An evaluation of multiple techniques for the creation of a diagnostic tool for Meloidogyne species identification in Alabama

Abstract

Species identification of Meloidogyne spp. (root-knot nematode, RKN) is an important tool to offer growers in the state of Alabama because it is beneficial for planning and implementing a crop rotation to reduce the impact of these yield-limiting nematodes. RKN has a very wide host range, but these host ranges are species dependent. By implementing a crop rotation, a grower can potentially lower RKN levels by planting a nonhost if species is known and economical. Species analysis also allows a grower to know RKN species levels, and determine if there is a need for resistant crop varieties, if they are available. The goal of this project was to evaluate multiple species identification techniques and determine the best combination of methods for implementing a practical and efficient assay for RKN species identification. To do this, three different techniques were evaluated for their ability to quickly and accurately identify RKN species. The techniques used in this study were morphological measurements, differential-host test, and molecular analysis. Each of these techniques was used on multiple RKN populations, starting with a known M. incognita race 3 population. This greenhouse population was previously identified via the differential-host test. Initial results showed a confirmation of species with the differential-host test and PCR amplification, but morphological measurements of juveniles did not distinguish our test population from M. arenaria and M. javanica. Soil and root samples were then collected from throughout Alabama for RKN species identification. Overall, 75 samples from 14 counties in Alabama were collected from grower fields for species analysis. Crops sampled during collection included cotton, soybean, corn, peanut, sweet potato, squash, pepper, kiwi, turmeric, and turf. Both molecular analysis (PCR) and the differential-host test were used for species identification. Primers used for PCR include those that identify commonly found RKN species: M. incognita, M. arenaria, M. javanica, M. hapla, M. fallax, M. chitwoodi, and M. enterolobii. Of these samples, 73 were identified as M. incognita (97%), and two were identified as M. arenaria (3%). These species were identified through the differential-host test and PCR using primer sets IncK-14F/IncK-14R (M. incognita) and Far/Rar (M. arenaria). Overall, M. incognita is the most prevalent species of root-knot nematode that has been found on cropping systems in Alabama during this project.