Disease resistance and spring phenological characteristics of Ribes L. germplasm

Graduation date: 2009North American cultivation of Ribes L. may expand as small fruit growers seek species to diversify horticultural crops. The Ribes industry was suppressed for decades out of fear that cultivated black currants and gooseberries would intensify the fungal disease white pine blister rust (WPBR) on five-needle pine (Pinus L. section Quinquefoliae) species. These pines were historically vital to the timber industry. Today, plant breeders seek to strengthen the Ribes small fruit industry through production of material suitable for North American conditions. Paramount to this effort is the development of resistance against major pests and diseases. Growers must be able to recognize the attributes of available genotypes prior to field establishment. The objectives of this research were to determine disease resistance and phenological characteristics of Ribes selections at the United States Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository (NCGR) in Corvallis, Oregon.\ud Since the early 1930's, plant breeders have used immune black currant (R. nigrum L.) germplasm as a control tactic against the exotic WPBR, caused by the\ud basidiomycete fungus Cronartium ribicola J.C. Fischer. In 1999, a seedling population was generated at the NCGR from a cross involving susceptible pistillate R. nigrum 'Ben Lomond' and immune staminate parent R. ussuriense Jancz. x R. nigrum 'Consort.' To test the inheritance of resistance in the F₁ population, aeciospore and urediniospore treatments were applied in 2008 to single-leaf softwood cuttings under controlled conditions in a greenhouse. Resistant F₁ phenotypes segregated in a 1:1 ratio consistent with the pattern of simple dominant inheritance of a single gene. Artificial inoculations testing aeciospore and urediniospore infectivity produced equivalent disease severity in the experimental Ribes genotypes. Resistance to the native powdery mildew fungus, Podosphaera mors-uvae (Schwein.) U. Brown and S. Takamatsu, was also evaluated in the F₁ population. Individuals segregated for resistance in a 1:3 ratio after exposure to elevated disease pressure in the greenhouse. Fifteen F₁ genotypes were resistant to both fungal pathogens and are candidates for further breeding trials.\ud In a second study, five years of spring phenological survey data were analyzed using a growing degree-day (GDD) model, with the objective to identify cultivars adapted to North American conditions. Ribes section Calobotrya was the earliest group to reach "first bloom," followed sequentially by R. [superscript]xnidigrolaria Bauer hybrid species, section Symphocalyx, section Grossularia, section Ribes, and lastly, section Botrycarpum. Early and late-flowering accessions were identified for each taxon