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P. Perkins-Veazie, J.K. Collins, and B. Strik

Harvesting raspberry fruit with an attached receptacle prevents compression of the fruit in storage containers and permits harvesting of immature fruit. This study was done to determine the effects of receptacle retention on fruit quality during storage. `Heritage' raspberry fruit from Oregon and Arkansas were harvested at light red (red ripe) and dark red stages of maturity, and stored at 2C, 95% RH for 7 days. Dark red fruit with receptacles were firmer than those without receptacles, but there were no differences in light red fruit. Ethylene production was higher from raspberries stored with receptacles. Total anthocyanin increased in all fruit after storage and was slightly higher in fruit without receptacles. Soluble solids concentration did not change but titratable acidity decreased during storage for all treatments. When fruit were harvested after several days of rain, decay incidence in fruit held with receptacles increased. Harvesting raspberries with attached receptacles did not increase postharvest fruit quality.

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Kim S. Lewers*, Eric T. Stafne, John R. Clark, Courtney A. Weber, and Julie Graham

Some raspberry and blackberry breeders are interested in using molecular markers to assist with selection. Simple Sequence Repeat markers (SSRs) have many advantages, and SSRs developed from one species can sometimes be used with related species. Six SSRs derived from the weed R. alceifolius, and 74 SSRs from R. idaeus red raspberry `Glen Moy' were tested on R. idaeus red raspberry selection NY322 from Cornell Univ., R. occidentalis `Jewel' black raspberry, Rubus spp. blackberry `Arapaho', and blackberry selection APF-12 from the Univ. of Arkansas. The two raspberry genotypes are parents of an interspecific mapping population segregating for primocane fruiting and other traits. The two blackberry genotypes are parents of a population segregating for primocane fruiting and thornlessness. Of the six R. alceifolius SSRs, two amplified a product from all genotypes. Of the 74 red raspberry SSRs, 56 (74%) amplified a product from NY322, 39 (53%) amplified a product from `Jewel', and 24 (32%) amplified a product from blackberry. Of the 56 SSRs that amplified a product from NY322, 17 failed to amplify a product from `Jewel' and, therefore, detected polymorphisms between the parents of this mapping population. Twice as many detected polymorphisms of this type between blackberry and red raspberry, since 33 SSRs amplified a product from NY322, but neither of the blackberry genotypes. Differences in PCR product sizes from these genotypes reveal additional polymorphisms. Rubus is among the most diverse genera in the plant kingdom, so it is not surprising that only 19 of the 74 raspberry-derived SSRs amplified a product from all four of the genotypes tested. These SSRs will be useful in interspecific mapping and cultivar development.

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Thierry Vrain, Robyn DeYoung, John Hall, and Stan Freyman

Cover crops used in red raspberry plantings (Rubus idaeus L.) are often good hosts of the root-lesion nematode (Pratylenchus penetrans Filipjev & Sch. Stekoven), a major soilborne pathogen of raspberry. The effects of two susceptible cover crops, white clover (Trifolium repens L.) and barley (Hordeum vulgare L.), planted in between rows, on nematode density and growth of raspberry plants were compared to those of three cover crops resistant to the nematode: redtop (Agrostis alba L.), creeping red fescue (Festuca rubra L.), and `Saia' oat (Avena sativa L.). Nematode multiplication in raspberry roots and in cover crop roots was assessed over 4 years. Growth and vigor of plants were estimated at the end of the experiment by counting primocanes and determining height and biomass. Nematode multiplication was suppressed in roots of `Saia' oat, fescue, and redtop compared to barley or white clover. Nematode density in roots and rhizosphere soil of raspberry was not affected by the choice of cover crops. Nematode suppression in the three resistant cover crops did not translate into increased vigor of raspberry plants.

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Rebecca L. Darnell, Horacio E. Alvarado, Jeffrey G. Williamson, Bryan Brunner, María Plaza, and Edna Negrón

There is increasing interest in red raspberry (Rubus idaeus) production worldwide due to increased demand for both fresh and processed fruit. Although the United States is the third largest raspberry producer in the world, domestic demand exceeds supply, and the shortage in fresh market raspberries is filled by imported fruit from Canada during July and August, and from Mexico and Chile during November through May. The raspberry harvest season is well defined and the perishability of the fruit limits postharvest storage. Winter production of raspberry in tropical and subtropical climates could extend the harvest season and allow off-season fruit production during periods of high market prices. The objective of the current study was to examine growth and yield of red raspberry cultivars grown in an annual winter production system in Florida and Puerto Rico. Long cane cultivars were purchased from a nursery in the Pacific northwestern U.S. in 2002 (`Heritage' and `Tulameen'), 2003 (`Tulameen' and `Willamette'), and 2004 (`Tulameen' and `Cascade Delight') and planted in raised beds in polyethylene tunnels in December (Florida) or under an open-sided polyethylene structure in January-March (Puerto Rico). In Florida, harvest occurred from ∼mid-March through the end of May, while in Puerto Rico, harvest occurred from the end of March through early June (except in 2002, when canes were planted in March). Yields per cane varied with cultivar, but ranged from ∼80 to 600 g/cane for `Tulameen', 170 to 290 g/cane for `Heritage', 135 to 350 g/cane for `Willamette', and ∼470 g/cane for `Cascade Delight'. Economic analysis suggests that, at this point, returns on this system would be marginal. However, increasing cane number per unit area and increasing pollination efficiency may increase yields, while planting earlier would increase the return per unit. The key to success may hinge on developing a system where multi-year production is feasible in a warm winter climate.

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Adam Dale and Theo J. Blom

The objectives of the study were to determine whether raspberries responded to decreased red to far-red ratio and whether it was more effective at the beginning or end of the dark period. Increased proportions of far-red light increased the internode length when at the beginning of the dark period on the three raspberry cultivars `Lauren',`Reveille', and `Titan'. Cultivars varied in that internode length also increased in ambient daylength compared to short days in `Lauren' and `Reveille', but not in `Titan'. They also responded differently to photoperiod: `Titan' and `Lauren' grew under short days, whereas `Reveille' ceased growth.

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Artemio Z. Tulio Jr., Mustafa Ozgen, R. Neil Reese, Steven J. Schwartz, Qingguo Tian, Gary D. Stoner, A. Raymond Miller, and Joseph C. Scheerens

Anthocyanins in black raspberry extracts may play a key role in the regulation of oncogene expression in cancer cell cultures. Variations in anthocyanin levels of `Jewel', `Mac Black', and `Bristol' black raspberries grown at seven commercial farms in Ohio were investigated using HPLC and uv-vis spectrometry. Cyanidin-3-rutinoside (cy-3-rut) and cyanidin-3-(2G-xylorutinoside) (cy-3-2-xyl), the two major compounds present in all cultivars (≈2:1), were highly correlated with total anthocyanin contents. Sample variation in total anthocyanin, cy-3-rut, and cy-3-2-xyl levels was greater among commercial farms than among cultivars grown at the same location. The antioxidant activities of cy-3-rut, cyanidin-3-glucoside, cyanidin-3,5-diglucoside (cy-3,5-diglc), and pelargonidin-3-glucoside from purified extracts were determined using the free radical scavenging assays DPPH and ABTS, and the ferric reducing power assay FRAP. All pure anthocyanins showed strong antioxidant potentials except for cy-3,5-diglc. Cy-3-rut was identified and quantified as the dominant anthocyanin in black raspberries and was also the most potent antioxidant. Results suggest that anthocyanins, cy-3-rut in particular, may function as the primary antioxidants in black raspberries. Genetic and environmental variation in the anthocyanin contents necessitate characterization of the antioxidant and anthocyanin levels in fruits from any given source prior to measuring biological and medicinal activities.

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Barbara M. Reed

Medium-term in vitro cold storage of Rubus germplasm was investigated using various temperatures, photoperiods, and storage containers. Shoot cultures of several Rubus taxa were grown either in tissue-culture hags or 20 × 150-mm glass tubes. Cultures stored at 10C in darkness were in poor condition after 6 months. Overall survival and condition ratings were significantly better for bags than tubes when cultures were kept at 4C. Contamination was present in 14% of the tubes, but only 3% of the bags. Addition of a 12-hour photoperiod to 4C storage significantly improved both condition ratings and survival percentages of many individual genotypes. Evaluation of the 250-accession germplasm collection after 12 months at 4C (dark) showed 92% of accessions in bags and 85% in tubes in suitable condition to remain in storage. Storage of cold-sensitive genotypes in tissue-culture bags at 25C with a 16-hour daylength was extended to 9 months when the MS-medium nitrogen level was reduced to 25% of standard concentration. Survival of `Mandarin' raspberry stored for 9 months improved from 40% at 4C (100% N) to 90% at 25C (25% N). Results of these studies suggest that most Rubus germplasm can be stored safely at 4C with 12 hours of light. Plastic tissue-culture bags are preferred over tubes due to higher survival and lower contamination rates. Storage at 25C on reduced-nitrogen medium is an alternative method for cold-sensitive genotypes.

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Hugh A. Daubeny

The indigenous North American red raspberry, Rubis strigosus has been neglected in breeding programs. Only four cultivars, `Cuthbert', `Latham', `Herbert' and `Ranere' provide most of the germplasm contained in present-day cultivars; no more than six individual wild genotypes of the species are represented by the four cultivars. In recent years, the B.C. breeding program has screened seedling populations of hitherto unexploited genotypes of the species from various locations in North America. Useful traits identified in selections from the populations include levels of resistance to 1) the North American aphid vector, Amphorophora agathonica, of the raspberry mosaic virus complex, 2) to several cane diseases and 3) to root rot caused by Phytophthora fragariae var rubi, as well as desirable fruit traits, such as bright, non-darkening red color and easy release. Selections with cultivar potential have now been identified in the second and third backcross generations from the species.

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Joseph A. Fiola and Harry J. Swartz

Raspberry cultivars and hybrids were screened for reaction to Verticillium alboatrum Reinke and Berth to determine the mode of inheritance of resistance and to assist in the development of resistant germplasm. Greenhouse-grown seedlings of an incomplete partial diallel of two black, purple, and red raspberry Rubus subgenus Idaeobatus progeny were root-dipped in a mycelial slurry and stem-inoculated with a conidial suspension of V. albo-atrum. Fourteen weeks after the initial inoculation, disease symptoms were observed in the seedlings. Disease symptom severity and percentage of black raspberry parentage in the seedlings were correlated (P ≤ 0.01; r 2 = 0.90). A similar significant (P ≤ 0.05; r 2 = 0.66) linear trend was found with fungus reisolation percentages, although isolation of the fungus from symptomless plants indicates Verticillium tolerance among genotypes in Idaeobatus. These trends, coupled with large significant general combining ability (P ≤ 0.01), suggest primarily additive inheritance of resistance. However, considering noninoculated control scores, the possibility of escapes, and skewing of populations, one may hypothesize a gene-gene model for symptom expression, with partial dominance of resistance alleles.

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Horacio E. Alvarado, Rebecca L. Darnell, and Jeffrey G. Williamson

Raspberry root growth during fruiting appears to be a strong sink for assimilates, and may decrease carbon availability for fruits and, consequently, cane yield. Both floricanes and primocanes may contribute to root carbon supply in raspberry during fruiting. To test this, `Tulameen' raspberry canes were grown outdoors in containers filled with perlite and peat (1:1). One-half of the plants were girdled and the rest were nongirdled. Within each girdling treatment, either 0 or 3 primocanes were allowed to grow. Treatments were applied at early bloom (10 May), and 50% fruit harvest occurred the first week in June. Fruit number and yield per plant decreased in girdled plants and plants without primocanes compared with nongirdled plants and plants with primocanes. Individual fruit fresh weight was not affected by treatments, but individual fruit dry weight and the dry weight to fresh weight ratio was higher in girdled plants without primocanes than in the other treatments. Neither girdling nor the presence of primocanes affected dry weight allocation to primocanes or floricanes. Root dry weight was higher in girdled plants with primocanes than in nongirdled plants without primocanes. It appears that primocanes supply carbon to roots during fruiting, and subsequently, roots mobilize carbon to floricanes. Thus, roots appear to serve primarily as a translocation pathway for carbon from primocanes to floricanes. However, when primocane growth is suppressed, root carbon is mobilized to support floricane development. If carbon flow from roots to floricanes is restricted, fruit number and yield is significantly decreased.