Diagnosis and integrated management of onion wilt caused by Fusarium sp.

Abstract

Onion wilt is an endemic disease in producing farms of Michoacán, Mexico that can reduce yields up to 25-30%. From onion plants with wilting symptoms, a monosporic isolate of the fungus Fusarium spp. was obtained, and its pathogenicity was verified. The fungus was morphologically and molecularly identified as Fusarium sp. Also, Fusarium sp. susceptibility to biological, botanical, and chemical pesticides was determined through four different bioassays. In experiment I, Trichoderma spp. in vitro antibiosis was tested using the cellophane technique. In Trials II and III, the in vitro effect of botanical and chemical fungicides on the pathogen was evaluated through the amended potato dextrose agar (PDA) culture technique. In Study IV, the biological efficacy of the products previously selected during in vitro assays was evaluated under greenhouse conditions. During the antibiosis trials, the commercial strain of Trichoderma virens (PHC Root Mate®) inhibited 33.3% of Fusarium sp. mycelial growth. Among botanical pesticides, cinnamon-neem extract (NeemAcar®) at doses of 0.06, 0.08- and 0.10-mL L-1 inhibited 100% mycelial growth of Fusarium sp. The fungicides benomyl, prochloraz, and pyraclostrobin completely suppressed Fusarium sp. development. Under greenhouse conditions, the incidence of wilt of plants treated with Trichoderma spp. and botanical extracts applied individually and in combination did not present significant differences from chemical fungicides treated. These results will help to develop an integrated disease management program for onion wilt.