Abstract
Colletotrichum boninense is the main pathogenic fungus causing leaf spot disease in Sorghum sudangrass hybrids, which seriously impairs its quality and yield. In order to find an efficient and green means of control, this study used the agar disk diffusion method to screen for a fungicide with the strongest inhibitory effect on C. boninense from among several bacteria, fungi, and chemicals. Then, the changes in the plant's antioxidant system and metabolic levels after treatment were used to compare the three means of control. The lowest inhibitory concentration of Zalfexam was 10 mg/mL, at which point C. boninense did not grow, and the inhibition rates of Bacillus velezensis (X7) and Trichoderma harzianum were 33.87-51.85% and 77.86-80.56%, respectively. Superoxide dismutase (SOD) and chitinase were up-regulated 2.43 and 1.24 folds in the Trichoderma harzianum group (M group) and SOD activity was up-regulated 2.2 folds in the Bacillus velezensis group (X7 group) compared to the control group (CK group). SOD, peroxidase (POD), and chitinase activities were elevated in the Zalfexam group (HX group). The differential metabolites in different treatment groups were mainly enriched in amino acid metabolism and production, flavonoid production, and lipid metabolism pathways. Compared with the diseased plants (ZB group), the M, X7, HX, and CK groups were co-enriched in the tryptophan metabolic pathway and glutamate-arginine metabolic pathway, and only the CK group showed a down-regulation of the metabolites in the two common pathways, while the metabolites of the common pathways were up-regulated in the M, X7, and HX groups. In addition, the salicylic acid-jasmonic acid pathway and ascorbic acid-glutathione, which were unique to the M group, played an important role in helping Sorghum sudangrass hybrids to acquire systemic resistance against stress. This study fills the gap in the control of Colletotrichum boninene, which causes leaf spot disease in Sorghum sudangrass hybrids. This paper represents the first reported case of biological control for leaf spot disease in Sorghum sudangrass hybrids and provides a reference for the control of leaf spot disease in Sorghum sudangrass hybrids as well as other crops infected with Colletotrichum boninense.