Effect of Trichoderma viride pre‐inoculation in pine species with different levels of susceptibility to Fusarium circinatum: physiological and hormonal responses

Abstract

Pine pitch canker (PPC), caused by Fusarium circinatum, affects Pinus species worldwide. Although no effective solutions have yet been found to control it, there is a growing interest in using biological control agents (BCA) such as Trichoderma to avoid the application of chemical‐based products. Using species with an increasing level of susceptibility to PPC (Pinus pinea, Pinus pinaster and Pinus radiata), this study aimed to evaluate the effect of Trichoderma viride pre‐inoculation on disease development, assessing several physiological and hormonal parameters. A 2‐week period elapsed between T. viride and F. circinatum inoculation. Sampling for each species was performed independently when at least 50% of the plants of one of the inoculated groups developed disease symptoms. Fusarium circinatum infection reduced water status and photosynthesis, but increased proline, abscisic acid and jasmonic acid concentrations in plants of P. radiata and P. pinaster with symptoms; while in P. pinea water relations were maintained and anthocyanin accumulation occurred in the presence of F. circinatum. In P. radiata, T. viride pre‐inoculation accelerated disease progression, with some PPC‐induced responses augmented (decreased water potential and photosynthesis; increased substomatal CO2 concentration) and novel changes not found in seedlings inoculated exclusively with F. circinatum (increased electrolyte leakage and salicylic acid; decreased relative water content). This suggests that T. viride may be initially recognized as an invading organism, subverting the plant defence mechanisms for successful root colonization. If seedlings are not allowed to recover from this state, pathogen infection may thus be facilitated, highlighting the importance of application timing in BCA strategies.

Comparative proteomics of Pinus–Fusarium circinatum interactions reveal metabolic clues to biotic stress resistance

“…In these studies, the manipulation of susceptible hosts by F. circinatum showed to disturb ethylene homeostasis, block jasmonic acid (JA) signalling and arrest salicylic acid biosynthesis. The role of JA regulation in PPC has been also discussed based on hormone quantification data (Amaral et al 2019a(Amaral et al , 2019bCerqueira et al 2017), as well as the importance of abscisic acid (ABA) biosynthesis and catabolism in determining pine resistance/susceptibility to PPC (Amaral et al 2020a).…”

Potential Interactions between Invasive Fusarium circinatum and Other Pine Pathogens in Europe

“…The relationship of F. circinatum with the internal microbiota of seedlings has been poorly described, but some studies have shown that certain fungal endophytes isolated from pines are able to produce an antagonistic effect against F. circinatum [266], reducing the severity of F. circinatum when applied to seedlings as a preventive measure. Other studies have revealed how the exudates obtained from avirulent strains of a plant pathogen, living as an endophyte, induce systemic resistance against the virulent strain of the same pathogenic species [272]. Thus, the study of this relationship may reveal potential strategies for the biological control of PPC disease.…”

“…However, several aspects, such as the application timing in biological control agents, should be taken into account. Amaral et al [272] demonstrated that T. viride preinoculation accelerated disease progression of PPC. They suggested that T. viride may subvert the plant defence mechanisms for successful root colonization, which would facilitate F. circinatum infestation.…”

“…The relationship with other pathogens is poorly understood at present. Probably, simultaneous infection of plants by F. circinatum and other pathogenic species may exacerbate losses, while possible competition between two or more pathogens deserves further research in order to develop biological control strategies [272].…”

Pine Pitch Canker (PPC): Pathways of Pathogen Spread and Preventive Measures

“…BCAs that target F. circinatum have gained considerable support in recent research and were recently reviewed in Martín-García et al [143]. In general, the control of woody plant diseases using BCAs is highly context dependent [165,166] and pathogen-specific but it seems to be more effective when applied as a preventive treatment [142,[167][168][169].…”