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Virulence Forms of Ascochyta rabiei Affecting Chickpea in the Palouse. Hamidullah Jan, Assistant Plant Pathologist, Agricultural Research Institute, Tarnab, Peshawar, Pakistan, and M. V. Wiese, Professor, Plant Pathology Division/PSES, University of Idaho, Moscow 83843. Plant Dis. 75:904-906. Accepted for publication 5 March 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0904.

Ascochyta blight, caused by the fungus Ascochyta rabiei, is a serious yield-limiting disease of chickpea (Cicer arietinum) in the Palouse region of northern Idaho and eastern Washington. To supplement the development of blight-resistant chickpea lines for release in the region, the virulence of local A. rabiei isolates was investigated. Thirty-nine isolates of A. rabiei were collected from infected chickpea seeds, plants, and residues from different Palouse locations. Each isolate was inoculated onto seedlings of 15 differential chickpea lines in the greenhouse. The resultant spectrum of disease reactions rated on a 19 scale on each set of differential hosts distinguished 11 different virulence forms among the 39 isolates. Three virulence forms accounted for 21 of the 39 isolates. Two isolates produced unique virulence spectra. Seven isolates closely resembled A. rabiei International Center for Agricultural Research in the Dry Areas (ICARDA) race 3. None of the isolates resembled ICARDA race 6, which was highly virulent on all but one of the host lines. Neither geographic origin nor morphological characteristics such as pycnidial diameter, spore size, colony color, or radial growth of each isolate were related to virulence. This study provided evidence that the population of A. rabiei in the Palouse is composed of diverse virulence forms. Local breeding efforts to develop blight-resistant chickpea cultivars may need to incorporate broad-spectrum or multigenic resistance to be successful.