Context-dependent effects of Trichoderma seed inoculation on anthracnose disease and seed yield of bean (Phaseolus vulgaris): ambient conditions override cultivar-specific differences

Root colonizing Trichoderma fungi can stimulate plant immunity, but net
effects are strain × cultivar-specific and changing ambient conditions
further contribute to variable outcomes. Here, we used four Trichoderma
spp. to inoculate seeds of four common bean (Phaseolus vulgaris) cultivars
and explored in three different experimental setups the effects on fungal
anthracnose after leaf inoculation with Colletotrichum lindemuthianum.
Plants growing in pots with field soil under greenhouse conditions
exhibited the highest and those in the open field the lowest overall
levels of disease. Among 48 Trichoderma strain × bean cultivar × setup
combinations, Trichoderma-inoculation enhanced disease in six and
decreased disease in ten cases, but with the exception of T. asperellum
B6-inoculated Negro San Luis beans, the strain × cultivar-specific effects
on anthracnose severity differed among the setups, and anthracnose
severity did not predict seed yield in the open field. In the case of Flor
de Mayo beans, Trichoderma even reduced yield in anthracnose-free field
plots, although this effect was counterbalanced in anthracnose-infected
plots. We consider our work as a case study that calls for stronger
emphasis on field experiments in the early phases of screenings of
Trichoderma inoculants as plant biostimulants.