ISOLATION OF SOLANAPYRONE-A, SOLANAPYRONE-B AND SOLANAPYRONE-C FROM CULTURE FILTRATES AND SPORE GERMINATION FLUIDS OF ASCOCHYTA-RABIEI AND ASPECTS OF PHYTOTOXIN ACTION

Nine isolates of the fungus Ascochyta rabiei have been assayed for their ability to produce solanapyrone toxins. All isolates formed solanapyrone A, B and C which were secreted into the culture medium. Pronounced production of the toxins only occurred after onset of sporulation. The identification of the fungal products was achieved by cochromatography (TLC, HPLC), H-1-NMR (solanapyrone A and B) and mass spectrometry (solanapyrone B). Work with A. rabiei isolate X showed that cultivation in chickpea seed extract medium in a surface culture provided best conditions for maximal toxin production. The accumulation of solanapyrones over the growth cycle was monitored. Germinating spores produced solanapyrones C and B whereas solanapyrone A was formed from the 6th day of the culture period on. Application of a mixture of solanapyrones A, B and C to leaflets of intact plants from an A. rabiei resistant cultivar (ILC 3279) and a susceptible cultivar (ILC 1929) led to characteristic changes in leaf morphology which had earlier been observed in susceptible plants following infection with spores of A. rabiei. Attempts to demonstrate the occurrence of toxins in the infected leaf were unsuccessful. Application of solanapyrones to chickpea cell suspension cultures (derived from both cultivars) led to pronounced losses in viability and to plasmolysis of cells.