First Report of Meloidogyne marylandi Infecting Bermudagrass in Costa Rica

Molecular characterization of root-knot nematodes (Meloidogyne spp.) from Arkansas, USA

Root-knot nematodes (Meloidogyne spp.) are the most common major pathogens of many crops throughout the world, impacting both the quantity and quality of marketable yields. In this study, a total of 244 root-knot nematode populations from various hosts from 39 counties in Arkansas were tested to determine the species diversity. Molecular characterization was performed on these populations by DNA sequencing of the ribosomal DNA 18S-ITS-5.8S, 28S D2/D3 and a mitochondrial DNA fragment flanking cytochrome oxidase gene subunit II - the intergenic spacer. Five species were identified, including M. incognita (Kofoid & White, 1919) Chitwood, 1949 from soybean, cotton, corn and various vegetables (232 samples); M. hapla Chitwood, 1949 from rose (1 sample); M. haplanaria Eisenback, Bernard, Starr, Lee & Tomaszewski, 2003 from okra, tomato, peanut, Indian hawthorn, ash, willow and elm trees (7 samples); M. marylandi Jepson & Golden in Jepson, 1987 from grasses (3 samples); and M. partityla Kleynhans, 1986 from pecan (1 sample) through a combined analysis of DNA sequencing and PCR by species-specific primers. Meloidogyne incognita is the most abundant species that was identified in 95% samples and was the only species in field crops including soybean and cotton, except for one population of M. haplanaria from soybean in Logan County (TK201). Species-specific primers were used to verify M. incognita through PCR by species-specific primers. Unlike historical data, M. arenaria, M. javanica and M. graminis were not detected from any of the samples collected during this study. This result is essential for effective and sustainable management strategies against root-knot nematodes in Arkansas.

18S rRNA and COI haplotype diversity of Trichodorus obtusus from turfgrass in South Carolina

The stubby-root nematode, Trichodorus obtusus, was recently identified on zoysiagrass in South Carolina, USA. In Florida, T. obtusus causes more damage than other stubby-root nematodes encountered in turfgrass. The objective of this study was to use morphological analysis, mitochondrial DNA (COI: cytochrome oxidase 1) and nuclear (18S rRNA) sequence data to study the genetic structure and haplotype diversity of populations recovered from turfgrasses in South Carolina. Numerous morphological differences were observed among populations. Three 18S haplotypes were shared among South Carolina and Florida populations, and six mitochondrial haplotypes were identified in South Carolina samples. Of the six COI haplotypes, four haplotypes were restricted to one population from St Augustinegrass. The lowest haplotype diversity was found in samples from zoysiagrass. Sequences of the COI mtDNA gene of T. obtusus were published in GenBank and represent the first mtDNA sequences for the genus Trichodorus.

Molecular Characterisation and Diagnosis of Root-Knot Nematodes (Meloidogyne spp.) from Turfgrasses in North Carolina, USA

Root-knot nematodes (Meloidogyne spp.) are the most common and destructive plant-parasitic nematode group worldwide and adversely influence both crop quality and yield. In this study, a total of 51 root-knot nematode populations from turfgrasses were tested, of which 44 were from North Carolina, 6 from South Carolina and 1 from Virginia. Molecular characterisation was performed on these samples by DNA sequencing on the ribosomal DNA 18S, ITS and 28S D2/D3. Species-specific primers were developed to identify turfgrass root-knot nematode through simplex or duplex PCR. Four species were identified, including M. marylandi Jepson & Golden in Jepson, 1987, M. graminis (Sledge & Golden, 1964) Whitehead, 1968, M. incognita (Kofoid & White, 1919) Chitwood, 1949 and M. naasi Franklin, 1965 through a combined analysis of DNA sequencing and PCR by species-specific primers. M. marylandi has been reported from North Carolina and South Carolina for the first time. Molecular diagnosis using PCR by species-specific primers provides a rapid and cheap species identification approach for turfgrass root-knot nematodes.

Molecular Characterization and Phylogenetic Relationships of Plant-Parasitic Nematodes Associated with Turfgrasses in North Carolina and South Carolina, United States

The near-full-length 18S ribosomal DNA (rDNA) gene and internal transcribed spacer 1 region were amplified and sequenced from 52 nematode populations belonging to 28 representative species in 13 families recovered from turfgrasses in North Carolina (38 populations) and South Carolina (14 populations). This study also included 13 nematode populations from eight other plant hosts from North Carolina for comparison. Nematodes were molecularly characterized and the phylogenetic relationships were explored based on 18S rDNA sequences. Phylogenetic analysis using Bayesian inference was performed using five groups of the plant-parasitic nematode populations Tylenchids, Criconematids, Longidorids, Xiphinematids, and Trichodorids. The 65 nematode populations were clustered correspondingly within appropriate positions of 13 families, including Belonolaimidae, Caloosiidae, Criconematidae, Dolichodoridae, Hemicycliophoridae, Hoplolaimidae, Heteroderidae, Longidoridae, Meloidogynidae, Paratylenchidae, Pratylenchidae, Telotylenchidae, and Trichodoridae. This study confirms previous morphological-based identification of the plant-parasitic nematode species found in turfgrasses and provides a framework for future studies of plant-parasitic nematodes associated with turfgrasses based upon DNA sequences and phylogenetic relationships.

Meloidogyne lopezi n. sp. (Nematoda: Meloidogynidae), a new root-knot nematode associated with coffee (Coffea arabica L.) in Costa Rica, its diagnosis and phylogenetic relationship with other coffee-parasitising Meloidogyne species

Coffee (Coffea arabica L. cv. Catuai) seedlings with abundant small root galls caused by an unknown root-knot nematode were found in southern Costa Rica. Morphology, esterase and malate dehydrogenase isozyme phenotypes and DNA markers differentiated this nematode from known Meloidogyne spp. A new species, M. lopezi n. sp., with common name Costa Rican root-knot nematode, is suggested. Meloidogyne lopezi n. sp. is distinguished from other coffee-associated Meloidogyne spp. by size of female lips and stylet, male body length and stylet and second-stage juvenile body and tail morphology. The region of the mitochondrial genome between COII and 16S rRNA showed a unique amplicon size of 1370 bp, and digestions with restriction enzymes HinfI, AluI, DraI and DraIII revealed characteristic PCR-RFLP patterns that differed from the tropical root-knot nematode species M. arabicida, M. incognita, M. izalcoensis, M. javanica and M. paranaensis. Characterisation of the protein-coding map-1 gene and phylogenetic analyses suggested that M. lopezi n. sp. might reproduce by mitotic parthenogenesis. Phylogenies estimated using Bayesian analyses based on the region between the COII and 16S rRNA mitochondrial genes, as well as the 18S and 28S ribosomal nuclear genes, indicated that M. lopezi n. sp. is closely related to other tropical Meloidogyne spp. that infect coffee, especially M. arabicida, M. izalcoensis and M. paranaensis from Central and South America. Isozyme analyses and PCR-RFLP of the COII-16S rRNA mitochondrial gene region enable a clear diagnostic differentiation between these species.