Peh, Eng Kok; (1994) Evaluation of the role of solanapyrone toxins in Ascochyta blight of chickpea. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Toxigenicity and virulence of twelve isolates of Ascochyta rabiei (Pass) Lab. were studied. All isolates produced the phytotoxins solanapyrones A, B and C and these compounds explained 70% - 80% of the toxicity of culture filtrates. The toxins were separated and quantified by High Performance Liquid Chromatography using an isocratic solvent system developed through application of solvent optimization techniques. Toxin production was affected by isolate, medium and growth conditions. Initially, Czapek Dox nutrients supplemented with chickpea seed extract was used but later a defined medium, in which various cations were substituted for the extract was developed. Zinc was essential for solanapyrone production and a concentration of 50mg/l was optimal. Isolate 6K (PUT7) produced the greatest total quantity of solanapyrone in the defined medium (solanapyrone A, 2.36mM; B, 0.924mM and C, 1.216mM) and isolate TAV the least (solanapyrone A, 0.201 mM; B, 0.012mM and C, 0.009mM). Virulence of isolates was tested using cultivars Amdoun, ILC-482 and ILC- 3279. Isolate 6K was the most virulent and isolate AR-8710 the least. A close correlation between the quantity of solanapyrones produced by twelve isolates and their virulence was observed, (r2 = 61%) and when two outliers were ignored the value for r2 increased to 82%. This suggests that the virulence of isolates may, at least in part, be explained by their ability to produce the solanapyrones. Also, sensitivity of cultivars to solanapyrones appears to explain their susceptibility to A. rabiei, the most sensitive cultivar being the most susceptible and the least sensitive being the most resistant. Genome organisation of fungal isolates was studied using the Polymerase Chain Reaction with decamer oligonucleotide primers to identify Random Amplified Polymorphic DNA. Although many primers, variations of temperature and time regimes as well as concentrations of the constituents of the reaction mixtures were tried none gave consistent results. Attempts to mate isolates of the fungus and produce pseudothecia were unsuccessful.

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