir Colin Berry, was enlivened by a protester who cut the wires to the lectern microphone with a shout which sounded like "anti-GMO - corporate scum!".  Neil Carmichael (Aventis Crop Science), who was discussing the philosophy of hazard assessment at the time, was unperturbed.  A radio microphone was provided and he completed his talk, concluding that existing methods of pesticide toxicity evaluation ensure safety but are very inefficient; new techniques could allow more efficient evaluation and perhaps avoid valuable compounds being lost.  The double standard between public acceptance of risk from natural toxicants compared with the unacceptability of risk from pesticides was emphasised by Joel Mattson (Dow AgroSciences): he argued that, in terms of overall food safety, the risks associated with pesticides should be set against their ability to limit expression of natural toxins.

While pesticide risk assessment is a fairly standardised process, assessment of GM hazard is based on a process of comparison of the transformed plant with its parent using the principle of substantial equivalence; Mark Martens (Monsanto) stated that this has been applied successfully to date.  However, the immense gulf between the industry perception of GM crop safety and the environmental groups' perception of their hazards was highlighted by Joyce Tait.  In a thought-provoking paper, she argued that it is crucial to distinguish between interest-based and value-based motivations.  Where motivation is value-based, as for environmental pressure groups who have an almost religious commitment to their cause, then it cannot be swayed by facts and rational argument.  As a scientist, this is an alarming concept and I was left uncertain how it can be tackled.

The main conference started with the Bawden lecture from Dr David Evans of the newly-formed Syngenta.  His paper presented a very positive view of the future of crop protection.  However, the reduced number of agrochemical industry receptions (less free food!) and the anxious aspects of the former Novartis and Zeneca personnel, who were wondering about their futures in Syngenta, told a rather different story.  Rationalisation continues to be the order of the day, which, given the state of the farming industry, is perhaps scarcely surprising.

In terms of new fungicides, this year we got two new strobilurins, Syngenta's picoxystrobin and BASF's BAS500F.  A fluorine-containing dimethomorph analogue has been developed in China (a potentially useful addition to potato blight control, but will it be commercialised here?) and another DMI (simeconazole) in Japan, the latter intended for rice sheath blight control (may yet be of interest to me if global warming makes a UK rice crop feasible!).  A biocontrol agent, Brevibacillus brevis, was also announced.  This has a dual mode of action (produces gramicidin S and a biosurfactant), broad spectrum activity against a range of plant pathogens including Botrytis cinerea and is suited for moderate efficacy situations, perhaps it may be an option in organic production.

A session on the economics of pest and disease management in cereals provided food for thought.  Whilst Andy Leadbeater of Syngenta concluded that use of cereal fungicides continues to be profitable, Nigel Hardwick of the Central Science Laboratory (CSL), York pointed out that 25 years' research into cereal fungicides hasn't led to a major reduction in disease.  On the contrary, winter wheat disease levels in the UK are now higher than in the late 1970s, despite increasing fungicide use: 99% of UK winter wheat is now fungicide-treated compared with 12% in 1975.  So much for progress in crop protection!  Our understanding of the reasons for changes in cereal pathogen populations over this period also seems very incomplete.  The switch from Septoria nodorum to S. tritici as the dominant foliar pathogen of wheat was probably unrelated to fungicide application.  However, Geoff Bateman suggested that the shift in the eyespot population from the W (Tapesia yallundae) to the R form (T. acuformis), may be related to prochloraz use and could be positively beneficial since T. acuformis is a slower-developing pathogen.

I was sorry to miss the session on Resistance Risk Assessment, but opted for the simultaneous one on Strobilurins to catch up with the latest on resistance to the QoI-STAR group, as Steve Heaney (Syngenta) reminded us to call them.  His paper demonstrated how a combination of bioassay and molecular diagnostics allows the development of resistance to be tracked.  With one exception, in pathogens where resistance has been identified to date, it is associated with a single base mutation at position 143 in the cytochrome b gene (the G143A mutation); only Venturia inaequalis from northern Germany has a different, non-target site resistance mechanism.  Despite the rapid and unpredicted appearance of resistant strains, it is encouraging to hear how quantitative monitoring of the frequency of the resistant allele in pathogen populations can permit more rational development of anti-resistance strategies.  There are differences in fitness between resistant and sensitive strains in some pathogens, e.g. Plasmopara viticola, but in others, resistant and sensitive are equally fit e.g. Erysiphe graminis f. sp. tritici. However, as Steve Heaney commented, our lack of knowledge of the evolutionary biology of pathogens makes it hard to determine the basis for this.

The decision to timetable the poster sessions on the Tuesday and Wednesday afternoons was good in theory, since it avoided clashes between papers and posters.  Unfortunately the area allocated to the Tuesday session was so cramped that it proved extremely difficult to read the posters, let alone talk to authors.  In the pathogen resistance area, I managed to look at the IACR-Long Ashton poster on in planta gentoyping of Erysiphe graminis f.sp. tritici isolates for strobilurin resistance by Bart Fraaije and colleagues, exploiting the G143A mutation using a fluorometric PCR assay (rather than quantitative real-time PCR, used by Syngenta), making it a more widely-accessible technique. Neil Gudmestad's poster on mefenoxam (metalaxyl-M) resistance in Phytophthora erythroseptica in the US caught my attention as it provided a welcome diversion from wall-to-wall strobilurins and DMIs: in the US phenylamide-resistant potato pink rot is becoming a problem in some areas.

By the last morning, delegate numbers had dwindled, but the few who attended the session on International Plant Health and Quarantine for the New Millennium were rewarded by some fascinating insights into the creatures which are trying to take over the world.  Paul Bartlett (CSL) discussed potential new pests and diseases in Europe ranging from the starry sky longhorn beetle to pepino mosaic virus, commenting that over the last 10 years, there has been too great a harmonisation of the world's pests.  His comment that it is certain that there will be new surprises in the near future should encourage the next generation of plant pathologists.

Overall, the Brighton Conference again provided a forum for presentation of a wide range of current research in the crop protection area and an opportunity to interact with delegates from nearly 70 different countries.  I am very grateful to the BSPP for their travel grant which enabled me to attend.

Louise Cooke
Department of Agriculture & Rural Development, Northern Ireland