Inheritance of beta-carotene-associated flesh color in cucumber (Cucumis sativus L.) fruit

The nutritional value of cucumber (Cucumis sativus L.) can be improved by the introgression of beta-carotene (i.e., provitamin A and/or orange flesh) genes from "Xishuangbanna gourd" (XIS; Cucumis sativus var. xishuangbannanesis Qi et Yuan) into US pickling cucumber. However, the genetics of beta-carotene content has not been clearly defined in this US market type. Thus, three previous populations derived from a US pickling cucumber ('Addis') x XIS mating were evaluated for beta-carotene content, from which the high beta-carotene inbred line (S-4), 'EOM 402-10', was developed. A cross was then made between the US pickling cucumber inbred line 'Gy7' [gynoecious, no beta-carotene, white flesh; P-1] and 'EOM 402-10' [monoecious, possessing beta-carotene, orange flesh; P-2] to determine the inheritance of beta-carotene in fruit mesocarp and endocarp tissue. Parents and derived cross-progenies (F-1, F-2, BC1P1, and BC1P2) were evaluated for beta-carotene content in a greenhouse in Madison, Wisconsin. While F-1 and BC1P1 progeny produced mature fruits possessing white, light-green, and green (0.01-0.02 mu g g(-1) beta-carotene) mesocarp, the F-2 and BC1P2 progeny mesocarp segregated in various hues of white, green, yellow (0.01-0.34 mu g g(-1) beta-carotene), and orange (1.90-2.72 mu g g(-1) beta-carotene). Mesocarp and endocarp F-2 segregation adequately fit a 15:1 [low-beta-carotene (0.01-0.34 mu g g(-1)): high-beta-carotene (1.90-2.72 mu g g(-1))] and 3:1 (low-beta-carotene: high-beta-carotene) ratio, respectively. Likewise, segregation of carotene concentration in mesocarp and endocarp tissues in BC1P2 progeny adequately fit a 3:1 (low-beta-carotene: high-beta-carotene) and 1:1 (low-beta-carotene: high-beta-carotene) ratio, respectively. Progeny segregations indicate that two recessive genes control the beta-carotene content in the mesocarp, while one recessive gene controls beta-carotene content in the endocarp. Single marker analysis of F-2 progeny using the carotenoid biosynthesis gene Phytoene synthase determined that there was no association between this gene and the observed beta-carotene variation in either fruit mesocarp or endocarp.