Chickpea Ascochyta Blight: Disease Status and Pathogen Mating Type Distribution in Syria

Abstract

Chickpea fields were surveyed in nine major chickpeagrowing provinces of Syria in 2008 and 2009 to determine the prevalence and severity of Ascochyta blight, and the distribution of Didymella rabiei mating types (MATs) in the country. A total of 133 Ascochyta rabiei isolates were assayed for mating type, including isolates from older collections that date back to 1982. Multiplex MAT-specific PCR with three primers was used for MAT analysis. Out of the 133 tested isolates, 64% were MAT1-1 and 36% were MAT1-2. Both MATs were found in six provinces but MAT1-1 alone was found in three provinces. Chi-squared analysis was used to test for a 1 : 1 ratio of MAT frequencies in all samples. The MAT ratios in the six provinces were not significantly different from 1 : 1, suggesting that there is random mating of the pathogen population under natural conditions. The presence of the two MATs is expected to play a role in the evolution of novel virulence genes that could threaten currently resistant chickpea varieties. Overall analysis of the 133 isolates showed a significant deviation from the 1 : 1 ratio with almost twice as many MAT1-1 isolates than MAT1-2 isolates, which indicates a competitive advantage associated with MAT1-1 in Syria. However, the overall picture of an unequal frequency in MATs indicates that there may be limited sexual recombination occurring in the Syrian population.