Variability in Fusarium oxysporum f.sp. ciceris, the incitant of chickpea (Cicer arietinum) wilt
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Date
2014
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Abstract
Evolution of new races of Fusarium oxysporum f.sp. ciceris (Padwick) Matuo and K. Sato poses a serious threat to successful deployment of wilt resistant chickpea genotypes. Therefore, in the present study, 24 isolates of F. oxysporum f.sp. ciceris collected from different chickpea growing areas of Punjab and adjoining states were assessed for morphological, pathogenic and molecular variations. Among 24 isolates, the maximum (8.78 mm/days) and minimum (5.00 mm/day) growth rate were exhibited by Foc-21 and Foc -15, respectively. The isolates showed growth pattern from appressed, fluffy to less fluffy and mycelial colour varied from different shades of white to purplish white. A significant variation with respect to size of micro (8.9-16.9 x 3.1-6.3 µm) and macro (21.7-64.9 x 2.7-10.0 µm) conidia was also observed. At pathogenic level, Foc-3, Foc-7 and Foc-22 showed virulence pattern, similar to existing races 1, 2, 3 and 4 on three standard differentials viz. JG 62, WR 315 and L 550 whereas rest of the isolates did not match with any of the existing race reaction. Further, the six selected genotypes could differentiate the isolates into four pathotypes based on their aggressiveness and Foc-8 was found more aggressive (98.48 % wilt incidence) whereas Foc-24 was found least aggressive (7.22 % wilt incidence). The sequences of ITS genomic regions of 19 isolates showed 99 % similarity with Foc sequences by BLAST analysis. Furthermore, these 19 isolates converged into three groups based on ITS region sequence homology. Besides, a set of 91 wild derivative lines was also evaluated in wilt sick plot. Two derivative lines viz. GLW 59 and GLW 107 were found free from wilt and remaining 37 and 52 lines were found moderately resistant and susceptible to highly susceptible respectively.