Pathotype IV, a new and highly virulent pathotype of Didymella rabiei, causing ascochyta blight in chickpea in Syria.

摘要

The causal agent of Ascochyta blight disease of chickpea is highly variable because of the presence of a sexual phase (D. rabiei [Mycosphaerella rabiei]). There is also selection pressure on the pathogen due to wide adoption of improved resistant chickpea cultivars in some countries. The pathogen is able to produce pathotypes with specific virulence on particular cultivars. Three pathotypes (I, II and III) have been reported. In this study, the presence of a new and highly virulent pathotype designated as pathotype IV was confirmed. To test the pathogenicity of the isolates collected and maintained at ICARDA, 10 isolates representing a wide spectrum of pathogenic variation, including those classified by S. M. Udupa et. al (3) and a putatively identified more virulent type, which was collected from a chickpea production field in the Kaljebrine area, Syria, were inoculated onto a set of differential chickpea genotypes. On the basis of pathogenicity tests, the isolates were classified into 4 pathotypes (I, II, III and IV). Of the 10 single-spore isolates, 4 showed similar disease reactions unique to pathotype I, 4 revealed pathotype II and one isolate each behaved like pathotype III or IV. SSR fingerprinting of these isolates provided evidence for genetic diversity. MAT-type analysis showed that 7 isolates were MAT1-1, while the remaining 3 isolates were MAT1-2 type. Initially, a number of chickpea wild relatives were screened to identify sources of resistance to pathotype IV, but none of the accessions tested showed resistance.