). With the advent of molecular markers, QTL mapping has become increasingly important in molecular breeding. Marker-assisted selection and gene discovery are now widely used for the breeding of field crops and vegetables ( Cheng et al., 2011 ; Sabouri
Yanbin Su, Yumei Liu, Huolin Shen, Xingguo Xiao, Zhansheng Li, Zhiyuan Fang, Limei Yang, Mu Zhuang, and Yangyong Zhang
Ryan J. Hayes, Carlos H. Galeano, Yaguang Luo, Rudie Antonise, and Ivan Simko
‘La Brillante’ and other cultivars is also expressed in whole heads. Efficient phenotypic or marker-assisted selections strategies to breed for slow decay can be designed based on an understanding of trait inheritance. In a diploid (2 n = 2 x = 18
Cecilia E. McGregor, Vickie Waters, Tripti Vashisth, and Hussein Abdel-Haleem
candidate genes toward the development of functional markers ( Andersen and Lübberstedt, 2003 ) for marker-assisted selection (MAS) for flowering time in watermelon. We are currently sequencing the Cla009504 and Cla000855 alleles in this population and
Verónica Raga, Guillermo P. Bernet, Emilio A. Carbonell, and Maria J. Asins
al., 2003 ; Syvertsen et al., 2010 ). Because only a 5% of V × P progeny induced higher fruit yield than the salt-tolerant parent, and the heritabilities of rootstock effects were low, selection assisted by associated markers might be useful to
Jason Prothro, Hussein Abdel-Haleem, Eleni Bachlava, Victoria White, Steven Knapp, and Cecilia McGregor
have identified QTL associated with sex expression in watermelon including major QTL (LG 11A) that we propose is the location of the a gene responsible for andromonoecy in the species. This research is an important step toward the use of marker-assisted
Geoffrey Meru and Cecilia McGregor
isolation of a full-length cDNA clone of stearoyl-ACP protein desaturase in cucumber ( Shanklin et al., 1991 ; Shanklin and Somerville, 1991 ). However, no DNA markers have been developed for cucurbit crops for application in marker-assisted selection (MAS
Jeremy A. Pattison*, Suren K. Samuelian, and Courtney A. Weber
RAPD and AFLP markers were first used to construct a molecular map in a BC1 red raspberry population consisting of 70 individuals that segregated for Phytophthora root rot resistance. RAPD markers linked to root rot resistance were identified by bulk segregant analysis and through QTL anlaysis. Two common genomic regions were identified by both analyses and were estimated to explain ≈50% of the phenotypic variation. RAPD markers flanking the QTL were cloned and made into sequence specific markers for potential use in marker assisted selection. In addition to the linked markers, RAPDs spread throughout the linkage map were also sequenced and developed into either SCARs, CAPs, or codominant SSRs. Attempts were made to locate red raspberry resistance gene analogs using degenerate primers designed on conserved regions encoding known resistance genes. Results on the type and map position of identified RGA's and selection efficiency of linked markers analyzed in red raspberry cultivars of characterized root rot resistance will be discussed.
Zhan'ao Deng, Fred G. Gmitter Jr., Shunyuan Xiao, and Shu Huang
Citrus tristiza virus (CTV) is the most-significant viral pathogen of citrus in the world. Rapid decline of trees on sour orange and stem pitting of grapefruit and sweet orange, two diseases induced by CTV, severely jeopardize citrus production worldwide. It is recognized that all future rootstocks should be resistant to this virus, and scion resistance to stem pitting stains is desirable. To facilitate introgression of the CTV resistance gene from Poncirus trifoliata and development of CTV-resistant varieties in citrus, gene mapping projects have been initiated and more than a dozen RAPD markers have been identified with tight linkage to the resistance gene. As part of our efforts to use marker-assisted selection with a large number of crosses, and ultimately to accomplish map-based cloning of the CTV resistance gene, we have been converting the most tightly linked RAPD markers into SCAR (sequence characterized amplified region) markers by cloning, sequencing the marker fragments, and designing locus-specific primers. One codominant and several dominant SCARs have been developed thus far. The updated progress and utilization of these SCARs in marker-assisted selection and possibly in characterization of a BAC library will be presented and discussed.
Kang-Hee Cho, Il-Sheob Shin, Seong-Sig Hong, Ki-Taek Kim, Hwa-Suk Song, Sang-Jo Kang, and Il Gin Mok
Pear scab caused by Venturianashicolais one of the most important diseases of oriental pear. Breeding a variety resistant to scab can be improved through marker-assisted selection (MAS). Bulked segregant analysis (BSA) and amplified fragment length polymorphic (AFLP) analysis were performed to identify DNA markers linked to the scab-resistant gene (Vn) using a population from a cross between PS2-93-3-98 (resistant parent) and Yali (susceptible parent). A total of 480 EcoR I/MseI primer combinations were used to identify markers specific to PS2-93-3-98 and resistant pool. Three AFLP markers linked to Vn, E-AGT/M-CCA245, E-ATT/M-CCG300, and E-GGT/M-TCT225, were selected. Linkage analysis between the selected markers and Vn locus was conducted with 51 individual plants. The selected markers, E-AGT/M-CCA245, E-ATT/M-CCG300, and E-GGT/M-TCT225, were located at 3.9, 3.8, and 1.2 cm away from Vn, respectively. For practical application, we are currently converting selected markers to simple PCR-based markers. The markers could be used to increase selection efficiency in pear-breeding programs for scab resistance.
Prunus, which includes peach/nectarine, almond, apricot, cherry, and plum, is a large and economically important genus in the family Rosaceae. The size and long generation time of these tree crops have hampered improvement through classical breeding and long-term selection programs. With the advent of DNA-based molecular diagnostics, an exciting era in germplasm improvement has dawned. Efforts are underway, notably in the United States (e.g., California, Michigan, North Carolina, and South Carolina) and the European Community (e.g., England, France, Italy, and Spain), to apply the tools of molecular mapping and marker-assisted selection to this important genus. The objective of these projects is to develop molecular linkage maps of sufficient marker density to tag phenotypic trait loci of agronomic importance. These include traits controlled by single genes (e.g., flower color, compatibility, flesh color, pest resistance), as well as more-complex, quantitative traits (e.g., cold hardiness, tree architecture, sugar content). An immediate outcome of these mapping efforts has been the development of DNA “fingerprints,” allowing for the discrimination of cultivars—both scion and rootstock. The maps will be used by breeders and molecular biologists to monitor gene introgression from wild species into elite lines, for marker-assisted selection of desired trait combinations, and for map-based cloning of specific genes. The molecular markers used in these mapping projects include RFLPs, RAPDs, and microsatellites. Each has their appropriate applications and advantages depending upon the resources at hand and the project's specific goals.