The efficacy of wild type and two mutants of Trichoderma arundinaceum and Trichoderma brevicompactum spores against Acanthoscelides obtectus and effect on Phaseolus vulgaris seed vitaly

Abstract

Wild and cultivated common beans are susceptible to attack by the insect pest Acanthoscelides obtectus. In this study, four Trichoderma strains were evaluated: T. arundinaceum IBT 40837 (Ta37, wild type strain), which produces the trichothecene harzianum A (HA); two transformants of Ta37, Ta37–17.139 and Ta37–23.74, in which the tri17 and tri23 genes, respectively, involved in the biosynthesis of HA, have been deleted; and T. brevicompactum IBT 40841 (Tb41, wild strain), which produces trichodermin, another trichothecene. These four strains were evaluated to determine the response of A. obtectus adults’ behaviour and virulence to the compounds or intermediates produced by the deleted mutants. The Δtri23 strain was more attractive to insects compared to the other strains and led to a greater number of insects emerging from damaged bean. In contrast, Ta37 and Tb41 strains exhibited repellent effects on insects and resulted in a lower number of damaged beans. Beans treated with Δtri23, Δtri17, and Tb41 strains showed higher accumulated mortality of insects. Furthermore, emergence of insects was reduced in beans treated with Ta37, Δtri17, and Tb41 strains. Application of Ta37, Δtri23, and Δtri17 strains on undamaged beans favoured germination, while application of Tb41 and Δtri17 strains on damaged seeds increased germination capacity at 12 and 24 days after sowing, respectively, provided the embryos were undamaged by insect larvae. These findings highlight the different abilities of Trichoderma strains to control A. obtectus, with Tb41 and Δtri17 showing promising insect control effects while promoting germination capacity in both damaged and undamaged beans.