EFFECT OF PREHELMINTHOSPOROL, A PHYTOTOXIN PRODUCED BY BIPOLARIS-SOROKINIANA, ON BARLEY ROOTS

The effects of prehelminthosporol, a toxin produced by Bipalan's sorokiniana, were investigated on barley roots. A concentration of 30 mu g.mt(-1) prehelminthosporol or higher in nutrient solution significantly increased the rate of nuclear disintegration in the root cortex cells. The toxin also increased leakage of ATP from intact roots of barley seedlings grown in nutrient solution, but the growth rate of the seedlings was not significantly affected. However, diluted filtrate from liquid shake cultures of the fungus inhibited the growth of the seedlings by 21-73% over a 5-day period. The results indicate that the toxin may play an important role in pathogenesis by killing or weakening plant cells in advance of the growing hyphae and facilitating nutrient uptake and further growth of the fungus in plant tissue. Different cultivars of barley differed in sensitivity to prehelminthosporol, but sensitivities were not correlated with known levels of resistance to B. sorokiniana.