Morphological and cultural variability of Alternaria Macrospora causing leaf Bilght in cotton

Abstract

Cotton (Gossypium hirsutum L.) is an important cash crop which played a dominant role in the industrial and agricultural economy of India. Alternaria a major foliar fungal pathogen showed wide variability in morphology as well as in culture. The morphological study of four isolates of A. macrospora spores showed that the mean mycelial width (7.95 μm), conidia size (70.11x21.845 μm), length of beak (7.58 μm), no. of transverse septa (3 to 7) and longitudinal septa (0 to 3) was maximum in Bharuch isolate and least mean mycelial width (5.09 μm), conidia size (42.46x10.66 μm), length of beak (5.02 μm), no. of transverse (3 to 4) and longitudinal septa (0 to 1) was observed in Navsari isolate. In Surat and Narmada isolate the mean mycelial width (4.33 and 5.48 μm), conidia size (46.51x12.88 and 48.51x12.90 μm), length of beak (5.73 and 5.79 μm), no. of transverse septa (3 to 8 and 3 to 5) and longitudinal septa (0 to 2 and 0 to 1), respectively. In case of cultural variability the colony color of Navsari, Surat, Bharuch and Narmada was grayish white, gray, grayish with sector and grayish black with sector, respectively. The excellent sporulation was observed in Bharuch isolate followed by Surat and Narmada. The Navsari isolate produced medium raised colony growth while other isolates showed raised pattern of mycelial growth.