SCREENING METHODOLOGY FOR POSTHARVEST FUNGAL RESISTANCE IN ALFALFA

Forage deterioration due to field and storage fungi represents a major economic loss for hay producers. A series of experiments was conducte d to develop a methodology for screening alfalfa plants for resistance to post-harvest fungal colonization. Pure cultures of Aspergillus gla ucus, Aspergillus repens, Aspergillus flavus, Aspergillus versicolor a nd Aspergillus fumigatus, isolated from alfalfa forage sampled during field wilting and storage, were established and maintained to produce a 10(5) spore mL(-1) suspension containing an equal proportion of spor es from each Aspergillus spp. Alfalfa leaves were dipped in concentrat ions of propionic acid solution to simulate levels of resistance to fu ngal activity. Fully-developed trifoliate leaves were placed adaxial s ide down onto petri plates containing a dichloran (2 mg mL(-1)) and gl ycerol (18% vol/vol) agar. The Aspergillus spp. spore suspension was s prayed onto each petri plate and the plates were incubated under dark conditions at 25 degrees C and 70% relative humidity. Plates were moni tored daily for percent of leaf area colonized. The random screening o f a small population of cloned alfalfa genotypes using this screening procedure indicated that variation in post-harvest resistance to funga l attack does exist for greenhouse and field-grown plants harvested at an early vegetative stage. Leaf dry matter was not related to genotyp e variation in post-harvest susceptibility to fungal colonization; how ever, leaf soluble carbohydrate level was negatively correlated (P < 0 .05) with leaf area colonized, The screening procedure did not detect consistent differences among genotypes when dried leaves were used.