February 14, 2005
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of the Root-Knot Nematode _Meloidogyne arenaria_ Race 2 from several vegetable crops in Jordan
M. Karajeh, Laboratory of Plant Pathology, Department of Plant Production, Mut'ah University, Karak 7, Jordan; W. Abu-Gharbieh, Department of Plant Protection, University of Jordan, Amman 11942, Jordan; and S. Masoud, Laboratory of Plant Pathology, Department of Plant Production, Mut'ah University, Karak 7, Jordan. Plant Dis. 89:206, 2005; published on-line as DOI: 10.1094/PD-89-0206B. Accepted for publication 31 Oct 2004.

_Meloidogyne arenaria_ (Neal) Chitwood (race 2) is reported for the 1st time in Jordan. The nematode populations were recovered from several vegetable crops, including tomato (_Lycopersicon esulentum_ Mill), squash (_Cucurbita pepo_ L.), cucumber (_Cucumis sativus_ L.), and bean (_Phaseolus vulgaris_ L.), at Dier Alla in the northern area of the Jordan Valley. Symptoms included root galling, leaf chlorosis, and stunting. Galled plant root samples were collected during a survey conducted from May 2002 to August 2003 covering most of the
irrigated agricultural areas of Jordan.

83 _Meloidogyne_ spp. populations were collected from various vegetable crops and fruit trees. Identification to species and race levels of the nematode populations was based on a combination of currently available methods, including nematode morphology, host preference based on the North Carolina (NC) differential host test (1), and cytogenetics and DNA-fingerprinting. 70 of the 83 collected populations were identified as _M. javanica_, 5 as _M. incognita_ (race 1), 3 as _M. incognita_ (race 2), and 5 as _M. arenaria_ (race 2).

The perineal patterns of _M. arenaria_ were characterized by a low, round to indented dorsal arch near the lateral field with irregular forks in the lateral field, fine smooth striae, and a distinct whorl. Race 2 was identified with the NC differential host test. Cytogenetic studies indicated that _M. arenaria_ populations were triploid with an average of 52.2 chromosomes, while the populations of _M. incognita_ (race 1), _M. incognita_ (race 2), and _M. javanica_ were hypotriploid with an average of 45.2, 46.1, and 46.7 chromosomes, respectively.

2 polymerase chain reaction (PCR)-based assays were used to confirm species identification and to study genetic variability of the _Meloidogyne_ spp. populations, including sequence characterized amplified regions (SCAR) and random amplified polymorphic DNA (RAPD). In the SCAR-PCR-based assay (2), typical DNA products of 420, 670, or 1200 bp in size were amplified by using extracted DNA of _M. arenaria_ (race 2), _M. javanica_, or _M. incognita_ (race 1 or 2), respectively, as template DNA. The RAPD-PCR primer, OPA-01, produced DNA patterns with bands that clearly distinguished _M. arenaria_ from the other 2 _Meloidogyne_ spp.

To our knowledge, this is the 1st report of the root-knot nematode, _M. arenaria_ race 2, in Jordan.

References:
(1) A. Taylor and J. Sasser, North Carolina State University Graphics, Raleigh, NC, 1978.
(2) C. Zijlstra et al. Nematology 2:847, 2000.

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[Root-knot nematodes, especially _M. incognita_ [Mi], _M. arenaria_ [Ma] and _M. javanica_ [Mj], cause serious damage to cucumber, melon, watermelon, pumpkin and squash. The finding of _M. arenaria_ [Ma] in Jordan is certain to cause considerable yield losses in important food crops. Ma is considered one of the "major" _Meloidogyne_ species due to its worldwide economic importance. It is commonly encountered in warmer regions and is seldom found in areas where average monthly temperatures approach freezing. It is the most morphologically and cytologically variable of the _Meloidogyne_ species. 2 host races have been differentiated, one that reproduces on peanut (race 1), and race 2 which does not.

Differences in field resistance to _Meloidogyne_ spp. among 21 melon cultivars and breeding lines have been reported in Florida, but good resistance in muskmelon or other cucurbits is not available. A high level of resistance to the 4 major root-knot nematode species is present in the African horned cucumber (_Cucumis metuliferus_), but attempts to develop interspecific hybrids with cucumber cultivars have failed. Resistance to Mj
and Ma races 1 and 2 occur in _Cucumis sativus_ var. line 90430, and cucumbers resistant to these species or races currently are being developed at North Carolina State University. Resistance to Mi, Mj and Ma has also been
identified in the West Indian gherkin (_C. anguria_) and other wild _Cucumis_ spp.

Disease management involves use of nematicides for high-value crops such as peanuts, tobacco, and peach. Where available, resistant cultivars provide the most economical and environmentally benign means of control. A PCR-based system has been developed using species-specific DNA fragments, and it identified all 4 major species present in South Carolina, but further refinements are required to maximize its potential. The research has provided a foundation to develop an accurate root-knot nematode species identification system (based only on a single 2nd stage juvenile) that can be integrated into a nematode management system. Rotation experiments are underway to test the modified PCR-based system when reliability can be improved. - Mod.DH]