Abstract
Trichoderma species are soil-borne filamentous fungi widely utilized for their many plant health benefits, such as conferring improved growth, disease resistance and abiotic stress tolerance to their hosts. Many Trichoderma species are able to produce the auxin phytohormone indole-3-acetic acid (IAA), and its production has been suggested to promote root growth. Here we show that the production of IAA is strain dependent and diverse external stimuli are associated with its production. In in vitro assays, Arabidopsis primary root length was negatively affected by the interaction with some Trichoderma strains. In soil experiments, a continuum effect on plant growth was shown and this was also strain dependent. In plate assays, some strains of Trichoderma spp. inhibited the expression of the auxin reporter gene DR5 in Arabidopsis primary roots but not secondary roots. When Trichoderma spp. and A. thaliana were physically separated, enhancement of both shoot and root biomass, increased root production and chlorophyll content were observed, which strongly suggested that volatile production by the fungus influenced the parameters analyzed. Trichoderma strains T. virens Gv29.8, T. atroviride IMI206040, T. sp. “atroviride B” LU132, and T. asperellum LU1370 were demonstrated to promote plant growth through volatile production. However, contrasting differences were observed with LU1370 which had a negative effect on plant growth in soil but a positive effect in plate assays. Altogether our results suggest that the mechanisms and molecules involved in plant growth promotion by Trichoderma spp. are multivariable and are affected by the environmental conditions.
Highlights
Plant-microbe interactions in the rhizosphere are key determinants of plant health, productivity and soil fertility (Souza et al, 2015)
Trichoderma atroviride IMI206040 and T. sp. “atroviride B” LU660 increased Arabidopsis fresh biomass by 72% and 73% respectively, whereas T. asperellum LU1370 significantly inhibited Arabidopsis growth as measured by a reduction of up to 74% (P < 0.05) in biomass with respect to the plants grew in non-inoculated soil
It has been reported that several species of Trichoderma have the ability to induce growth promotion on diverse crop plants regardless of the place from which they were isolated (Harman et al, 2004; Mastouri et al, 2010; Lee et al, 2016)
Summary
Plant-microbe interactions in the rhizosphere are key determinants of plant health, productivity and soil fertility (Souza et al, 2015). The mechanism by which microorganisms promote plant growth has previously been studied for both bacteria (Crozier et al, 1988; Ahmad et al, 2005; Idris et al, 2007) and fungi (Contreras-Cornejo et al, 2009; Salazar-Badillo et al, 2015). It has been suggested that over 80% of rhizosphere bacteria synthesize indole-3-acetic acid (IAA) (Patten and Glick, 1996), the plant hormone auxin that controls many aspects of plant growth and development (Grossmann, 2010). The ability to synthesize indole-3-acetic acid (IAA) is an attribute that many microorganisms possess, including both plant growth-promoters and some plant pathogens (Duca et al, 2014). IAA synthesis can modify root architecture, resulting in increased root mass, and an increased area suitable for microbial colonization and a larger root system for nutrient uptake by the plant (Spaepen et al, 2007; Berg, 2009; Contreras-Cornejo et al, 2009)
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