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United States Department of Agriculture

Agricultural Research Service

Staub: Accomplishments
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Germplasm Enhancement

USDA Vegetable Crops Research Unit
Cucumber and Melon Genetics

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Demonstrated Accomplishments of the Laboratory

1. Accomplishment: Germplasm Enhancement

The incorporation of genes for disease resistance, unique plant architecture, and stable sex expression from exotic germplasm is important to the improvement of adapted cucumber (Cucumis sativus L.) germplasm. The laboratory has genetically and physiologically characterized the effect of genes derived from exotic germplasm. The laboratory has characterized genes having detrimental effects on stand establishment and yield (#38, #53, #69), and defined the use of bisexual (male and female organs in the same flower) parents as paternal parents to stabilize femaleness and the release of high quality bisexual lines (#29, #31). The laboratory was a team member in a project which biochemically identified and genetically mapped the location of a regulatory enzyme (ACC synthase) closely linked (associated) [<1 cM (centiMorgan; a genetic measurement unit)] to female gene (F) which controls its expression (#105, #39, #40). The laboratory has determined that selection for disease resistance can decrease yield potential (#74, #33), and that heritable differences (i.e., sequential fruiting and multiple branching habits) exist among exotic cucumber germplasm which determine their potential usefulness for hybrid production and breeding (#107, #44, #55, #108; the laboratory has developed, evaluated, and released eight USDA cucumber lines or hybrids which provide industry in the U.S., Europe, and Asia with high yielding, multiple disease resistant germplasm (#22, #26, #30, #96, and #153). Role: The laboratory has provided the germplasm, determined the linkage relationship and wrote the genetic portions of the manuscript in the ACC synthase mapping study . The senior author of the determination of the usefulness of exotic germplasm was a postdoctoral fellow under Dr. Staub's supervision where he conceived the research, attracted funding and assisted in manuscript preparation. Impact: The laboratory's research supports NP #301 by furnishing genomic information and genetic raw materials to enhance American agricultural productivity. Poor or non-uniform germination can result in erratic stands and reduced yield due to seed dormancy. The incorporation of useful genes from exotic cucumber germplasm often results in the transfer of detrimental traits such as seed dormancy. The inheritance and physiology of dormancy in cucumber documented by the laboratory has allowed breeders and commercial seed production personnel (ie., Sunseed, Seminis, and Harrison Moran seed companies) to better manage unique ARS released germplasm derived from exotic sources. The fact that the incorporation of disease resistance genes during plant improvement can reduce yield potential in elite lines has led to a reconsideration of breeding strategies in public and private cucumber breeding programs. Breeders of the major U.S. companies (stated above) are now decreasing selection intensity for disease resistance and critically assessing yield potential in early generations in populations and lines where exotic germplasm (mostly ARS releases) is being used extensively. Stable female sex expression is essential for early, uniform yields in mechanical harvesting operations (~40% of the U.S. acreage). Although femaleness is controlled by one major gene (F), sex changes (female to male) can occur when abiotic and biotic stresses during production affect sex-modifying genes (genes on other chromosomes). Such changes occur frequently during production and can dramatically reduce fruit yield and quality by as much as 75%. Data obtained by the laboratory documents the use of bisexual parents to stabilize femaleness under stress conditions, and nearly isogenic bisexual and sex-stable female lines have been released by the laboratory for use in hybrid production. The mapping of a gene controlling ACC synthase (closely linked to F) has allowed for the cloning and sequencing of a gene(s) which regulates biochemical processes (ethylene production) associated with femaleness. Such knowledge is fundamental to the understanding of floral biology in angiosperms, and the application biotechnologies that will lead to the regulation of sex in crop species for improved yield and quality. The laboratory's research is the first to identify the number, genomic location and effect of genes that modify sex expression in cucumber; the genetics of which has been applied to other cucurbit species (e.g., melon, squash). The use and fine mapping of linked markers is currently being evaluated by the laboratory in selection experiments to determine their utility for cucumber improvement (2001). Knowledge and manipulation of these modifying genes via marker-assisted selection will produce cucumber germplasm with increased gynoecious sex stability under stress conditions, thus increasing yield potential in commercial hybrids. The release of multiple disease resistant germplasm with unique plant habits has increased the genetic diversity among North American adapted germplasm with an extremely narrow genetic base through the incorporation of exotic alleles conditioning resistance to downy mildew, target leafspot, angular leafspot, anthracnose, fusarium, and bacterial wild resistance. Such germplasm has provided commercial cucumber breeders with genotypes that increase hybrid productivity and broaden their commercial genetic base. See publications #105; #107; #108.

Figure: ACC synthase map positionFigure 1. Map position of a regulatory enzyme (ACC synthase) closely linked (associated) [<1 cM (centiMorgan; a genetic measurement unit)] to female gene (F) which controls its expression.

Varietial releases

  • Peterson, C. E., J. E. Staub, M. Palmer, and L. Crubaugh. Wisconsin 2843, a multiple disease resistant population. HortScience 20:309-310:1985.
  • Peterson, C.E. and J. E. Staub. 'Wautoma' cucumber. HortScience 21:326:1986.
  • Peterson, C.E., J.E. Staub and M. J. Palmer. Wisconsin 5207, a multiple disease resistant population. HortScience 21:335-336:1986.
  • Peterson, C.E., J.E. Staub, P. H. Williams, and M. J. Palmer. Wisconsin 1983 cucumber. HortScience 21:1082-1083:1986.
  • Staub, J.E., C.E. Peterson, L. K. Crubaugh and M. J. Palmer. Cucumber population WI 6383 and derived inbreds WI 5098 and WI 5551. HortScience 27: 1340-1341:1993.
  • Staub, J. E., V. Meglic, L. K. Crubaugh and L. D. Knerr. Cucumber germplasm: isozyme genetic stocks W6743, W6744, W6745. HortScience 31:1243-1245:1996.

Figure 2. Released lines and cultivars have multiple disease resistance and possess unique plant habits (multiple lateral branching, sequential fruiting, determinate/indeterminate growth habit, standard sized leaves/little leaves, etc.) introgressed from exotic germplasm

Figure: High fruit quality linesTypical high fruit quality lines in the USDA cucumber breeding project
Figure: Prototype multiple lateralPrototype multiple lateral determinate genotype (right) compared to standard unilateral branching type (left)

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Last Modified: 8/13/2016
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