Epidemiology of sugarcane wilt: predisposition by root borer Polyocha depresella a myth or reality

Abstract

Sugarcane wilt caused by Fusarium sacchari is an important stalk disease in India which affects sugarcane production both in tropical and sub-tropical regions. Both the sett (stem cutting) and soil borne pathogen are responsible for pre and post-germination death of settlings, pokkah boeng (PB) and wilt during different growth stages leading to losses in number of millable (harvestable) canes, cane weight and juice quality. It is presumed that F. sacchari infection and severity are associated with different biotic and abiotic factors in different regions and the root borer, Polyocha depressella is assumed to play a major role in wilt epidemiology. During 2014-2017 we observed severe outbreaks of wilt in the parental collections, and hence undertook a detailed study on wilt and infestation of insect pests with more emphasis on root borer (RB). We analysed the data to establish the possible role played by the insect pest in predisposing the wilt in sugarcane clones. Of the total clones it was found that 321 (57.6 %) clones were infested by root borer and 354 (63.6%) clones were prone to wilt at various levels of severities either as mild drooping / yellowing of leaves to severe wilting and drying of canes. Among the 354 clones with wilt infection, ~223 had RB infestation and ~131 exhibited wilt alone with no RB infestation. Of the 321 clones with RB infestation, 98 remained free from any wilt incidence which indicated that 37% of the wilt affected canes did not show an association of RB and 30.5% of RB infested canes did not show F. sacchari infection revealing a weak relation between the two. Further, the severity of RB infestation remained low at 10% or less and ~23 clones exhibited moderate incidence. The present study established that F. sacchari infection in sugarcane occurs independently of RB and other pests attack under field conditions