Vol. 11, Special Issue 7 (2022)

Author(s):
Sanjeet Kumar, AK Mishra and CS Choudhary

Abstract:
The variability study of fifteen isolates of A. brassicae each collected from different district locations covering all 4 agroclimatic zones I, II, IIIA and IIIB of Bihar infecting mustard (Brassica juncea) revealed a distinct variation in terms of morphological characteristics viz. length, breadth, beak length and septations of conidia. The average conidial length, thickness, beak length, no. of transverse septa and no. of longitudinal septa varied from 150 to 243µm, 22.1 to 31.5 µm, 67 to 113.4 µm, 10.8 to 16 and 2.6 to 4.2 respectively. Severity of Alternaria blight disease of mustard in the term of percent disease intensity (PDI) also varied among source location of 15 isolates from 35.3 to 61.85%. Cultural characteristics like colony diameter, colour, growth pattern, margin and pigmentation among isolates also showed variability. The pathogenicity testing of isolates on mustard cultivar Varuna, revealed variable response among fifteen isolates. Four isolates namely MAB 01 Mzp, MAB 06 Prn, MAB 09 Bnk and MAB 14 Rts belonging to different districts under agroclimatic zones of Bihar as zone I, II, IIIA and IIIB respectively were found highly pathogenic and virulent in aggressiveness by causing spot size of more than 20 mm. However, seven isolates namely MAB 02 Gog, MAB 03 Swn and MAB 04 Cpr from zone I; MAB 07 Kth from zone II; MAB 08 Bgp and MAB 11 Skp from zone IIIA and MAB 15 Kmr from zone IIIB were found moderately virulent or pathogenic by causing mean spot size of 10-20 mm. Other 4 isolates were found as virulent or least pathogenic by causing spot size < 10 mm. This study may be useful in the development of integrated disease management strategy for Alternaria blight of mustard using breeding programs.