ALLIUM, CUCUMIS, AND DAUCUS GERMPLASM ENHANCEMENT, GENETICS, AND BIOCHEMISTRY
Location: Vegetable Crops Research Unit
Title: Inheritance of Beta-Carotene-Associated Flesh Color in Cucumber (Cucumis Sativus L.) Fruit
Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 22, 2009
Publication Date: February 1, 2010
Citation: Cuevas, H.E., Song, H., Staub, J.E., Simon, P.W. 2010. Inheritance of Beta-Carotene-Associated Flesh Color in Cucumber (Cucumis Sativus L.) Fruit. Euphytica. 171(3):301-311.
Interpretive Summary: Carotenoids play indispensable roles in plants which includes phyto-hormone precursor regulation and modulation of biosynthetic pathways for environmental adaptation. Strong evidence suggests that diets rich in b-carotene (synom., pro-vitamin A; precursor of retinol) and other carotenoids (e.g., lycopene) can prevent the onset of some chronic diseases such as phrynoderma, anemia and certain cancers (e.g., prostate). The United States recommended dietary allowance (RDA) of retinol is 1 mg day-1 equivalent
(i.e., approximately 6 mg of b-carotene equivalents). However, practical implementation of this recommendation is often not achieved in rural and underdeveloped areas of the world. As a result, vitamin A deficiency (VAD) is a major public problem in over 75 countries in the developing world. Although commercial cucumber fruit do not have carotenoids, an exotic cucumber was acquired by the USDA which has relatively high levels of ß –carotene as seen by its orange-colored fruit interior. Although increased carotene cucumber would be of value to the human diet, little is know about the inheritance of carotene in cucumber fruit. Such information is needed to introduce high carotene producing genes (elements of control found in the cells of plants) into commercial cucumber. Therefore, a study was initiated to determine the genetic control of ß –carotene in cucumber using the exotic cucumber acquired from China genetic studies. Crosses were made between the orange-fruited Chinese cucumber and commercial US cucumber to determine the inheritance of ß –carotene in cucumber. It was determined that the inheritance of ß –carotene was controlled by relatively few genes, which suggested that introduction of this trait into commercial cucumber was possible. The information obtained in this work will allow plant breeders to design effective ways to transfer the genes for ß –carotene from exotic cucumber to commercial cucumber. This will lead to the development and release of high ß –carotene commercial cucumber varieties which will increase the competitiveness of the U.S. grower and provide a source of vitamin A to the U.S. consumer.
The nutritional value of cucumber (Cucumis sativus L.) can be improved by the introgression of ß-carotene (i.e., provitamin A and/or orange flesh) genes from “Xishuangbanna gourd” (XIS; Cucumis sativus var. xishuangbannanesis Qi et Yuan) into U.S. pickling cucumber. However, the genetics of ß-carotene content has not been clearly defined in this U.S. market type. Thus, three previous populations derived from a U.S. pickling cucumber (‘Addis’) x XIS mating were evaluated for ß-carotene content, from which the high ß-carotene inbred line (S4), ‘EOM 402-10’, was developed. A cross was then made between the U.S. pickling cucumber inbred line ‘Gy7’ [gynoecious, no ß-carotene (0.01 µg g-1), white flesh; P1] and ‘EOM 402-10’ [monoecious, possessing ß-carotene (1.87 µg g-1), orange flesh; P2] to determine the inheritance of ß-carotene in fruit mesocarp and endocarp tissue. Parents and derived cross-progenies (F1, F2, BC1P1, and BC1P2) were evaluated for ß-carotene content in a greenhouse in Madison, Wisconsin. While F1 and BC1P1 progeny produced mature fruits possessing white, light-green, and green (0.01-0.02 µg g-1 ß-carotene) mesocarp, the F2 and BC1P2 progeny mesocarp segregated in various hues of white, green, yellow (0.01-0.34 µg g-1 ß-carotene), and orange (1.90-3.00 µg g-1 ß-carotene). Mesocarp and endocarp F2 segregation adequately fit a 15:1 [low-ß-carotene (0.01-0.34 µg g-1): high-ß-carotene (1.90-3.00 µg g-1)] and 3:1 (low-ß-carotene: high-ß-carotene) ratio, respectively. Likewise, segregation of carotene concentration in mesocarp and endocarp tissues in BC1P2 progeny adequately fit a 3:1 (low-ß-carotene: high-ß-carotene) and 1:1 (low-ß-carotene: high-ß-carotene) ratio, respectively. Progeny segregations indicate that two recessive genes control the ß-carotene content in the mesocarp, while one recessive gene controls ß-carotene content in the endocarp. Single marker analysis of F2 progeny using the carotenoid biosynthesis gene Phytoene synthase determined that there was no association between this gene and the observed ß-carotene variation in either fruit mesocarp or endocarp.