Potent Attractant for Root-Knot Nematodes in Exudates from Seedling Root Tips of Two Host Species.

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.

First Report of Meloidogyne haplanaria Infecting Mi-Resistant Tomato Plants in Florida and Its Molecular Diagnosis Based on Mitochondrial Haplotype.

Meloidogyne haplanaria is a species originally found infesting peanut in Texas and, more recently, in Arkansas. In this study, we confirmed the presence of M. haplanaria in Florida based on morphological and molecular characterization. This species was identified from a sample submitted for diagnosis collected from Mi-resistant tomato rootstock grown in Naples, FL. The major diagnostic criteria to distinguish M. haplanaria from other closely related root-knot nematode (RKN) species are based on morphological differences and host range tests, which are time consuming and labor intensive and require living or well-preserved specimens. In our study, we provide an easy diagnostic strategy to distinguish M. haplanaria from other RKN species based on amplification of two mitochondrial DNA regions. These regions span the intergenic spacer and part of the adjacent large subunit ribosomal RNA gene (lrDNA) and sequence polymorphisms in lrDNA revealed by the restriction pattern following digestion with the restriction enzymes HinfI and MnlI. A unique haplotype pattern, which has not been observed in any of the RKN species described thus far, was observed in M. haplanaria. The outcome of molecular analysis of M. haplanaria aligned with morphological measurement and characteristics as well as perineal pattern originally described for M. haplanaria.