PJB-2004-43
PATHOGENIC DIVERSITY IN ASCOCHYTA RABIEI ISOLATES COLLECTED FROM PAKISTAN
S.M. IQBAL*, A. GHAFOOR, N. AYUB** AND Z. AHMAD
Abstract
Pathogenecity of 42 isolates derived from single spore cultures representing 15 collecting sites of Pakistan were studied on 7 chickpea varieties. The isolates exhibited variation in morphological and cultural characteristics. Chickpea varieties C-727 and C 44 revealed high degree of susceptibility and suggested to be used as susceptible checks for screening experiments. The factor analysis revealed that first principal component (PC) was more related to blight reaction, second PC contributed more for isolate colony colour. The variability for other morphological traits was distributed among all the three components. The first PC was a weighted average of all the variables. Two clusters were observed using UPGMA that was able to separate A. rabiei isolates on the basis of virulence or aggressiveness. The virulent isolates gave same intensity of infection, whereas others were observed with varying degrees of infection. Multivariate analyses were able to distinguish isolates on the basis of virulence rather than origin or morphological/cultural characterization. The susceptible differentials were identified but no variety could be established as resistant that might be due to complex nature of A. rabiei. The situation suggests to modify chickpea breeding for blight resistance and to use multiple crosses to build resistance pyramids involving parents with known level of tolerance. Clustering pattern indicated the exchange of breeding material and disease cultures among the researchers or high heterogeneity in the isolates.
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