Integrated control of avocado white root rot combining low concentrations of fluazinam and Trichoderma spp.

Two monoconidial isolates of Trichoderma atroviride Miller and one of Trichoderma virens Giddens and Foster were combined with the contact fungicide fluazinam to improve the in vitro inhibition of Rosellinia necatrix Prillieux and the control of avocado white root rot caused by this fungus. A fluazinam concentration of 0.01 mg L-1 was obtained as the most effective minimum concentration for in vitro combinations of antagonist-fungicide, significantly reducing (on average, by 41%) the growth of a representative collection of pathogen isolates. The combinations of one isolate of Trichoderma atroviride or virens, plus fluazinam at 0.01 mg L-1 showed a greater in vitro growth inhibition of R. necatrix (36 and 65%, respectively) than the use of fluazinam alone (23%). However, the inhibition of R. necatrix growth by the other T. atroviride plus fluazinam was less than 20% and not significantly different from the control plus fluazinam. The isolate of T virens applied alone or with fluazinam at 0.01 mg L-1 induced growth inhibition (65%) of the pathogen similar to that induced by the control with fluazinam at a concentration of 0.05 mg L-1. A fluazinam concentration of 0.01% has been confirmed as effective for controlling white root rot of avocado. Furthermore, the combination of fluazinam at 0.001% with Trichoderma improves significantly the effective control of avocado white root rot on infected plants in comparison with treatments with the fungicide or the antagonist alone. In this way, our results suggest that applications of these antagonist/fungicide combinations should be recommended in order to avoid the development of resistance to the fungicide by the pathogen and improve the control of avocado white root rot. (C) 2017 Published by Elsevier Ltd.