Mycovirus and mycoviroid-like infections affect Trichoderma harzianum interaction with tomato plants under control and stressed conditions
Author(s)
Date Issued
2025
Type
conferenceObject
Abstract
Aim of the Study: The genus Trichoderma is widely recognized for its role as a biological control agent, enhancing plant growth and stress tolerance through direct antagonism of pathogens and the induction of systemic resistance. However, the impact of viruses and subviral infectious agents on the efficacy of beneficial fungi remain poorly understood. Mycoviruses are known to affect fungal biology, often reducing the virulence of phytopathogens, but their effect on mutualistic fungi like Trichoderma, remains still elusive. The effect of viroid-like RNAs on fungal biology is even less explored. This study aims to investigate the functional role of a mycovirus and a mycoviroid-like in the interaction between tomato plants (Solanum lycopersicum cv. San Marzano nano) and T. harzianum, using infected (+) and not infected (-) fungal isogenic lines. In addition, we evaluated the impact of both infectious elements on the ability of T. harzianum to protect tomato plants against Botrytis cinerea infection.
Methods: T. harzianum T100+ was generated by anastomosis using as donor T. spirale T45 infected with a Trichoderma spirale viroid-like RNA 1 (TsvlRNA1). TsvdlRNA1 has a circular RNA genome of 712 nt containing a self-cleaving ribozyme in one polarity strand. T. harzianum T101+, infected with Trichoderma harzianum negative-sense virus 2 (ThNV2), was isolated from the soil of an extensively grazed site in southern Sardinia. T101- was derived through single spore isolation from T101. Tomato seeds were surface sterilized and germinated on sterile filter paper soaked with sterile water. Seedlings were transplanted to 8 cm diameter pots and after one week were irrigated twice, at one-week interval, with 25 mL of T. harzianum T100 +/- or T101 +/- conidial suspension (1x107 conidia mL-1), achieving a final concentration of 1×106 conidia mL−1 in 250 mL soil volume. Control plants were watered with sterile water. To assess the effect of fungal colonization, morphological parameters and biochemical markers were measured one week after the second treatment. B. cinerea infection was carried out three days after the second treatment by applying 5 μl droplets of a spore suspension (1x105 spores mL-1) on two leaves of each plant. Disease severity was quantified three days after infection, and the previously mentioned biochemical parameters were measured. Ten plants were used for each treatment and three independent experiments were carried out.
Results and Conclusions: Both T. harzianum T100 +/- and T101 +/- did not affect tomato plants growth parameters, revealing a lack of biostimulatory effect regardless of the presence or absence of the infectious elements. As for biochemical parameters, we found that plants colonized with T. harzianum 101- exhibited higher resistance to B. cinerea, while behaving like the control for all other measured parameters. On the other hand, T. harzianum 101+ triggered plant defense responses, reducing its resistance to B. cinerea and highlighting a negative effect of the mycovirus on the antagonistic ability of the fungus. On the contrary, in T. harzianum 100+, the presence of TsvlRNA1 appeared to enhance plant performance against the fungal pathogen, despite causing higher oxidative stress and impairing photosynthetic performance. This prevented us from unambiguously establishing the functional role of the mycoviroid-like RNA in fungal biology.
Future research will focus on elucidating the molecular mechanisms underlying this tripartite interaction, aiming to identify promising biocontrol agents. Such efforts are essential for advancing sustainable agricultural practices that harness microbial symbionts while mitigating unintended ecological trade-offs.
Conference(s)
9 th National Congress of the Italian Society for Virology "One Virology One Health"