Studies on Cultural and Morphological Variability in Isolates of Exserohilum turcicum, Incitant of Turcicum Leaf Blight of Sorghum

Abstract

Sorghum [Sorghum bicolor (L.) Moench] belongs to family Poaceae. It is termed, as 'poor man's crop' as it performs well even in marginal lands under moisture stress conditions, low availability of fertilizers and other inputs as compared to other crops. The foliar pathogens are potential yield reducers, and may cause substantial yield losses when occur in epidemic form. Leaf blight of sorghum caused by Exserohilum turcicum (Pass.) Leonard and Suggs is a major foliar disease, which substantially damages the foliage. The foliar blights and spots cause direct loss of foliage due to premature drying and early seedlings blights, or loss in other forage components like fodder weight and reduced carbohydrate translocation to other parts of plants due to reduced photosynthesis and transpiration. A total of 20 isolates of E. turcicum were obtained from district of Northern Karnataka. These isolates were grown in Potato Dextrose Agar (PDA). They varied in their cultural and morphological behaviour. All the isolates were found pathogenic to sorghum. The virulent isolate (E04) showed significant variations in colony colour, colony texture, surface and topography, margin, lustre, sporulation and consistency in the media viz., PDA, Malt extract Agar, Saboraud's Medium, Richard's Medium, Czapek's dox medium, Yeast extract mannitol agar and Oat meal agar. The maximum average growth of the isolate (E04) was supported by PDA medium (7.35 cm) whereas minimum growth was recorded in V-8 juice agar medium (3 cm). Conidia were observed in all the isolates except Et07, Et09 and Et17. Among the isolates, conidia size was maximum in isolate Et10 (87.13 × 12.31 µm) with an average of 7-10 septation and minimum in isolate Et14 (33.92 × 12.23 µm) with 3-4 septation.