Decreased aggressiveness of Bipolaris sorokiniana conidia in response to nutrient stress

Aggressiveness of Bipolaris sorokiniana conidia on wheat seedlings was decreased when conidia were incubated on either a sandy loam soil at −50 mb matric potential for 15 days or a sand bed through which a salts solution was percolated for 5, 10 or 15 days. Seedlings inoculated with treated conidia showed significantly (P = 0·05) less disease and had longer roots and coleoptiles in most treatments, than seedlings inoculated with nontreated conidia. Conidia that had been incubated on soil or leached sand for 15 days showed less germination than nonincubated conidia in a salts solution or wheat seedling exudate. The germination rate of treated conidia on potato dextrose agar was lower than that of nontreated conidia, but viability was not affected. Loss of ¹⁴C from labelled conidia incubated for 15 days on soil or leached sand was 11·2 and 12·0%, respectively, of total label. The results indicate that incubation of conidia under conditions of nutrient stress can attenuate the aggressiveness and germinability of B. sorokiniana conidia, and that these changes were associated with loss of endogenous carbon from the conidia.