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Howard F. Harrison Jr., W. Patrick Wechter, and Chandrasekar S. Kousik

, 406-1-x 7, a watermelon germplasm accessions, PI 167125, three citron melon, C. lanatus var. citroides germplasm accessions, PI 482246, PI 500354, and PI 532738, and two accessions from the related species C. colocynthis , PI 432334 and PI 432337

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Judy A. Thies and Amnon Levi

. for resistance to root-knot nematodes ( Thies and Levi, 2003 ). In that study, moderate resistance to M. arenaria race 1 was identified among C. lanatus var. citroides PIs. The objective of this study was to evaluate the group of C. lanatus var

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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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Leigh K. Hawkins, Fenny Dane, and Thomas L. Kubisiak

Morphological traits were examined in an F3 generation derived from a cross between C. lanatus var. lanatus [(Thunb.) Matsum. & Nakai] and C. lanatus var. citroides. At least three genes, C (yellow) vs. c (red), i (inhibitory to C) vs. I (non-inhibitory to C), and y (yellow) vs. yw (white), with epistatic and inhibitory actions were found to govern the inheritance of fruit flesh color. The high frequency of yellow-fleshed fruit and low frequencies of white and red fruits can be explained by the presence of a new allele (yw recessive to y) in the multiple allele series at the Y locus. The low frequency of tan colored seeds in segregating populations could be explained by at least three genes governing inheritance of seed-coat color. Single factor analysis of variance was conducted for each pairwise combination of random amplified polymorphic DNA (RAPD) locus and fruit or seed characteristics. Several RAPD loci were identified to be loosely linked to morphological characteristics.

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Kelechi Ogbuji, Gloria S. McCutcheon, Alvin M. Simmons, Maurice E. Snook, Howard F. Harrison, and Amnon Levi

( C. lanatus var. lanatus ) and in a representative PI of the citron watermelon ( C. lanatus var. citroides ). Materials and Methods Plant material. The plants in this study included the watermelon cultivars Charleston Gray and Mickey Lee ( C

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W. Patrick Wechter, Chandrasekar Kousik, Melanie McMillan, and Amnon Levi

., 1997 ; Levi et al., 2001 , 2011 ; Thies and Levi, 2007 ). The objective of this study was to evaluate the USDA, ARS C. lanatus var. citroides PI collection for resistance to Fon Race 2 (using a seed inoculation procedure in addition to a root

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Haiying Zhang, Guoyi Gong, Shaogui Guo, Yi Ren, Yong Xu, and Kai-Shu Ling

represented three species, C. lanatus var. lanatus (766), C. lanatus var. citroides (53), and C. colocynthis (one). The other 246 watermelon cultivars or inbred lines ( C. lanatus var. lanatus ) were selected from watermelon breeding projects at

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

considerable number of C. lanatus var. citroides PIs that show resistance to RKNs ( Thies and Levi, 2003 , 2007 ). Several of these resistant PIs were selected and self-pollinated in three successive generations to obtain pure line selections. These lines

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Angela R. Davis, Amnon Levi, Antonia Tetteh, Todd Wehner, Vincent Russo, and Michel Pitrat

NPGS at the Southern Regional Plant Introduction Station, USDA-ARS, Griffin, GA, were evaluated. The accessions represent 75 countries of origin and five species, belonging to C. lanatus var. lanatus , C. lanatus var. citroides , C. colocynthis

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Nihat Guner, Zvezdana Pesic-VanEsbroeck, Luis A. Rivera-Burgos, and Todd C. Wehner

PI accessions from Zimbabwe (PI 482342, PI 482318, and PI 482379), one PI accession from Botswana (PI 485583), and one PI accession from Nigeria (PI 595203). All of the resistant PI accessions except PI 595203 are C. amarus (formerly C. lanatus