CBN-V Video Archives - S8-08
Pathogenicity and Resistance in Xanthomonas Blight of Cassava

Kemp B.P., J.R. Beeching and R.M. Cooper

School of Biology and Biochemistry, University of Bath, Bath, BA2 7AY, UK r.m.cooper@bath.ac.uk

        Resistant genotypes offer the only durable, practicable means of controlling X. axonopodis pv. manihotis (Xam) but the nature of defence in this key, staple crop is unknown. Host resistance (HR) is not expressed to Xam and resistance, based on many genes, is incomplete and dependent on environment and pathogen inoculum level. Preformed putative defences include copious latex production, which contains protease __1-3 glucanase and lysozyme activities. ESTs from a latex cDNA library have revealed constitutive expression of many defence related genes including chitinase, glucanase and PAL. cDNA-AFLP of cassava leaves undergoing HR to Pseudomonas syringae pv. tomato has revealed genes new to cassava; homolgues of a metalloprotease, glucanase, peroxidase and ACC oxidase were all found to be upregulated. Pathogenicity determinants of Xam are being investigated by disruption of a gum biosynthesis gene (EPS is produced copiously in planta) and a pel gene (pectate lyase appears as a single isoform).

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