Effect of Setophoma terrestris, Sclerotium cepivorum, and Trichoderma spp. on in vitro onion (Allium cepa) root tissues and the final yield at the field

Trichoderma is a rhizosphere fungus widely used in agriculture due to the variety of mechanisms of biological control. It can establish a direct relationship with the plant root cells, modifying the morphology and physiological processes, conferring a better defensive capacity against the attack of pathogens in the soil. This research aimed to study the interaction of T. asperellum, T. harzianum, T. virens, Setophoma terrestris and Sclerotium cepivorum on onion roots (Allium cepa), both in vitro and in field trials, to evaluate the histological modifications and the effect on in vitro growth promotion, and to test the effect of Trichoderma in the field, over the incidence of these pathogens and the crops harvest. In vitro plant promotion assay was made using T. asperellum, T. harzianum, and T. virens to test their effect on the development of onion seedlings from disinfected seeds. Roots of these plants were subjected to histological analysis using Transmission Electronic Microscopy (TEM) to examine changes in cell structure. This analysis also included the pathogens S. cepivorum and S. terrestris, the major soilborne pathogens of onion worldwide. To verify the effect of the Trichoderma species used in the study, a field experiments were performed where the fresh and dry weight of onion bulbs and the incidence of pathogens were measured. Histological modifications were observed in the root cells in the different treatments and were related to the effects caused for Trichoderma. It was shown that although T. asperellum did not stimulate in vitro root growth it can have an important effect in the field by reducing the incidence of S. cepivorum and S. terrestris while improving the onion’s harvest. On the contrary, species that have a root promoting effect do not necessarily improved yield. Besides, rather than this study, there are no other histological studies published in the onion- S. terrestris pathosystem.