VIRULENCE FOR FABA BEAN AND PRODUCTION OF ASCOCHITINE BY ASCOCHYTA-FABAE

The production of ascochitine by seven isolates of Ascochyta fabae acc ounted for the toxicity of culture filtrates of the fungus to cells is olated from leaves of Vicia faba. The LD(50) value for cells from cult ivars that were susceptible, tolerant or resistant to the fungus was s imilar i.e. 3.0 x 10(-5) M, 3.8 x 10(-5) M and 2.9 x 10(-5) M, respect ively. Ascochitine affected neither the germination of seeds nor the g rowth of mature plants at 5.17 x 10(-4) M but caused necrosis and wilt ing of plant cuttings at 2.5 x 10(-4) M and 5 x 10(-4) M. There was no association between virulence of 16 isolates of A. fabae for three cu ltivars of V.faba and the production of ascochitine in vitro. One isol ate produced no ascochitine in vitro and yet was the most virulent for two of three cultivars. The toxin could not be extracted from infecte d plants.