Widespread Occurrence of Colletotrichum falcatum Pathotype CF13 in the Subtropical India Dictates Continuous Pathogenic Virulence and Severe Sugarcane Crop Destructions

Red rot of sugarcane caused by Colletotrichum falcatum continues to be a serious threat to sugarcane production in India especially in the subtropical region. Elite varieties with red rot resistance succumb to new variants of the pathogen that leads to recurrent epidemics of the disease, resulting in enormous crop/economic losses. Recently, C. falcatum pathotype CF13 responsible for breakdown of disease resistance in the popular cv Co 0238 has been characterized and designated. Since the disease incidence and severity continue to affect the crop over large areas in the subtropical states in India, further studies were conducted to assess pathogenicity of 176 C. falcatum isolates, including eight designated pathotypes on a set of 10 host differentials at five locations in Punjab, Haryana, Uttar Pradesh and Bihar states and analysed the distribution of the pathotypes under field conditions. Among the 176 isolates, a majority of 112 isolates were from the popular variety Co 0238 (63.6%) which occupied about 50–60% of cane area in the subtropical region and the remaining isolates were isolated from the cvs CoJ 85, Co 89003, CoJ 64, CoPk 05191, CoS 08279, CoS 8436, Co 0118, Co 98014, CoJ 88, CoS 07250, CoS 08272, etc. The pathogenicity and virulence behaviour of the new isolates further confirmed the continued virulence of the isolates from the cv Co 0238, and all these isolates maintained a close similarity with the pathotypes CF13. In contrast, the isolates from other varieties exhibited differential reactions on Co 0238 depending on the location. In Punjab conditions, other host isolates exhibited an avirulent behaviour on Co 0238, whereas majority of them exhibited a virulent behaviour in Uttar Pradesh. Comparison of the pathogenic virulence of 112 Cf0238 isolates with 57 other host isolates across the locations in the subtropical region clearly revealed a uniform distribution of the pathotype CF13 with small islands of the pathotype CF08 in Punjab, Haryana and Bihar and overlapping behaviour of few isolates. These findings suggest immediate replacement of the variety Co 0238 to reduce the dominance of the pathotypes CF13 along with integrated disease management practices to contain the pathogenic virulence of C. falcatum to protect the new varieties from the pathogen attack.