DEVELOPMENT OF DIDYMELLA-RABIEI, THE TELEOMORPH OF ASCOCHYTA-RABIEI, ON CHICKPEA STRAW

The teleomorph of Ascochyta rabiei was induced to develop and mature on artificially infested chickpea straw. High moisture and low temperature (5-10 C) were the major factors required for pseudothecial development and maturation. At 8 C, pseudothecia developed and matured in about 8 wk. Morphological characteristics of pseudothecia, asci, and ascospores confirmed the identification as Didymella rabiei rather than Mycosphaerella rabiei. The fungus is heterothallic, and the two mating types have been referred to as MAT1-1 and MAT1-2. Under field conditions in the Palouse region of the Pacific Northwest, the teleomorph developed extensively on overwintered chickpea crop residues that remained on the soil surface. Pseudothecia appeared in early fall, matured during the fall and winter, produced ascospores during the spring, and were almost completely exhausted of ascospores by the beginning of the summer. The estimate of ascospore production by highly infested chickpea crop residues was about 15,000 ascospores per square millimeter of tissue surface. Most ascospores were discharged from the beginning of March to the end of May. The discharge period overlapped with the vegetative stage of the chickpea crop, indicating that ascospores may serve as primary inoculum for epidemics of Ascochyta blight in the Palouse region.