Variability in Alternaria brassicae and characterization of host response in Ethiopian mustard (Brassica carinata A. Braun)

Abstract

The present investigation was undertaken to determine variability in virulence among four isolates of
Alternaria brassicae (Berk.) Sacc., one each from Brassica juncea, B. rapa, B. napus and B. carinata
on the basis of conidial morphology, cultural characteristics, sporulation intensity and length of incubation
period. Results revealed that all parameters significantly affected virulence. The average length and breadth
of the most virulent B. napus (A.Bn) isolate were 171.0 μm and 26.1 μm, compared to only 134.0 and 19.0
μm, respectively, of the least virulent B. juncea (A.Bj) isolate. Similarly, the horizontal and vertical conidial
septations, diameters of both halo formation and concentric rings and sporulation intensity were significantly
higher in the most virulent (A.Bn) than in the least virulent (A.Bj) isolates; incubation period was shortest
(2 days) in the (A.Bn) isolate. Results of screening of 45 mutants of B. carinata against the most virulent A.Bn
isolate revealed longest incubation period of 4 to 5 days in the 17mutants; 10 of the 17 mutants showed very
poor sporulation intensity and smaller diameters of both halo formation and concentric rings. These 10
moderately resistant mutants viz; P7, (P10)2, P11, P74 in 50 kR, (P4)2, (P5)2, P2 in 70 kR, (P4)2 in 80 kR, P22 in 90
kR, and P13 in 100 kR were further field evaluated to confirm their reaction.