Mechanism of Carbendazim Resistance in Fusarium and its Management

Abstract

Carbendazim belonging to benzimidazole group of fungicides is one of the most widely newlineused fungicides for the management of various soil borne and foliar pathogens. Resistance in newlineFusarium species against carbendazim has increased because of its specific mode of action (i.e.) newlinebinding with and#946; -tubulin proteins and disrupting the mitotic cell division. Forty-two Fusarium newlinespecies isolated from horticultural crops were tested for resistance to carbendazim and other newlinebenzimidazole fungicides. Ten isolates were tolerant to carbendazim even at 5000 ppm. These newlineresistant isolates were from ornamental crops viz. carnation (7), marigold (1) and gladiolus (2). newlineIn seven of these carbendazim tolerant isolates there was cross resistance to benomyl and newlinethiabendazole. Occurrence of multiple resistance to fungicides in Fusarium species was newlineobserved in many isolates to different fungicides viz., copper oxychloride (9), tebuconazole (2), newlinebitertanol (2), mancozeb (2), azoxystrobin (1), tebuconazole (1) and propiconazole (1) upto 5000 newlineppm concentration. However all isolates were sensitive to captan, pyraclostrobin and newlinechlorothalonil. newlineThe mechanism of carbendazim resistance in Fusarium resistant isolates was examined to newlinefind point mutations in and#946;-tubulin gene. Point mutation from leucine to threonine at codons newlineL240T, L246T, L250T, L253T, L263T, L273T, L289T and L311T was observed in all resistant newlineisolates (FGS-SOL, FOD IIHR7 and FGA-HOS) whereas, no point mutation (amino acid newlinechanges) was found in sensitive isolates (FOGF11-IIHR and FGUA-IIHR). The cytological newlineobservations on nuclear material and germiling morphology indicated no adverse effects on newlinecarbendazim resistant Fusarium isolates when treated with carbendazim. However, sensitive newlineisolates produced abnormal branching, distorted, stunted germiling along with inhibition of germ newlinetube elongation and abnormal aggregation of nuclei. The efficacy of alternate fungicides viz., newlinechlorothalonil (0.2%), captan (0.2%), bitertanol (0.2%), pyraclostrobin (0.1%), propiconazole newline(0.1%), mancozeb (0.2%), tebuconazole (0.1%) was evaluated for wilt incidence in gladiolus and newlinemarigold through pot culture. Fungicides captan, mancozeb, bitertanol, pyraclostrobin, newlinechlorothalonil and propiconazole were highly effective in reducing the pathogen population and newlinewilt incidence in marigold and gladiolus. newlineEvaluation of biocontrol agent (Trichoderma harzianum) and fungicides against newlinecarbendazim resistant F. solani in marigold indicated that the combination of biocontrol agent newline(carbendazim tolerant TH-GJ16B isolate) with carbendazim (8.33% wilt) showed best result newlinefollowed by another isolate of TH-10 which is T. harzianum isolate tolerant to copper newlineoxychloride (16.66% wilt). Treatments with TH-GJ16B isolate with copper oxychloride (16.66% newlinewilt), TH-10 with copper hydroxide (25% wilt) and TH-GJ16B with copper hydroxide (25% newlinewilt) were also found effective in minimizing wilt disease in marigold. Use of alternative newlinefungicides and carbendazim tolerant Trichoderma isolates will not only help in the management newlineof Fusarium wilt in marigold and gladiolus but also in managing the carbendazim resistance by newlinereducing the inoculum level of resistant isolates in soil over a period of time in the target newlinelocations where fungicide resistant populations occur newline