Morphological, cultural and pathogenic variability in Alternaria brassicae, the causing agent of black spot of rapeseed and mustard

Abstract

The study on pathogenic diversity of twenty isolates of Alternaria brassicae collected from different locations of Uttarakhand and Central Uttar Pradesh infecting Brassica species (Brassica rapa, Brassica juncea and Eruca sativa) revealed that there was a distinct difference among isolates in terms of mycelial growth, spore length, width, spore beak length and width. The average spore length varied from 21.23?m to 38.13?m with minimum of isolate AUA-19, AUA-43 i.e 21.23?m and maximum of AUA-47 i.e. 38.13?m . The isolates tested on Brassica juncea var.Varuna in green house conditions revealed that all the twenty isolates behaved differently. Among all the isolates, Brassica juncea isolates i.e. AUA-25, AUA-39, AUA-41, AUA-47, AUA-19, AUA-24, AUA-22, AUA-21, AUA-31, AUA-43 and AUA-45 from Uttarakhand, and AUP-29 from Central Uttar Pradesh can be grouped into highly pathogenic with range of Alternaria spot size i.e. 5.03-8.30mm in diameter, while isolate of Eruca sativa i.e. AUA-38 was found least pathogenic with 1.63mm in dia. and eight isolates AUA-18, AUA-20, AUA-23, AUP-28, AUA-32, AUA-33 and AUA-36 were found moderately pathogenic. This study will be useful in developing integrated management strategies of Alternaria leaf spot and breeding programs of oilseed crops (Brassica sp.).