The beneficial effect of Trichoderma spp. on tomato is modulated by the plant genotype

Abstract

Rhizosphere-competent fungi of the genus Trichoderma are widely used as biofertilizers and biopesticides in commercial formulates because of the multiple beneficial effects on plant growth and disease resistance. In this work, we demonstrate that genetic variability among wild and cultivated tomato lines affects the outcome of the interaction with two 'elite' biocontrol strains of T. atroviride and T. harzianum. The beneficial response, which included enhanced growth and systemic resistance against Botrytis cinerea, was clearly evident for some, but not all, the tested lines. At least in one case (line M82), treatment with the biocontrol agents had no effect or was even detrimental. Expression studies on defence-related genes suggested that the fungus is able to trigger, in the responsive lines, a long-lasting up-regulation of the salicylic acid pathway in the absence of a pathogen, possibly activating a priming mechanism in the plant. Consequently, infection with B. cinerea on plants pretreated with Trichoderma is followed by enhanced activation of jasmonate-responsive genes, eventually boosting systemic resistance to the pathogen in a plant genotype-dependent manner. Our data indicate that, at least in tomato, the Trichoderma induced systemic resistance mechanism is much more complex than considered so far, and the ability of the plant to benefit from this symbiotic-like interaction can be genetically improved.

Figure 1

Effects of Trichoderma spp. treatments on the growth and development of tomato plants. The canopy size (a) and stem length (b) of 2‐month‐old Solanum lycopersicum (Corbarino, TA209, M82 and SM36) and S. habrochaites (LA1777) lines, developed from untreated (Cont), T. atroviride P1‐treated (P1) or T. harzianum T22‐treated (T22) seeds, are presented. Values indicated by the same letter are not statistically significantly different for P≤ 0.01 according to the Duncan test.

Figure 2

Effects of Trichoderma spp. treatments on the growth and development of tomato roots. The root dry weight (a) and development (b) of 2‐month‐old Solanum lycopersicum (Corbarino, TA209, M82 and SM36) and S. habrochaites (LA1777) lines, developed from untreated (Cont), T. atroviride P1‐treated (P1) or T. harzianum T22‐treated (T22) seeds, are presented. Values indicated by the same letter are not statistically significantly different for P≤ 0.01 according to the Duncan test.

Figure 3

Effects of Trichoderma spp. treatments on plant resistance to the pathogen Botrytis cinerea. Two‐month‐old plants of Solanum lycopersicum (Corbarino, TA209, M82 and SM36) lines, developed from untreated (Cont), T. atroviride P1‐treated (P1) or T. harzianum T22‐treated (T22) seeds, were artificially inoculated with a suspension of B. cinerea spores, and lesion development was measured at 48 h (a) and 96 h (b) post‐inoculation. Values indicated by the same letter are not statistically significantly different for P≤ 0.01 according to the Duncan test. Average lesion areas at 96 h post‐inoculation on control and T22‐treated plants of the wild S. habrochaites LA1777 line are reported in the inset (c).

Figure 4

Effects of Trichoderma spp. treatments on the transcription of defence‐related genes in tomato. The relative expression of PR1b1, PR‐P2, PINI, PINII, TomLoxA and TomLoxC was measured by quantitative reverse transcription real‐time polymerase chain reaction (qRT‐PCR) in 2‐month‐old plants of Solanum lycopersicum (Corbarino, TA209, M82 and SM36) and S. habrochaites (LA1777) lines, developed from untreated (Cont) or T. atroviride P1‐treated (P1) or T. harzianum T22‐treated (T22) seeds. Expression levels for each gene are reported as the fold increase relative to those of the untreated control. Values within the dotted lines were not considered to be statistically significantly different from the control. Data on PINII expression in the wild tomato line LA1777 are missing as no amplification of this gene could be obtained with the primer pair used. The results shown are from one representative experiment out of four.

Figure 5

Transcriptional analysis of defence‐related genes in tomato plants inoculated with the pathogen Botrytis cinerea and pretreated or not with Trichoderma spp. The relative expression of PR1b1, PR‐P2, PINI, PINII, TomLoxA and TomLoxC was measured by quantitative reverse transcription real‐time polymerase chain reaction (qRT‐PCR) at different times after pathogen infection [0, 24 and 48 h post‐inoculation (hpi)] in 2‐month‐old plants of Solanum lycopersicum (Corbarino, TA209, M82 and SM36) and S. habrochaites (LA1777) lines, developed from untreated (cont), T. atroviride P1‐treated (P1) or T. harzianum T22‐treated (T22) seeds. The expression levels for each gene are reported as the fold increase relative to that of the control plants not treated with Trichoderma before infection with the pathogen (0 hpi), in a semi‐logarithmic scale. Values within the dotted lines were not considered to be significantly different from the control. Data on PINII expression in the wild tomato line LA1777 are missing as no amplification of this gene could be obtained with the primer pair used. The results shown are from one representative experiment out of four.