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Johanne C. Cousineau and Danielle J. Donnelly

Isoenzyme staining was used to characterize 55 of 78 raspberry cultivars (Rubus idaeus L., R. × neglectus Peck, and R. occidentalis L.). Six enzymes were needed to achieve this characterization: isocitrate dehydrogenase, malate dehydrogenase, phosphoglucoisomerase, phosphoglucomutase, shikimic acid dehydrogenase, arid triose phosphate isomerase. The 23 cultivars that were not uniquely characterized were grouped into eight groups of two and two groups of three and four. Two of these groups comprised black raspberry cultivars, all of which were similar isozymically. Isoenzymes could not distinguish between the cultivar Willamette and a spine-free mutant of the cultivar. Analysis of cultivars obtained from several sources revealed that raspberry cultivar mislabeling exists but is not very prevalent. Regular isoenzyme analysis of raspberry cultivars held by germplasm repositories, certified and other propagators, and breeders is both feasible and advisable for early detection of cultivar mislabeling.

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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'.

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Marvin P. Pritts, Robert W. Langhans, Thomas H. Whitlow, Mary Jo Kelly, and Aimee Roberts

Floricane-fruiting (summer-bearing) raspberries (Rubus idaeus L.) were grown outdoors in pots in upstate New York until mid-December when the chilling requirement was fulfilled. They were moved into a greenhouse and placed at a density that is three times higher than field planting. Bumble bees (Bombus impatiens Cresson) were introduced at flowering for pollination. Fruiting occurred from mid-February through mid-April, a time when the retail price for raspberries is between $3.00 and $6.00 for a half pint (180 g). Fruit quality was high, and individual 2-year-old plants averaged 11 half pints (2 kg) of marketable fruit. These yields and retail prices are equivalent to 19,000 lb and $142,000 per acre (21 t, $350,000 per ha). Raspberry production during winter allows growers to dramatically extend the harvest season and to produce a high-value crop at a time when greenhouses often are empty.

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Patrick P. Moore

Harvest data from the first and second harvest seasons were compared for 264 plots in six red raspberry (Rubus idaeus L.) plantings established from 1987 to 1992 to determine year-to-year consistency of harvest data. Midpoint of harvest had the largest correlation coefficient (r = 0.81, n = 264), followed by fruit mass (r = 0.76) and fruit firmness (r = 0.47). The relationship between the first and second harvest seasons was weaker for yield (r = 0.33) and percent fruit rot (r = 0.24). Basing the correlation coefficients on genotype means did not greatly improve the consistency of data. Inconsistency of harvest data suggests that selections should not be discarded because of low yields after a single harvest season but should be evaluated for at least 2 years.

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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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Kim S. Lewers and Courtney A. Weber

Researchers developing new cultivars of red raspberry (Rubus idaeus subsp. idaeus L.) and black raspberry (R. occidentalis L.) observe progeny of breeding populations for several seasons to identify those that perform reliably. If a portion of any breeding population could be eliminated based on a qualitative character or molecular marker, resources used for that portion could be used for other progeny. Our objective is to identify such molecular markers for red raspberry and black raspberry. A black raspberry × red raspberry cross was made to develop a map of each parent, and an F2 population was generated to join the maps. Simple sequence repeat (SSR) markers derived from red raspberry and strawberry were used. The level of homozygosity for the red raspberry was 40%, and the level for the black raspberry was 80%. Severe segregation skewing was observed in the F2 generation and indicates problems with transmission. Our findings help quantify the relative levels of homozygosity previously reported for red raspberry and black raspberry. In addition, the severe skewing observed in the F2 generation provides a molecular perspective to the fertility problems previously reported for the black raspberry × red raspberry hybrids (purple raspberry). Since black raspberry is highly homozygous, purple raspberry has transmission and fertility problems, and black raspberry breeders have reported a frustratingly low level of diversity in this subgroup, development of a black raspberry map is expected to require twice the markers as for a red raspberry map, emphasizing the need for a black raspberry sequence from which to develop molecular markers.

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Pedro B. Oliveira, Cristina M. Oliveira, Luís Lopes-da-Fonseca, and António A. Monteiro

The spring shoots of `Autumn Bliss' red raspberry (Rubus idaeus L. var. idaeus; primocane-fruiting type) were cut on 2, 16, 31 July and 15 and 30 Aug. with the objective of delaying fruit harvest into the off-season under mild winter climatic conditions. Cutting shoots in August delayed fruit harvest until February and April of the following year, but shoot growth was weak and fruit yield low (4.8 and 2.1 g/cane). July cuttings delayed harvest until October to January with acceptable fruit yield (63.5, 52.8, and 26.5 g/cane for 2, 16, and 31 July, respectively). The differences in cane height and total node and fruiting node count between the three cutting dates of July were small, but there was a constant decrease in leaf area per cane from the first to the third date and a sharp decrease in fruit yield from the second to the third date. Vegetative shoot growth was less affected than yield when summer cutting was delayed until the end of July to induce a later harvest. Fruit quality always reached acceptable standards. This study confirms the practicability of using summer-cutting of primocane-fruiting red raspberries to induce off-season fruit production under protected cultivation in mild winter climates.

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Chad Finn, Michele Warmund, and Chris Starbuck

The vegetative growth and fruit yield of three types of micropropagated `Redwing' red raspberry (Rubus idaeus L. var. idaeus) nursery stock were compared. The three types of nursery material included: 1) stage IV (S-IV) actively growing plants; 2) dormant-stage IV (DS-IV) plants; and 3) nursery-matured (NM) S-IV plants, grown for 8 to 12 weeks in the field before harvest for cold storage. On 1 Apr. 1991, primocane-fruiting `Redwing' plants of each type were planted 0.6 m apart in ridged, drip-irrigated, and straw-mulched rows spaced 3 m apart in six, three-plant replications. In the establishment year, a small, but commercially viable, crop was harvested from 16 Aug. 1991 to 28 Oct. 1991. The S-IV and NM plants produced greater yields than DS-IV plants in the establishment year. However, by the end of the second year, the S-IV plants had the greatest fruit yield, followed by NM, with the DS-IV plants continuing to have the lowest yield. Fruit size of the S-IV plants was largest in both years. While there were differences in dry weight during the planting year, by the experiment's conclusion, the dry weights were similar among all nursery types. When planting `Redwing', the less-expensive, easier-to-handle, and higher-yielding S-IV plants would be recommended over the other nursery types.

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Michele R. Warmund and James T. English

In 1993, ice-nucleation-active (INA) bacteria were isolated from `Redwing' red raspberries (Rubus idaeus L. var. idaeus) at five pigmentation stages. Fruit were also subjected to thermal analysis to determine the ice nucleation temperatures. INA bacteria were recovered from nearly all fruit samples, and the bacterial populations tended to decrease with greater red color development (i.e., fruit maturation). However, the ice nucleation temperature was not affected by the stage of fruit pigmentation. In 1994, INA bacterial densities were similar among fruit at the three pigmentation stages sampled. INA bacteria were recovered more often from the calyx rather than the drupe surface of these fruit. INA bacteria also were detected on pistils of some fruit. Red and pink fruit, which were nucleated with ice, had greater receptacle injury than mottled, yellow, or green fruit, but INA bacterial densities apparently were not related to injury. Thus, the injury response of fruit at different pigmentation (or development) stages indicated that nonbacterial ice nuclei may be involved in freezing injury of developing raspberries.

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David L. Trinka and Marvin P. Pritts

Micropropagated (MP) raspberries (Rubus idaeus L. var. idaeus) are sensitive to moisture and temperature extremes and to certain preemergent herbicides used at transplanting. We examined fertilizer placement and row covers in conjunction with various weed management strategies to identify beneficial practices for newly planted, MP primocane-fruiting `Heritage' raspberries. Uncontrolled weed growth during plant establishment inhibited raspberry cane growth and production into the second and third growing seasons. Handweeding and herbicide treatments successfully controlled weeds, but soil moisture was apparently insufficient for optimum growth of the MP raspberries when these treatments were imposed, even with normal rainfall in early summer and drip irrigation in late summer. Polyethylene and straw mulches during the establishment year provided both weed control and adequate soil moisture, resulting in more cane growth in the first and 2nd year, and higher yields the 2nd year. Primocane density after the third growing season still was influenced by first-year weed management practices. Raspberry plants responded best to straw mulch without row covers as plant growth was better in both years. Canes were thicker, yields were higher, and a larger portion of the total crop was harvested early. Row covers were beneficial only in bare-soil treatments, and method of fertilizer placement had no effect on any measured variable. Mulching newly transplanted MP raspberries is an alternative to herbicide use that also provides physiological benefits to the plant through microclimate modification.