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Mary Ann D. Maquilan, Dominick C. Padilla, Donald W. Dickson, and Bala Rathinasabapathi

Plant-parasitic root-knot nematodes (RKNs; Meloidogyne spp.) can cause severe damage to their hosts, leading to reductions in crop yield and quality ( Taylor and Sasser, 1978 ). These pathogens become problematic, especially in warmer weather in

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Judy A. Thies, Jennifer J. Ariss, Richard L. Hassell, Sharon Buckner, and Amnon Levi

-plant fumigation of soil beds with methyl bromide has been the primary method for controlling root-knot nematodes and soilborne diseases in watermelon ( Thies et al., 2010 ). However, in accordance with the Montreal Protocol and the U.S. Clean Air Act, methyl

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Charles E. Barrett, Xin Zhao, and Alan W. Hodges

with high resistance/tolerance to soil-borne diseases for yield improvement in fields with a history of severe infestation. Root-knot nematode galling was not observed during the organic field trial conducted in 2010. There was root galling in the 2011

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I. Yates, D. Sparks, and W.M. Powell

Root-knot nematode infection of pecan trees results in reduced growth and vigor of above ground plant parts and gall formation on roots. One-year-old roots parasitized by nematodes were collected and examined by light and scanning electron microscopy for structural anomalies. The root's injury response to nematode feeding was dependent on the location of the nematode in the root. Location in the root exterior to the vascular cambium resulted in hyperplasia forming a burrow for the nematode. Root penetration interior to the vascular cambium resulted in giant cells contiguous to the anterior region of the root-knot nematode. The giant cells occupied extensive regions of the root disrupting the xylem and obliterating cells in the penetration pathway. Giant cells were multi-nucleate with dense cytoplasm and thickened cell walls.

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Peter Cousins and M. Andrew Walker

The grape Vitis champinii Planchon is one source of nematode resistance in grape rootstocks. Several selections valued for their resistance to the root-knot nematode (Meloidogyne incognita), a serious pest of grape production, are used as rootstocks and in rootstock variety development. However, V. champinii-based rootstock varieties are faulted for their excess vigor and susceptibility to other root pests. Root-knot nematode populations with the ability to damage important V. champinii-based rootstocks have been identified and may become more common. Other V. champinii accessions might be sources of nematode resistance genes with different specificities or might have more suitable horticultural characteristics than V. champinii varieties in commercial use. Nine V. champinii accessions from the National Clonal Germplasm Repository, Davis, Calif., and a V. champinii rootstock variety were screened for resistance to M. incognita. Resistance was assessed by counting eggs produced per root system. Eight of ten V. champinii accessions did not support nematode reproduction. Susceptible accessions supported lower nematode reproduction than susceptible V. vinifera control varieties. Progeny testing from crosses of resistant and susceptible accessions suggests that a dominant and a recessive gene may condition root-knot nematode resistance.

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

. Fig. 1. Root-knot nematode (RKN)-resistant F1 hybrid RKVL 301 × 318 watermelon root system with very minimal RKN galling and very fibrous root system (left); RKN-susceptible ‘Emphasis’ bottle gourd root system with severe RKN galling (right). Sept

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J.C. Cervantes, D.L. Davis, and G.C. Yencho

This study was conducted to determine whether the type of pot used for the evaluation affected the resistance response of the sweetpotato plants, and to assess the resistance response to different root-knot nematode species. Five sweetpotato [Ipomoea batatas (L.) Lam] cultivars, `Beauregard', `Exce'l, `Jewel', `Hernandez', and `Porto Rico', were screened for M. incognita (race 3), Meloidogyne arenaria (race 2), and M. javanica, in both 10-cm-side, square pots and 4-cm-diameter, cone pots. Gall index, necrosis index, and number of nematode eggs per gram of root were used to estimate nematode-resistance reaction. Mean of all indices between the 2 pot types were not significantly different (α = 0.05). Gall and necrosis indices were not correlated in any of the cultivars. Resistance response depended on cultivars and nematode species for all variables analyzed. `Beauregard' was the most susceptible to Meloidogyne. `Hernandez' and `Excel' were found to be the most resistant cultivars to the Meloidogyne species.

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Richard L. Fery and Judy A. Thies

conditioning a high level of resistance to the southern root-knot nematode [ Meloidogyne incognita (Chitwood) Kofoid and White], the peanut root-knot nematode [ M. arenaria (Neal) Chitwood], and the tropical root-knot nematode [ M. javanica (Treub) Chitwood

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Richard L. Fery and Judy A. Thies

nematode resistance gene into a ‘Pimiento L’-type genetic background. ‘Pimiento L’ is a root-knot nematode-susceptible, pimento-type cultivar that is widely grown in the southern states where it can produce good yields under high-temperature conditions. The

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S. Alan Walters, Todd C. Wehner, and Kenneth R. Barkel

Cucumber (Cucumis sativus L.) and horned cucumber (C. metuliferus Naud.) germplasm were evaluated for their resistance to root-knot nematodes (Meloidogyne spp.). All 24 C. metuliferus cultigens evaluated were resistant to all root-knot nematodes tested-M. incognita (Kofoid and White) Chitwood race 3, M. arenaria (Neal) Chitwood race 2, and M. hapla Chitwood. All 884 C. sativus cultigens (cultivars, breeding lines, and plant introduction accessions) tested were resistant to M. hapla and few to M. incognita race 3. Only 50 of 884 C. sativus cultigens evaluated were somewhat resistant to M. arenaria race 2 and M. incognita race 3. A retest of the most resistant C. sativus cultigens revealed that LJ 90430 [an accession of C. sativus var. hardwickii (R.) Alef.] and `Mincu' were the only cultigens that were moderately resistant to M. arenaria race 2. LJ 90430 was the only cultigen, besides the two retested C. metuliferus cultigens, that was resistant to M. javanica (Treub) Chitwood. All C. sativus cultigens retested, including LJ 90430, were highly susceptible to M. incognita races 1 and 3. The two C. metuliferus cultigens retested were highly resistant to all root-knot nematodes tested-M. arenaria race 2, M. incognita races 1 and 3, and M. javanica.