The project was set up to increase the yield of arable (protein) peas by control of the main diseases, bacterial blight, pea seed borne mosaic virus and leaf and pod spot (Mycosphaerella pinoides). The major activity in the first stage of the programme was concerned with diagnostics. Highly specific polyclonal antiserum for the bacterial blight (Pseudomonas syringae pv pisi) was produced although a problem of cross reactivity with one organism remains to be resolved. Esterase profiles were shown to provide an additional check on the identity of pv pisi. Antiserum to pea seed borne mosaic virus was produced and preparation of antisera for Mycosphaerella pinoides was initiated. In 1991, pathogen dissemination and disease severity was restricted by dry conditions. However, tolerance limits for seed infection need to be determined under conditions favourable for the pathogen. Early in the application of the programme, a source of resistance to pv pisi was found, including race 6 which had no previously known source of resistance. The source was an accession of Pisum abyssinicum. Subsequent tests on 12 more accessions of this species indicated that they were all resistant. A new race specific resistant gene was found in a Chinese accession of P sativum.
Arable (protein) peas are widely grown in Northern Europe, specifically for use in animal feed. The main production areas are : France, UK and Denmark; the Netherlands is a major seed producer. Variability in crop yields are mainly attributable to diseases and environmental factors. In particular there are a number of important seed-borne pathogens; bacterial blight (Pseudomonas syringae pv. pisi), leaf and pod spot (Mycosphaerella pinoides) and pea seed-borne mosaic virus. Bacterial blight is subject to quarantine restrictions in the UK.
Bacterial and viral diseases cannot be controlled by chemical methods. With this in mind, there are two possible control strategies : (1) disease avoidance through a clean seed policy, monitored by effective diagnostic procedures (seed tests); (2) deployment of plant resistance appropriate to the main pathogenic variants (strains/races) of the pathogens.
Since neither strategy is likely to offer a complete solution to all three pathogens, we will attempt to combine both strategies. Some of the information required to carry this out and especially to implement the clean seed policy for bacterial blight will be obtained from a detailed study of disease epidemiology relating levels of seed-borne infection to primary and secondary infection in the crop, seed yield and infection levels in the harvested product. Diagnostic procedures based on serological methods will be developed to enable the simultaneous detection of the three pathogens from the same seed sample. The project will enable the setting of tolerance limits for detection methods, quality standards for seed production within the EC and quarantine standards for imported seeds.