GENOTYPING WITH RAPD AND MICROSATELLITE MARKERS RESOLVES PATHOTYPE DIVERSITY IN THE ASCOCHYTA BLIGHT PATHOGEN OF CHICKPEA

The poor definition of variation in the ascochyta blight fungus (Ascoc hyta rabiei) has historically hindered breeding for resistance to the chickpea (Cicer ar arietinum L,) blight disease in West Asia and North Africa. We have employed 14 RAPD markers and an oligonucleotide probe complementary to the microsatellite sequence (GATA)(4) to construct a genotype-specific DNA fragment profile from periodically sampled Syri an field isolates of this fungus. By using conventional pathogenicity tests and genome analysis with RAPD and microsatellite markers, we dem onstrated that the DNA markers distinguish variability within and amon g the major pathotypes of A. rabiei and resolved each pathotypes into several genotypes. The genetic diversity estimate based on DNA marker analysis within pathotypes was highest for the least-aggressive pathot ype (pathotype I), followed by the aggressive (pathotype II) and the m ost-aggressive pathotype (pathotype III). The pair-wise genetic distan ce estimated for all the isolates varied from 0.00 to 0.39, indicating a range from a clonal to a diverse relationship. On the basis of geno me analysis, and information on the spatial and temporal distribution of the pathogen, a general picture of A. rabiei evolution in Syria is proposed.