Abstract
Interspecies interactions play a key role in soil-borne disease suppression in intercropping systems. However, there are limited data on the underlying mechanisms of soil-borne Phytophthora disease suppression. Here, a field experiment confirmed the effects of maize and soybean intercropping on Phytophthora blight of soybean caused by Phytophthora sojae. Experimentally, the roots and root exudates of maize were found to attract P. sojae zoospores and inhibit their motility and the germination of cystospores. Furthermore, five phenolic acids (p-coumaric acid, cinnamic acid, p-hydroxybenzoic acid, vanillic acid, and ferulic acid) that were consistently identified in the root exudates and rhizosphere soil of maize were found to interfere with the infection behavior of P. sojae. Among them, cinnamic acid was associated with significant chemotaxis in zoospores, and p-coumaric acid and cinnamic acid showed strong antimicrobial activity against P. sojae. However, in the rhizosphere soil of soybean, only p-hydroxybenzoic acid, low concentrations of vanillic acid, and ferulic acid were identified. Importantly, the coexistence of five phenolic acids in the maize rhizosphere compared with three phenolic acids in the soybean rhizosphere showed strong synergistic antimicrobial activity against the infection behavior of P. sojae. In summary, the types and concentrations of phenolic acids in maize and soybean rhizosphere soils were found to be crucial factors for Phytophthora disease suppression in this intercropping system.
Highlights
Intercropping, or the practice of growing two or more crops in the same field, is widely used in Asia, Latin America, and Africa, providing as much as 15–20% of the global food supply (Machado, 2009; Lithourgidis et al, 2011)
The disease incidence of soybean Phytophthora blight was significantly decreased in the maize/soybean intercropping systems compared with that of the monoculture
Our results indicated that maize roots and root exudates could attract P. sojae zoospores and suppress zoospore motility and cystospore germination, causing the pathogens to lose their infection ability (Figure 2)
Summary
Intercropping, or the practice of growing two or more crops in the same field, is widely used in Asia, Latin America, and Africa, providing as much as 15–20% of the global food supply (Machado, 2009; Lithourgidis et al, 2011). Many previous studies have shown that intercropping could control the occurrence of airborne crop diseases by forming a physical barrier, diluting pathogens, and improving field microclimates while effectively inhibiting soil-borne diseases through root interactions (Zhu et al, 2000, 2005; Yang et al, 2014). Plant roots interact with many soil-inhabiting microbes that can colonize them and provide plants with key functions for plant longevity and fitness (Pascale et al, 2020). Benzoxazinoids and triterpenes from plant root exudates could optimize the microbial community in the plant rhizosphere, which helped plants to resist pathogens (Hu et al, 2018; Huang et al, 2019). Intercropped maize has been found to cause a twofold increase in flavonoid exudations and increased soybean nodulation by Rhizobium (Li B. et al, 2016)
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