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Title: Fine genetic mapping of a locus controlling short internode length in melon (Cucumis melo L.)

item HWANG, JIHYUN - Pusan National University
item OH, JUYOUL - Agricultural Research And Extension Service, Korea
item KIM, ZOOHYUN - Gyeongsang National University
item Staub, Jack
item CHUNG, SANG-MIN - Dongguk University
item PARK, YOUNGHOON - Pusan National University

Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2015
Publication Date: 6/20/2015
Citation: Hwang, J., Oh, J., Kim, Z., Staub, J.E., Chung, S., Park, Y. 2015. Fine genetic mapping of a locus controlling short internode length in melon (Cucumis melo L.). Molecular Breeding. doi: 10.1007/S.11032-014-0088-1.

Interpretive Summary: Melon is an economically important tropical, old world species that likely originated in Africa, Afghanistan, China, India, Iran, Saudi Arabia, southern Russia, and Turkey are important secondary gene centers for the domestication and cultivation of melons. Wild forms of C. melo are found south of the Sahara Desert, only in eastern tropical Africa. Melons have been associated with human nutrition and culture for more than 12,000 years. They are of commercial importance in the United States and Europe as well as in Mediterranean and Asian countries, and are consumed to an increasing extent in South Korea. Plant dwarfism is economically important in some major crop species because of its potential positive contribution to lodging resistance, yield, early maturity, and tillering capacity. Dwarf or bush melon types may have commercial importance since they typically possess concentrated fruit set and can be planted in higher plant densities than standard vining types. A unique dwarf plant habit observed in Korean melon has potential utility in Korean plant improvement programs where dwarf plant types are desirable for cultivation under greenhouse growing environments. A study was therefore designed to characterize the inheritance of the dwarfing gene and its location on a chromosome associated with the diminutive plant habit in this unique melon type. The inheritance and gene location was found to be relatively simple and controlled by one recessive gene. This information allows for the development of breeding strategies that can rapidly incorporate traditional and molecular approaches for the development of dwarf melon cultivars for the Korean commercial market, which will lead to improved commercial productivity.

Technical Abstract: Compact and dwarfing vining habits in melon (Cucumis melo L.; 2n = 2x = 24) may have commercial importance since they can contribute to the promotion of concentrated fruit set and can be planted in higher plant densities than standard vining types. A diminutive (dwarf) melon mutant line (PNU-D1) with short internodes was obtained as a segregant after self-pollination of the F1 hybrid cultivar 'Alaska' (Cucumis melo ssp. cantalupensis). Line PNU-D1 (maternal parent) was crossed with line PNU-WT1 [paternal parent; inbred wild-type melon C. melo ssp. agrestis (Naudin) Pangalo] and resultant F1 progeny were then self-pollinated to produce an F2 population that segregated as dwarf and vining plant types. The inheritance of dwarfism in this population is not known, and given the trait's potential commercial importance, a study was designed to determine the genetics of dwarfism associated with line PNU-D1. Primary stem length at the 4th and 24th node of F2 progeny assessed under greenhouse conditions indicated that a single recessive gene, designated mdw1, controlled dwarfism in this population. To identify the chromosomal location associated with mdw1, an SSR-based genetic linkage map was constructed using 94 F2 progeny. In parallel, a candidate gene approach was employed using cytokine oxidase gene (CKX) sequence information that is associated with promoting a shortened internode compact growth habit (cp) in cucumber. Using 76 SSR markers positioned on 15 linkage groups (LG) spanning 462.84 cM, the location of mdw1 was localized to Chromosome 7 (LGVII). A cleaved amplified polymorphic sequence (CAPS) marker (MCKX) developed from melon, co-segregated with mdw1. Fine genetic mapping of the mdw1-mCKX genomic region was facilitated using 1,194 PNU-D1 x PNU-WT1 derived F2 progeny that defined the genetic distance between these loci to be 1.7 cM. The putative dwarfing-associated genes ERECTA (serin/theronin kinase) and UBI (ubiqitin) were also mapped to genomic regions flanking mdw1 at distances of 0.6 and 1.2 cM, respectively. The high level of synteny previously defined between cucumber Chromosome 4 and melon LGVII was confirmed at the level of gene order and DNA sequence.