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M.A.R. Mian, R.M. Skirvin, M.A. Norton and A.G. Otterbacher

To study the causes of low germinability in dried blackberry seeds, seeds harvested from fresh `Thornless Evergreen' (TE) blackberry (Rubus laciniatus Willd.) were either air-dried (12, 24, 36, 48, 60, 72, 96, or 120 hours) or explanted directly onto growth-regulator-free medium after bleach disinfestation. Seeds were either cut in half before explanting or kept intact. None of the intact seeds germinated. Fewer of the halved seeds dried 12 hours or more germinated than control (fresh moist) seeds (42.7% and 54.5%, respectively). Germination decreased to <12% following >48 hours of air-drying. In a separate study, fresh seeds of TE and `Navaho' were either dried as described or held in sealed petri dishes on moist filter paper (moist treatment) for up to 60 hours. After 60 hours, germination of dried seeds of both cultivars had decreased significantly; there was no significant change in germination percentage for moist seeds. Since moist halved seeds germinated well and dried halved seeds did not, the inability of dried blackberry seeds to germinate is due to more factors than just the hard seedcoat typical of the genus.

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Jessica M. Cortell and Bernadine C. Strik

In Spring 1993 and 1994, treatments of 0, 4, 8, and 12 floricanes per plant were established in a mature `Marion' planting. Primocanes were measured weekly for the number and length of primocanes and primocane branches. Maximum hardiness of primocanes was determined in Jan. 1994 and 1995 by controlled freezing. Yield components were measured in both the current and following season. Additional plants were harvested in summer and winter for dry-weight partitioning. Plants with no floricanes had an increased number and length of primocanes and branches than plants with floricanes in 1993, with similar trends in 1994. Primocane growth on plants without floricanes showed a 65% increase in primocane dry weight in 1993. However, in 1994, there were no significant differences among treatments. Primocane branch dry weight generally increased with decreasing floricane number. The relationship between primocane growth and the following season's yield components will be presented.

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Ann Marie Connor, M. Joseph Stephens, Harvey K. Hall and Peter A. Alspach

Variance components and narrow-sense heritabilities were estimated for antioxidant activity (AA), total phenolic content (TPH), and fruit weight in red raspberry (Rubus idaeus L.) fruit from offspring of a factorial mating design. Forty-two full-sib families utilizing seven female and six male parents were evaluated in each of two years in Motueka, New Zealand. In a single year, values within individual half-sib families ranged as widely as 25.3-79.4 μg·g-1 fruit for AA, 205-597 mg/100 g fruit for TPH, and 1.06-7.69 g for fruit weight. Analyses of variance for these three variates demonstrated significant parental source variation in both individual and combined year analyses. For AA and TPH, female parental effects accounted for ≈7% to 19% of total variation, while male effects accounted for ≈6% to 8%. A partially pigment deficient R. parvifolius L. derivative female parent accounted for some of these differences. Female × male parent interaction was not significant for AA and TPH and was marginally significant for fruit weight in combined year analysis. Year had a significant effect on the overall mean AA and TPH, but contributed less than genetic effects to the overall variation in all three traits. Interactions of year with genetic effects were not statistically significant for AA or TPH, indicating that between-year rank or scale changes among families were negligible. The largest proportion of variation was found within rather than among full-sib families. However, variation among plots within full-sib families accounted for 12% to 19% of total variation, indicating environmental differences accounted for some of the observed within-family variation in AA and TPH. Antioxidant activity and TPH were highly phenotypically correlated (r = 0.93); their genetic correlation (r = 0.59) implies that substantial additive genetic factors underlie the phenotypic correlation, but that nonadditive genetic or environmental influences are also important. Both AA and TPH were weakly negatively phenotypically correlated with fruit weight (r = -0.34 and -0.33, respectively), but the corresponding genetic correlations were close to zero. Thus, selection for both high AA or TPH and high fruit weight is possible. Narrow-sense heritability estimates based on variance components from combined year data were h 2 = 0.54, 0.48, and 0.77 for AA, TPH, and fruit weight, respectively. These estimates imply a rapid response to selection is possible.

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Ann Marie Connor, Tony K. McGhie, M. Joseph Stephens, Harvey K. Hall and Peter A. Alspach

We determined variance components and narrow-sense heritability estimates for total and individual anthocyanin (ACY) content and antioxidant activity (AA) in fruit from 411 genotypes in a red raspberry (Rubus idaeus L.) factorial mating design based on 42 full-sib families derived from seven female and six male parents, harvested in 2002 and 2003. Within half-sib family total ACY content ranged from ≈1-60+ mg/100 g fruit in both seasons. The four major ACYs quantified by high-performance liquid chromatography also showed wide ranges each year. Female and male parent contributions to variation in total and individual ACYs were significant (P ≤ 0.001) in combined year analysis, and together accounted for 29% to 48% of the total variation. A substantial proportion of the female contribution was attributed to the use of a pigment-deficient R. parvifolius L. × R. idaeus hybrid derivative as a female parent. Female × male interaction was nonsignificant and contributed negligibly to total variance. Year effects accounted for <2.5% of variation in ACYs and were only marginally significant. Year interactions were negligible. Within family variation (among plots and within plot) accounted for ≈50% of the variation in total ACY and 62% to 69% of the variation in individual ACYs. Combined year narrow-sense heritability estimates were high (h 2 = 0.54-0.90 for individual ACYs, 1.00 for total ACY) among all factorial genotypes, but moderate when the progeny of the R. parvifolius derivative were excluded (h 2 = 0.45-0.78 for individual ACYs, 0.74 for total ACY). The latter estimates are applicable to breeding programs in which pigment-deficient genotypes are rarely or never used in breeding. Parental main effects were significant for AA, together accounting for 19% of total variance; female × male interaction was nonsignificant. Year effects were marginally significant and year interactions nonsignificant; together these sources of variation contributed <2% of total variation in AA. The majority of AA variation was found within- and among-plots within family. The phenotypic correlation between AA and total ACY was r = 0.53, and ranged from r = 0.21-0.46 between AA and individual ACYs; genetic correlations between AA and the ACYs were similar to the phenotypic correlations, suggesting predominantly additive genetic effects accounted for the phenotypic correlations. Linear modelling for AA based on individual ACYs and their interactions explained ≈0.53 of AA variation, substantially less than that explained by total phenolic content (R 2 = 0.88). Our results show substantial variation and moderate to high narrow-sense heritability estimates for red raspberry ACYs, but ACY content and profile information are ineffective proxies and predictors for AA in red raspberry fruit.

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Chad E. Finn, Brian M. Yorgey, Bernadine C. Strik, Robert R. Martin and Michael Qian

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Jose Lopez-Medina, James N. Moore and Kyung-S. Kim

Scanning electron microscopy (SEM) and light microscopy (LM) were used to study the transition of meristems from vegetative to floral phase in erect primocane-fruiting (PF) blackberries [Rubus (Tourn.) L. subgenus Rubus] developed at the Univ. of Arkansas. Dormant root cuttings of A-1836 and APF-13 blackberries were dug from the field and planted on 28 Dec. 1996 and 1 Mar. 1997 to produce plants for use in a greenhouse study. In a field study, terminal buds of field-grown A-1836, APF-13, NC194, and summer-fruiting `Arapaho' were sampled on 21 Mar 1997 (before shoot emergence from soil), and then weekly from 14 to 28 May 1997. Flower bud primordia were first observed at five and six nodes of growth in greenhouse-grown A-1836 and APF-13 plants, respectively, 35 to 42 days after root cuttings were planted (DAP). Under field conditions, floral primordia were not observed until 21 May when A-1836 and APF-13 had at least 20 nodes of growth; NC194 did not differentiate floral structures until 10 July. The developmental patterns of the vegetative apical meristem in the PF selections, both field- and greenhouse-grown plants, were similar to those of `Arapaho'. Opening of the terminal flower of the inflorescence occurred 32 to 35 days after floral initiation in APF-13, and 8 to 10 days later on A-1836. Field-grown NC194 bloomed in late August. The first fruits of greenhouse-grown APF-13 were harvested 120 DAP. These findings demonstrate that PF blackberries form flower buds after a short period of vegetative growth.

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Ellen Thompson, Bernadine C. Strik, Chad E. Finn, Yanyun Zhao and John R. Clark

Primocane-fruiting blackberries (Rubus subgenus Rubus Watson) may offer opportunities for season extension and off-season fruit production, particularly in mild climates with protected culture. In May 2005, plants of ‘Prime-Jan’® were established at the Oregon State University–North Willamette Research and Extension Center, Aurora, OR. Half of the planting was established under a high tunnel and the remainder planted in an adjacent open field. In 2006 to 2007, primocanes were subjected to four treatments to promote branching and/or delay harvest: 1) all primocanes within the plot were cut to the ground when averaging 0.25 m tall, then later emerging canes soft-tipped when reaching 0.5 m tall (C0.25m/T0.5m); 2) all primocanes within the plot were cut to the ground when averaging 0.5 m tall, then later emerging canes soft-tipped when reaching 0.5 m (C0.5m/T0.5m); 3) primocanes double-tipped: all primocanes within the plot were soft-tipped when averaging 0.5 m tall with subsequent lateral branches then soft-tipped when reaching 0.5 m long (T0.5m/Tb0.5m); and 4) primocanes were soft-tipped when averaging 0.5 m tall (T0.5m; control). The tunnel was covered with plastic from 5 Sept. 2006 and 31 Aug. 2007, ≈1 to 2 weeks before harvest until the end of harvest to protect fruit from inclement weather. On average, fruit harvest began on 12 Sept. in the open field and tunnel, but lasted ≈3 weeks longer in the tunnel, ending on 16 Nov., on average. Primocanes that were double-tipped had nearly twice the flowers and fruit than canes that were soft-tipped only once (T0.5m; control). In the tunnel, cumulative yield of double-tipped primocanes averaged 10.7 t·ha−1 in 2006 and 19.3 t·ha−1 in 2007, a 267% and 159% increase compared with the control, respectively. On average, cumulative yield for all treatments was less in the open field than in the tunnel, although cultural systems could not be compared statistically. Harvest was not delayed in the C0.25m/T0.5m treatment in 2006 compared with the control and the double-tipped treatments; however, in 2007, harvest was delayed by 2 weeks in C0.25m/T0.5m. In contrast, harvest was delayed by ≈4 weeks when primocanes were cut to the ground at 0.5 m (C0.5m/T0.5m). Primocanes that were double-tipped produced heavier fruit than other treatments (33% heavier than the control, on average). Double-tipped primocanes did not have more ovules per flower, but had significantly more drupelets set compared with the control. In addition, plants growing under the tunnel tended to produce heavier fruit (32%, on average) than those grown in the open field. Harvest date affected fruit pH in 2006, but not in 2007. In 2006, fruit pH was highest in the early season. All other differences in fruit chemistry were not significant. The pruning and tipping systems used here increased yield and offered options for season extension.

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Jose Lopez-Medina and James N. Moore

Root cuttings of A-1836, APF-13, and NC194 primocane-fruiting (PF) blackberry (Rubus subgenus Rubus) genotypes were dug from the field on 31 July 1997 and stored in plastic bags at 2 °C for 32 days. On 1 Sept. freshly dug root cuttings, along with the cold-treated ones, were planted in pots, which were kept in a lath house for 4 weeks and then moved to a heated greenhouse under natural daylength. Cold-treatment hastened emergence of all genotypes. Transition from vegetative to floral phase was first observed in cold-treated A-1836 and APF-13 at the fifth node, with floral appendages clearly evident in both genotypes at the seventh node 45 days after planting (DAP). Bloom started on 26 Nov. and 5 Dec. 1997 and the first fruits were picked on 10 and 25 Jan. 1998 in cold-treated APF-13 and A-1836, respectively. Plants of cold-treated NC194 and of all non-cold-treated genotypes remained stunted with rosetted leaves, showing no signs of floral initiation until 150 DAP. These findings show that exposure to chilling prior to shoot emergence greatly promotes flowering in PF blackberries, and may have application in greenhouse culture of blackberry.