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Blair J. Sampson, Stephen J. Stringer and Donna A. Marshall

We evaluated relationships between floral traits of 23 genotypes of southern blueberries and indices of pollination efficiency (fruit set, fruit abortion, seed number, and berry size) for Osmia ribifloris Cockerell, a manageable solitary bee. Flower size in Vaccinium and presumably ovary size were proportional to berry size, except for the tiny blooms of one V. tenellum clone (NC7808), which produce large commercial-sized berries of ≈2 g. Longer-styled blueberry flowers visited by O. ribifloris produced the heaviest berries with the most seeds. Osmia ribifloris reliably pollinated ‘Climax’ and ‘Tifblue’ rabbiteye blueberries. However, the peculiarly misshapen blooms of ‘Premier’ rabbiteye blueberry receive less pollination from O. ribifloris and yield berries containing 25% fewer seeds. Fruit set for these misshapen ‘Premier’ flowers was equivalent to that of intact flowers indicating that this floral polymorphism would not greatly alter cultivar performance. For seven Vaccinium species, wild and cultivated alike, 80% to 100% of a plant’s fruit production depends on efficient cross-pollination by bees such as O. ribifloris.

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Stephen J. Stringer, Donna A. Marshall and Dennis J. Gray

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Donna A. Marshall*, Stephen J. Stringer and James M. Spiers

A study was initiated in November, 2002 to determine the effects of exposing two Southern Highbush blueberries (Vaccinium corybosum L) to artificial chilling hours on initiation of bud break and advancement of floral and vegetative bud maturity. Plants of `Jubilee' and `Misty' were divided into 2 groups in which one was left outdoors, allowing chilling to occur and accumulate naturally, while the other group was placed in a growth chamber set at a constant artificial temperature of 4 °C. Five plants of each cultivar were then placed into a heated greenhouse after 0, 200, 400, 600, or 800 hours of chilling (total hours of exposure to <5 °C) had accumulated for forcing of flower bud development. The progression of floral bud development of the terminal three buds on five tagged stems was observed at 7-10 day intervals for 30 days. At the end of the forcing period observations were also made on total percent vegetative and floral bud break. Prior to accumulating sufficient chilling requirements, chilling delivery method did not appear to influence the rate of floral bud development since none advanced past stage 3 regardless of chilling regime used. However after chilling requirements were met, flower buds of plants that were allowed to chill naturally developed more quickly than did those chilled by artificial means.

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Stephen J. Stringer*, Arlen Draper and James M. Spiers

Ornamental blueberries are increasing in popularity in southern landscaping due to their attractive foliage and also since they provide food and serve as attractants to birds and other wildlife. `Native Blue', tested as MS611, resulted from a cross of two native diploid Vaccinium darowii clones, Florida 4B X US 799. US 799 was selected from seedlings grown from open-pollinated seed collected by Dr. Paul Lyrene in Ocala National Forest, Florida. The Cross was made by Dr. Arlen Draper and selected in the greenhouse in 1987. Plants of `Native Blue' are low growing, compact, and finely branched with small, glaucous leaves and are quite typical of V. darowii. In test plots in Mississippi, the plants set many small berries and after four years have have grown to a height of approximately 18 inches. Desireable characteristics include beautiful pastel foliage, hardy and vigorous plants producing much fruit that are attractive to native birds.

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Stephen J. Stringer, Penelope Perkins-Veazie and Donna A. Marshall

The consumption of fresh fruit and vegetables has always been known to provide essential nutrition to mankind and, both anecdotally and clinically, has been linked to the prevention or alleviation of chronic diseases. The muscadine grape, a fruit native to the southeastern U.S., contains numerous phenolic compounds that act as antioxidants and also other compounds, such as resveratrol, that acts as a chemopreventative. The concentrations of these compounds present in the muscadine grape equal or exceed that known for any other small fruit. Fruit of selected muscadine grape genotypes, including breeding lines and cultivars, were evaluated over a 2-year period to assess the existing genetic base for these nutraceutical compounds. Results demonstrated that concentrations of total phenolics, ellagic acid, and resveratrol differ significantly among cultivars and breeding lines. These results suggest that it should be possible to breed for increased concentrations of the health-promoting compounds in muscadine grapes.

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Donna A. Marshall, James M. Spiers and Stephen J. Stringer

To improve the quality of berries during handling and shipping, blueberry breeders have strived to develop a fruit that is firm in texture. However, some previous studies have suggested that blueberry cultivars with firmer fruit were more susceptible to splitting. This study was conducted to further investigate the correlation between splitting susceptibility and fruit firmness. Various cultivars and selections of rabbiteye (Vaccinium ashei) and southern highbush (interspecific hybrids primarily consisting of V. corymbosum) blueberry were used to determine whether berries displaying higher fruit firmness also have a higher incidence of splitting. Three distinctly different measurements of berry firmness were obtained using two instruments: QTS25 and FirmTech2. Berries were subsequently submitted to laboratory procedures to induce splitting. In general, firmness measured as either deformation (FirmTech2) or modulus of elasticity (QTS25) correlated with splitting tendencies. There are exceptions, however, that need to be further examined.

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Stephen J. Stringer, Arlen D. Draper, Donna Marshall-Shaw, Blair J. Sampson and John J. Adamczyk Jr.

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Ebrahiem M. Babiker, Stephen J. Stringer, Hamidou F. Sakhanokho, Barbara J. Smith and James J. Polashock

Species of Botryosphaeria and Neofusicoccum are major pathogens of blueberry worldwide. Accurate identification of these species is essential for developing effective management practices. A multigene sequencing strategy was used to distinguish between six isolates of stem blight pathogens collected from two different regions of the United States. The temperature growth study revealed that the optimal temperature for growth of five of the tested isolates ranged from 25 to 30 °C, although no significant difference was detected for the growth of Neofusicoccum spp. isolate SD16-86 at 20, 25, 30, and 35 °C. In vitro fungicide assays showed four fungicides, cyprodinil + fludioxonil, propiconazole, pyraclostrobin + boscalid, and azoxystrobin, were effective against the tested isolates with isolate SD16-86 being less sensitive compared with the other isolates. In a detached stem assay, none of 39 blueberry accessions displayed immunity or a high level of resistance to the two tested isolates, and no significant difference in lesion length was detected among the seven tested Vaccinium species inoculated with the two isolates.

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Stephen J. Stringer, Arlen D. Draper, James M. Spiers, Donna A. Marshall and Barbara J. Smith

Open access

Ebrahiem M. Babiker, Stephen J. Stringer, Barbara J. Smith and Hamidou F. Sakhanokho

Blueberry leaf rust caused by Thekopsora minima is a serious threat to blueberry production. To investigate the host range and characterize new sources of resistance, 15 southern highbush accessions (Vaccinium corymbosum), two interspecific hybrids (V. elliottii × V. pallidum and V. corymbosum × V. pallidum), and accessions from five diploid Vaccinium species were inoculated with an isolate of T. minima. Of 15, only two southern highbush accessions displayed resistance, whereas both accessions of V. arboreum displayed immunity against T. minima. Accessions of V. darrowii exhibited necrosis but with limited sporulation, indicating a high level of resistance. Sporulating lesions and brown spots were observed in accessions of V. elliottii and V. tenellum. Brown lesions, large pustules, and abundant sporulation were observed on V. pallidum accessions and their interspecific hybrids. As the lesions expanded, defoliation was observed in V. pallidum accessions. When tested against rabbiteye (V. virgatum) and southern highbush blueberries, urediniospores of T. minima from overwintering leaves of V. pallidum were found to be virulent, suggesting that T. minima overwinters on V. pallidum. Based on symptoms and scanning electron microscopy (SEM) of urediniospores, we hypothesize that V. elliottii, V. tenellum, V. pallidum, and V. corymbosum exhibit no host specificity to T. minima.