Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2006
Publication Date: 9/15/2006
Citation: Sun, Z., Lower, R.L., Staub, J.E. 2006. Analysis of generation means and components of variance for parthenocarpy in cucumber (Cucumis sativus l.). Plant Breeding. 125:277-280. Interpretive Summary: Cucumber is one of the most popular vegetable species in Cucurbitaceae family worldwide. In the United States, it is widely used as a fresh market and processing product. However, beginning in 1984, the average yield in processing cucumber in the United States has plateaued at 12.6 ' 0.2 metric tons per hectare. The yield limitation in seeded cucumber is due to a phenomenon known as crown-fruit dominance or first-fruit inhibition. Fruit with developing seeds from the first pollinated (pollen from the male plant fertilizes the female plant) fruit inhibits the development of subsequent fruits (fruits develop sequentially on the vine). Therefore, in once-over destructive mechanical harvest of seeded cucumber, only one to two dominant fruits develop per plant. Fruit set inhibition is less in seedless cucumber when compared to its seeded counterpart [unpollinated fruit does not produce seed (parthenocarpic) and pollinated fruit produces seeds]. The genetics of parthenocarpy in cucumber has been investigated because of this potential importance in crop improvement. It is clear that parthenocarpy is genetically controlled (genes cause changes in plants that are manifested by traits, one of which is parthenocarpy), but there is little agreement regarding the number and kinds of genes affecting this trait. A knowledge of the genetics of parthenocarpy would allow scientists to be more effective and efficient in incorporating such genes in commercial cultivars. Therefore, a study was designed to determine the inheritance of parthenocarpy in cucumber. Data indicate that parthenocarpy is controlled by several genes making its incorporation into commercial cucumber difficult. This study identified ways in which this complex process could be simplified. The incorporation of such strategies will allow plant breeders to become more efficient in their breeding practices, and therefore increasing the possibility of producing commercial, high-yielding cucumber cultivars. Such cultivars will make the U.S. grower more competitive in the global market place.
Technical Abstract: Parthenocarpy (seedless fruit) has potential for increasing yield in cucumber (Cucumis sativus var. sativus L.). However, the inheritance of parthenocarpy in gynoecious, U.S. processing and fresh market type cucumber is unclear. Therefore, a series of studies were designed to determine the inheritance of parthenocarpy in these market types using segregating generations derived from crossing two non-parthenocarpic gynoecious inbred lines [Gy8 (P2) and ‘Marketmore 80’(P3; MM)] with a highly parthenocarpic inbred line [2A (P1)]. Six generations (P1, P2/3, F1, F2, BC1P1, and BC1P2/3) were evaluated by the analysis of generation means from each population in Wisconsin in a greenhouse at Arlington in 1999 (designated 2A x Gy8 1999) and in the open-field at Hancock in 2000 (designated 2A x Gy8 2000 and 2A x MM 2000). There were significant location and location x generation interaction effects based on combined yield data of 2A x Gy8 1999/2000 population performances. Therefore, generation means analyses were conducted separately for each location. The minimum number of effective factors controlling parthenocarpy were estimated to be at least one (2A x Gy8 1999), two (2A x Gy8 2000), and four (2A x MM 2000), respectively. Duplicate epistasis was detected in all populations. While an additive-dominance model explained the variation in generation means for parthenocarpy in the 2A x Gy8 1999 population, a model including epistatic parameters was necessary to adequately describe the variation observed for parthenocarpy in the 2A x Gy8 2000 and 2A x MM 2000 populations. The sign of the dominance effect in a six-parameter generation means model varied in the 2A x Gy8 mating across locations, and genes with positive effects for parthenocarpy from both parents were detected in both populations. Narrow-sense heritability estimates ranged from low to moderate [0.25 – 0.56 (2A x Gy8 1999), 0.15 – 0.24 (2A x Gy8 2000), and 0.15 - 0.67 (2A x MM 2000)]. These results suggest that selection for parthenocarpy for multiple hand harvest operations will likely be more effective than that for once-over machine harvest operations. However, the selection efficiency will likely vary across different populations and environments.