The guava root-knot nematode (RKN), Meloidogyne enterolobii, is a particularly aggressive pathogen with limited known distribution in the United States. In 2011, M. enterolobii was identified on field crops in North Carolina for the first time. In collaboration with the North Carolina Department of Agriculture and Consumer Services Nematode Assay Laboratory, RKN-positive samples from the eastern half of North Carolina submitted to the laboratory were analyzed for Meloidogyne species identification using polymerase chain reaction (PCR) of individual nematodes. PCR primers specific for Meloidogyne incognita, M. javanica, M. arenaria, M. hapla, and M. enterolobii were used to analyze DNA from 203 RKN-positive samples representing a variety of field and vegetable crops grown in counties in the eastern half of North Carolina. M. incognita was the predominant species identified (32% of samples), and M. enterolobii was identified in 6% of samples including ones from sweetpotato, tobacco, and soybean crops. New detections of M. enterolobii were found in Nash, Greene, Sampson, and Harnett counties in addition to the previously identified locations in Johnston, Wayne, Columbus, and Wilson counties. Four isolates of M. enterolobii populations were collected from soybean and sweetpotato crops in Johnston, Greene, and Wilson counties and reared on ‘Rutgers’ tomato plants in the greenhouse. Potential differences in virulence among the four M. enterolobii populations were not detected in greenhouse infection assays on six selected resistant and susceptible sweetpotato genotypes in two independent tests.

Root-knot nematodes (Meloidogyne spp.) are important contributors to yield reduction in tomato. Though resistant cultivars to common species (Meloidogyne arenaria, M. incognita, and M. javanica) are available, they are not effective against other major species of root-knot nematodes. Cultivars or lines of Solanum sisymbriifolium were examined to assess the presence and level of resistance to five major species: M. arenaria race 1, M. incognita race 3, M. haplanaria, M. javanica, and M. enterolobii. Differences in S. sisymbriifolium response to the nematode infection were apparent when susceptibility or resistance was classified by the egg counts per gram fresh weight of root and the multiplication rate of the nematodes. The cultivar Diamond was highly susceptible, Quattro and White Star were susceptible, while Sis Syn II was resistant to M. arenaria. Quattro, White Star, and Sis Syn II exhibited a moderate to high level of resistance to M. incognita but the nematode increased 2.5-fold from the initial population of the M. incognita on Diamond. All S. sisymbriifolium cultivars were highly resistant to both M. haplanaria and M. enterolobii, while highly susceptible to M. javanica. A microplot study under field conditions using Sis Syn II confirmed that M. arenaria, M. incognita, and M. haplanaria were not pathogenic on the plant. Likewise, an examination on cross-sections of galled root tissues confirmed the susceptibility and resistance of S. sisymbriifolium lines to Meloidogyne spp. Using S. sisymbriifolium as a resistant rootstock or a new source of resistance may result in the development of nonchemical and sustainable management strategies to protect the tomato crop.

Potential resistance to the guava root-knot nematode, Meloidogyne enterolobii, in ninety-one selected sweetpotato [Ipomoea batatas (L.) Lam.] genotypes was evaluated in six greenhouse experiments. Ten thousand eggs of M. enterolobii were inoculated on each sweetpotato genotype grown in a 3:1 sand to soil mixture. Sixty days post inoculation, percent of total roots with nematode-induced galls was determined, and nematode eggs were extracted from roots. Significant differences (P ˂ 0.001) among sweetpotato genotypes were found in all six tests for gall rating, total eggs, and eggs per gram of root. Resistant sweetpotato genotypes were determined by final eggs per root system divided by the initial inoculum where Pf/Pi < 1 (reproduction factor; final egg count divided by initial inoculum of 10,000 eggs), and statistical mean separations were confirmed by Fisher’s LSD t test. Our results indicated that 19 out of 91 tested sweetpotato genotypes were resistant to M. enterolobii. Some of the susceptible genotypes included ‘Covington’, ‘Beauregard’, ‘NCDM04-001’, and ‘Hernandez’. Some of the resistant sweetpotato genotypes included ‘Tanzania’, ‘Murasaki-29’, ‘Bwanjule’, ‘Dimbuka-Bukulula’, ‘Jewel’, and ‘Centennial’. Most of the 19 resistant sweetpotato genotypes supported almost no M. enterolobii reproduction with less than 20 eggs/g root of M. enterolobii. A number of segregants from a ‘Tanzania’ x ‘Beauregard’ cross demonstrated strong resistance to M. enterolobii observed in the ‘Tanzania’ parent. In collaboration with NC State University sweetpotato breeding program, several of the genotypes evaluated in these tests are now being used to incorporate the observed resistance to M. enterolobii into commercial sweetpotato cultivars.

Meloidogyne enterolobii is an invasive and highly aggressive root-knot nematode pathogen impacting the Southeastern United States. Winter cover cropping may be a cost-effective method for reducing populations of M. enterolobii in between summer cash crops, yet a gap in the knowledge remains about the response of these cover crops to M. enterolobii and their utility in suppressing nematode populations prior to a cash crop. A “two-step” glasshouse bioassay was performed to evaluate eight winter cover crops popular in North Carolina for their direct response to M. enterolobii infection, and to quantify their effect in reducing nematode populations for the following soybean plants. Data on cover crop root galling, soybean root galling, soybean shoot fresh weight, soybean root fresh weight, eggs per gram of soybean root, and a modified reproductive factor were collected. Cereal cover crops did not display root galling, and there was significantly less root galling in those soybean plants following cereal winter cover crops when compared to those following broadleaf winter cover crops. Broadleaf winter cover crops resulted in significantly higher eggs per gram of soybean root and modified reproductive factor in the soybean plants, compared to cereal cover crops and non-inoculated controls. Results from this study suggest that cereal winter cover crops may be poor-hosts to M. enterolobii and may significantly reduce M. enterolobii populations before a soybean crop, compared to broadleaf winter cover crops. This study lays the groundwork for management recommendations and future field trials to assess management of M. enterolobii through winter cover cropping.