Submitted to: Nematropica
Publication Type: Abstract Only
Publication Acceptance Date: 9/4/2011
Publication Date: 12/1/2011
Citation: Brito, J.A., Stamler, R.A., Thomas, S.H., Nyczepir, A.P., Dickson, D.W. 2011. Distribution, hosts and identification of Meloidogyne partityla in the USA. Nematropica. 41(2):322. Interpretive Summary: Pecan is North America’s most valuable native tree-nut, with worldwide cultivation and substantial production in the USA and Mexico. In 1996, the pecan root-knot nematode, Meloidogyne partityla, was first reported in the USA and has been shown to be of economical importance to this valued nut crop. This symposium presentation provides current knowledge about the distribution, symptomatology, host range, economic importance, and identification of M. partityla in pecan growing regions of the USA. This pecan root-knot nematode currently occurs in 6 states and is associated with dead branches in the upper canopy, stunted growth, and Mouse-ear leaves due to nickel deficiency. The nematode has a narrow host range which includes pecan, hickory, walnut, and laurel oak. Genetic DNA studies from seven geographically distinct M. partityla populations from all infested states have shown the species to be similar to M. hapla. Isozyme analysis and classic morphological features also provide a fast and reliable diagnosis of this root-knot nematode. This overview provides useful insights for growers and scientists with the most current information available for the pecan root-knot nematode throughout the USA.
Technical Abstract: Pecan, Carya illinoensis, is an economically important nut crop and member of the Juglandaceae native to the southern USA. Discovered in South Africa in 1986, Meloidogyne partityla was first found infecting pecan in USA in 1996 and currently occurs in Texas, New Mexico, Georgia, Arizona, Oklahoma and Florida. Above-ground symptoms of M. partityla infection in commercial pecan orchards include dieback of young branches, stunted growth, mouse-eared leaves due to nickel deficiency, and gradual tree decline have been reported in mature orchards in TX, NM, GA, AZ and OK. Below-ground symptoms include root galling associated with egg masses. This nematode has a narrow host range which includes pecan, hickory (C. ovata) and walnut (Juglans hindsii and J. regia). More recently, this nematode was also found infecting laurel oak (Quercus laurifolia) in Florida. However, in the field conditions in the USA M. partityla has only been found infecting pecan. Phylogenetic studies using nuclear and mitochondrial DNA from seven geographically distinct M. partityla populations from all infested states have shown the species to be most similar to M. hapla when compared to 19 other Meloidogyne species. Isozyme analysis of individual female nematodes, especially esterase phenotype (Mp3), provides a fast and reliable diagnosis of the pecan root-knot nematode. A species-specific PCR primer set has also been developed for rapid DNA-based diagnosis of all life stages. Additionally, morphological features of high diagnostic values include stylet knobs of the males and females deeply grooved longitudinally and the presence of a swollen rectum and deeply grooved in the second-stage juveniles.