Induction of Terpenoid Synthesis in Cotton Roots and Control of Rhizoctonia solani by Seed Treatment with Trichoderma virens

Abstract

Research on the mechanisms employed by the biocontrol agent Trichoderma virens to suppress cotton (Gossypium hirsutum) seedling disease incited by Rhizoctonia solani has shown that mycoparasitism and antibiotic production are not major contributors to successful biological control. In this study, we examined the possibility that seed treatment with T. virens stimulates defense responses, as indicated by the synthesis of terpenoids in cotton roots. We also examined the role of these terpenoid compounds in disease control. Analysis of extracts of cotton roots and hypocotyls grown from T. virens-treated seed showed that terpenoid synthesis and peroxidase activity were increased in the roots of treated plants, but not in the hypocotyls of these plants or in the untreated controls. Bioassay of the terpenoids for toxicity to R. solani showed that the pathway intermediates desoxyhemigossypol (dHG) and hemigossypol (HG) were strongly inhibitory to the pathogen, while the final product gossypol (G) was toxic only at a much higher concentration. Strains of T. virens and T. koningii were much more resistant to HG than was R. solani, and they thoroughly colonized the cotton roots. A comparison of biocontrol efficacy and induction of terpenoid synthesis in cotton roots by strains of T. virens, T. koningii, T. harzianum, and protoplast fusants indicated that there was a strong correlation (+0.89) between these two phenomena. It, therefore, appears that induction of defense response, particularly terpenoid synthesis, in cotton roots by T. virens may be an important mechanism in the biological control by this fungus of R. solani-incited cotton seedling disease.

Isolation and Identification of Indigenous Microorganisms of Cocoa Farms in Côte d’Ivoire and Assessment of Their Antagonistic Effects Vis-À-Vis Phytophthora palmivora, the Causal Agent of the Black Pod Disease

“…This germination would stimulate the mechanisms of defense, and consequently would strengthen the resistance to the penetration and the dissemination of the parasite. Similar results were obtained by Bigirimana et al (1997), Howell et al (2000, Sid Ahmed et al, 2000 andHarman et al (2004) on bean, cotton, hot pepper and corn inoculated by T. virens and T. harzianum, subjected to the attacks of Rhizoctonia sp., Colletrotrichum sp. and Phytophthora sp.…”

Enhanced biocontrol activity of Trichoderma through inactivation of a mitogen-activated protein kinase

“…These data suggest that Trichoderma uses different mechanisms to control different hosts. An additional consideration that must be made is that some Trichoderma species are capable of inducing defense responses in plants, as shown for T. virens (28). To the best of our knowledge, this is the first report indicating that the deletion of a MAPK gene generates a more aggressive parasite and, consequently, a better biocontrol agent.…”

Influence of phylloplane colonizing biocontrol agents on the black spot of rose caused byDiplocarpon rosae

“…Increased peroxidase activity was observed on 7 days after challenge inoculation with Plasmodiophora brassicae and Meloidogyne incognita in cabbage and cauliflower pretreated with TVMNT7 and Pf1 along with chitin (Loganathan 2002). Seed treatment of cotton seeds with Trichoderma virens showed increased synthesis of terpenoid and increased activity of peroxidase in the roots of treated plants (Howell et al 2000).…”