BSPP Presidential Meeting 2002

Plant Pathology and Global Food Security


Improving pearl millet, the staple cereal crop of some of the worlds poorest people, whilst keeping one step ahead of downy mildew.

By: Wendy A. Breese1, C. Tom Hash2, Arun Sharma2 and John R. Witcombe1.

1Centre for Arid Zone Studies, University of Wales, Bangor, Gwynedd, LL57 2UW, UK
ICRISAT, Patancheru, Andhra Pradesh 502 324, India

Pearl millet (Pennisetum glaucum (L.) R. Brown) is the staple food and fodder crop of millions of poor rural families living in the hottest, driest agricultural environments of Asia and sub-Saharan Africa. Although grain and stover of this crop are not commercially important commodities, since most are consumed in the homesteads where they are produced, crop losses due to plant disease are economically important. In 1990 the Plant Sciences Research Programme of the UK Overseas Development Agency (ODA), now known as the Department for International Development (DFID), began funding a collaborative research project on pearl millet. The objective of the collaboration was to use molecular plant breeding methods to address long-standing problems of pearl millet production. Specifically, the projects targeted downy mildew epidemics (caused by Sclerospora graminicola (Sacc.) J. Schrt.) and yield losses due to drought.

There have been three major milestones in this work undertaken in previous DFID-funded research: 1) The creation of a molecular marker-based genetic linkage map of the pearl millet genome. 2) The successful mapping of downy mildew resistance genes. 3) Most importantly, the incorporation of marker-assisted selection (MAS) into the ongoing resistance breeding programme at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). Although pearl millet in India is a crop of the rural poor grown in the countrys harshest agricultural environments, F1 hybrid seed is used to sow over half of the 10 m hectares on which this crop is grown. Pearl millet seeds are tiny in one kilogram there are typically over 100,000 seeds, enough to sow a quarter hectare so the potential yield advantage of hybrids more than pays for seed costs and other risks associated with their cultivation. Unfortunately, although the best pearl millet hybrids often give better grain yields than locally adapted open-pollinated cultivars, the genetically uniform single-cross hybrid cultivars currently available in India are much more vulnerable to epidemics of pearl millet downy mildew. Such epidemics constitute the major risk to cultivation of well-adapted pearl millet hybrids that can be reduced by effective crop improvement research. Losses in individual fields can reach nearly 100%, and are estimated to average 14% across India.

Because of the narrow range of closely related parental lines that have historically been used in breeding pearl millet hybrids in India, when disease resistance of one hybrid is overcome by rapidly evolving pathogen populations, other hybrids having a genetically identical parental line soon follow. This results in rapid cultivar turnover most of which is driven by disease pressure rather than yield or quality improvements. Pearl millet consumers, producers, and all those involved in the seed trade, lose out.

Single-cross hybrids are now the most widely grown pearl millet cultivar type in India and they are grown by all categories of farmers. There are many pearl millet hybrids from private-sector programmes, but public sector-bred hybrids, such as HHB 67 from Haryana Agricultural University, are widely grown. This particular hybrid was released in 1989 and has many traits that farmers appreciate, including early maturity (about 65 days from sowing to grain harvest) that often allows it to escape end-of-season droughts. It is probably the most popular public-sector pearl millet hybrid in India today and occupies over half of the pearl millet area in Haryana (over 300 thousand hectares during the rainy season of 2001). It is grown in rainfed farming systems where its short duration allows farmers time to prepare land for a following crop grown largely on residual moisture, such as chickpea, wheat, barley, or oilseed mustard. However, its popularity makes it vulnerable to an epidemic of downy mildew. In the past, every highly popular single-cross pearl millet hybrid in India has ultimately succumbed to this disease. When this happens, farmers not only suffer the direct losses caused by the epidemic, but they lose the management options associated with growing their most preferred hybrid. The hybrid seed industry also faces losses as it takes time to gear up seed production of the next best alternatives, and for farmers to then identify which of these best match their needs. Downy mildew was observed on HHB 67 plants in farmers fields in the 2001 growing season, and if nothing were done to prevent it, an epidemic could be expected from 2003 onwards.

To prevent this scenario, marker-assisted backcrossing (MABC) has been used to improve the disease resistance of the parental lines of HHB 67. MABC is rapid, and more effective than conventional breeding where it is impracticable to deliberately add several resistance genes (so-called resistance gene pyramiding) into a genotype. In conventional breeding, once a single effective resistance gene is included it is impossible to detect the presence of a second without expensive and time-consuming progeny testing of every backcross generation. MABC also allows the introduction of the resistance genes while ensuring that other genetic changes are minimal. These minimal genetic changes greatly assist the uptake of the improved products. All that is needed is the replacement of new lines for old in the seed multiplication chain. This can be done once it is confirmed that: the new parental lines have better disease resistance; are identical to the old lines as far as seed certification is concerned; and that the new version of the hybrid performs at least as well as the old. This is much faster and easier than releasing a new hybrid that requires more extensive trials and complex and uncertain release procedures. Seed of the new versions of HHB 67 should first reach farmers in the rainy season of 2003.

Development of integrated pest management techniques for the control of Ascochyta blight of chickpea

Estelle Gewiss and Richard N. Strange

Department of Biology, University College London, Gower Street, London, WC1E 6BT, United Kingdom. Email:

Chickpea (Cicer arietinum) is a major source of protein for people living in Developing Countries but the plant is susceptible to blight caused by the fungal pathogen, Ascochyta rabiei. The fungus sporulates prolifically and, under favourable conditions, may destroy the entire crop. We are part of a European Union consortium (Project No. ICA-4T-2000-30003) developing integrated pest management techniques for the control of the disease with partners in Spain, Tunisia and Turkey. Our role is to determine the importance of the phytotoxin solanapyrone A produced by the fungus in the disease syndrome by creating toxin-minus mutants. In order to screen for such mutants two assays have been developed for the detection of the toxin. The fungus is grown on a defined medium (2 ml) in wells of a culture plate. Samples of the medium after growth of the fungus are tested for the production of a blue formazan dye with methylbenzothiazolinone hydrochloride or, alternatively, transferred to a microtest plate and read by a plate reader set at 327 nm, the l max of solanapyrone A. Loss of toxin production is confirmed by High Performance Liquid Chromatography. Samples of culture filtrates are partially purified by solid phase extraction on an end-capped C18 cartridge before separation on a C18 column (Apex II; 5 micron; 150 X 4.6 mm) with methanol/water/tetrahydrofuran (23.1%; 56.3%; 20.6% v/v/v) as mobile phase. We are also developing fermenter techniques for the large-scale production of solanapyrone A for the screening of chickpea genotypes by other members of the consortium.

Towards managing virus infection of field vegetables in Kenya

Sara L Hughes, Noah A Phiri, Duncan Chacha, Alex Kuria, Alice Mwaniki, Beryn Achieng, Stephen Ndirangu, Sarah Simons, Gilbert Kibata and Nicola J Spence

Smallholder vegetable farmers in Kenya, who supply to the peri-urban markets of Nairobi, consider viruses to be one of the most important disease constraints. However, 87% farmers do nothing to manage virus disease. We have identified Turnip mosaic virus (TuMV) and Cauliflower mosaic virus (CaMV) as the major virus diseases of Brassica that farmers are faced with. Integrated control methods are required for effective management of these virus diseases due to the different methods in which they are transmitted. To achieve effective control methods it is important to identify the extent of damage to the crops, the variability of the viruses and which disease management methods might be successful. We have used virology screenhouses to carry out controlled environment experiments to assess the economic impact of TuMV and CaMV on yield in cabbage and kale with single and mixed virus infections. The variability of TuMV isolates, collected from different regions, has also been assessed using pathotyping and serology. As there is currently no method for assessing variability of CaMV isolates, we have developed monoclonal antibodies for detection and are currently optimising tests to assess variation. We have assessed different sustainable, low impact control methods to identify optimum control methods in the field using participatory research with farmers. Plant resistance can be a very effective control method and we have collected seed from local farms and markets and assessed them for resistance to viruses in the glasshouses and for resistance to viruses and other pests and diseases in the field. The long-term goal of this project is to use this data to produce effective integrated virus control methods for use by smallholder farmers in Kenya.

Toxigenicity of Fusarium oxysporum f. sp. ciceri, the wilt pathogen of chickpea

S. Gopalakrishnan and Richard N. Strange

Department of Biology, University College London, Gower Street, London WC1E6BT, UK

The toxigenicity of a devastating fungal pathogen, Fusarium oxysporum f.sp.ciceri (FOC) which causes wilt of chickpea, Cicer arientinum, the third most important legume crop in the world was studied. The fungus was grown in liquid culture on a defined medium and the filtrates were tested for their ability to kill isolated cells of chickpea. Cell death was determined by the inability of cells to fluoresce when treated with fluorescein diacetate. The relationship between probit percent cell death and Log2 of the dilution of a given toxin preparation was linear, enabling an LD50 value to be extracted. This was defined as 1 unit of activity. Cultural filtrates of five isolates of the fungus gave 15.8, 11.6, 15.9, 42.8 and 71.2 units/ml for Race1, Race2, V2, Jabalpur and FOC5, respectively. Since filtrates of FOC5 were the most toxic this isolate was singled out for toxin isolation. Toxic activity partitioned quantitatively into ethyl acetate but about 11% of the activity was not adsorbed by solid phase C18 cartridges. Desorbtion of the cartridges with incrementally increasing concentrations of methanol yielded a further 34% of the activity. Further purification has been achieved of both the fractions adsorbed and non-adsorbed by the C18 cartridges and this will be detailed in the poster.

Biological control of Allium white rot and degradation of sclerotia in different UK soils

JP Clarkson, T Payne, JM Whipps

Three Trichoderma isolates L4, S17A and 99-27, previously selected for their ability to degrade sclerotia of Sclerotium cepivorum, were tested for efficacy as biological control agnets (BCAs) in four soils and against four isolates of S. cepivorum. All isolates degraded at least 40% of sclerotia in silty clay, sand and silt soils but showed no activity in the peat soil. However, in onion seedling bioassays L4 and S17A could control white rot in all soil types except the silt soil. Isolate 99-27 was more variable in suppressing white rot on onions and only showed some activity in silty clay or sand soils. All BCAs degraded sclerotia irrespective of the isolate source and reduced white rot on onion seedlings in at least one experiment. In field trials, BCAs L4 and S17A reduced white rot symptoms on bulb onions when applied in guar gum with the seed at drilling, but stem base treatments were ineffective.

Understanding Biological Invasion Using Plant Epidemics

Joo Filipe1, Wilfred Otten1, Gavin Gibson2, and Christopher A. Gilligan1

1Department of Plant Sciences, Epidemiology and Modelling Group, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK; 2Department of Actuarial Mathematics and Statistics, Heriot-Watt University, Edingburgh,UK.

Forecasting and manipulating the invasion and persistence of harmful and beneficial organisms within and between glasshouses or fields is increasingly important in agriculture, horticulture and forestry. This arises from concerns with the spread of new diseases and pesticide-resistant strains of indigenous diseases and by the deployment of genetically modified and other organisms for biofertilization and biocontrol. There is already a substantial theory on criteria for invasion (the introduction and subsequent spread of an organism) in animal and human populations. Much of this work is based on deterministic mean-field models, which ignore variability and spatial distribution of individuals, and on data sets which do not allow for model testing. However, increasing attention is being given to stochastic and spatial models. Further understanding of invasion in crops requires further development and testing of models. Microcosms experiments offer an efficient means for model testing by allowing high degrees of replication under controlled conditions and rapid through-put of epidemics. Here we describe an experimental protocol for the collection of data for epidemics of the damping-off fungus, Rhizoctonia solani together with model analysis and fitting using pairwise approximation to identify mechanisms of invasion.

The objectives of the work are: 1. To monitor epidemics in space and time in highly replicated microcosms in order to identify mechanisms underlying invasion. 2. To test the fit of semi-spatial models for disease progress using pairwise and mean-field closure approximations. 3. To use the model to quantify the relative contributions of primary and secondary infection in the invasion and establishment of epidemics.

Healthy quality seed for improved food security The farmer as a seed tester

Solveig Danielsen, Carmen Nieves Mortensen, S.B. Mathur, Danish Government Institute of Seed Pathology for Developing Countries, Thorvaldsensvej 57, 1871 Frederiksberg C, Denmark

Despite large investments in formal seed systems in developing countries over the past 30 years, the vast majority, about 9095% of smallholder farmers seed demands are still met by informal sources at the farm and community levels. Although the informal seed sector provides a dynamic and flexible system of seed supply, usage, handling, trade and exchange, continuous use of untested seed inevitably leads to a degeneration of the seed quality. Farmers depend on their own seed for sowing, not only because of the inadequate access to seeds from the formal seed sector, but also because the formal seed sector often provides seeds of a limited range of cultivars and varieties, which not always fulfil the needs of the farmers to diversify the production. On-farm growing and maintenance of locally adapted landraces, cultivars and wild species help the farmer decrease the impact of a series of production constraints like drought, flooding, heat, cold, pests and diseases. However, problems created by seed-borne diseases are highly ignored and control measures unknown or inadequate. The consequence is poor seed quality, dissemination and build-up of seed-borne diseases and yields far below the potential. An improvement in quality and health of seed for sowing constitutes a large unexploited potential for increased food production of unknown dimensions.

Seed health and quality critical traits for increased food security: To illustrate the magnitude of the problems, a few conspicuous examples are mentioned. In Vietnam, the second largest exporter of rice in the world, the quality and health of rice seed is so poor that the Vietnamese only receive half the price at the international market. In addition, farmers use high planting densities to compensate for the poor planting value of the seeds. In West Africa, where the importance of rice production is increasing, problems with seed-borne diseases are tremendous. Due to the lack of knowledge and seed testing practices diseases are spread in an uncontrolled manner from field to field and from country to country. Diseased seeds are even used uncritically for breeding and research purposes.

The farmer as a seed tester: The quality of the seed must be known before it is sown. A farmer using only healthy seed will increase the yield of his harvest dramatically. The current research and development strategy of DGISP for improved health and quality of farmers seed is based on development and transfer of simple, cheap and reliable technologies directly to the farmers. Farmers have been trained in Bangladesh and Tanzania to test and improve their own seed, and efforts are made to introduce a variety of technologies for seed testing and seed cleaning, such as use of jute mats for germination tests and manual cleaning leading to better sanitation in the rice field and increased yield. Manual cleaning is applicable when dealing with low numbers of seed and when visual signs of infection and discolouration are observed. Other simple and less labour intensive methods for seed cleaning are introduced successfully, for instance physical separation of good and bad seed using salt solution. In Cameroon, simple seed treatments with local natural plant substances, like essential oils, have shown promising results for improving seed health and seed quality. The strategy for technology transfer must be made on a case-by-case basis involving multiple stakeholders and taking into account the socio-economic, political and environmental conditions in each community or region. A variety of channels should be considered for dissemination of knowledge and technologies: Extension services, NGOs, IPM programmes, participatory breeding programmes, Farmers Field Schools, workshops, field days and local fairs.

Inhibition of Fusarium culmorum and Alternaria alternata by clove oil and eucalyptus oil

Elizabeth Byron, University of Hertfordshire, Department of Environmental Science, College Lane, Hatfield, AL10 9AB

There is a growing need to find an alternative method of control for common pathogenic fungi on cereals because of the current amount of environmental pollution involved with the conventional methods. Fusarium culmorum and Alternaria alternata are the fungi studied in this report and the aim has been to see if two essential oils, clove oil and eucalyptus oil inhibit these fungi. The three methods reported here are poison plate, filter disc and stitch plate which were used to show that there is some activity of the oils against Fusarium culmorum and Alternaria alternata. The effects of eucalyptus oil showed fungistatic inhibition and clove oil showed both fungicidal and fungistatic inhibition of the fungi. Other experiments were conducted to study the minimum inhibitory concentration of the oils and the mode of inhibition. The oils were also tested for their phytotoxicity to wheat.

Assessing the research and development needs for yam in Nigeria and Ghana

L. Kenyon1, S. Morse2 and CC Asiabaka3

1Natural Resources Institute, Central Ave, Chatham, Kent ME4 4TB UK, 2 Department of Geography, University of Reading, Reading, RG6 6AT UK, 3 Department of Agricultural Economics & Extension, Federal University of Technology PMB 1526, Owerri, Imo State, Nigeria

Yams, particularly the tubers of Dioscorea rotundata, have been the preferred starchy staple in much of West Africa probably since pre-historic times. Yams are more nutritious than cassava or sweet potato having greater levels of proteins and vitamins, but despite this, yams are being displaced by these other relatively recently introduced root crops in West Africa. The reason given for this displacement is that yams are more expensive to grow, and this is probably resulting in a permanent erosion of genetic diversity in the crop in some regions. The objective of this brief study was to explore, through consultation with agricultural researchers, extension agents and some yam growers, the perceived causes for the high production costs for yams, and to identify areas of research and development whose outputs might reduce the production costs. There was general agreement that the main cost was for labour for land preparation, planting, staking, weeding and harvesting the crop. The next major cost was for planting material. Underlying both of these are the physiology and pathology of the crop. Yams are vegetatively propagated through the planting pieces of tuber, and generally, to ensure a high survival rate, relatively large planting pieces (setts) are used. There is the expectation that ware yams should be large, and planting large setts results in these if other conditions are right. However, use of large setts results in a low multiplication rate (up to 25% of the harvest has to be saved for use as planting material the following season), and storage and transport of such bulky planting material is expensive. Also, land preparation and weeding have to be good, and the large size tubers produced means that harvesting is difficult and time consuming. The minisett technique for rapid multiplication of yams was developed in Nigeria in the 1970s, but only works well with certain varieties and special care has to be taken to control fungal and bacterial diseases of the minisetts if they are to survive. Although it was promoted quite widely in Nigeria, and to a lesser extent in Ghana, growers have not taken up the minisett technique because it is perceived as being too complex and unreliable, and the cost-benefits have not been demonstrated. However, it would be worth investigating if there might be some economic benefit in the establishment of specialist producers who can produce healthy seed yams of preferred varieties to meet the growers needs (much as seed of Solanum potatoes is produced in Europe). Another potentially useful area of research and development is in the breeding and selection of yam varieties that are less susceptible to the main pests and disease, are amenable to rapid multiplication methods, and that have the desired cooking and eating qualities. By developing these systems for the provision of good quality, disease-free planting material of improved/selected yam varieties at an affordable cost, yam production might once again be economically viable, and this may help to enhance food security since the risks will be spread over a number of different crops.

Soil temperature and water potential effects on carpogenic germination of Sclerotinia sclerotiorum

JP Clarkson, JM Whipps, CS Young

The effects of soil water potential and temperature on carpogenic germination by sclerotia of S. sclerotiorum was studied in the laboratory and field. Stipes and apothecia were produced between 5 and 23C but there was little germination above 25C and none at 30C. The optimum rate of production was at approx. 18-23C where stipes appeared after 2 weeks and apothecia after 3 weeks. Sclerotia only germinated when the soil water potential was above a threshold water potential of approx. -40 kPa. Sclerotia were also buried every two weeks and monitored for germination in the field at two locations with simultaneous collection of environmental data. Sclerotia buried before May germinated to produce large numbers of apothecia but their appearance was temporarily halted by dry periods when the soil water potential fell below the threshold. In later burials, there was a sharp decline in final numbers of sclerotia germinating with no apothecia produced at all in some cases even though conditions were appropriate. Further work is required to explain this observation but high temperatures and low water potentials occurring at a critical time during germination may be responsible. The development of a sclerotial germination model to predict appearance of apothecia in the field in relation to disease control is discussed.

The heterogeneous soil environment: Are there preferential pathways for fungal spread?

Wilfred Otten1, Kirsty Harris2, Darroch Hall1, Iain M. Young3, Karl Ritz2,4, and Christopher A. Gilligan1

1Department of Plant Sciences, Epidemiology and Modelling Group, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK,, fax +44-(0)1223-333953; 2Soil-Plant Dynamics Unit, Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, UK; 3SIMBIOS Centre, University of Abertay, Bell Street, Dundee, DD1 1HG, UK; 4National Soil Resources Institute, Cranfield University, Silsoe, Bedfordshire MK45 4DT, UK.

Most studies with soil fungi have been done with little explicit characterisation of soil structure within which fungi spread and biotic interactions occur. We present epidemiological (colonisation efficiency) and biological techniques (soil thin section) to investigate the existence of preferential pathways in soil for fungal spread.

We use the colonisation efficiency as a link between soil physics and fungal growth dynamics. The colonisation efficiency is the saprotrophic equivalent of the pathozone, and defined as the relationship between the probability of successful colonisation and the distance of inoculum from a host such as a seed or a fragment of organic matter. The colonisation efficiency is a convenient way to summarise the complicated growth dynamics of fungi spreading over or through soil, with predefined soil physical properties. Here we use the colonisation efficiency to infer fungal colony growth dynamics in controlled replicated microcosms comprising soil samples in which cracks or larger pores are introduced. R. solani was capable of crossing cracks more then 6 mm wide. Fungal spread was either reduced (crack acts as a barrier) or enhanced (crack acts as a preferential pathway), depending on the orientation of the crack. When spreading through soil and encountering a large continuous volume, fungal spread is enhanced in the direction of the larger pore volume as the fungus by-passes the more tortuous pathway through the bulk soil. Analysis of the underlying mechanisms for preferential spread requires observation of microscopic interactions between fungal hyphae and soil. We used a soil thin sectioning technique to estimate the hyphal densities in relation to the distance from a crack in soil. Fungal hyphae at the advancing edge of a colony were mostly restricted to an area of 2 mm surrounding a crack. Further work will use this technique to identify which soil physical properties mediate fungal preference for cracks. Cracks and larger pores can act either as preferential pathways or barriers for fungal spread through soil. Structured soil constitutes a framework of surfaces formed by old root channels, cracks or biopores in combination with aggregates. Tillage operations may act to break up the continuity in these pathways and as such minimise their effects. We expect that preferential pathways for fungal spread can have major consequences for the interaction between soil organisms (including antagonists) and for pathogen-root interactions. Understanding the consequences of these pathways for pathogen dynamics is therefore critical for our understanding of epidemics and the development of control strategies in a heterogeneous soil environment.

Occurrence of three distinct begomoviruses in cassava in Madagascar


Laboratory of Plant Pathology, Department of Agricultural Research, P O Box 1444, Ambatobe, Antananarivo 101, Madagascar Department of Plant Pathology, Tomil Nadu Agricultural University, Coimbatore-3, 641003 Tamil Nadu, India, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK

The presence of East African cassava mosaic virus in association with cassava mosaic disease in Madagascar has previously been reported. We now describe virus isolates from mosaic-affected Madagascan cassava with epitope profiles typical of African cassava mosaic virus, and an isolate with a nucleotide sequence similar to that of South African cassava mosaic virus. Thus, three distinct begomoviruses occur in cassava in Madagascar.

Evidence for host differential resistance and pathogenic variability from interactions between Brassica juncea Albugo candida

J.A. Townsend, N.I. Nashaat,IACR-Rothamsted, Harpenden, Herts AL5 2JQ, United Kingdom

A.K. Shukla,National Research Centre on Rapeseed-Mustard, Bharatpur-321303, India

J.N. Sachan, G.B. Pant University of Agriculture and Technology, Pantnagar-263145, India

White rust, caused by the biotrophic oomycete pathogen Albugo candida, is an important disease of Brassica juncea (BJ) and Brassica rapa (BR) which account for almost one-third of the oilseed crops in India. Severe infection culminates in systemic "staghead" infection of the inflorescence (often in association with Peronospora parasitica), which under favourable conditions causes heavy yield losses in susceptible cultivars. Forty-five accessions of Brassica juncea were screened for their responses at the seedling stage to individual and a mixture of isolates of A. candida. Of the nine isolates tested, five were from BJ in India, two from BJ in Canada and two from BR in India. Preliminary results indicated that 43 accessions were uniformly susceptible to the mixture of the four Indian plus two Canadian isolates of BJ, the percentage of plants expressing a resistance response in the remaining two accessions ranged between 1-4%. With the exception of Cutlas, all accessions expressed a heterogeneous reaction to at least four individual isolates, where resistance among the seedling population ranged between 1-64%. Cutlas was fully susceptible to one Canadian isolate (2V) from BJ, whereas resistance was ranged between 14% to an Indian isolate from BR (IA07) up to 100% to another Indian isolate from BJ (IA10). In the majority of cases, resistant frequency among the seedling population of accessions to isolates from BR was higher than that with isolates from BJ. The response of host accessions to individual and mixed isolates gave strong evidence of distinct pathogenic variability among isolates used in this study. To our knowledge, this is the first report of such evidence among Indian isolates from BJ as well as BR. The results of screening against individual isolates could be explained either by a gene-for-gene model or an additive gene model. Interpretation of the results was complicated by the heterogeneous nature of the host plant accessions. Selections were made to develop differential lines in a homogeneous genetic background for future studies of the genetics of the host-pathogen interaction and for breeding for disease resistance.

Distribution and genetic diversity of phytoplasmas associated with Sugarcane Yellow Leaf Syndrome in Cuba 

Arocha, Y., Horta, D., Ruiz, M., Peralta, E. L. and Jones, P1.National Centre for Plant and Animal Health (CENSA), San Jose de las Lajas,  Cuba. 1Plant Pathogen Interactions Division, IACR Rothamsted, Harpenden, Herts., AL5 2JQ. UK.

Sugarcane Yellow Leaf Syndrome (YLS) is widespread throughout Cuba, but is most serious in the Central and Oriental regions where it affects 39% and 33% of plantings respectively. YLS was first associated with phytoplasmas of the Aster Yellows Group (16Sr ??) from samples of sugarcane collected in Matanzas, Cuba (Arocha et al 1999). During recent surveys of sugarcane crops in the Occidental, Central and Oriental regions more than 600 leaf samples with and without YLS symptoms were collected.  Total nucleic acids were extracted and the resulting DNA used as template for analysis by a nested polymerase chain reaction (nPCR) using phytoplasma-generic primers SN910601/P6 and R16F2n/R16R2. For phytoplasma characterisation nPCR products were digested with HaeIII, RsaI and AluI restriction enzymes and the 16S/23S intergenic region of the phytoplasmas was amplified, direct sequenced and compared with those of other using BLAST analysis.  Restriction profiles similar to those of phytoplasmas belonging to the Apple Proliferation (16SrX) and Peanut Witches-Broom (16SrII) Groups were found in samples from each province ranging from 25% to 75% in frequency, with the remainder being similar to those of the Aster Yellows Group (16Sr ??) previously found in Matanzas. The intergenic sequence of the most frequent phytoplasma detected was 94% homologous with that from Mexican Periwinkle Virescence phytoplasma (GenBank Accession number: ??) belonging to the 16SrXIII Group (Mexican Periwinkle Virescence).  These results show that there is diversity of phytoplasmas associated with the current outbreak of YLS in Cuba and suggest that a new subgroup of phytoplasmas has been identified 

Arocha Y, Gonzalez L, Peralta E.L, Jones P. 1999. First report of virus and phytoplasma pathogensassociated with yellow leaf syndrome of sugarcane in Cuba. Plant Disease 83.1171.

Characterisation of finger millet blast pathogen populations in East Africa and strategies for disease management

J.P. Takan, S. Muthumeenakshi and S. Sreenivasaprasad* (Horticulture Research International, Wellesbourne, Warwickshire CV35 9EF,UK), B. Akello, SAARI, (Uganda), A. Obilana, (ICRISAT, Kenya) & R. Bandyopadhyay, (IITA, Nigeria), R. Coll and A. E. Brown, (The Queens University of Belfast, UK) and N.J. Talbot, (University of Exeter, Exeter, UK).

Finger millet (Eleusine corocana) is a staple food crop in East Africa and is grown in a number of countries in the lake region. It is highly nutritious, being one of the highest in minerals and protein among cereals. Finger millet is important for food security in the region as it is more drought tolerant than maize and less susceptible to bird damage than sorghum. Moreover, its greatest advantage is that it stores for long periods without chemical treatment. The crop is indigenous to East Africa and the region has tremendous diversity in finger millet. It is estimated to comprise about 8 % of the area and 11 % of production of all millets in the world. Finger millet is grown by small-holder farmers and Uganda (up to 500, 000 ha) and Kenya (around 65, 000 ha) are two of the main producers of the crop. Blast caused by Magnaporthe grisea is a serious constraint to finger millet production causing yield reductions up to 64% and 80% in Kenya and Uganda, respectively. During the 1997 needs assessment excercise in Uganda, farmers identified blast as one of the major constraints to millet production. However, information for the development and implementation of effective blast management measures is currently lacking. This collaborative project aims to assess the intensity of blast in farmers fields to ascertain the extent of the problem and to conduct participatory rural appraisal to obtain farmers perception of the blast disease and its management in both countries. On-going work on characterisation of the blast pathogen populations using molecular tools has provided an assessment of the genetic diversity of the pathogen. Occurrence of isolates containing genetically distinct elements has also been observed. Pathogenic diversity/spectrum of various characterised isolates is being assessed using a range of finger millet varieties from the collections of ICRISAT and SAARI. To identify sources of resistance to blast, a collection of finger millet accessions including farmers varieties are being screened under natural conditions in Kenya. Further, a PCR based diagnostic test for identification of blast has been developed which would enable rapid screening of seed and weed samples to better understand the pathogen epidemiology. This would complement filed epidemiological studies in Uganda to identify sources of primary inoculum and assess the progress and spread of the disease from infection foci. The outputs generated will be useful in identifying intervention points for blast control and utilisation of host resistance, with the ultimate objective of developing an integrated disease management strategy.

*For correspondence Work funded by UK DFID-CPP Project R8030.

Rice blast pathogen population structure in West Africa for improved disease management

J. Chipili and S. Sreenivasaprasad* (Horticulture Research International, Wellesbourne, Warwickshire CV35 9EF,UK), Y. Sere,( WARDA, Cote d Ivoire), S.K. Nutsugah, (SARI, Ghana), J. Twumasi, (CRI, Ghana), A.E.Brown, (The Queens University of Belfast, UK) and N.J. Talbot (University of Exeter, UK).

Rice is the staple food and leading source of calorific intake for more than half of the worlds population. In West Africa rice is an increasingly important crop with raising consumption. However, average yield of 1.7 t ha 1 in the region is lowest in the world due to a number of bio-physical constraints. Blast caused by Pyricularia grisea (teleomorph: Magnaporthe grisea), occurs in all rice-growing ecologies and is a major constraint in upland environments where predisposition factors could favour disease development to epidemic proportions. In West Africa yield losses of 3.3 77 % have been reported, depending on the agro-ecological conditions. Globally, rice blast is primarily controlled by using resistant cultivars and/or application of fungicides, although problems are associated with both forms of management. Where blast is prevalent, resistant cultivars have an expected field life of only 2-3 growing seasons due to the high diversity of the virulent forms of the pathogen. With fungicides, pathogen resistance, economic as well as social costs to the farmers are issues of concern. Biotechnological approaches are being explored to identify pathogen-specific targets for developing environmentally compatible fungicides. We have generated baseline data on the genetic and pathotypic diversity of the rice blast pathogen populations in four West African countries Cote d Ivoire, Burkina Faso, Ghana and Nigeria. Key rice screening sites have been characterised and the dominant lineage/pathotype groups identified. This data is being used as a framework to identify resistance sources. Farmer participatory evaluation of these resistant material and utilisation of partial and major gene resistances is critical to the development and deployment of durable blast resistance in the West African region. Integrated management of blast as well as other major biotic constraints such as weeds needs to be further developed as blast populations present on wild rice and weeds appear to be closely related to rice pathogenic forms. Many of the current needs of the developing world, in particular, arise from a mixture of economic and social problems. Sustainable crop management approaches and improved varieties are essential if the doubling of agricultural output necessary for food security is to be achieved for a projected world population of eight billion or more by 2020. In this regard, scientists world-wide have embarked on various research strategies for rice blast management. For instance, using the lineage exclusion strategy, cultivar Oryzica Llanos 5 has shown durable resistance to rice blast for over 10 years in Columbia. Recently, by planting mixed stands of rice cultivars with a different spectrum of resistance to M. grisea, considerable reduction in rice blast has been achieved in Yunnan province in China. Both these approaches are based on a sound understanding of the biodiversity of the pathogen populations. These management strategies, coupled with appropriate cultural practices including seed hygiene and continued disease monitoring, could lead to sustainable control of rice blast in developing countries.

*; Work funded by the UK DFID-CPP Project R7552.

Towards understanding the diversity and epidemiology of Rhizoctonia species involved in rice sheath blight complex in Bangladesh: Molecular approaches

S. Muthmeenakshi and S. Sreenivasaprasad* (Horticulture Research International, Wellesbourne, Warwickshire CV35 9EF,UK), N. R. Sharma, S. Akter, M. Rahman, M. A. Taher Mia and M. Nahar, (Bangladesh Rice Research Institute, Bangladesh) and A.E. Brown, (The Queens University of Belfast, UK)

Rice accounts for about 80 % of total cropped area in Bangladesh and is the staple for more than 125 million people providing nearly 70 % of the daily calories. Upland (aus), irrigated (boro) and rainfed lowland (aman) are three of the major rice ecosystems and there is a major shift towards irrigated rice. Modern varieties (MVs) cover varying areas in these production systems and MVs make up nearly 90 % of irrigated rice. Sheath blight is recognised as a major disease of rice in Bangladesh, particularly in the irrigated system. Most of the modern and popular varieties, which are high tillering, high yielding and fertiliser responsive, are susceptible to this disease. Rhizoctonia solani (RS) is known as the principal pathogen of sheath blight, but recent studies in India have shown the presence of R. oryzae sativae (ROS) and R. oryzae (RO) in sheath blight-like symptoms. Sheath blight is difficult to control in view of the lack of host resistance and the ineffectiveness of chemical control. The three Rhizoctonia spp. described above are known to cause overlapping symptoms making disease/pathogen diagnosis difficult and unreliable. There is also a lack of information on these pathogens in Bangladesh. This collaborative project is aimed at assessing the prevalence of these three species from sheath blight-like symptoms from hot spots in major agro-ecological zones covering different production systems and understanding the diversity among pathogen populations using a range of molecular tools. This underpins approaches for efficient management of this important disease in rice-based cropping systems, where different susceptible and probably alternative hosts may be cultivated alongside rice or seedlings may be raised in an infested bed and transplanted in different farms. Disease incidence and yield loss surveys are being conducted and various management options such as organic amendments/biocontrol explored by the collaborative partners, working with farmers, in Bangladesh to develop sustainable disease management strategies. Robust diagnostic PCR tests have been developed combining the use of specific PCR primers designed from rRNA sequences for all three species and a simple and rapid protocol for DNA extraction from fungal cultures as well as infected plant samples. PCR tests of more than 40 isolated fungal cultures from across Bangladesh suggest R. solani as the dominant pathogen. However, diagnostic tests on DNA directly extracted from sheath samples indicate occurrence of R. oryzae-sativae/aggregate sheath spot and also mixed infections particularly by RS and ROS. Analysis of samples from four hot spots in Bangladesh is in progress to validate these observations. SSR-PCR and AFLP analysis of the RS isolates identified from 15 locations indicate their variable nature. Further analysis is ongoing to consolidate these markers to be able to compare Rhizoctonia spp. isolates originating from diseased rice tissue, soil samples and weed as well as other crop hosts. This would enable the identification of inoculum sources and understand pathogen epidemiology, laying the basis for improved disease management.; Work funded by the UK DFID-CPP Project R7778.

Air pollution - an increasing threat to food production in the developing world

Marshall F M & te Lintelo D J H

Imperial College of Science, Technology and Medicine, Department of Environmental Science & Technology,Faculty of Life Sciences, Silwood Park, Ascot, Berkshire, Contact: and/or 

The livelihoods of inhabitants of urban and peri-urban areas are dependent on access to cheap and safe food of high nutritional quality. In rapidly growing populations, food insecurity is becoming more of an urban problem, with poor families in developing countries spending as much as 60 to 80 per cent of their income on food. Agriculture in these areas in Asia is dominated by small scale farmers who depend on cultvation for both household food provision and income generation. Air pollution is one of the major threats to crop production in urban and peri-urban areas. Furthermore the levels of air pollutants are rapidly increasing in these areas. Increased number of motor vehicles, power generation, domestic fuel use, refuse burning and other sources all contribute to the problem. Air pollution has the potential to reduce both the yield and the nutritional quality of crop plants, with important implications for consumers, particularly the poor. In addition to direct impacts on crops, gaseous air pollution can also be associated with increased pest and disease damage. Air pollution is also a major source of heavy metals (for example lead, cadmium, zinc and copper) which can accumulate at toxic levels in the edible portion of crop plants. The poster describes recent and ongoing research in India (in and around the cities of Delhi and Varanasi) to assess the impacts and policy implications of  air pollution (focusing on the impacts of gaseous pollutants and heavy metal deposition) on the yield and quality of important food crops such as wheat, rice, mustard and vegetables. The research has been funded by the British Department for International Development, Environmental Research Programme (project ERP6992) and Crop Post Harvest Programme (project R7530).

Unravelling the molecular mechanisms of resistance in potato to Phytophthora infestans, the causal agent of late blight

Taleb N, Avrova A, Stewart H E, Cardle L, Jauffeerally-Fakim Y and Birch R P J., SCRI

Potato, Solanum tuberosum, is the world's fourth most important crop, being exceeded only by wheat, rice and maize in global human food consumption. Among the disease-causing pathogens of potato are Erwinia carotovora (causing blackleg and soft rot in storage), Ralstonia solanacearum (causing bacterial wilt), Alternaria solani (causing early blight) and Phytophthora infestans (causing late blight). Late blight is the most threatening potato disease, leading to economic losses worth US $ 3 million worldwide each year. Sources of natural resistance to late blight in potato germplasm have been intensively studied. Resistance can be of two forms, either race-specific or race-non-specific (field). Race-specific resistance is characterised by the interaction of the products of dominant resistance (R) genes from the host with the products of corresponding avirulence (Avr) genes from the pathogen. Conversely, field resistance is believed to be polygenic and durable, affecting a number of factors in the pathogen including growth rate and sporulation capacity. Both forms of resistance are present in cultivar (cv.) Stirling. As yet, the molecular bases of either form of resistance are unknown, either in terms of the recognition of the pathogen, or the subsequent activation of signalling pathways to defend against its invasion. In this project, a cross between cv. Stirling and field resistant cv. Maris Piper has generated progeny that have segregated for R-gene resistance or field resistance. Clones of this progeny: one possessing an R gene and another showing field resistance only, have been inoculated with an incompatible P.infestans race to trigger the defence mechanism and RNA extracted at several time-points post-inoculation. A two-way suppressive subtractive hybridisation (SSH) procedure was carried out to isolate sequences that are unique to either the R gene-resistant or the field-resistant plants. cDNA libraries for genes expressed specifically in each of these progeny clones upon infection with P.infestans have been generated and the sequences analysed. Most of the sequences isolated have proved to be interaction-specific, i.e. picked up in the 'R-gene' interaction but not in the 'field resistance' interaction and vice-versa. Among the sequences present in the 'field resistance' library are some interesting regulatory genes such as protein kinase MK5-like, homeodomain proteins and a G-box binding protein. The 'R-gene' interaction includes an interesting kinase (SNF1), transcription factors and an oncogene (elongation factor 5), which could have a role in cell death.