Spores of Trichoderma Strains over P. vulgaris Beans: Direct Effect on Insect Attacks and Indirect Effect on Agronomic Parameters

SIMPLE SUMMARY: Acanthoscelides obtectus is an insect pest that attacks wild and cultivated common beans (Phaseolus vulgaris L). Four Trichoderma strains, T. arundinaceum IBT 40837, Ta37-17.139 (=Δtri17), and Ta37-23.74 (=Δtri23), and T. brevicompactum IBT 40841 were assessed to establish their direct effect on insect attacks and their indirect effect on the plants grown from the beans treated with those fungal strains and exposed to insect attacks. Treatments of bean seeds with different Trichoderma strains led to different survival rates in the insects. Insect cadavers (in contact with Δtri23) showed growth of this strain. The emergence of insects was reduced in the beans treated with the Ta37, Tb41, and Δtri17 strains. The undamaged beans (treated with Ta37 and Δtri23) provided a high capacity of germination, whereas the Δtri17 and Tb41 treatments increased the capacity of germination in the damaged beans. The undamaged beans treated with Δtri23 obtained the greatest dry weights of the aerial part and root system in the plants. More studies on the mechanisms of insect control, plant growth promotion, and volatile compound production by Δtri23 and Tb41 should be explored in order to commercialize these fungal species on a massive scale. ABSTRACT: Acanthoscelides obtectus is an insect pest that attacks wild and cultivated common beans (Phaseolus vulgaris L). Four Trichoderma strains, the T. arundinaceum IBT 40837 wild-type strain (=Ta37), a producer of trichothecene harzianum A (HA), two transformants of T. arundinaceum strain, Ta37-17.139 (=Δtri17) and Ta37-23.74 (=Δtri23), and the T. brevicompactum IBT 40841 wild-type strain (=Tb41), which produces the trichothecene trichodermin, were assessed to establish their direct effect on insect attacks and their indirect effect on the plants grown from the beans treated with those fungal strains and exposed to insect attacks. Treatments of bean seeds with different Trichoderma strains led to different survival rates in the insects, and the Tb41 strain caused the lowest survival rate of all. An 86.10% of the insect cadavers (in contact with Δtri23) showed growth of this strain. This was the treatment that attracted the greatest number of insects. The daily emergence was reduced in beans treated with the Ta37, Tb41, and Δtri17 strains. The undamaged beans treated with Ta37 and Δtri23 showed a high capacity of germination (80.00% and 75.00%, respectively), whereas the Δtri17 and Tb41 treatments increased the capacity of germination in the damaged beans (66.67%). The undamaged beans treated with Δtri23 had the greatest dry weights for the aerial part (4.22 g) and root system in the plants (0.62 g). More studies on the mechanisms of insect control, plant growth promotion, and trichodermol and trichodermin production by Δtri23 and Tb41, respectively, should be explored in order to commercialize these fungal species on a large scale.