Abstract
Root-knot nematodes (RKN; Meloidogyne spp.) can parasitize over 2,000 plant species and are generally considered to be the most agriculturally damaging group of plant-parasitic nematodes worldwide. Infective juveniles (J2) are non-feeding and must locate and invade a host before their reserves are depleted. However, what attracts J2 to appropriate root entry sites is not known. An aim of this research is to identify semiochemicals that attract RKN to roots. J2 of the three RKN species tested are highly attracted to root tips of both tomato and Medicago truncatula. For both hosts, mutants defective in ethylene signaling were found to be more attractive than those of wild type. We determined that cell-free exudates collected from tomato and M. truncatula seedling root tips were highly attractive to M. javanica J2. Using a pluronic gel-based microassay to monitor chemical fractionation, we determined that for both plant species the active component fractionated similarly and had a mass of ~400 based on size-exclusion chromatography. This characterization is a first step toward identification of a potent and specific attractant from host roots that attracts RKN. Such a compound is potentially a valuable tool for developing novel and safe control strategies.
Highlights
As Root-knot nematodes (RKN) attractants and repellents[13,15], the chemical nature of such compounds is largely unknown
Using Pluronic F-127 (PF-127)-based assays, we previously demonstrated that attractiveness of host roots to the temperate-climate RKN species M. hapla is modulated by ethylene (ET) signaling[19]
We show here that PF-127 gel that has been exposed to tomato root tips is attractive to RKN J2
Summary
As RKN attractants and repellents[13,15], the chemical nature of such compounds is largely unknown. Studies of exudates collected from host roots have often found them to be repellent rather than attractive to J211,16, and to date there have been few reports of specific attractants[17,18]. Infective juveniles of plant-parasitic nematodes suspended in PF-127 migrate to and accumulate on the roots of host plant seedlings[6]. Using PF-127-based assays, we previously demonstrated that attractiveness of host roots to the temperate-climate RKN species M. hapla is modulated by ethylene (ET) signaling[19]. The effect of the Nr mutation on attractiveness of tomato roots to the tropical RKN species M. incognita and M. javanica was not examined in that study. We present evidence that aqueous exudate from seedling root tips is highly attractive to RKN. We carried out fractionation of tomato and Medicago root exudates to characterize the activity and as initial steps toward identification of the active component(s)
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