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G. Craig Yencho, Kenneth V. Pecota, Jonathan R. Schultheis, Zvezdana-Pesic VanEsbroeck, Gerald J. Holmes, Billy E. Little, Allan C. Thornton, and Van-Den Truong

‘Covington’ is an orange-fleshed, smooth-skinned, rose-colored, table-stock sweetpotato [Ipomoea batatas (L.) Lam.] developed by North Carolina State University (NCSU). ‘Covington’, named after the late Henry M. Covington, an esteemed sweetpotato scientist at North Carolina State, was evaluated as NC98-608 in multiple state and regional yield trials during 2001 to 2006. ‘Covington’ produces yields equal to ‘Beauregard’, a dominant sweetpotato variety produced in the United States, but it is typically 5 to 10 days later in maturity. ‘Covington’ typically sizes its storage roots more evenly than ‘Beauregard’ resulting in fewer jumbo class roots and a higher percentage of number one roots. Total yields are similar for the two clones with the dry matter content of ‘Covington’ storage roots typically being 1 to 2 points higher than that of ‘Beauregard’. ‘Covington’ is resistant to fusarium wilt [Fusarium oxysporum Schlect. f.sp. batatas (Wollenw.) Snyd. & Hans.], southern root-knot nematode [Meloidogyne incognita (Kofoid & White 1919) Chitwood 1949 race 3], and moderately resistant to streptomyces soil rot [Streptomyces ipomoeae (Person & W.J. Martin) Wakswan & Henrici]. Symptoms of the russet crack strain of Sweet Potato Feathery Mottle Virus have not been observed in ‘Covington’. The flavor of the baked storage roots of ‘Covington’ has been rated as very good by standardized and informal taste panels and typically scores as well or better in this regard when compared with ‘Beauregard’.

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Judy A. Thies and Richard L. Fery

Expression of the N gene, which confers resistance to southern root-knot nematode (Meloidogyne incognita Kofoid and White) in bell pepper [(Capsicum annuum L. var. annuum (Grossum Group)], is modified at high temperatures (28 °C and 32 °C), but its expression in the heterozygous condition (Nn) has not been documented at moderate or high temperatures. Responses of the near-isogenic bell pepper cultivars, Charleston Belle and Keystone Resistant Giant (differing at the N locus), and the F1 and reciprocal F1 crosses between these cultivars to M. incognita race 3 were determined at 24, 28, and 32 °C in growth chamber experiments. `Keystone Resistant Giant' (nn) was susceptible at 24, 28, and 32 °C. `Charleston Belle' (NN) exhibited high resistance at 24 °C and resistance was partially lost at 28 and 32 °C. However, at 32 °C root gall and egg mass severity indices for `Charleston Belle' were still in the resistant range, and the number of M. incognita eggs per gram fresh root and reproductive index were 97% and 90% less, respectively, than for `Keystone Resistant Giant'. Responses of the F1 and F1 reciprocal hybrid populations to M. incognita were similar to the response of the resistant parent at all temperatures. Root fresh weights and top dry weights indicated that both hybrid populations tolerated M. incognita infections at least as well as `Charleston Belle'. These findings indicate that i) only one of the parental inbred lines needs to be converted to the NN genotype to produce F1 hybrid cultivars with fully functional N-type resistance to M. incognita; and ii) cytoplasmic factors are not involved in expression of N-type resistance and the resistant parental inbred can used to equal advantage as either the paternal or the maternal parent.

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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 Philip D. Dukes

Greenhouse experiments were conducted to determine the inheritance of the high level of southern root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] resistance exhibited by `Carolina Hot' cayenne pepper (Capsicum annuum L.) and to compare the genetic nature of this resistance to that exhibited by `Mississippi Nemaheart.' Evaluation of parental, F1, F2, and backcross generations of the cross `Mississippi Nemaheart' × `California Wonder' confirmed an earlier published report that the `Mississippi Nemaheart' resistance is conditioned by a single dominant gene. Evaluation of parental, F1, F2, and backcross generations of a cross between highly resistant and highly susceptible lines selected from a heterogeneous `Carolina Hot' population indicated that the resistance exhibited by `Carolina Hot' is conditioned by two genes, one dominant and one recessive. Evaluation of the parental and F2 populations of a cross between `Mississippi Nemaheart' and the highly resistant `Carolina Hot' line indicated that the dominant resistance gene in `Mississippi Nemaheart' is allelic to the dominant resistance gene in `Carolina Hot.' Comparison of the data that were collected on the parental lines in the latter cross demonstrated the superior nature of the resistance exhibited by `Carolina Hot.' The presence of the second resistance gene in `Carolina Hot' probably accounted for the higher level of resistance. The ease and reliability of evaluating plants for resistance to root-knot nematodes and the availability of a simply inherited source of resistance makes breeding for southern root-knot nematode resistance a viable objective in pepper breeding programs. This objective should be readily obtainable by the application of conventional plant breeding methodologies.

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Judy A. Thies and Richard L. Fery

Several species of root-knot nematodes [Meloidogyne incognita (Kofoid & White) Chitwood, M. arenaria (Neal) Chitwood, M. javanica (Treub) Chitwood, and M. hapla Chitwood] are major pests of peppers (Capsicum spp.) in the United States and worldwide. Resistance to M. incognita, M. arenaria, and M. javanica has been identified in several Capsicum accessions, but there are few reports of resistance to M. hapla. Therefore, we selected a 10% core (440 accessions) of the 14 available Capsicum spp. in the Capsicum germplasm collection (3,731 accessions) maintained by the U.S. Dept. of Agriculture (USDA), and evaluated this core for resistance to M. hapla in unreplicated greenhouse tests. The 11 best (most resistant) and the 3 worst (most susceptible) accessions identified in these unreplicated tests were re-evaluated in a replicated greenhouse test. Seven of these 11 “best” accessions (PI 357613, PI 357503, PI 439381, PI 297493, PI 430490, PI 267729, and PI 441676) exhibited root gall severity indices <5.0 (1 = no galls; 9 = more than 80% of the root system covered with galls) in the replicated test, and each of these indices was significantly lower than the indices of the “worst” accessions and susceptible controls. Although a gall index <5.0 indicates a moderate level of resistance, more than 3000 M. hapla eggs were extracted per gram of fresh root tissue and the reproductive index was >1.0 for each of these accessions. These observations suggest that the most resistant accessions tested are somewhat susceptible to M. hapla. The results of our evaluation of a core of the USDA Capsicum germplasm collection demonstrates clearly that there is significant genetic variability within the overall collection for M. hapla resistance. Additionally, these results identify portions of the collection where future evaluations for M. hapla resistance should be focused. For example, the origin of the two most promising C. annuum accessions (PI 357613 and PI 357503) in the core was Yugoslavia. Thus, additional accessions from this temperate region of the world should receive priority attention in any effort to identify better sources of resistance in C. annuum to M. hapla.

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

southern RKN ( Meloidogyne incognita ), peanut RKN ( Meloidogyne arenaria ), and Javanese RKN ( Meloidogyne javanica ). The watermelon plants grafted on ‘RKVL-318’ rootstock had considerable yield advantage over non-grafted watermelon plants in fields

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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

Open access

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

’, ‘Charleston Belle’, ‘Jalapeño’, and ‘UFRJ107(6)A3’ in decreasing order. Table 1. Reproductive potential of Meloidogyne incognita race 3 on six varieties of Capsicum species after 30 d from inoculation under two temperature regimes in the growth chamber

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Cody L. Smith, Joshua H. Freeman, Nancy Kokalis-Burelle, and William P. Wechter

watermelon cultivar ‘Royal Sweet’ was estimated with an initial population equal to 122 eggs/100 cm 3 of soil, 1.6 gal on bioassay roots/100 cm 3 of soil, or 3.6 J2/100 cm 3 of soil ( Xing and Westphal, 2012 ). Meloidogyne incognita is a common pest in

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Wenjing Guan, Xin Zhao, Donald W. Dickson, Maria L. Mendes, and Judy Thies

the southern United States and in other semitropical and tropical regions of the world. Meloidogyne incognita , M. javanica , and M. arenaria are the most widespread RKN species in the southeastern United States ( Zitter et al., 1996 ), and all of