Mapping of the genome of Cucurbita pepo L.and the genetics of the hull-less-seed type oil pumpin

Growing pumpkin (Cucurbita pepo L.) in Austria has a long-standing tradition, and today, an increasing economic importance. Pumpkin seed is highly valued for its nutritional and pharmaceutical qualities, it is a significant source of income for more than 10.000 farmers. Breeding efforts especially introducing virus resistance is an urgent task. Nonetheless, using molecular tools, C. pepo belongs to the least-studied species among the Cucurbitaceae. Modern plant breeding relies increasingly on achievements of molecular genetics, making use of maps and markers. Therefore, this application is designet to achieve two major research goals: (1) A molecular map of the oil-pumpkin, using mainly AFLP markers, will be developed based on an F2 population derived from a cross between a zucchini genotype and a Styrian oil-pumpkin breeding line. In addition, more than 200 SSR markers produced by other laboratories for melon and cucumber will be tested on pumpkin. Those showing polymorphism between the two parents will be included in the map as anchor markers to provide a skeletal map for C. pepo, independent of population or cultivar groups. For the same purpose, a selected number of RAPD markers will be converted to more robust PCR-based markers (ERPAR). The construction of a molecular marker map for pumpkin provides a starting point for genetic mapping of agronomically important traits, (e.g. seed characteristics, growth habit, disease resistance, oil content). The immediate utility of the map will be the location of markers linked to ZYMV resistance genes on the map, since the zucchini parent possesses genes conferring resistance against the virus. Other marker-trait associations may also assist in the selection of specific alleles and will improve breeding efficiency. (2) RAPD markers will be used in a "bulked segregant analysis" to identify a marker linked to a major gene responsible for the hull-less phenotype of Styrian oil pumpkin, referred to as varietas styriaca. Attempt will be made to trace the origin and elucidate the inheritance of the hull-less characteristic. For this purpose more than 60 hulled, semi hull-less, and hull-less seeded varieties and accessions have been collected world wide.

Pumpkin is a scientifically neglected crop among the Cucurbitaceae. This became especially obvious when in 1997 a severe virus epidemic destroyed half of the Austrian pumpkin harvest. Pumpkin, Cucurbita pepo var. styriaca, turned out to be without any genetic protection (resistance) against the virus. On the other hand, the culinary, nutritional and medicinal value of pumpkin seed oil receives increasing attention and is a significant source of income for more than 3.000 farming families. This is also reflected in the dramatic increase of growing area for oil pumpkin in Austria in the last 10 years. Moreover, oil-pumpkin is undoubtedly part of Austria`s cultural heritage. The project P15773-B14, financially supported by the Austrian Science Fund (FWF), yielded three main results: (1) Today very few crop plants exist without a genetic map, pumpkin being one of them. We established the first comprehensive genetic map of Cucurbita pepo L. (2n=40). This map provides a first insight into the structure of the pumpkin genome. Genetic maps have many theoretical and practical uses up to the possibility to isolate single genes. Of more immediate use are markers mapped close to resistance genes, which in turn can be used for selecting resistant plants in a breeding program. (2) The most outstanding feature of the Austrian oil-pumpkin is its hull-less seed type. The finding and mapping of markers linked to the hull-less character of the Styrian oil pumpkin is an important achievement from the viewpoint of practical breeding. The hull-less character is basically determined by a major recessive gene. In any backcross breeding program, such as introducing resistance from an alien source into a cultivated form, a molecular marker which can simply be followed, indicating the presence of a non-expressed allele, is undoubtedly of great help for the plant breeder. Besides, although it appears simple, the genetics of the hull-less character of the Austrian oil pumpkin are not completely solved yet. It manifests itself as a residual lignification of basically hull-less seeds, in the progeny of hulled x hull-less crosses, the control of which is controversially discussed in the literature. (3) We carried out comprehensive segregation studies and histological analysis of the seed coat (testa) of many progenies. From the results we conclude, that Mendelian segregation of a reasonable number of genes, i.e., the presence or absence of specific alleles, can not be made responsible for the varying degree of residual lignification. The cause might better be sought at the level of gene regulation.