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United States Department of Agriculture

Agricultural Research Service

Research Project: GENETICS AND GENETIC IMPROVEMENT OF DISEASE RESISTANCE AND QUALITY TRAITS IN WATERMELON, BROCCOLI, AND LEAFY GREEN BRASSICAS Title: Exploiting genetic diversity in Citrullus spp. to enhance watermelon cultivars

Authors
item Levi, Amnon
item Thies, Judy
item Wechter, William
item Kousik, Chandrasekar
item Ling, Kai-Shu
item Harrison, Howard
item Simmons, Alvin
item Reddy, U -
item Nimmakayala, P -
item Fei, Z -

Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: April 30, 2012
Publication Date: October 11, 2012
Citation: Levi, A., Thies, J.A., Wechter, W.P., Kousik, C.S., Ling, K., Harrison Jr, H.F., Simmons, A.M., Reddy, U.K., Nimmakayala, P., Fei, Z. 2012. Exploiting genetic diversity in Citrullus spp. to enhance watermelon cultivars. Acta Horticulturae. Pp. 41-48.

Technical Abstract: Due to many years of cultivation and selection for desirable fruit quality, a narrow genetic base exists among watermelon cultivars. There is a continuous need to enhance watermelon cultivars for disease and pest resistance. U.S. Plant Introductions (PIs) representing the different groups of watermelon, including the desert watermelon Citrullus colocynthis (L.) Schrader (CC), the “cow” or Tsamma watermelon Citrullus lanatus subsp. lanatus var. lanatus [also known as C. lanatus (Thunb.) Matsum. et Nakai subsp. lanatus var. citroides (Bailey) Mansf. ex Greb.] (CLC), and Citrullus lanatus subsp. lanatus (CLL) are a useful source for enhancing disease or pest resistance in watermelon cultivars. However, there is limited information about genetic relationships among these PIs. In this study, we examined genetic diversity among Citrullus spp. accessions representing CC, CLC and CLL groups collected in their center of origin in Africa. High frequency oligonucleotides - targeting active gene (HFO-TAG) primers were used in polymerase chain reaction (PCR) experiments to produce over 600 polymorphic markers among the Citrullus genotypes. Cluster and multidimensional scaling plot analysis produced distinct groups of CLC, CLL, and CC PIs. Several PIs that were designated as CLC or CLL were in transitional positions, indicating that they are the result of gene flow between the major Citrullus groups or subgroups. Population structure analysis indicated that CLC comprises two subgroups; each containing a set of unique alleles. Also, unique alleles exist in the CLL and the CC genotypes. The PCR-based results here are consistent with our recent findings using fluorescence in situ hybridization (FISH) technology, showing major differences in configuration of ribosomal DNA markers between the CLC and CLL or CC genotypes. The wide genetic diversity and plethora of unique alleles that exist among Citrullus spp. should be useful for enhancing disease or pest resistance in elite watermelon cultivars.

Last Modified: 10/25/2014
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