A fungus Fusarium oxysporum F. sp. niveum (FON) is the causal organism of Fusarium wilt in watermelon. In this study, we evaluated the effect of wheat intercropping on the Fusarium wilt of watermelon. Our results showed that wheat intercropping decreases the incidence of Fusarium wilt of watermelon, likely due to the secretion of
coumaric acid from the roots of wheat that dramatically inhibits FON spore germination, sporulation, and growth. The secretion of p-
hydroxybenzoic acid,
ferulic acid, and
cinnamic acid from the roots of watermelon stimulates FON spore germination, sporulation, and growth. The secretion of phenolic
acids and organic
acids from the roots of watermelon is also promoted by FON
infection. However, secretion of phenolic
acids and organic
acids from the roots of watermelon is substantially reduced under wheat intercropping systems. FON
infection increases the accumulation of free and conjugated
salicylic acid (SA) in watermelon grown under wheat intercropping systems through
isochorismate (ICS) and
phenylalanine ammonia-lyase (PAL) pathways. Furthermore, wheat intercropping up-regulates the expression of disease-and defense-responsive genes and improves the activities of corresponding pathogenesis-related (PR)
enzymes in the roots of watermelon. In conclusion, the secretion of
coumaric acid from the roots of wheat and changes in the composition of
phenolic acid and organic
acid secretion from the roots of watermelon suppress Fusarium wilt of watermelon under wheat intercropping system. Meanwhile, wheat intercropping also enhanced the resistance of watermelon to FON by up-regulating the expression of disease-and defense-responsive genes in watermelon.