Impacts of arbuscular mycorrhizal and Trichoderma viride on enhancing physicochemical properties and triggering defense mechanisms of tomato plants challenged with potato virus Y

Abstract

The utilization of arbuscular mycorrhizal fungi (AMF) and Trichoderma spp. correlates with improved plant nutrition and the stimulation of systemic plant defenses in response to pathogen challenges. Nonetheless, studies examining the effects of AMF colonization and the foliar application of the Trichoderma viride isolate Tvd44 on viral infection are limited. By analyzing the phenotypic, biochemical, and transcriptional expression of eleven defense genes, we investigated the effects of AMF colonization, foliar application of Tvd44, and their combined (dual) application on tomato plants challenged with potato virus Y. Interestingly, the dual application significantly suppressed viral symptoms and decreased viral accumulation levels, disease incidence, and disease severity by 88.1%, 40%, and 53.4%, respectively. Furthermore, both single and dual treatments significantly enhanced the activity of antioxidant enzymes, chlorophyll concentration, and macronutrient levels in the tomato tissues. In the realm of transcriptional analyses, the CHS gene served as a master key in understanding the physiological and pathway relationships among various genes (F3'H, HQT, C3H, GST, JERF, CHI, WRKY-1, WRKY-19, FLS, and F3H) involved in plant defense. These results suggest a sophisticated network of interactions that governs multiple facets of plant defense responses, encompassing the biosynthesis of flavonoids and other secondary metabolites, as well as the activation of transcription factors related to defense mechanisms. The obtained data indicate that AMF colonization and T. viride foliar spraying enhance tomato resistance to PVY by activating defense systems, thereby affecting viral replication. This finding highlights the significance of AMF and T. viride within the ecosystem and their crucial role in managing plant viruses.

Keywords: PVY; Trichoderma viride; arbuscular mycorrhizal; defense genes; tomato.

Figure 1

Impacts of arbuscular mycorrhizal and Trichoderma viride on PVY symptoms at 25 dpi. (a) control plants, (b) AMF plants colonized with AM fungi, (c) sprayed with Tvd44, (d) PVY-infected tomato plants, (e) colonized with AMF and infected with PVY, (f) sprayed with Tvd44 and infected with PVY, (g) colonized with AMF and infected with PVY and sprayed with Tvd44.

Figure 2

Impacts of arbuscular mycorrhizal and Trichoderma viride on tomato roots at 25 dpi. (a) control plants, (b) AMF plants colonized with AM fungi, (c) sprayed with Tvd44, (d) PVY-infected tomato plants, (e) colonized with AMF and infected with PVY, (f) sprayed with Tvd44 and infected with PVY, (g) colonized with AMF and infected with PVY and sprayed with Tvd44.

Figure 3

Image showing light micrographs of tomato roots colonized with AMF displaying typical mycorrhizal structures (at 25 dpi), control root (a), and AMF-colonized tomato roots (b–d), where Hr, host root; Ar, arbuscule; Eh, exteraradical hyphae; Sc, sporocarp; Sp, spore; and V, vesicle.

Figure 4

Impact of 7 treatments at 25 dpi on shoot length (cm) (a), shoot fresh weight (g) (b), root fresh weight (g) (c), shoot dry weight (g) (d), root dry weight (g) (e), and leaf number (f) traits using Tukey's HSD test at p ≤ 0.05. Statistical significance was indicated alphabetically above the histogram in ascending order, whereas a>b>c>d. The means in each column that share the same letter do not show significant differences.

Figure 5

Impact of 7 treatments at 25 dpi on chlorophyll (a), chlorophyll (b), catalase (CAT) (c), peroxidase (POX) (d), and total protein (TP) (e) traits using Tukey's HSD test at p ≤ 0.05. Statistical significance was indicated alphabetically above the histogram in ascending order, whereas a>b>c>d. The means in each column that share the same letter do not show significant differences.

Figure 6

Volcano plots of change in gene expression for eleven genes in tomato leaves infected with PVY in response to AMF colonization and T. viride at 25 dpi. Where y-axis represents P-values (-log10), the x-axis represents fold change (log₂), the black color represents unchanged genes, and the red color represents significantly upregulated genes. Because P-values on the y-axis in volcano plots were transformed and became negative, the higher the number on the y-axis, the smaller the P-value and the greater the significance. Threshold indicator dashed lines were drawn on volcano plots, where genes above the horizontal dashed line are significantly expressed at a p-value of 0.05. Genes beyond the right vertical dashed line are upregulated, genes behind the left vertical dashed line are downregulated, and genes between the two vertical dashed lines are unchanged. Relative gene expression changes among PVY and control (a), AMF and control (b), Tvd44 and control (c), AMF+PVY and PVY (d), Tvd44+PVY and PVY (e), and Dual+PVY and PVY (f) treatments.

Figure 7

Heatmap and hierarchical clustering of change in gene expression for eleven genes in tomato leaves infected with PVY in response to AMF colonization and T. viride at 25 dpi. Cell color intensities were based on gene expression, represented as log₂, where blue indicates downregulated genes and red indicates upregulated genes.

Figure 8

(a) Principal component analysis (PCA) biplot illustrates the contribution of each dimension to the total variance of 7 treatments and 11 physiological traits. Longer arrows specify higher contribution, while shorter arrows show lower contribution. (b) The bar plot indicates the percentage of contribution of PCs to the total variance. (c, d) bar plots of the contribution of the 11 studied traits to PCs where traits above the dashed red line specify significant contribution.

Figure 9

Gene co-expression network: nodes (circles) represent genes, while edges (lines) represent associations among genes based on the Spearman rank correlation coefficient. Faded lines represent non-significant correlations.

Figure 10

Gene and physiological traits network, where nodes (circles) represent genes and physiological traits, and edges (lines) represent associations among genes and physiological traits based on the Spearman rank correlation coefficient. Faded lines represent non-significant correlations.