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Richard L. Fery and Judy A. Thies

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]. Root-knot

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Craig J. Frey, Xin Zhao, Jeffrey K. Brecht, Dustin M. Huff, and Zachary E. Black

vegetable production systems, where many disease and pest problems persist as a result of conducive environments. In Florida, root-knot nematodes ( Meloidogyne spp.) thrive in sandy soils under warm, moist conditions, but little is known regarding the

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W. R. Maluf, S. M. Azevedo, and V.P. Campos

Heritabilities for resistance to root knot nematodes (Meloidogyne javanica and Meloidogyne incognita races 1, 2, 3, and 4) were studied in a population of 226 sweetpotato clones of diverse origin. For each nematode isolate tested, 128-cell speedling trays were filled with previously inoculated substrate (30000 eggs/1000 mL substrate). Sweetpotato clones suitably tagged and identified were randomly planted in the cells (one plant/cell), with a total of four plants per clone per isolate. Ninety days after inoculation, sweetpotato plants had their roots washed for substrate removal, and treated with 150 mg·L–1 Phloxine B to stain nematode egg masses. The number of egg masses per root was recorded, and plants were accordingly assigned scores from 0 (highly resistant) to 5 (highly susceptible). Broad-sense heritability estimates were 0.87, 0.91, 0.81, 0.95, and 0.93 respectively for resistance to M. javanica and races 1, 2, 3, and 4 of M. incognita. The frequencies of resistant genotypes were higher for M. javanica and lower for M. incognita race 2. Genotypic correlations (rG) among the resistances to the various Meloidogyne isolates utilized were weak, ranging from 0.11 to 0.57, suggesting independent genetic controls. Clones could be selected, however, with high levels of resistance to all nematode isolates tested. (This work was supported by CNPq, CAPES, FAPEMIG, and FAEPE/UFLA.)

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J.A. Thies

Thirteen sweetpotato (Ipomoea batatas) genotypes were characterized for resistance to Meloidogyne incognita, M. javanica, M. hapla, and M. arenaria races 1 and 2 in greenhouse tests. The following sweetpotato genotypes representing a range of reactions to M. incognita were evaluated: U.S. Plant Introduction (PI) 399163 (highly resistant = HR), Sumor (HR), Nemagold (HR), Excel (HR), Tinian (HR), Hernandez (resistant = R), Jewel (R), Regal (R), Porto Rico (intermediate = I), Centennial (susceptible = S), Georgia Jet (S), Sulfur (S), and Beauregard (S). Meloidogyne incognita was most pathogenic to sweetpotato of the four Meloidogyne spp. evaluated in these studies. The U.S. Plant Introduction (PI) 399163 and Sumor were resistant to M. incognita in all tests. Only two genotypes, Beauregard and Porto Rico, were susceptible to M. javanica. All genotypes evaluated were resistant to M. hapla, M. arenaria race 1, and M. arenaria race 2. Sumor, U.S. PI 399163, and Nemagold appear to provide the highest levels of resistance against the four Meloidogyne spp. used in these studies. Since M. incognita is the most commonly occurring root-knot nematode species in sweetpotato growing areas of the southern U.S. and is pathogenic to most of the commonly grown sweetpotato cultivars, efforts to develop resistant cultivars that have desirable horticultural characteristics for the U.S. market should be directed toward this root-knot nematode species.

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S. Alan Walters and Todd C. Wehner

Root-knot caused by Meloidogyne spp. is the primary disease of cucumber (Cucumis sativus L.) in North Carolina, causing an annual yield loss of approximately 12 %. All cucumber cultivars we have tested are resistant to M. hapla, but none are resistant to any of the four important nematodes found on cucumber in North Carolina: M. incognita, M. arenaria races 1 and 2, and M. javanica. However, we are preparing to release three cucumber inbreds with resistance to four out of five of those nematodes. `Marion' (NC-44), `Shelby' (NC-45), and `Lucia' (NC-46) are high yielding, monoecious pickling cucumber inbreds that have resistance to M. arenaria races 1 and 2, M. javanica, and M. hapla. Length: diameter ratio was 3.4, 3.0, 3.9 for `Marion', `Shelby', `Lucia' (`Calypso' was 2.9 in the same trial), respectively. Thus, different length requirements for the pickling industry can be met with the three cultivars. Based on the 1995 North Carolina stage 1 pickle trial, performance (as % of `Calypso') for `Marion', `Shelby', and `Lucia' respectively was 79%, 94%, and 115% for total fruit number/ha; 71%, 96%, and 113% for marketable fruit number/ha; and 102%, 84%, and 97% for fruit quality rating. Therefore, nematode resistant cultivars are available that match the performance of the gynoecious hybrid check cultivar for the region.

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Ke Cao, Lirong Wang, Gengrui Zhu, Weichao Fang, Chenwen Chen, and Pei Zhao

Root-knot nematodes are damaging pests of fruit tree crops and numerous other perennial or annual plants. Several rootstock breeding programs using interspecific hybridization have introduced useful traits for size control, adaptation to the new

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Judy A. Thies and Amnon Levi

Root-knot nematodes [Meloidogyne arenaria (Neal) Chitwood, Meloidogyne incognita (Kofoid & White) Chitwood, and Meloidogyne javanica (Treub) Chitwood] are serious pests of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] in the southern United States and worldwide. Watermelon cultivars with resistance to any of these nematode pests are not available. Therefore, we evaluated all accessions of Citrullus colocynthis (L.) Schrad.(21) and Citrullus lanatus (Thunb.) Matsum. & Nakai var. citroides (L.H. Bailey) Mansf.(88), and about 10% of C. lanatus var. lanatus (156) accessions from the U.S. Plant Introduction (PI) Citrullus germplasm collection for resistance to M. arenaria race 1 in greenhouse tests. Only one C. lanatus var. lanatus accession exhibited very low resistance [root gall index (GI) = 4.9] and 155 C. lanatus var. lanatus accessions were susceptible (GI ranged from 5.0 to 9.0, where 1 = no galls and 9 = ≥81% root system covered with galls). All C. colocynthis accessions were highly susceptible (GI range = 8.5 to 9.0). However, 20 of 88 C. lanatus var. citroides accessions were moderately resistant with a GI range of 3.1 to 4.0; overall GI range for the C. lanatus var. citroides accessions was 3.1 to 9.0. Resistance to M. arenaria race 1 identified in the C. lanatus var. citroides accessions was confirmed on a subset of accessions in a replicated greenhouse test. The results of our evaluations demonstrated that there is significant genetic variability within the U.S. PI Citrullus germplasm collection for resistance to M. arenaria race 1 and also identified C. lanatus var. citroides accessions as potential sources of resistance.

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Richard L. Fery* and Judy A. Thies

Root-knot nematodes (Meloidogyne spp.) are major pests of pepper (Capsicum spp.) in the United States, and parasitism of susceptible plants can result in severe yield losses. Although cultivars belonging to the species C. annuum account for most of the peppers grown in the United States. Habanero-type cultivars belonging to the species C. chinense are becoming increasingly popular. Unfortunately, all commercial Habanero-type cultivars are susceptible to root-knot nematodes. In 1997, the USDA released three C. chinense germplasm lines that exhibit high levels of resistance to root-knot nematodes. The resistance in these lines is conditioned by a single dominant gene, and this gene conditions resistance to the southern root-knot nematode (M. incognita), the peanut root-knot nematode (M. arenaria race 1), and the tropical root-knot nematode (M. javanica). A recurrent backcross breeding procedure has been used to transfer the C. chinense root-knot nematode resistance gene in Habanero-type germplasm. Several root-knot nematode resistant, Habanero-type candidate cultivars have been developed. Each of these Habanero-type candidate cultivars has a compact plant habit and produces a high yield of orange-colored, lantern-shaped fruit.

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Richard L. Fery and Judy A. Thies

The USDA–ARS has released a new Habanero-type pepper cultivar named TigerPaw-NR. The new cultivar is the product of a conventional recurrent backcross breeding procedure to transfer a dominant root-knot nematode resistance gene from the Scotch Bonnet accession PA-426 into the Habanero-type accession PA-350. TigerPaw-NR was derived from a single F3BC4 plant grown in 2002. TigerPaw-NR is homozygous for a dominant gene conditioning a high level of resistance to the southern root-knot nematode, the peanut root-knot nematode, and the tropical root-knot nematode. TigerPaw-NR has a compact plant habit and produces attractive lantern-shaped, orange-colored fruit. The results of three replicated field studies conducted at Charleston, S.C., indicate that the fruit and yield characteristics of TigerPaw-NR are comparable to those of currently available Habanero-type cultivars. A typical fruit weighs 7.8 g, is 2.7 cm wide × 4.4 cm long, and is extremely pungent (348,634 Scoville heat units). Root-knot nematodes are major pests of peppers in the United States, and all Habanero-type cultivars currently available to commercial growers and home gardeners are susceptible. The root-knot nematode resistant TigerPaw-NR is recommended for use by both commercial growers and home gardeners. Protection for TigerPaw-NR is being sought under the Plant Variety Protection Act.

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Kittipat Ukoskit, Paul G. Thompson, Gary W. Lawrence, and Clarence E. Watson

The inheritance of root-knot nematode race 3 [Meloidogyne incognita (Kofoid & White) Chitwood] resistance was studied in 71 progenies of the F1 backcross population produced from the resistant parent `Regal' and the susceptible parent `Vardaman'. The distribution frequency of the progenies measured on total nematode number (eggs + juveniles) indicated a bimodal distribution with a ratio of 4 resistant: 1 susceptible. Based on this phenotypic ratio, the proposed genetic model was duplex polysomic inheritance (RRrrrr = resistant). Bulk segregant analysis in conjunction with the RAPD technique was employed to identify RAPD marker linked to the root knot nematode-resistant gene. Nine of 760 random decamer primers screened showed polymorphic bands. Primer OPI51500 produced a band in the resistant bulk, but not in the susceptible bulk. Estimated recombination frequency of 0.24 between the OPI51500 marker and the root-knot nematode-resistant gene indicated linkage.