Trichoderma longibrachiatum, a biological control agent of Sclerotium cepivorum on onion plants under salt stress

Salt stress and pathogen infection cause damage to onion crops and limit production. Application of Trichoderma species could be an option for reducing crop damage. The objective of this work was to evaluate the capacity of Trichoderma longibrachiatum to reduce damage to onion plants caused by salinity and infection by Sclerotium cepivorum. The two fungi showed differences in their tolerance to NaCl depending on the NaCl concentration. At low concentrations of NaCl, S. cepivorum was more tolerant than T. longibrachiatum, while at high concentrations of NaCl the tolerance of T. longibrachiatum was reduced to 17% and S. cepivorum did not grow. However, T. longibrachiatum maintained antagonistic activity against S. cepivorum in the presence of NaCl. Compared with uninoculated plants, inoculation with T. longibrachiatum increased the biomass of plants infected with S. cepivorum, plants treated with NaCl, and also plants treated with the combined treatment of S. cepivorum and NaCl. In plants infected with S. cepivorum and with the combined treatment of NaCl and S. cepivorum, the disease severity index was 69 and 89 %, respectively. However, inoculation with T. longibrachiatum reduced the disease severity index to 12 and 60 % in plants infected with S. cepivorum and in the combined treatment of S. cepivorum and NaCl, respectively. Chlorophyll and carotenoid content were maintained in plants inoculated with T. longibrachiatum and then subjected to salinity and infection; T. longibrachiatum decreased electrolyte leakage caused by salinity and infection. In conclusion, inoculation of onion plants with T. longibrachiatum reduced damage caused by infection with S. cepivorum and NaCl in onion plants; this was achieved by maintaining biomass and the content of photosynthetic pigments and by reducing electrolyte leakage. T. longibrachiatum is a fungus with potential as a biological control agent of S. cepivorum on onion plants under salt stress.