Pathogenic variability in isolates of Alternaria brassicae (Berk.) Sacc. from different agro-climatic zones of India
Pathogenic diversity of twenty four isolates of Alternaria brassicae (Berk.) Sacc. collected from different agro-climatic zones of India infecting rapeseed and mustard were studied. Each isolate was derived from single lesions and compared for morphological and pathological diversity. Results revealed that there were distinct differences among isolates in terms of conidial length, breadth and number of septation. The average conidial length varied appreciably from 57.60 to 271.79µm. The minimum conidial length was recorded in case of BRT isolate and maximum in case of VRN. The isolates BTD, BBK, DSA, GNR, HSR and PNT appeared to have wide virulence pattern as these isolates could infect all the seventeen host differentials. Isolates BHP, BRT, GDP, HSRP, JPR, NGN, B. alba and Midas-1 were able to infect sixteen host differentials. Virulence of isolates B chin and VRN was confined to 13 host differentials. The host differential B. alba variety ‘Local’ was least susceptible as only twelve isolates were pathogenic on it. In terms of incubation period, majority of the isolates took 3–5 days to initiate the disease whereas, isolates ASM, BHP, FRD, JPR and RSR took longer period to produce symptoms on cruciferous vegetables. Eight host differentials differentiated all the twenty isolates into fourteen categories and each category could be designated as one pathotype/race. These studies confirmed the existence of variability among isolates of Alternaria brassicae in India.
Alternaria brassicae, isolates, variations, rapeseed-mustard, agro-climatic zones, India.