Evaluation of carbendazim tolerant strain of Trichoderma harzianum GJ16B for its efficacy in the management of carbendazim resistant Fusarium solani isolate causing marigold wilt

Abstract

Use of benzimidazole fungicides is commonly followed to manage Fusarium wilt disease in many crops. Recently we reported benzimidazole resistance in Fusarium wilt pathogens infecting marigold, carnation and gladiolus. The strategies to manage fungicide resistance include (i) use of alternate compounds (ii) use of combination products and (iii) use of fungicide tolerant bioagents. In this study, Trichoderma harzianum isolates that were tolerant to carbendazim and/or insensitive to copper oxychloride (COC) were evaluated under pot culture for their efficacy against marigold wilt. Isolate Th-GH16B was tolerant to carbendazim and insensitive to COC while isolate Th10 was sensitive to carbendazim and insensitive to COC. Per cent wilt and root colonization by Fusarium solani were recorded at 15, 30, 45 and 60 days after inoculation. The rhizosphere population of T. harzianum was also recorded at 15, 30, 45 and 60 days after inoculation. The wilt incidence in pathogen alone inoculated pots was 83.3% while there was only 8.33% wilt incidence with combined application of TH-GJ16B isolate and carbendazim at 0.1%. There was 16.66% wilt incidence with application of Th-10 or Th-GH16B along with 0.2% COC. Combination of Th-10 or Th-GJ16B with CuOH (0.2%) could reduce the wilt incidence to 25% compared to 100% infection in inoculation with pathogen alone. There was corresponding reduction in the recovery of Fusarium colonies in treated pots. The treatment TH-GJ16B along with carbendazim reduced Fusarium population by 61.88% compared to Fusarium alone inoculated plants. TH-GJ16B along with COC reduced Fusarium population by 59.3%. The use of carbendazim tolerant strain Th-GJ16B along with carbendazim will more effectively help in management of Fusarium wilt in marigold.