Abstract
Tomato (Solanum lycopersicum) crops can be severely damaged due to parasitism by the root-knot nematode (RKN) Meloidogyne incognita, but are protected when intercropped with crown daisy (Chrysanthemum coronarium L.). Root exudate may be the determining factor for this protection. An experiment using pots linked by a tube and Petri dish experiments were undertaken to confirm that tomato-crown daisy intercropping root exudate decreased the number of nematodes and alleviated nematode damage, and to determine crown daisy root exudate-regulated nematode chemotaxis. Following a gas chromatography-mass spectrometry assay, it was found that the intercropping protection was derived from the potent bioactivity of a specific root exudate component of crown daisy, namely lauric acid. The Mi-flp-18 gene, encoding an FMRFamide-like peptide neuromodulator, regulated nematode chemotaxis and infection by RNA interference. Moreover, it was shown that lauric acid acts as both a lethal trap and a repellent for M. incognita by specifically regulating Mi-flp-18 expression in a concentration-dependent manner. Low concentrations of lauric acid (0.5-2.0mM) attract M. incognita and consequently cause death, while high concentrations (4.0mM) repel M. incognita. This study elucidates how lauric acid in crown daisy root exudate regulates nematode chemotaxis and disrupts Mi-flp-18 expression to alleviate nematode damage, and presents a general methodology for studying signalling systems affected by plant root exudates in the rhizosphere. This could lead to the development of economical and feasible strategies for controlling plant-parasitic nematodes, and provide an alternative to the use of pesticides in farming systems.
Highlights
Endoparasitic root-knot nematodes (RKNs, Meloidogyne species) have broad host plant specificity and are responsible for >US$125 billion annually in world-wide crop losses (Chitwood, 2003)
Real-time PCR revealed that J2 ingestion of Mi-flp-18 double-stranded RNA (dsRNA) resulted in a reduction of >85.5% in Mi-flp-18 transcripts compared with J2s treated with soaking buffer alone or treated with gfp dsRNA
The relative expression of Mi-flp-1 was reduced by 17.9% compared with the controls; the relative expression of other Mi-flp genes increased by 2.7–34.2% compared with the J2s soaked in buffer alone or treated by soaking buffer with gfp dsRNA
Summary
Endoparasitic root-knot nematodes (RKNs, Meloidogyne species) have broad host plant specificity and are responsible for >US$125 billion annually in world-wide crop losses (Chitwood, 2003). Tomato is highly susceptible to RKN infestation, which reduces crop yields and results in significant economic losses (Bird and Kaloshian, 2003). Chemical nematicides effectively control parasitic nematodes, they are being withdrawn due to their human and environmental toxicity (Abad et al, 2008). It is important to identify safe and effective control strategies that have low toxicity to staple crops, humans, and animals. The intercropping of tomato–crown daisy (a popular and sustainable cropping system in Chinese greenhouse environments) reduces nematode infection and maintains profitability for farmers, because the crown daisy itself is a popular vegetable and cash crop in China (Tian et al, 2011; Dong et al, 2012).
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