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P. Perkins-Veazie, J.K. Collins, and J.R Clark

Measurement of firmness of blackberries is challenging because of their nonspherical shape, large pyrenes, and mixture of receptacle and epidermal tissues. Firmness at harvest is important to minimize damage from finger compression and after harvest, as fruit that soften during storage often have more decay and leakiness than firmer fruit. We have done subjective ratings over the last 4 years using a scale of 1 (firm) to 5 (mush) and find that discerning between ratings of 2 and 3 is the most difficult subjective decision. We have used a hand-held penetrometer adapted with an insect pin to measure epidermal thickness and receptacle firmness after storage, but correlation with subjective ratings has been unsatisfactory. We have also measured whole fruit compression using a Texture Technologies ® TA2 texture analyzer that collects 500 data points per second. While this works well with fruit subjectively rated 1 to 3, it cannot measure soft fruit rated 4 and 5. However, both puncture and compression tests have successfully quantified firmness loss with ripening.

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John R. Clark

‘Prime-Ark ® Freedom’ (to be U.S. plant-patented as ‘APF-153T’) is the world’s first commercially released thornless primocane-fruiting blackberry ( Rubus L. subgenus Rubus Watson). This novel development is intended primarily as a home garden

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P. Perkins-Veazie, J.K. Collins, E. Baldwin, and Fumi Takeda

Erect-fruited blackberries are often described as having a wild blackberry flavor. Flavor can be greatly affected by sugar and volatile composition, neither of which is known for erect-fruited blackberries. This study was done to characterize changes in sugar and volatile composition in ripening blackberries. Blackberries of `Navaho', `Arapaho', `Shawnee', and `Choctaw' were harvested at red, mottled, shiny, and dull black ripeness stages. Sucrose was found in small amounts (4% to 15%) in all stages of ripeness in all cultivars. Total sugars increased from ≈20–30 to 60–80 mg/g dry weight as fruit ripened from red to dull black. Fructose and glucose maintained a constant 1:1 ratio with ripeness stage and cultivar. Three of the four cultivars had a linear increase in total sugars with ripening; total sugars increased 4% to 40% as fruit ripened from shiny to dull black. Twenty to 25 volatile peaks were found by headspace gas chromatography in ripening blackberries. Six volatiles, tentatively identified as α-pinene, eugenol, limonene, p-cymene, α-terpinol, and gernaylacetone, appeared in all cultivars, but only in ripe (shiny and dull black) fruit. Few volatile peaks were observed in red (unripe) fruit. Data indicate that blackberries continue to increase in sugars in the latter stages of ripeness and that volatiles unique to ripe blackberries are produced during this period.

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F. Takeda, B. C. Strik, and J. R. Clark

Western trailing blackberries (e.g., `Boysen' and `Marion') are grown in Oregon. USDA-released semi-erect thornless blackberries (e.g., `Chester Thornless') and erect, thorny blackberries (e.g., `Cherokee') from Arkansas are grown across the United States from the mid-Atlantic coast region to Oregon. Flower bud development in several blackberry cultivars growing at three sites (Arkansas, Oregon, and West Virginia) was studied. In buds of `Boysen' and `Marion' blackberries from Oregon, sepal primordia were first observed in September and November, respectively. Further floral bud development continued into January. Sepal development in `Cherokee' buds occurred in November in Oregon and in December in Arkansas. At all subsequent sampling dates, the development was more advanced in Oregon than in Arkansas. Buds of `Chester Thornless' blackberry from all three sites remained undifferentiated until spring. Preliminary findings indicated that the time of flower bud initiation varied considerably among the cultivars examined. The results suggest that floral bud development in blackberry, once initiated, is continuous, but periods of low temperature can arrest bud development.

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Richard C. Funt, Henry M. Bartholomew, Mark C. Schmittgen, and John C. Golden

Annual yields of thornless blackberries may be inconsistent due to low winter or early spring temperatures. Under ideal conditions thornless blackberries can produce two or three times more berries per acre and ripen over a longer period of time than the erect, thorny type.

Yields of several thornless blackberry cultivars were improved by using straw mulch. In experiment one standard cultivars were compared to numbered clones. In experiment two Chester, Black Satin, Dirksen and C-65 were compared. Over a six year period, straw increased yields from 1670 to 8300 pounds per acre. Straw mulch appeared to be effective during years where low temperatures did not affect bearing surface.

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Penelope Perkins-Veazie and John R. Clark

The postharvest life of blackberries is shortened by decay, leakage, and softness. Shelf life is shortened after periods of rainfall, and often fruit that appear firm in the field soften rapidly in storage. Blackberry selections of interest for advanced selections from plants without fungicide application are routinely screened for shelf life at Lane by storing fruit at 5 °C for seven days. Blackberry varieties are increasingly being used for farmer's markets, national, and international markets. A rapid test to gauge shelf life of blackberry varieties new to growers would be useful in determining the best type of marketing. Ripe blackberries were harvested from Clarksville, Ark., and transported in 260 g plastic clamshells on ice (about 5 °C) to Lane, Okla. Berries were weighed upon arrival and placed at 5 or at 20 °C for 7 and 2 days, respectively. Overall ratings were considerably worse at 20 °C compared to 5 °C, often with decay on all fruit in clamshells held at 20 °C. Separate subsamples of berries, placed individually in egg cartons and held over water at 20 °C (a 99% relative humidity) yielded Rhizopus, Collectotricum, and Botrytis cinerea growth after 24 hours. Because 2 days at 20 °C proved to cause decay in blackberries too quickly, fruit will be held for 1 day at 20 °C in the next season.

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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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Mark M. Bray, John R. Clark, and Rose C. Gergerich

Latent infection of Blackberry yellow-vein associated virus (BYVaV) in `Chickasaw' blackberry has been reported. However, plants with characteristic leaf symptoms, such as vein yellowing, chlorotic mottling, and oak-leaf patterns, have tested positive for BYVaV using reverse-transcription polymerase chain reaction. Experiments were initiated to determine if the symptoms expressed in BYVaV infected `Chickasaw' were caused by mixed virus infections. BYVaV, a recently identified crinivirus, was evaluated for synergistic interactions with Tobacco ringspot virus (TRSV), Tomato ringspot virus (ToRSV), and Raspberry bushy dwarf virus (RBDV). `Chickasaw' blackberry plants infected with BYVaV (single infection) were used as receptor plants to establish mixed virus infections with TRSV and ToRSV transmitted by nematodes and RBDV transmitted by bottle grafts. Characteristic symptoms of multi-virus infection will be presented and discussed.

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Stanta Cotner, John R. Clark, and Eric T. Stafne

A study was conducted in the Winter–Spring 2004 to evaluate the effects of seed (pyrene) scarification period on blackberry (Rubus L. subgenus Rubus) genotypes that had a range of seed weights. The study was done in an attempt to identify optimum scarification period for variable seed weights for the purpose of increasing germination of blackberry seeds produced from hybridizations in the Arkansas blackberry breeding program. Scarification treatments of 1, 2, or 3 hours were used on 14 genotypes. Seeds were then stratified for 3.5 months and sowed on a commercial potting medium in a heated greenhouse. Germinating seedlings were counted over a 15-week period and total germination determined. Data analysis indicated significant genotype effect on germination but no scarification treatment nor genotype × scarification treatment interaction significance. The results indicated that scarification period did not affect germination and varying this period predicated on seed weight was not beneficial based on the genotypes used in the study.

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J.N. Moore, John R. Clark, and Justin R. Morris

The impending release of a new blackberry cultivar and a new grape cultivar by the University of Arkansas Agricultural Experiment station will be discussed. The blackberry, tested as A-1536, is an erect, thornless type ripening two weeks before 'Navaho'. It produces very firm, highly flavored fruit similar to 'Navaho'. The grape, tested as A-1335, is a blue-seeded juice grape with good adaptation to areas with high summer temperatures where 'Concord' does not ripen evenly. Fresh fruit and processed juice quality has been rated equal to or better than 'Concord' juice for quality attributes.