<i>In Planta</i> Inoculation of <i>Trichoderma viridarium</i> Reduces Seed Transmission of the Fungal Pathogen <i>Alternaria brassicicola</i>

ABSTRACT Biological control by beneficial microorganisms is considered as one of the best alternatives to decrease the use of chemical fungicides. However, reliable and efficient solutions to manage crop diseases are still limited, and this is particularly true for seedborne fungal pathogens. As a first step towards identification of potential biological control agents (BCAs), a new methodological approach in planta was developed to control Alternaria brassicicola , a problematic fungal disease of Brassica crops. The method was used to evaluate the antagonistic activity of Trichoderma viridarium on transmission of the pathogen to seeds of Capsella bursa‐pastoris (sheperd's purse). In vitro, inhibition of A. brassicicola and overgrowth by T. viridarium suggested mycoparasitism, which was confirmed by microscopical observations. In planta , siliques of C. bursa pastoris were co‐inoculated with T. viridarium and A. brassicicola and seed transmission of each fungal species was evaluated. Pre‐inoculation of T. viridarium 24 h before A. brassicicola significantly reduced the transmission of the pathogen to the seeds by almost 70%, compared with inoculation of A. brassicicola alone. The capacity of T. viridarium to reduce A. brassicicola seed transmission offers a promising alternative to conventional fungicides. However, in order to develop reliable biocontrol strategies, future research should focus on the underlying mechanisms involved in the interactions between T. viridarium , A. brassicicola and the host plant.