Characterization of Bipolaris maydis isolates of different maize cropping zones of India

An experiment was conducted to study cultural, morphological and pathogenic variability in 12 isolates of Bipolaris maydis from different maize cropping zones of India. The isolates showed considerable variability in their cultural characteristics, morphology and pathogenicity to maize ( Zea mays L.). All the isolates produced dark coloured, fusoid conidia, measuring 6.14-23.41 µm × 2.15-5.70 µm. The conidia of MDCh1 isolate was largest (19.6 µm × 5.0 µm), whereas MUCh3 isolate produced smallest (9.7 µm × 3.3 µm) conidia. The average number of septa varied from 2 to 8. The isolate, MLCh1, showed highest number of septa (5.0). Isolate, MDCh1 (Delhi), showed maximum colony diameter and MLCh1 (Ludhiana), the minimum. However, growth on different culture media, revealed that, MKCh1 (Kangra), MDCh1 (Delhi) and MUCh6 (Udaipur) registered highest colony growth on PDA and Richard’s agar respectively, while MLCh1 (Ludhiana) registered minimum colony growth on both PDA and Richard’s agar media. The colour of mycelium of specific isolates varied between media. In a majority of the isolates, the colour was black ranging from light black, light grey, light green and grey. The colony texture was rough to smooth, regular to irregular margin with or without zonation. Pathogenicity test of isolates conducted under glasshouse conditions revealed that MKCh1 isolate was highly virulent with the highest disease score (3.6) in susceptible hybrid line and MUCh3 as the least virulent with disease score of 1.4 only. Apparently, all the isolates of B. maydis were virulent under glasshouse conditions.