Abstract
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.
Highlights
Watermelon (Citrullus lanatus L.) is an important crop that is widely cultivated across the world
The experiment consisted of four treatments: (1) watermelon monocropping (M) in which one watermelon seedling was grown alone in the pot; (2) watermelon monocropping with FON inoculation (MF); (3) watermelon/wheat intercropping (I) in which one watermelon seedling was grown with 40 wheat seedlings; and (4) watermelon/wheat intercropping with FON inoculation (IF)
Wheat intercropping in watermelon reduces the population, germination, sporulation, and growth of FON, and suppresses the incidence of Fusarium wilt of watermelon, and contributes to improved plant growth and development
Summary
Watermelon (Citrullus lanatus L.) is an important crop that is widely cultivated across the world. Niveum (FON), which poses a serious threat to watermelon cultivation Different techniques, such as grafting onto disease-resistant rootstocks (Ling et al, 2013; Bie et al, 2017; Nawaz et al, 2017), biological control (Zhang et al, 2011; Zhao et al, 2014), and use of disease-resistant cultivars (Bai and Shaner, 1996) are utilized to overcome this menace. Phenolic acids released by the roots act as signaling molecules or attractants (Lanoue et al, 2010; Mandal et al, 2010) Phenolic acids, such as p-coumaric acid, can inhibit FON colonization (Hao et al, 2010; Zhou and Wu, 2012c). The interaction between plant root exudates and soil-borne pathogens shows that different types and concentrations of phenolic acids in root exudates differ in their mode of action on pathogens such as F. oxysporum (Hao et al, 2010; Ling et al, 2013)
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