Context-Dependent Effects of Trichoderma Seed Inoculation on Anthracnose Disease and Seed Yield of Bean (Phaseolus vulgaris): Ambient Conditions Override Cultivar-Specific Differences

Karina Gutiérrez-Moreno,Michelina Ruocco,Octavio Martínez de la Vega,Maurilia Maria Monti,Martin Heil

doi:10.3390/plants10081739

Abstract

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.

Highlights

Plant roots are colonized by highly diverse microbiomes that comprise mutualistic, commensal and pathogenic bacteria and fungi [1]
The effects of Trichoderma on anthracnose disease of common of common bean differed on depending the even type of soil plants even when kept in a bean differed depending the type on of soil when were plants kept inwere a greenhouse, greenhouse, i.e., undercontrolled otherwise ambient controlled ambient conditions
‘intermediate’ experimental setup, at least if the final aim is the identification of Trichoderma strains that reliably reduce anthracnose disease in common bean

Summary

Introduction

Plant roots are colonized by highly diverse microbiomes that comprise mutualistic, commensal and pathogenic bacteria and fungi [1]. Soilborne fungi in the genus Trichoderma stand out because they promote plant growth and benefit plant health via a wide range of mechanisms, including the solubilization of nutrients, the protection from soilborne pathogens via direct antibiosis and mycoparasitism, and an activation of the plant’s innate immune system. All these mechanisms and effects have been reviewed, and reviewed well, by others [2,3,4,5,6,7,8,9,10]. Even under completely controlled conditions, a specific T. asperellum strain promoted the growth of Arabidopsis thaliana seedlings on MS medium, but had inhibitory effects in sterile soil [34]

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