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Hemp is a crop that has gained interest in Washington and Oregon. As with other crops, hemp production faces challenges due to biotic factors, including plant-parasitic nematodes. During a survey for plant-parasitic nematodes associated with hemp, Meloidogyne sp. was found in a composite root sample collected in Oregon. Morphological characterization of second-stage juveniles identified the nematode as Meloidogyne hapla. Molecular identification confirmed the population as M. hapla. To our knowledge, this is the first report of M. hapla on hemp in the Pacific Northwest of the United States.

Assuming that the seeds of Vicia sativa L. have a stressful effect on J2 stage Meloidogyne hapla, we undertook research on the effect of these seeds on the motility and mortality of J2 and determined the expression levels of selected hsp genes in J2. The assessment of the effect of V. sativa seeds on the motility of M. hapla specimens consisted of observing the movement of J2 immersed in a seed diffusate or in a tomato root filtrate at temperatures of 10, 17, and 21°C. In J2 treated with V. sativa (cv. Ina) seed diffusates, the expression level of hsp genes was determined by qPCR. J2 exposed to V. sativa diffusates were found to lose their motility, while their mortality did not exceed 30%. J2 in the seed diffusate were characterized by an increase in the expression levels of the Mh-hsp90, Mh-hsp1, and Mh-hsp43 genes. It is suggested that the hsp90 gene may be a potential bioindicator of the environmental impact on Meloidogyne nematodes. The impaired ability to move in J2 of M. hapla is attributable to the occurrence of V. sativa seeds in their habitat. These studies may contribute to developing methods of reducing crop damage caused by M. hapla.

Tomato plants are susceptible to significant yield losses when infested by the northern root-knot nematode, Meloidogyne hapla. While there are many options for conventional chemical management, few of these options offer effective control for organic growers or those who seek to adopt more environmentally considerate strategies. In this study, we showed that a new, biologically based product (referred to as “MN21.2”) has potential for controlling populations of the northern root-knot nematode, Meloidogyne hapla, as a pest of susceptible tomato (cv. Rutgers) in a greenhouse trial. This is significant because if this product’s efficacy is supported under field conditions, it may provide organic tomato growers with a valuable tool for fighting the plant-parasitic nematode pest, M. hapla.

Root-knot nematodes in the genus Meloidogyne are an important group of plant-parasitic nematodes causing severe damage on agricultural crops worldwide. A study was conducted to identify the species of root-knot nematodes causing damage on honeybush monocultures and to assess the seasonal variations in the nematode population. Soil samples were collected from six experimental sites in Genadendal, Western Cape province of South Africa from 2016 to 2017. DNA was extracted from single-second stage juveniles and species identifi cation was done using species-specifi c sequence-characterised amplifi ed regions (SCAR) primers. Meloidogyne hapla and M. javanica were identifi ed from the sites. Mean population density of the nematodes varied significantly (p < 0.05) in the six sites, with the peak population being recorded in summer of 2017. The study suggests that seasonal variation in temperature and moisture could contribute to changes in the population density of root-knot nematodes in the soil.

Gene expression studies often require reliable housekeeping (HK) genes to accurately capture gene expression levels under given conditions. This is especially true for root-knot nematodes (RKN, Meloidogyne spp.), whose drastic developmental changes are strongly dependent upon their environment. Here we utilized a publicly available M. hapla RNAseq database to identify putative HK genes throughout the nematode lifecycle. We then validated these candidate HK genes on M. incognita in order to develop a small library of suitable HK genes for RKN. Seven putative HK genes were selected for validation based on high expression level and ease of primer design. The expression of these genes was quantified by qPCR at different developmental stages to capture the entire life cycle of M. incognita which included eggs and naive infective juveniles through 3-wk post inoculation. Two algorithms, geNorm and Normfinder, identified three genes (Disu, Poly, and Skinase) constitutively and uniformly expressed throughout the entire life cycle of RKN. We believe these genes are superior HK genes suitable to be used as internal reference genes at all stages of RKN. Importantly, while we identified Actin, a commonly used HK gene, as a candidate gene within our RNAseq analyses, our qPCR results did not demonstrate stable expression throughout the nematode life cycle of this gene. This study successfully validated suitable HK genes utilizing both RNAseq data and standard qPCR methods across two species of RKN; suitable HK genes are likely applicable to other species of RKN, or even plant-parasitic nematodes. Additional lists of potential HK genes are also provided if the nematode of interest does not have homologues of the three superior reference genes described here. Gene expression studies on RKN should use validated HK genes to ensure accurate representation of transcript abundance.

Root-knot nematodes (RKN; Meloidogyne spp.) are among the most damaging pests to tomato production in the USA and worldwide, with yield losses ranging from 25 to 100%. Host resistance conferred by the Mi gene in tomato is effective against some species of RKN (e.g. M. incognita, M. javanica, and M. arenaria); however, there are virulent species and lines including M. hapla and M. eterolobii that break Mi-mediated resistance. Plant innate immunity is another possible form of defense against pathogen attack and is known to be induced by chemical elicitors. Nicotinamide adenine dinucleotide (NAD) is one such chemical elicitor that regulates plant defense responses to multiple biotic stresses. In this study, we investigated the role of NAD in the context of induced tomato innate immunity and RKN pathogenicity in two tomato cultivars; VFN and Rutgers, with and without Mi, respectively. Single soil drench application of NAD 24 hr before nematode inoculation significantly induced defense response pathways, reduced infective-juveniles penetration, number of galls, and increased plant mass in both cultivars. Importantly, we observed no direct toxic effects of NAD on nematode viability and infectivity. The results presented here suggest that NAD induces resistance against RKN pathogenicity likely through the accumulation of tomato basal defense responses rather than the direct effect on the infective-juveniles behavior.

Root-knot nematodes (RKN; Meloidogyne spp.) are among the most damaging pests to tomato production in the USA and worldwide, with yield losses ranging from 25 to 100%. Host resistance conferred by the Mi gene in tomato is effective against some species of RKN (e.g. M. incognita, M. javanica, and M. arenaria); however, there are virulent species and lines including M. hapla and M. eterolobii that break Mimediated resistance. Plant innate immunity is another possible form of defense against pathogen attack and is known to be induced by chemical elicitors. Nicotinamide adenine dinucleotide (NAD) is one such chemical elicitor that regulates plant defense responses to multiple biotic stresses. In this study, we investigated the role of NAD in the context of induced tomato innate immunity and RKN pathogenicity in two tomato cultivars; VFN and Rutgers, with and without Mi, respectively. Single soil drench application of NAD 24 hr before nematode inoculation significantly induced defense response pathways, reduced infective-juveniles penetration, number of galls, and increased plant mass in both cultivars. Importantly, we observed no direct toxic effects of NAD on nematode viability and infectivity. The results presented here suggest that NAD induces resistance against RKN pathogenicity likely through the accumulation of tomato basal defense responses rather than the direct effect on the infective-juveniles behavior. [ABSTRACT FROM AUTHOR]

Gene expression studies often require reliable housekeeping (HK) genes to accurately capture gene expression levels under given conditions. This is especially true for root-knot nematodes (RKN, Meloidogyne spp.), whose drastic developmental changes are strongly dependent upon their environment. Here we utilized a publicly available M. hapla RNAseq database to identify putative HK genes throughout the nematode lifecycle. We then validated these candidate HK genes on M. incognita in order to develop a small library of suitable HK genes for RKN. Seven putative HK genes were selected for validation based on high expression level and ease of primer design. The expression of these genes was quantified by qPCR at different developmental stages to capture the entire life cycle of M. incognita which included eggs and naive infective juveniles through 3-wk post inoculation. Two algorithms, geNorm and Normfinder, identified three genes (Disu, Poly, and Skinase) constitutively and uniformly expressed throughout the entire life cycle of RKN. We believe these genes are superior HK genes suitable to be used as internal reference genes at all stages of RKN. Importantly, while we identified Actin, a commonly used HK gene, as a candidate gene within our RNAseq analyses, our qPCR results did not demonstrate stable expression throughout the nematode life cycle of this gene. This study successfully validated suitable HK genes utilizing both RNAseq data and standard qPCR methods across two species of RKN; suitable HK genes are likely applicable to other species of RKN, or even plant-parasitic nematodes. Additional lists of potential HK genes are also provided if the nematode of interest does not have homologues of the three superior reference genes described here. Gene expression studies on RKN should use validated HK genes to ensure accurate representation of transcript abundance. [ABSTRACT FROM AUTHOR]