Abstract
Gummy stem blight caused by Stagonosporopsis cucurbitacearum is the most destructive disease of muskmelon cultivation. This study aimed to induce disease resistance against gummy stem blight in muskmelon by Trichoderma asperelloides PSU-P1. This study was arranged into two crops. Spore suspension at a concentration of 1 × 106 spores/mL of T. asperelloides PSU-P1 was applied to muskmelon to investigate gene expression. The expression of PR genes including chitinase (chi) and β-1,3-glucanase (glu) were determined by reverse transcription quantitative polymerase chain reaction (RT-qPCR), and enzyme activity was assayed by the DNS method. The effects of T. asperelloides PSU-P1 on growth, yield, and postharvest quality of muskmelon fruit were measured. A spore suspension at a concentration of 1 × 106 spore/mL of T. asperelloides PSU-P1 and S. cucurbitacearum was applied to muskmelons to determine the reduction in disease severity. The results showed that the expression of chi and glu genes in T. asperelloides PSU-P1-treated muskmelon plants was 7–10-fold higher than that of the control. The enzyme activities of chitinase and β-1,3-glucanase were 0.15–0.284 and 0.343–0.681 U/mL, respectively, which were higher than those of the control (pathogen alone). Scanning electron microscopy revealed crude metabolites extracted from T. asperelloides PSU-P1-treated muskmelon plants caused wilting and lysis of S. cucurbitacearum hyphae, confirming the activity of cell-wall-degrading enzymes (CWDEs). Application of T. asperelloides PSU-P1 increased fruit weight and fruit width; sweetness and fruit texture were not significantly different among treated muskmelons. Application of T. asperelloides PSU-P1 reduced the disease severity scale of gummy stem blight to 1.10 in both crops, which was significantly lower than that of the control (2.90 and 3.40, respectively). These results revealed that application of T. asperelloides PSU-P1 reduced disease severity against gummy stem blight by overexpressed PR genes and elevated enzyme activity in muskmelon plants.
Highlights
Gummy stem blight is a devastating disease of muskmelon cultivation
To examine the effect of biotic stress by T. asperelloides PSU-P1 on inducing the defense response in muskmelon, the expression of chi and glu genes was analyzed by reverse transcription quantitative polymerase chain reaction (RT-qPCR)
In T. asperelloides PSU-P1-treated muskmelon plants, the expression levels of chi were 0.2–0.32 for the 1st crop and 0.21–0.37 for the 2nd crop (Figure 1), while the expression levels of glu were 1.34–1.68 for the 1st crop and 1.34–1.55 for the 2nd crop (Figure 2); both these expression patterns were significantly higher than the levels in the control
Summary
Gummy stem blight is a devastating disease of muskmelon cultivation. The disease is caused by the fungal pathogen Stagonosporopsis cucurbitacearum [1,2]. Interactions between the plant and fungi trigger a defense response in the plant, which is associated with disease resistance [3]. Plants have developed an elaborate defense response to combat such stresses [4,5]. Plants are capable of producing pathogenesis-related (PR) protein to defend themselves from infecting fungi [6,7]. The PR proteins, PR2 (β-1,3-glucanase) and PR3 (chitinase), produced by plants are considered the main key enzymes responsible for degrading fungal cell walls, resulting in resistance against plant diseases [8,9]. Β1,3-Glucanase and chitinase hydrolyze the fungal cell wall components β-glucan and chitin, respectively, into small molecules [10,11]. Plants that contain high activity of β-1,3glucanase and chitinase are able to resist plant diseases [12]
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