Efficacy of biological agent Lecanicillium lecanii for the management of coffee leaf rust in India

The coffee leaf rust (CLR) in Coffea arabica L. caused by a fungal pathogen Hemileia vastatrix Berk. & Br. is the most serious disease causing severe crop losses in almost all growing countries including India. Growing CLR tolerant cultivars and use of fungicides are the two important strategies in the CLR management and the biological control strategy has been exploited to a limited extent. The field observations revealed that a hyper parasite colonises completely over the CLR lesions and inactivates uredospores of H. vastatrix. The hyperparasite was isolated and identified as Lecanicillium lecanii Zare & Gams. The culture filtrate (CF) as well as the spore suspension (SS) of which were prepared and used for in vitro and in vivo studies. In vitro studies revealed that the germination of uredospores was significantly (P ≤ 0.01) reduced in all treatments containing the CF of L. lecanii. In in vivo studies, the orange-coloured uredospores discoloured (white) in T₁ (inoculation of H. vastatrix uredospores after 24 h. of spraying L. lecanii suspension) and T₂ (Inoculation of H. vastatrix uredospores after 48 h. of spraying L. lecanii suspension), one week after the imposition of treatments. The germination and establishment of L. lecanii on H. vastatrix was clearly evident by microscopic observation. Among the field grown 11 different Arabica coffee cultivars, maximum (63%) hyperparasitisation of uredospore pustules by L. lecanii was observed in CLR infected leaves of Selection.3 (Sln.3, popularly known as S.795) followed by Sln.12 (51%). This hyperparasitic mycoparasite could be exploited as a prophylactic biological measure before or after disease expression especially in varieties that are moderately tolerant or susceptible to CLR.