J. A. Brito

Identification and isozyme characterisation of Meloidogyne spp. infecting horticultural and agronomic crops, and weed plants in Florida.

A total of 327 root samples collected from horticultural and agronomic crops, and weeds associated with these crops in Florida crop production regions, were examined. Isozyme phenotypes, esterase (EST) and malate dehydrogenase (MDH) phenotypes were used to characterise and identify the species of Meloidogyne present in these samples. At least 26 females from each sample were examined using polyacrylamide gel electrophoresis. Sixteen major bands of EST activity were found, corresponding to 12 phenotypes. A species-specific EST phenotype was consistently associated with each of the Meloidogyne spp. identified: Meloidogyne arenaria, M. floridensis, M. graminicola, M. hapla, M. incognita, M. javanica, M. mayaguensis and M. partityla. Two unique EST phenotypes, which have not been described, were found associated with three unidentified nematode populations. Five bands of MDH activity and four phenotypes were also found among the populations. During this study, new host records were determined for M. floridensis and M. mayaguensis, two recently reported Meloidogyne spp. in Florida. Plant species found as new hosts of M. floridensis were Cucumis sativus, Phaseolus sp., Solanum melongena and one weed species, Emilia sonchifolia, and the M. incognita-resistant peach rootstock ‘Flordaguard’. New hosts for M. mayaguensis were Carica papaya, Capsicum annuum var. Longum, and six weed plants, including Eclipta prostrata, Fatoua villosa, Panicum sp., Poinsettia cyathophora, Solanum americanum and also one unidentified weed species belonging to the family Acanthaceae. To our knowledge, Florida is the only geographic area of North America where M. floridensis and M. mayaguensis have been detected.

First Report of Laurel Oak as a Host for the Pecan Root-Knot Nematode, Meloidogyne partityla, in Florida

Roots of laurel oak (Quercus laurifolia Michx.), member of the family Fagaceae, were found to be heavily galled by the pecan root-knot nematode, Meloidogyne partityla, in two separate home gardens between 2010 and 2012, in Alachua Co., FL. Distinct round galls were observed on secondary and tertiary roots. Internally, root-knot nematode females were clearly visible when the roots were thinly sliced and egg masses were seen protruding from the root surfaces. The nematode species identification was performed using morphology of the male stylet, selected characters of the second-stage juveniles (J2), female perineal patterns, and esterase (EST) and malate dehydrogenase (Mdh) isozyme phenotypes. Morphology of perineal patterns of females, body, stylet, and tail length of the J2 and males all matched those of the original description of M. partityla (2). A swollen deeply grooved rectum was observed in the J2. The male stylet had a blunt tip with a prominent thickening at the junction between the cone and shaft. The stylet knobs of males and females were bipartite, each incised by a deep medium longitudinal groove (2). The isozyme phenotypes (EST = Mp3; Mdh = N1a) were consistent with those previously reported for M. partityla from Florida (1). Mitochondrial DNA (mtDNA) (3) and ribosomal internal transcriber spacer (ITS) DNA (4) of females were amplified to further confirm the nematode species identification. The mtDNA amplification using the C2F3/1108 primer set (3) and the ITS amplification using a recently available M. partityla specific primer set (4) produced fragments of approximately 530 bp and 550 bp, respectively. These were consistent with those already reported for this nematode species. This first report of a plant host for the pecan root-knot nematode outside of the family Juglandaceae indicates that the nematode may have migrated from Quercus species to pecan trees during the period when orchards were being established in Florida. To our knowledge, this is the first report of the pecan root-knot nematode infecting laurel oak. References: (1) J. A. Brito et al. Nematology 10:757, 2008. (2) Kleynhans, K. P. N. Phytophylatica 18:103, 1986. (3) T. O. Powers et al., J. Nematol. 37:226, 2005. (4) R. A. Stamler. M. S. thesis, New Mexico State University, Las Cruces, 2009.

First report of Meloidogyne enterolobii infecting Euphorbia punicea in Florida.

Euphorbia punicea (Euphorbiaceae), commonly known as Jamaican poinsettia, is an evergreen shrub with dark green leaves and flashy red bracts. Bracts are sharply contrasted by rosettes of dark green leaves and can be observed in early summer, spring, fall, and winter. This shrub, native to Jamaica, is suitable in southern climates both in the landscape and as a seasonal patio container plant. Outdoors, the plants can reach as high as 5 meters. In January of 2012, E. punicea plants growing in an ornamental nursery in Dade Co., Florida, were observed with stunted growth and yellowing leaves. Root systems of affected plants were collected and sent to the Florida Department of Agriculture and Consumer Services, Nematology Laboratory, Gainesville, FL. Root systems showing symptoms of root-knot nematode infections were heavily galled and had already started rotting. Galls were observed in the primary, secondary, and tertiary roots. Species identification was initially performed using morphology and morphometrics. The morphology of the perineal patterns and measurements of selected characters of the second-stage juveniles fit those of the original description for M. enterolobii (3). The nematode species identification was confirmed using PCR to amplify mtDNA with the C2F3/1108 primer set (1) and a species-specific SCAR primer set, MK7-F/MK7-R (2). The PCR products were approximately 700 bp for mtDNA and approximately 520 bp for the SCAR, which were identical to those previously reported for M. enterolobii (1, 2). Sanitation practices should be implemented to avoid the spread of this nematode species within and between ornamental nurseries. Planting material should be produced in media free of this pathogen to avoid its introduction into uninfested nurseries and landscape areas. M. enterolobii has a wide host range, including cover and vegetable crops, fruit trees, herbs, and ornamental and weed plants. To our knowledge, this is the first report worldwide of E. punicea as a host of M. enterolobii. References: (1) T. O. Powers et al. J. Nematol. 37:226, 2005. (2) M. S. Tigano et al. Plant Pathol. 59:1054, 2010. (3) B. Yang and J. D. Eisenback. J. Nematol. 15:381, 1983.

A first report of Paulownia elongata as a host of Meloidogyne spp. in Florida.

Paulownia elongata S.Y. Hu (Scrophulariaceae) is a fast-growing tree cultivated for highly prized timber. In April 2007, root-knot nematodes were found to be infecting 5-year-old plants of P. elongata growing on a farm in Levy County, Florida. Symptoms included leaf yellowing, stunted growth, and reduced trunk diameter. Infected roots were severely galled and frequently rotted. Large and coalesced galls were observed on secondary roots and distinct galls were present on tertiary roots. Species identifications were done by morphological characters of females and isozyme phenotypes (esterase and malate dehydrogenase) extracted from young egg-laying females and resolved with polyacrylamide gel electrophoresis in a BioRad Mini Protean III system (BioRad, Hercules, CA). Four species of root-knot nematodes were found to be infecting P. elongata. Morphology of perineal patterns and the isozyme phenotypes were consistent with those of M. arenaria, M. incognita, M. javanica, and M. mayaguensis (1). M. incognita and M. javanica have been described earlier on P. fortunei and P. tomentosa (2), but to our knowledge, this is the first report of P. elongata as a host of these four Meloidogyne spp. References: (1) R. M. D. G. Carneiro et al. Nematology 6:287, 2004. (2) V. Sharma and M. D. Mehrotra. Indian J. For. 22:149, 1999.