Morpho-cultural and pathogenic variability among isolates of Stemphylium vesicarium (Wallr.) E. Simmons, causing Stemphylium blight in onion collected from different geographical regions of Kashmir valley

Stemphylium blight is the most destructive disease of onion crop and poses a grave threat to the very existence of its cultivation in Kashmir. Thirty six (36) isolates of Stemphylium vesicarium (Wallr.) E. Simmons were collected from different locations and characterized for cultural, morphological and pathogenic variations. Isolates produced velvety, cottony or fullfy colonies of different colours like whitish, light to dark grey, olivaceous with greenish tinge and brownish with filliform, entire and undulate margins. Significant variation in colony diameter and sporulation was observed among isolates. Mean hyphal width ranged from 3.11 to 5.48 µm. Conidiophore length varied from 20.07 to 92.56 µm. Similarly, mean conidiophore breadth varied from 2.84 to 7.58 µm. and were either light brown, light brown to brown, brown and dark brown in colour. Conidial colour of isolates varied from light brown, brown, light brown to brown and dark brown and are ovoid, ovoid to oblong and oblong in shape. Transverse septation varied from 0 to 6 and longitudinal from 0 to 5. Average ascus size of isolates varies from 103.74–204.24 × 23.00–33.11 µm. Average ascospore size varied from 12.08–41.96 × 10.06–17.38 µm among the isolates. Transverse and longitudinal septation varied from 3 to 7 and longitudinal from 0 to 6. Ascospores varied in colour from light brown, to dark brown. In shape the ascospores of different isolates were oblong with rounded base and conical apex, oblong with both ends rounded and ellipsoidal. Isolates exhibited variations in incubation period, number, size and colour of the lesions.