Seed‐Associated <i>Trichoderma</i> and Their Potential as Biocontrol Agents Against Plant Diseases

Trichoderma is a genus of beneficial fungi widely used in agriculture disease suppression, plant growth promotion, and soil health improvement. Although some studies have shown that Trichoderma spp. can be seed-borne, albeit at low frequency, no specific study has so far focused on the diversity of Trichoderma isolates capable of adapting to this particular environment. Over 2 years of routine seed health analyses, we isolated 107 Trichoderma strains associated with seeds from 32 cultivated plant species, and we investigated the diversity of this specific library using multi-locus analysis. These isolates are distributed among 18 different species, but Trichoderma atroviride is by far the most frequent. Representative strains of each species all have the ability to parasitise damping-off agents, although the intensity of parasitism can vary greatly from one strain to another and depending on the targeted plant pathogens. For two isolates of T. atroviride, we showed that these fungi can be transmitted from fruit to seed and limit the transmission of the plant pathogen Alternaria brassicicola. Furthermore, these strains stimulated seedling growth and provided protection against Globisporangium ultimum. Together, these findings support the benefits of focusing on certain selected seed-borne Trichoderma which seem particularly well suited to improving seed health.