SAPROTROPHIC ABILITY OF DIAPORTHE-PHASEOLORUM VAR CAULIVORA ON HOST AND NONHOST PLANTS, AND ON ABIOTIC SUBSTRATES

Four single-spore isolates of Diaporthe phaseolorum var. caulivora ori ginating from diverse, soybean-growing locations in the United States were investigated for their saprotrophic ability and production of per ithecia on host, non-host and abiotic substrates, Stem pieces of the h ost, Glycine max; non-hosts, Triticum aestivum, Euphorbia heterophylla , Aeschynomene americana, Xanthium strumarium and Sesbania macrocarpa; toothpicks; and capillary glass tube were used as substrates. Autocla ved substrates were placed on acidified potato-dextrose agar and the m edium was seeded with the four isolates of D. phaseolorum var. caulivo ra and incubated at 24 +/- 1-degrees-C. All isolates formed perithecia on substrates of plant origin. The pattern of perithecial arrangement was either clustered, solitary or both. Optimum carbon: nitrogen rati os for the production of perithecia were between 1:1 and 10:1. Ratios of 50:1, 100:1 and 500:1 supported either abundant, poor or no mycelia l growth, respectively. Some isolates produced perithecia on acidified potato-dextrose agar without any plant substrates, suggesting that fe rtile isolates exist in the homothallic Diaporthe phaseolorum var. cau livora.