Role of Melanin Production by Helminthosporium species on Pathogenicity in Graminaceous Hosts

Fifty foliar blight diseased samples collected from wheat, barley and oat growing areas of north-western India revealed that Bipolaris sorokiniana was present in all the isolates collected from barley, wheat and Phalaris minor, while Drechslera avenae was associated with isolates from oats. All the test isolates were pathogenic on their susceptible check viz., PL426 (barley), HD-2329 (wheat), OL-9 (oats) and Phalaris minor. Minimum incubation period (2 days), maximum no. of lesions per leaf (9.29), maximum size of lesions (9.30 mm) and highestterminal disease severity score (89) were recorded with isolate Bsb1 from barley, followed by Bsw32 from wheat. The highest melanin production was recorded in isolate Bsb1 (2.58 μg g⁻¹) followed by 2.52 μg g⁻¹and 2.49 μg g⁻¹ in isolate Bsp43 and Bsw32, respectively. Comparison of melanin production and pathogenic behaviour of different isolates revealed that more aggressive isolates on their respective hosts also produced higher melanin as compared to other isolates and strong positive correlation (r=0.749) existed between the pathogenicity and melanin production in different isolates of Helminthosporium.