Pathogenic and genetic diversity of Didymella rabiei affecting chickpea in Syria

Abstract Simple sequence repeats and mating type markers were used to estimate the genetic diversity of 133 Didymella rabiei isolates collected from nine provinces of Syria. Moreover, phenotyping was done on 56 isolates randomly selected from the different genetic groups using five chickpea genotypes. The genetic diversity of D. rabiei population was high with inter-population variability accounting for 83% of the total variation, whereas the genetic diversity among populations was very low (17%). Principal component analysis grouped the isolates from Aleppo, Idlib, Hama, Homs and Hassakeh provinces together, while Daraa and Tartous were in different groups. Isolates from Lattakia and Suweida provinces formed very distinct clusters compared to the others. The 56 isolates were grouped into four pathotypes, namely, pathotype-1 (12 isolates), pathotype-2 (13 isolates), pathotype-3 (5 isolates) and pathotype-4 (26 isolates) with varying degrees of virulence on the chickpea genotypes. Our findings showed a clear genetic shift toward more virulence over time and space in the populations of D. rabiei in Syria. These results stress the need for chickpea breeding materials to be tested for resistance to the more virulent pathotypes. Also, concerted action should be taken to ensure the shipment of healthy seeds of international chickpea nurseries to avoid D. rabiei genotypes or pathotypes flow from Syria to other countries.