Summary
Crop damage inflicted by Meloidogyne enterolobii justifies an updated literature review focusing on recent discoveries about its identification, biology and management. Since its description in 1983, M. enterolobii has become a pest of great concern, particularly due to its virulence, which renders controlling this nematode pest a challenge. The global distribution of M. enteroblii is summarised, with emphasis placed on limited research done for the species in sub-Saharan Africa where food production and security is threatened by root-knot nematode parasitism. Novel advances in methods used to detect M. enterolobii are touched upon, especially the improvement in advanced molecular techniques that complements shortcomings in morphology and morphometic approaches. Despite these exciting developments, the employment of effective management strategies to combat the species remains problematic. Future research on various aspects of M. enterolobii is crucial, with focus to be placed on the use of available resources to contain damage caused by this species.
Tylenchulus semipenetrans was identified morphologically from root samples collected from citrus orchards in Shahdad region, southeastern Iran. The number of juveniles and females averaged 648/100 g soil and 65/10 g root, respectively, in infected samples. Monitoring these orchards for two years (2012)(2013) indicated no significant correlation between soil pH (7.21-7.70) and EC (0.56-1.98) values and populations densities of T. semipenetrans. With respect to seasonal distribution, T. semipenetrans attained the highest density during fall and the lowest in spring. Sequence analysis of the D2-D3 segment of 28S rDNA confirmed this population as T. semipenetrans. Nblast indicates that the sequence from this population differs in only three or five nucleotides from corresponding sequences from T. semipenetrans populations from Korea (FJ969715, FJ060713, and FJ969712), with 99% identity. The phylogenetic position and a table of measurements of this species are provided.
Summary
A new species of Aporcelaimellus, collected in a watermelon field in Nigeria, is described, including its morphological and molecular (D2-D3 28S-rDNA, 18r-DNA) characterisation. Aporcelaimellus nigeriensis sp. n. is distinguishable by its 2.76-3.55 mm length, very coarse ventral body pores, lip region offset by deep constriction and 24-27 μm broad odontostyle 30-36 μm long at its dorsal and 28-31 μm at its ventral side, neck 648-779 μm long, pharyngeal expansion occupying 54-60% of total neck length, uterus 300-473 μm or 2.1-3.2 body diam. long and tripartite, V = 49-54, tail short and convex conoid (27-41 μm, c = 72-115, c′ = 0.5-0.7), spicules 108-137 μm long, and 9-10 spaced ventromedian supplements with hiatus. LSU analysis revealed a close relationship of A. nigeriensis sp. n. with other Aporcelaimellus species and questioned, once more, the monophyly of Aporcelaimidae. SSU phylogenetic tree was not able to resolve the relationship between the new species and other closely related species.
Meloidogyne species cause great crop losses worldwide. Although genetic host plant resistance is an effective control strategy to minimize damage caused by Meloidogyne, some resistant genes are ineffective against virulent species such as Meloidogyne enterolobii. Detailed knowledge about the genetic composition of Meloidogyne species is thus essential. This study focused on genotyping-by-sequencing (GBS) and Pool-Seq to elucidate the genetic relation between South African M. enterolobii, M. incognita and M. javanica populations. Hence, 653 common single nucleotide polymorphisms (SNPs) were identified and used to compare these species at genetic level. Allele frequencies of 34 SNPs consistently differed between the three Meloidogyne species studied. Principal component and phylogenetic analyses grouped the M. enterolobii populations in one clade, showing a distant relation to the M. javanica populations. These two species also shared genetic links with the M. incognita populations studied. GBS has been used successfully in this study to identify SNPs that discriminated among the three Meloidogyne species investigated. Alleles, only occurring in the genome of M. enterolobii and located in genes involved in virulence in other animal species (e.g. a serine/threonine phosphatase and zinc finger) have also been identified, accentuating the value of GBS in future studies of this nature.
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