Morphological, Cultural and Physiological Variations among Isolates of Colletotrichum Falcatum went That Cause Red Rot Disease of Sugarcane

Abstract

Sugarcane is an important economical cash crop grown over an area of about 5.07 Mha in India. Red rot disease caused by the fungus Colletotrichum falcatum Went., is the most important and the dreaded disease affecting adversely the production of millable canes in India. Five isolates of C. falcatum were procured from ISSR, Lucknow; the culture was maintained on slants and Petri plates at 29°C. Variation in the cultural, morphological and physiological characteristics among the 5 isolates was investigated. These isolates were morphologically differentiated into two distinct groups: light colour and dark colour types based on the colony colour character. Three isolates (RR-08, RR-02 and RR-07) in the dark type produced gray colour colonies whereas isolates Cf-09 and Cf-08 in the light type had white colour colonies. The growth rate among all isolates varied from 10.6 to 11.9 mm.d-1 and was not significantly different. The five isolates produced setae and conidia that were hyaline, one-celled, falcate or sickle-shaped. The conidia of all isolates ranged between 31.2 and 36.5 μm in length and from 10.1 and 11.2 μm μm in width. All isolates were varied in their physiological characteristics. The optimum physical parameters for mycelial growth of the five strains was found to be 30°C for temperature, 5.5 (for four isolates viz., Cf-09, Cf-08, RR-08, RR-07) and 6.0 (for isolate RR-02) for pH. Host extract media maintained the highest mycelial growth in all the five isolates followed by PD broth. Dextrose and potassium nitrate were found to the best sources of carbon and nitrogen, respectively for maximum mycelial growth of Cf-09, Cf-08, RR-08 and RR-02 isolates while glucose and sodium nitrate were the best source of carbon and nitrogen, respectively for RR-07 isolate of C. falcatum. We have found that Colletotrichum falcatum isolates were culturally, morphologically and physiologically dissimilar.