Location: Forage and Range ResearchTitle: Marker-assisted backcross selection in an interspecific Cucumis population broadens the genetic base of cucumber (Cucumis sativus L.) Author
Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2011
Publication Date: 4/17/2011
Citation: Behera, T.K., Staub, J.E., Delannay, I.Y., Chen, J.F. 2011. Marker-assisted backcross selection in an interspecific Cucumis population broadens the genetic base of cucumber (Cucumis sativus L.). Euphytica. 178:261-272. Interpretive Summary: Cucumber improvement is a complex process often involving the refinement of populations derived from intercrossing elite and/or exotic (unadapted) germplasm, the extraction of inbred lines from such populations; and the subsequent identification of commercially acceptable F1 hybrids. The genetic diversity (relatedness) is very low (many cucumber varieties are related) and thus it has been difficult to increase the yield and quality of cucumber in the last 20 years. One way to increase genetic diversity in cucumber is to introduce genes from wild species into cucumber using classical plant breeding methods (manual cross pollination). A species of cucumber (known as Hystrix) has been found that is very dissimilar to cucumber, but has high yield attributes that if incorporated into cucumber could increase its genetic diversity and yield potential. Therefore, an experiment was designed to introduce Hystrix into commercial cucumber by crossing it with a unique set of commercial plants. The high-value traits were introduced into cucumber during continued crossing and selection using biotechnologies. The use of these technologies and common plant breeding methods allow for the development of high-yielding lines that possess high genetic diversity. These lines can be used directly by plant breeders to produce novel high-yield plants that will increase the global competitiveness of the U.S. producer.
Technical Abstract: Cucumber (Cucumis sativus L.) is a major cucurbit vegetable species whose genetic base has been drastically reduced during its domestication. The crop's narrow genetic base (3-12% DNA polymorphism) has resulted from the use of limited genetic material and intense selection during plant improvement. Recently, however, an interspecific hybridization has been successful in Cucumis via the mating of C. hystrix Chakr. and C. sativus, which resulted in the amphidiploid, C. hytivus. We report herein a marker-assisted strategy for increasing genetic diversity in cucumber through introgression backcrossing employing C. hytivus. The comparatively late flowering but high yielding, indeterminate, monoecious line WI 7012A (P1; donor parent) derived from a C. hytivus x C. sativus-derived line (long-fruited Chinese C. sativus cv. Beijingjietou) was initially crossed to the determinate, gynoecious C. sativus line WI 7023A (P2; recurrent parent 1) and then advanced backcross generation progeny (BC2) were crossed with the gynoecious indeterminate line WI 9-6A (P3; recurrent parent 2). More specifically, a single F1 individual (P1 x P2) was backcrossed to P2 and then BC progeny were crossed to P2 and P3, where marker-assisted selection (MAS) for genetic diversity (8 mapped and 16 unmapped markers; designated Sel) or no selection (designated NSel) was applied to produce BC3P2 (Sel) and BC3P3 (Sel) and BC2P2 (NSel) and BC2P2S1 (NSel) progeny. Relative vegetative growth, number of lateral branches (LB), days to flowering (DF), yield (fruit number), and fruit quality [as measured by length diameter (L:D) and endocarp:total diameter (E:T) ratio] were assessed in parents and cross-progeny. The DF varied from ~20 (BC3P2Sel) to ~25 (BC2P3Sel) days among the populations examined, where progeny derived from P2 possessed the shortest DF. DIfferences in cumulative yield among the populations over six harvests were detected which varied from ~18 in BC3P2 (Sel) to ~39 in BC2P3 (Sel) fruits per plant. Although the vigorous vegetative growth of line P1 was observed in its backcross progeny, highly heterozygous and polymorphic backcross progeny derived from P3 were comparatively more vigorous and bore many high, quality fruit. Response to selection was detected for LB, DF, L:D, and E:T, but the effectiveness of MAS depended upon the parental lines used. Data indicate that the genetic diversity of commercial cucumber can be increased by the introgression of the C. hystrix genome through backcrossing.