Muskmelons (Cucumis melo L.) play an important role in the American diet. Ranked as one of the top 10 most-consumed fruits by the USDA, cantaloupe melons have the highest amount of beta-carotene of all the ranked fruits. Beta-carotene, also called pro-Vitamin A, is an essential nutrient required for eye health, and may have the potential, as an antioxidant to reduce the risks associated with cancer, heart disease, and other illnesses. Breeding melons with increased levels of beta-carotene will benefit consumer health. Research has found phytonutrients are most bioavailable when consumed in their fresh form, rather than as vitamin supplements. The high level of beta-carotene found in some melons has a genotypic component, which may be exploited to breed melons high in beta-carotene. Molecular markers and marker-assisted selection (MAS) can be used to increase the efficacy of the breeding process, while lowering breeding costs. An F2 population was created using `Sunrise', the female parent, containing no beta-carotene crossed with `TAM Uvalde', a high beta-carotene variety. A field population consisting of 115 F2 individuals and a greenhouse population containing 90 F2 individuals were grown. The resulting fruit were screened phenotypically and ranked according to beta-carotene content. Chisquare values fit the previously reported model of a single dominant gene for presence of beta-carotene (orange-flesh) vs. absence (green or white flesh). A continuous distribution of beta-carotene concentrations from high to low suggested quantitative inheritance for this trait. Two eight-plant DNA bulks composed of either high or low beta-carotene F2 individuals were screened for polymorphic molecular markers using the amplified fragment-length polymorphism technique.
Alexandra B. Napier, Kevin M. Crosby, and Soon O. Park
Marrakech, Morocco. A third is projected in Turkey ( Essid, 2010 ). The joint use of different molecular DNA markers, diversity array technology and simple sequence repeated, and morphological descriptors ( Atienza et al., 2013 ; Trujillo et al., 2014
Wayne Loescher, Zhulong Chan, and Rebecca Grumet
. What should they select for and at what stage of development: at stand establishment, at flowering, at fruit or seed set, at seed fill, or fruit growth? Short-term selection procedures would likely reflect a response to the osmotic strength of the
John A. Juvik, Gad G. Yousef, Tae-Ho Han, Yaacov Tadmor, Fermin Azanza, William F. Tracy, Avri Barzur, and Torbert R. Rocheford
This study was conducted to identify the chromosomal location and magnitude of effect of quantitative trait loci (QTL) controlling sweet corn (Zea mays L.) stand establishment and investigate the impact of dry kernel characteristics on seedling emergence under field conditions. Genetic and chemical analysis was performed on two F2:3 populations (one homozygous for su1 and segregating for se1, the other homozygous for sh2 endosperm carbohydrate mutations) derived from crosses between parental inbreds that differed in field emergence and kernel chemical composition. A series of restriction fragment-length polymorphism (RFLP) and phenotypic markers distributed throughout the sweet corn genome were used to construct a genetic linkage map for each population. F2:3 families from the two populations were evaluated for seedling emergence and growth rate at four locations. Mature dry kernels of each family were assayed for kernel chemical and physiological parameters. Composite interval analysis revealed significant QTL associations with emergence and kernel chemical and physiological variables. Improved emergence was positively correlated with lower seed leachate conductivity, greater embryo dry weight, and higher kernel starch content. QTL affecting both field emergence and kernel characteristics were detected in both populations. In the su1 se1 population genomic regions significantly influencing emergence across all four environments were found associated with the se1 gene on chromosome 2 and the RFLP loci php200020 on chromosome 7 and umc160 on chromosome 8. In the sh2 population the RFLP loci umc131 on chromosome 2 and bnl9.08 on chromosome 8 were linked to QTL significantly affecting emergence. Since seedling emergence and kernel sugar content have been shown to be negatively correlated, undesirable effects on sweet corn eating quality associated with each emergence QTL is discussed. Segregating QTL linked to RFLP loci in these populations that exert significant effects on the studied traits are candidates for molecular marker-assisted selection to improve sweet corn seed quality.
Thomas M. Davis, Kevin M. Folta, M. M. Shields, Robin L. Brese, Laura M. R. DiMeglio, and Qian Zhang
The past year has brought substantial progress in the development of functional and structural genomic tools for strawberry. Sequencing of cDNA library clones from the cultivated strawberry Fragaria × ananassa and the diploid model species Fragaria vesca has provided more than 3000 new EST sequences. We have also constructed a large (∼40 kb) insert genomic (fosmid) library from F. vesca. About 33,000 fosmid clones have been picked and spotted onto hybridization filters. Filters have been successfully probed with three single copy gene probes, one gene family probe, and chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) probe sets. The combined cpDNA and mtDNA clone content of the library is about 11%. After correction for organelle insert content, the nuclear genome coverage of the library is about 6×. Complete sequencing of two fosmid clones identified 12 putative protein-encoding genes, four of which were organized in colinearity with the corresponding chromosomal region of Arabidopsis thaliana. We will sequence an additional 50 fosmid clones, and use the resulting sequence data as the basis for developing a novel marker technology, to be described. These genomic tools will provide a basis for connecting specific genes to specific traits in the octoploid, cultivated strawberry, paving the way for implementation of gene-based, marker assisted selection as a tool for strawberry breeders. Opportunity for cross-species comparisons of gene sequence and composition, as well as genome organization and linkage group structure, between Fragaria and other members of the economically important Rosaceae family has been significantly enhanced, thus expanding the relevance of the project results to peach, cherry, apple, rose, brambles, and many other Rosaceous species.
Jack E. Staub and Juan Zalapa
Plant improvement incorporating quantitatively inherited yield component traits is technically difficult, time consuming, and resource demanding. In melon (Cucumis melo L.), the inheritance of yield components is poorly understood. A unique highly branched fractal melon plant type has been developed by the U.S. Department of Agriculture (USDA) from exotic germplasm to improve yield of U.S. Western Shipping type melons (Group Cantalupensis). In order to more effectively develop useful germplasm for commercial use the genetic of components of yield must be clearly understood. Thus, the genetics of branching, an important yield component, was investigated. Melon progeny derived (F1, F2, F3, BC1P1, and BC1P2) derived from a cross between USDA line 846-1 (P1) and Top-Mark (P2) were used to evaluated in two locations (Wisconsin and California) to estimate of components of variance, and narrow-sense (h2N) and broad-sense (h2B) sense heritabilities. Lateral branch numbers among 71 to 119 F3 families were significantly different (P ¾ 0.01) regardless of test environment. Covariance analyses indicates that branching is moderately heritable (h2B = 0.62 to 0.76, h2N = 0.43 to 0.48), and conditioned by several additive factors (perhaps 2 to 4) that are highly additive. Although environment plays an important role in lateral branch development, family rankings over environments were relatively consistent, indicating that effective selection for this trait should be useful for incorporating the fractal plant habit into Western Shipping melon. The significant additive component underlying lateral branch number indicates that quantitative trait loci (QTL) conditioning this yield component might be identified for use in marker-assisted selection.
Yiqun Weng, Shanna Johnson, Jack E. Staub, and Sanwen Huang
is not the marker type of choice for broad-based applications in marker-assisted selection (MAS) (e.g., Bradeen et al., 2001 ; Fazio et al., 2003a ; Robbins et al., 2008 ; Serquen et al., 1997 ; Yuan et al., 2008a , 2008b ). The recent
Geoffrey Meru and Cecilia McGregor
similar chromosomal region as a QTL for SOP identified by Prothro et al. (2012a) , pointing to a potential role for seed size in SOP. The direct phenotypic selection for SOP and the indirect selection through correlated traits such as KP and seed size
James D. Kelly and Veronica A. Vallejo
Resistance to anthracnose in common bean is conditioned primarily by nine major independent genes, Co-1 to Co-10 as the Co-3/Co-9 genes are allelic. With the exception of the recessive co-8 gene, all other nine are dominant genes and multiple alleles exist at the Co-1, Co-3 and Co-4 loci. A reverse of dominance at the Co-1 locus suggests that an order of dominance exists among individual alleles at this locus. The nine resistance genes Co-2 to Co-10 are Middle American in origin and Co-1 is the only locus from the Andean gene pool. Seven resistance loci have been mapped to the integrated bean linkage map and Co-1 resides on linkage group B1; Co-2 on B11, Co-3 on B4; Co-4 on B8; Co-6 on B7; and Co-9 and Co-10 are located on B4 but do not appear to be linked. Three Co-genes map to linkage groups B1, B4 and B11 where clusters with genes for rust resistance are located. In addition, there is co-localization with major resistance genes and QTL that condition partial resistance to anthracnose. Other QTL for resistance may provide putative map locations for the major resistance loci still to be mapped. Molecular markers linked to the majority of major Co-genes have been reported and these provide the opportunity to enhance disease resistance through marker-assisted selection and gene pyramiding. The 10 Co-genes are represented in the anthracnose differential cultivars, but are present as part of a multi-allelic series or in combination with other Co-genes, making the characterization of more complex races difficult. Although the Co-genes behave as major Mendelian factors, they most likely exist as resistance gene clusters as has been demonstrated on the molecular level at the Co-2 locus. Since the genes differ in their effectiveness in controlling the highly variable races of the anthracnose pathogen, the authors discuss the value of individual genes and alleles in resistance breeding and suggest the most effective gene pyramids to ensure long-term durable resistance to anthracnose in common bean.
Xinyi Zhang, Li Liao, Zhiyong Wang, Changjun Bai, and Jianxiu Liu
and SRAP markers are valuable for marker-assisted selection, analysis of genetic diversity, and population genetic analysis ( Budak et al., 2004a , 2004b , 2004c ; Carvalho et al., 2009 ; Gupta and Varshney, 2000 ). Both marker types have been