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Arthur Villordon and Christopher Clark

’ sweetpotato adventitious root obtained from a plant subjected to high Meloidogyne incognita inoculum level ( A ). The same sample was scanned in gray scale for image analysis using WinRHIZO ( B ), showing nematode galls on lateral roots (LR) (inset, C

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Judy A. Thies, Sharon Buckner, Matthew Horry, Richard Hassell and Amnon Levi

’ bottle gourd (1114) and ‘Strong Tosa’ squash hybrid (2653) ( Table 1 ). Table 1. Percentage of root system galled and covered with egg masses of Meloidogyne incognita, numbers of M. incognita eggs per gram fresh root, and total fruit yield for ‘Tri

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E. Zamora, P.W. Bosland and S. Thomas

The resistance of `Carolina Cayenne' (Capsicum annuum L.) to root-knot nematode Meloidogyne incognita (Kofoid & White) Chitwood races 1, 2, 3, and 4 was measured. Egg counts from roots were used to determine the plant's resistance to M. incognita. Few eggs were observed on `Carolina Cayenne' roots, whereas all races of M. incognita produced numerous eggs on the susceptible `NuMex R Naky' roots. The results indicated `Carolina Cayenne' is a source of resistance to all known races of M. incognita.

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B.A. Mullin, G.S. Abawi, M.A. Pastor-Corrales and J.L. Kornegay

A stem grafting technique was used to determine the contribution of root and shoot tissues of bean (Phaseolus vulgaris L.) to the resistance response to the root-knot nematode, Meloidogyne incognita (Kofoid and White, 1919) Chitwood 1949. Stemgrafts were prepared between resistant (line A 211 or cultivar Nemasnap) and susceptible (Canario Divex) bean cultivars in all possible scion-rootstock combinations. Graft combinations in which the rootstock was resistant resulted in a resistant response to M. incognita, and those combinations in which the rootstock was susceptible resulted in a susceptible response, regardless of scion component. Resistance factors were therefore either localized within roots or not translocated basipetally through the stem graft union.

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G.B. Cap, P.A. Roberts, I.J. Thomason and T. Murashige

Genotypes of Lycopersicon peruvianum (L.) Mill. and L. peruvianum var. glandulosum (Rick), selected from accessions that possess resistance to Meloidogyne incognita [(Kofoid and White) Chitwood] at high soil temperature (30C), were used as male parents in crosses with L. esculentum (Mill.) susceptible cultivars UC82, Lukullus, Tropic, and male-sterile line ms-31, respectively. The incongruity barrier between the two plant species was overcome by embryo callus and embryo cloning techniques. Hybridity of the F, progeny obtained from each cross was confirmed by differences in leaf and flower morphology, plant growth habits, and by acid phosphatase isozyme phenotypes using polyacrylamide gel electrophoresis. In greenhouse inoculation experiments, F1 plants were highly resistant to M. incognita in soil at 25 and 30C. These results confirmed the successful transfer and expression of heat-stable resistance to M. incognita from L. peruvianum to hybrids with L. esculentum as a preliminary step to introgressing additional root-knot nematode resistance into tomato.

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Carolina Fernández, Jorge Pinochet, Daniel Esmenjaud, Maria Joao Gravato-Nobre and Antonio Felipe

The influence of salinity and plant age on nematode reproduction was determined on two susceptible and six root-knot-nematode-resistant Prunus rootstocks inoculated with Meloidogyne incognita (Kofoid and White). Experiments were conducted under greenhouse conditions over 120 (plant age study) and 75 (salinity study) days. Following inoculation with 4000 nematodes per plant, susceptible 2-month-old GF-677 (Prunus persica L. Batsch. × P. dulcis Mill. Webb) and Montclar (P. persica) were affected significantly more than 1-year-old plants. Barrier (P. persica × P. davidiana Carr. Franch.) plantlets showed a partial loss of resistance in relation to older plants, suggesting that a root tissue maturation period is required for expression of full resistance. Nemared (P. persica); G × N No 22 (P. persica × P. dulcis); and the plums GF 8-1 (P. cerasifera Ehrh. × P. munsoniana Wight and Hedrick), PSM 101 (P. insititia L.), and P 2980 (P. cerasifera) maintained their high level of resistance or immunity, regardless of plant age. Nematode reproduction was higher in GF-677 rootstock in saline soil. Nemared and Barrier showed similar low galling and nematode reproduction in nonsaline and saline soil. PSM 101 immunity to M. incognita was not affected by soil condition.

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Ghazala P. Hashmi, F.A. Hammerschlag, R.N. Huettel and L.R. Krusberg

Somaclonal variation has been reported in many plant species, and several phenotypic and genetic changes, including pathogen and pest resistance, have been described. This study was designed to evaluate somaclonal variation in peach [Prunus persica (L.) Batsch] regenerants in response to the root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood. Regenerants SH-156-1, SH-156-7, SH-156-11, and SH-156-12, derived from `Sunhigh' (susceptible) embryo no. 156, and regenerants RH-30-1, RH-30-2, RH-30-4, RH-30-6, RH-30-7, and RH-30-8, derived from `Redhaven' (moderately resistant) embryo no. 30, were screened in vitro for resistance to the root-knot nematode. Under in vitro conditions, fewest nematodes developed on regenerants SH-156-1 and SH-156-11, `Redhaven', and all `Redhaven' embryo no. 30 regenerants. The most nematodes developed on `Sunhigh', `Sunhigh' seedlings (SHS), and regenerant SH-156-7. Nematodes did not develop on `Nemaguard'. In greenhouse tests, fewer nematodes developed and reproduced on the no. 156-series regenerants than on `Sunhigh'. Under in vitro conditions, significant differences among uninfected (control) regenerants, cultivars, and rootstock `Nemaguard' were observed for shoot height and fresh root weights. Significant differences were also observed among infected regenerants, cultivars, and `Nemaguard' for these characteristics, but differences were not observed between control and infected regenerants. Different concentrations of α-naphthaleneacetic acid in half-strength Murashige and Skoog salt medium induced rooting of two peach cultivars, one rootstock, and four regenerants.

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Judy A. Thies, Richard L. Fery, John D. Mueller, Gilbert Miller and Joseph Varne

Resistance of two sets of bell pepper [(Capsicum annuum L. var. annuum (Grossum Group)] cultivars near-isogenic for the N gene that conditions resistance to root-knot nematodes [Meloidogyne incognita (Chitwood) Kofoid and White, M. arenaria (Neal) Chitwood races 1 and 2, and M. javanica (Treub) Chitwood] was evaluated in field tests at Blackville, S.C. and Charleston, S.C. The isogenic bell pepper sets were `Charleston Belle' (NN) and `Keystone Resistant Giant' (nn), and `Carolina Wonder' (NN) and `Yolo Wonder B' (nn). The resistant cultivars Charleston Belle and Carolina Wonder were highly resistant; root galling was minimal for both cultivars at both test sites. The susceptible cultivars Keystone Resistant Giant and Yolo Wonder B were highly susceptible; root galling was severe at both test sites. `Charleston Belle' had 96.9% fewer eggs per g fresh root than `Keystone Resistant Giant', and `Carolina Wonder' had 98.3% fewer eggs per g fresh root than `Yolo Wonder B' (averaged over both test sites). `Charleston Belle' and `Carolina Wonder' exhibited a high level of resistance in field studies at both sites. These results demonstrate that resistance conferred by the N gene for root-knot nematode resistance is effective in field-planted bell pepper. Root-knot nematode resistant bell peppers should provide economical and environmentally compatible alternatives to methyl bromide and other nematicides for managing M. incognita.

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Jim C. Cervantes-Flores, G. Craig Yencho, Kenneth V. Pecota, Bryon Sosinski and Robert O.M. Mwanga

, their extensive host ranges, and associations with fungi and bacteria in disease complexes rank RKN among the major pathogens affecting crops ( Sasser, 1980 ). Greater than 50 species of RKN have been described, but Meloidogyne incognita , M. javanica

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Susan L.F. Meyer, Dilip K. Lakshman, Inga A. Zasada, Bryan T. Vinyard and David J. Chitwood

the root-knot nematode Meloidogyne incognita Pest Mgt. Sci. 64 223 229 Montes-Belmont, R. Carvajal, M. 1998 Control of Aspergillus flavus in maize with plant essential oils and their components J. Food Prot. 61 616 619 Pandey, R.C. Dwivedi, B