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Chad E. Finn

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Chad E. Finn

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Michael Dossett and Chad E. Finn

The large raspberry aphid (Amphorophora agathonica Hottes) is an important vector of viruses in Rubus L. across North America. Although breeding for aphid resistance has long been recognized as an important tool for protecting red raspberries (Rubus idaeus L.) from viral infection, this is the first report of resistance to A. agathonica in black raspberry (Rubus occidentalis L.). Seedlings from 132 wild populations of black raspberries, representing the species' native range, were screened for resistance to A. agathonica. Strong resistance was found in three of these populations, one from Ontario (ORUS 3778), one from Maine (ORUS 3817), and one from Michigan (ORUS 4109). Resistance to the large raspberry aphid in ORUS 3778 and ORUS 3817 is dominant and appears to be conferred by different genes. We propose that the genes for resistance in ORUS 3778 and ORUS 3817 be designated Ag4 and Ag5, respectively. Resistance to A. agathonica in ORUS 4109 also appears to be controlled by a dominant allele at a single locus, but cannot be differentiated from Ag4 at this time.

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Jack Pinkerton and Chad E. Finn

The relative susceptibility of 44 genotypes of wild Fragaria L. and commercial cultivars of strawberry Fragaria ×ananassa Duch. to Meloidogyne hapla Chitwood and Pratylenchus penetrans (Cobb) Filipjev & Shuurmans Stekhoven was evaluated in the greenhouse. Eleven genotypes were highly resistant to populations of M. hapla from Washington State and Oregon, with Rf values (initial nematode density/final population density) less than 0.5. However, root growth of most genotypes, including resistant genotypes, was reduced by M. hapla. Thirteen genotypes were ranked more resistant to P. penetrans than F. ×ananassa `Totem', a susceptible cultivar. Root growth of most genotypes was not affected by P. penetrans under these experimental conditions. We conclude that commercial cultivars and wild Fragaria genotypes can provide a readily exploitable source of resistance to M. hapla. Conversely, sources of resistance to P. penetrans were uncommon in the germplasm evaluated. The F. ×ananassa cultivars, which already have commercially important characteristics, appear to be a better source of resistance for both nematode species than the wild, unimproved germplasm.

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Angela K. Anderson and Chad E. Finn

The superb flavor of trailing blackberry cultivars, such as `Marion', is derived from Rubus ursinus Cham. & Schlecht. Wild R. ursinus offer a range of horticulturally desirable traits to breeders, from high fruit quality to improved cold hardiness. Current cultivars are derived from relatively few sources of R. ursinus, selected primarily for fruiting characteristics. A replicated field trial of 460 clones, representing 20 populations from southern British Columbia, Washington, and Oregon, was established in 1994. Observations during the planting year have indicated that monitoring variability in the following reproductive traits will be useful in assessing diversity; budbreak, flowering, and fruiting date; lateral length; proportion of reproductive laterals; gender; flower and fruit number; and fruit size. In particular, there are clones that exhibit large fruit size (4 to 5 g), high flower number per lateral, and uniform fruit set. Analysis of these data will contribute to determination of relative genetic distances among the populations and enhance the understanding of the diversity available in R. ursinus.

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Chad E. Finn and James J. Luby

Progenies from a partial diallel mating scheme using 17 highbush (Vaccinium corymbosum L.), lowbush (V. angustifolium Ait.), and half-high (V. corymbosum/V. angustfolium hybrid) parents were subjectively evaluated for fruit color, picking scar, and firmness in two seasons. General combining ability (GCA) mean squares were significant (P ≤ 0.01 for all traits), but specific combining ability was significant for no traits (P > 0.05). However, the correlation coefficients between the GCA effects and the parental phenotype scores were low, indicating that selection of parents within this material based on their phenotype may not be indicative of progeny performance. GCA effects depended to some extent on the species ancestry. Vaccinium angustifolium parents produced progeny with relatively dark, soft fruit with large scars. Lowbush parents having light-blue fruit produced segregating progenies that were heavily skewed toward dark fruit, regardless of the color or species ancestry of the other parent. When the highbush and half-high parents were crossed with one another, segregation patterns were typical of predominately additive gene action.

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Angela K. Anderson and Chad E. Finn

Trailing blackberry cultivars, such as `Marion', can be traced to relatively few chance selections of Rubus ursinus Cham. & Schlecht. Wild R. ursinus offer a range of horticulturally desirable traits to breeders, from high fruit quality to improved cold hardiness. Cuttings from 460 plants, representing 20 populations in southern British Columbia, Washington, and Oregon, collected in 1993. Rooted clones were planted in 1994 in a replicated field trial to assess morphological variation. A greenhouse study was also undertaken, with 10 clones represented from each site, in two replications. Preliminary data from the greenhouse and field studies show variability in the following morphological characters: Glandular hairs; cane and prickle color; cane diameter; prickle density; internode length; leaf color, size, shape and density; and senescent leaf drop and color change. Floricane morphology will be assessed in 1995. Analysis of these data will determine relative genetic distances among the populations and enhance the understanding of the diversity available in R. ursinus.

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John R. Clark and Chad E. Finn