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F. Takeda

Tissue-cultured raspberry plants are not exposed to low temperatures during the propagation phase, yet the primocane that grows from the crown will flower terminally after developing 20 to 25 nodes. We studied the effect of duration of chilling (hours) (CH) on days to flower (DTF) in primocanes arising from root suckers of previously cropped fall-bearing `Heritage' and `'Summit' raspberries. Growth of `Heritage' plants with 0 or low CH was either short with rosetted leaves or indeterminate. Plants with 0 CH remained vegetative for >240 days, while plants with >750 CH flowered in <4 months when the primocane had 25 to 30 nodes. These results suggested that low-temperature exposure prior to shoot emergence was necessary for flower bud initiation in `Heritage' red raspberry. In contrast, all `Summit' flowered; DTF ranged from 120 days for 0 CH plants to <70 days for plants with 1000 CH. Low-temperature treatment affected flower bud development. Plants with 0 CH developed 15 flowering laterals, while plants with >750 CH had 25 flowering laterals. Although `Summit' needs no CH to flower, low temperature treatments definitely accelerated DTF and increased the number of fruiting laterals.

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K.S. Lewers, S.M.N. Styan, S.C. Hokanson, and N.V. Bassil

mapping population, and Sam Garrett, Dr. Courtney Weber, Dr. John Clark, and Eric Stafne for raspberry and blackberry leaf tissue. In addition, we would like to thank Dr. Tad Sonstegard and Tina Sphon for genotyping, and the Beltsville Agricultural

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Jo Ann Robbins

The growth, yield, and berry weight of nine June-bearing strawberry (Fragaria ×ananassa) cultivars (`Allstar', `Cavendish', `Honeoye', `Jewel', `Kent', `Mesabi', `Mira', `Northeaster', and `Winona') and six floricane fruiting (summerbearing) raspberry (Rubus idaeus) cultivars (`Algonquin', `K-81-6', `Lauren', `Nova', `Qualicum', and `Reveille') grown in southern Idaho were compared. `Cavendish', `Mesabi,' and `Winona' established quickly and maintained their spring vigor. Strawberry cultivars grew well during the summer but some cultivars had low spring vigor ratings. The most reliable yielding cultivars were `Cavendish' and `Mesabi' in spite of spring frosts, which damaged blossoms. `Mesabi' yielded best during a season where plants suffered spring freeze injury. Only `Mesabi' yielded above 6 tons/acre (2001). Spring freezing and relatively low yields are limiting factors in strawberry production in southern Idaho. Berry weight averaged 5.5 to 8.8 g in the second year of the study and may be too small for consumer acceptance and other commercial competition. `Cavendish' and `Mesabi' fruited earliest and `Honeoye' and `Winona' were latest. Raspberry shoot and cane growth was strong in all years. Over the course of the study, highest yielding in 2001 was `Nova' (7.65 tons/acre) and in 2002 `K-81-6' (10.4 tons/acre). In the second year of harvest (2002), all cultivars produced greater than the projected commercial production requirement of 3 tons/acre. Raspberry bloom occurred after the spring frosts. Berry weight was largest in `K-81-6' (3.3 and 2.5 g in 2001 and 2002, respectively) and smallest in `Algonquin' (1.8 and 1.5 g in 2001 and 2002, respectively). Early fruiting cultivars were `Nova' and `Reveille'.

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Patrick P. Moore

Randomly amplified polymorphic DNA markers (RAPDs) were used to distinguish among seven Pacific Northwest red raspberry (Rubus idaeus L.) cultivars. Random 10-base sequences were used to distinguish among `Chilcotin', `Chilliwack', `Comox', `Meeker', `Qualicum', `Tulameen', and `Willamette'. The seven cultivars could be distinguished even though there is considerable relatedness among the cultivars. `Chilliwack' and `Comox' share `Skeena' as a parent, and `Chilliwack' is a parent of `Qualicum'. `Willamette' is a parent of `Meeker'. This technology shows promise as a means of distinguishing cultivars and developing a genetic map to aid in breeding.

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T.C. Vrain, Hugh A. Daubeny, J.W. Hall, R.M. DeYoung, and A.K. Anderson

The inheritance of resistance to the root lesion nematode [Pratylenchus penetrans (Cobb) Filip. and Stek.] in red raspberry (Rubus idaeus L.) was studied in a four-member half diallel, involving two resistant genotypes and two susceptible genotypes. Estimates of general and specific combining abilities (GCA and SCA, respectively) were determined for nematode densities in roots alone and soil alone, nematode densities per plant, and plant root and foliage biomass. GCA were significant for nematodes in soil and for root and foliage biomass; SCA were significant for nematodes in the soil and for root biomass. Neither GCA nor SCA was significant for number of nematodes in the roots or per plant.

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David L. Trinka

Tissue-cultured (TC) plantlets are gaining wide acceptance as the standard transplanting stock within both the fruit and nursery industry. However, research and grower experiences suggest that management practices used for conventionally propagated raspberry plants may need to be tailored for successful field establishment of the TC plantlet. The effects of weed control practices, rowcovers, and fertilizer placement on the performance of newly planted TC `Heritage' red raspberry were evaluated during two years. Weed control treatments included straw mulch (ST), black polyethylene mulch (B), white on black polyethylene mulch (WB), napropamide herbicide (N), simazine herbicide (S), hand-weeding (HW), and an untreated control (U). Rowcovers were used during the first six weeks of establishment on the mulched and hand-weeded treatments. Calcium nitrate was placed in the planting hole or on the soil surface around the plant. Second year yields were directly proportional to soil moisture levels during the summer of the planting year. Plants mulched with ST, B, or WB during the planting year produced greater early yields during the fruiting year. Primocane density was highest in the ST treatment. Rowcovers consistently increased both soil temperature and soil moisture, but tended to cause a reduction in cane length the first growing season. Fertilizer placement had no consistent effect on any measured variable.

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Adam Dale, Patrick P. Moore, Ronald J. McNicol, Thomas M. Sjulin, and Leonid A. Burmistrov

Pedigrees of 137 red raspberry (Rubus idaeus L.) varieties released throughout the world since 1960 were used to calculate: 1) the genetic contribution of founding clones to these varieties; 2) genetic relatedness among them; and 3) their inbreeding coefficients. Fifty founding clones contributed to the pedigrees of these varieties with a mean genetic contribution ranging from <0.1% to 21%. Varieties were clustered according to the genetic contribution into groups strongly related to geographical origin. Varieties developed in the former USSR and derived from `Novost Kuzmina' formed a distinct cluster. The remaining varieties were clustered in groups based mainly on whether they were of North American or European origin. Varieties were clustered also on the basis of Wright's coefficient of relationship-a measure of genetic relatedness. Cluster groups were related to their geographical origin and the varieties within the groups could be traced to similar intermediate parents. Inbreeding coefficients ranged from 0.0 to 0.625 and were related, in part, to the numbers of generations of controlled hybridization from common ancestors. The British group, with the largest number of generations of breeding, had a low mean inbreeding coefficient, indicating that inbreeding can be minimized with attention to the mating system. Strategies are suggested for maintaining and increasing the genetic diversity in the world's red raspberry breeding populations.

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Adam Dale, Angela Sample, and Elizabeth King

Experiments were conducted to determine the chilling temperature and length of time required to break dormancy in red raspberry (Rubus idaeus L.). Five weeks of 7 °C with no light was sufficient to break dormancy in `Autumn Britten', `Nova', `Polana', and `Tulameen', while at least 8 weeks were needed for `Titan'. Comparisons with various chilling unit models allowed a model to be developed that could account for the observed chilling variation. In this model, each chilling hour was weighted as follows: below 5.6 °C = 1; 5.7 to 8.0 °C = 0.5; 8.1 to 11 °C = 0; 11.1 to 13 °C = -0.5; and >13 °C = -1. Plants of `Nova' and `Tulameen' chilled before flower initiation occurred, broke dormancy, and the resulting lateral branches remained vegetative. When the plants were fruited in the greenhouse, we were able to produce a second crop on the fruiting canes when the lateral branches that had fruited were removed. These experiments show that raspberries can be manipulated so that plants chilled in mid-September in the Northern Hemisphere can be induced to fruit by the beginning of January.

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Michele R. Warmund, Chris J. Starbuck, and Chad E. Finn

Micropropagated `Redwing' raspberry plants were grown with various mulch treatments to determine their influence on vegetative growth and fruit yield. Treatments included shredded hardwood bark mulch; degradable black plastic; sawdust; wheat straw; ground, shredded, or ground + shredded newspaper; and an unmulched control. During the year of establishment, high soil and air temperatures near the surface of the black plastic most likely reduced plant survival. The following year, vegetative growth and fruit yield of plants that were previously mulched with black plastic were also reduced. Plants mulched with bark, sawdust, straw, and all newspaper treatments had greater yields than those established with black plastic or in the unmulched control plots. Although yields were similar among plants in all newspaper mulch treatments, ground newspaper was lost under windy conditions and tended to mat down after rainfall, resulting in soggy soil conditions.

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Annette M. Zatylny, J.T.A. Proctor, and J.A. Sullivan

Two selections and two cultivars of red raspberry (Rubus idaeus L.) were evaluated for cold hardiness in vitro. Tissue-cultured shoots were exposed to temperatures from 0 to –18C and samples were removed at 2C intervals. Injury was assessed by a visual rating of tissue browning after freezing. Only shoots subjected to step-wise acclimation at low temperatures before freezing revealed significant differences among the four types in the lowest shoot survival temperature. Acclimation treatments increased the lowest survival temperatures of in vitro shoots by a mean of 3.1C. The hardiness obtained from this screening method agreed with that of winter survival in the field. Ranking, from the most to least cold hardy, was `Boyne', Gu 72, Gu 63, and `Comox'.