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  • Author or Editor: Gregory A. Lang x
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Pollen from six southern highbush blueberry cultivars derived from Vaccinium corymbosum L. and one or more other species (V. darrowi Camp, V. ashei Reade, and V. angustifolium Aiton) was incubated on nutrient agar to determine tetrad viability, pollen tube growth rates, and incidence of multiple pollen tube germinations. `Avonblue' pollen had a significantly lower tetrad germination percentage than `Georgiagem', `Flordablue', `Sharpblue', `Gulfcoast', or `O'Neal', all of which had >90% viable tetrads. The in vitro growth rate of `O'Neal' pollen tubes was significantly higher than the growth rates of `Sharpblue' and `Georgiagem pollen tubes. Of those tetrads that were viable, more than two pollen tubes germinated from 83% and 91% of the `Gulfcoast' and `Sharpblue' tetrads, respectively, while only 11% of the `Flordablue' tetrads produced more than two pollen tubes. The total number of pollen tubes germinated per 100 tetrads ranged from 157 (`Flordablue') to 324 (`Sharpblue'), resulting in actual pollen grain viabilities ranging from 39% to 81%. Genetic differences in pollen vigor, as indicated by pollen viability, pollen tube growth rates, and multiple pollen tube germinations, may influence blueberry growers' success in optimizing the beneficial effects of cross-pollination on fruit development.

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Southern highbush (“low chill tetraploid”) blueberries are an earlier-ripening, self pollen-compatible alternative to rabbiteye blueberries. `Sharpblue', the first southern highbush cultivar planted on a commercial scale, has been shown to require cross-pollination for optimal fruit size and earliness of ripening. `Gulfcoast', a recently released cultivar for Gulf states growers of about latitude 30 to 32 N, differs in heritage from `Sharpblue', incorporating about 50% more self-compatible northern highbush germplasm. `Gulfcoast' fruit development after honey bee-mediated self- or cross-pollination with `Sharpblue' was similar in terms of set (85.5 vs. 82.2%), weight (1.26 vs. 1.18g), and seed number (32.8 vs. 33.6), respectively. Cross-pollination did not result in significantly earlier ripening. Thus, `Gulfcoast' appears to be more self-fertile than `Sharpblue'. Other closely-related cultivars are being examined to determine the genetic influence on potential for self-fruitfulness.

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To initiate photosynthetic studies of sweet cherry (Prunus avium L.) canopy architectures and cropping management under high light and temperature conditions (Yakima Valley, Wash.), we developed a whole-canopy research cuvette system with a variable airflow plenum that allowed different patterns of air delivery (in concentric circles around the trunk) into the cuvette. Air and leaf temperatures (Tair and Tleaf, respectively) were determined at four horizontal planes and four directional quadrants inside cuvette-enclosed canopies trained to a multiple leader/open-bush or a multiple leader/trellised palmette architecture. Air flow rate, air delivery pattern, and canopy architecture each influenced the whole-canopy temperature profile and net CO2 exchange rate (NCER) estimates based on CO2 differentials (inlet-outlet). In general, Tair and Tleaf were warmer (≈0 to 4 °C) in the palmette canopy and were negatively correlated with flow rate. The response of Tair and Tleaf to flow rate varied with canopy position and air delivery pattern. At a flow of 40 kL·min-1 (≈2 cuvette volume exchanges/min), mean Tair and Tleaf values were 2 to 3 °C warmer than ambient air temperature, and CO2 differentials were 15-20 μL·L-1. Tair and Tleaf were warmer than those in unenclosed canopies and increased with height in the canopy. Carbon differentials declined with increasing flow rate, and were greater in the palmette canopy and with a less dispersed (centralized) delivery. Dispersing inlet air delivery produced more consistent values of Tair and Tleaf in different canopy architectures. Such systematic factors must be taken into account when designing studies to compare the effects of tree architecture on whole-canopy photosynthesis.

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Most sweet cherry (Prunus avium L.) cultivars grown commercially in the United States are susceptible to powdery mildew, caused by the fungus Podosphaera clandestina (Wall.:Fr.) Lev. Recently, hybrid populations segregating for resistance to powdery mildew were developed by crossing a mildew-resistant sweet cherry selection, PMR-1, with the susceptible cultivars Bing, Rainier, and Van. Although segregation within these populations indicated a single gene was responsible for the powdery mildew resistance conferred by PMR-1, the gene action could not be determined. Therefore, a reciprocal cross between `Bing' and `Van' was made to determine the allelic state of the susceptible parents used previously. All progeny (n = 286) from this cross were susceptible to powdery mildew. This information, combined with results from previous segregation data, indicate the powdery mildew resistance gene is inherited in a dominant manner and is present in PMR-1 in the heterozygous allelic state. We have named this gene Pmr1. Furthermore, in combination with known pedigree information, we have been able to predict the susceptibility of more than 60 additional commercial and recently released sweet cherry cultivars.

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Five-year-old `Sharpblue' southern highbush (Vaccinium corymbosum) plants were self- and cross-pollinated (`O'Neal') to study peroxidase activities and isozyme patterns during fruit development. Both soluble and bound peroxidase activities were present throughout development. Activities were very high during early fruit development, with peaks at 10 and 20 days after self- and cross-pollination, respectively. Activity was much higher for cross-pollinations. During rapid fruit development, peroxidase activities were low. During ripening, the activity of soluble peroxidases increased, then declined in both treatments. Bound peroxidase activity increased during the color transition from blue to dark blue, with the increase being much greater in self-pollinated fruits. Banding patterns of both soluble and bound isoperoxidases varied by pollination treatment as well as fruit developmental stage. Pollen sources alter peroxidase isozymes and activities in developing fruits. During fruit ripening, soluble peroxidase activity appears to be associate with the color transition from light blue to blue, while bound peroxidase activity appears to be associated with the color transition from blue to dark blue.

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`Gulfcoast' southern highbush blueberry (Vaccinium corymbosum × V. darrowi) plants were placed in 3 × 6 × 2.5 m net cages with one colony of honey bees per cage and one of three pollinizer treatments: “self (other `Gulfcoast' plants), “cross/highbush” (other southern highbush cultivars), or “cross/rabbiteye” (various rabbiteye blueberry cultivars). In addition to unlimited pollination, bee foraging was controlled on individual flowers by placing small bags over corollas after 0, 1, 5, or 10 visits. Fruit set, fruit weight, fruit development period, and seed number data were taken, as well as data to relate floral morphology to duration of bee foraging. All measures of fruiting increased significantly with increased bee visitation; the threshold for significant gains in production occurred between 1 and 5 visits. Ten visits generally provided a good approximation of unlimited pollination. Set, weight, and earliness of ripening was as good, or better, for fruit derived from rabbiteye pollen compared to fruit from self- or cross/highbush-pollination.

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We have previously demonstrated that a protein of ∼62 kD decreases in response to temperature during the final stages of chilling unit accumulation in dormant peach flower buds (Lang and Tao, 1991, HortSci. 26:733). To further examine proteins that potentially may be associated with endodormancy, floral buds, spurs, and/or shoots were collected during winter from `Anna' apple, various blueberry cultivars, `MidSouth' grape, `20th Century' pear, `Hawthorne' peach, and `Santa Rosa' plum. Soluble proteins were extracted and analyzed by one-dimensional SDS-PAGE. A major protein of ∼62 kD was present in plum, and lesser amounts of one or two similar proteins were found in blueberry, but not in apple or grape. The 62 kD peach protein originally found in buds was also present, in lesser proportions, in peach shoot xylem and phloem tissues, but not in petioles or seeds. Apple exhibited a major protein band at ca. 31 kD that may be a storage protein. The similarities and disparities in protein profiles between fruit crops, as well as changes that occur during winter, will be discussed with respect to dormancy, cold hardiness, and storage compounds.

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Fall application of 2-chloroethylphosphoric acid (ethephon) is known to delay spring budbreak in peach (Prunus persica). To study seasonal variation in peach response to dormancy-breaking plant bioregulators and their possible interaction with ethylene, peach shoots were cut in the field at various intervals during endodormancy. Shoots were dipped in the dormancy-breaking bioregulators hydrogen cyanamide (H2CN2, 100 mM) or gibberellic acid (KGA3, 130 μm), alone or in combination with 1.38 mM ethephon. Treated shoots were held in beakers of either tap water or 1 mM silver thiosulfate (STS), and placed in growth chambers with potassium permanganate traps, 12/12 h photoperiods and 21/26 C temperature regimes. Dormancy-breaking efficacy (apical budbreak at 21 days) of both bioregulators increased as endodormancy progressed. At all intervals, H2CN2, broke dormancy more effectively than KGA3. The addition of ethephon to H2CN2 application prior to any CU accumulation (20 Oct) had no effect on efficacy (80% budbreak), but its addition after accumulation of ∼50 CU (8 Nov) or ∼320 CU (14 Dec) reduced subsequent budbreak to 25% and 40%, respectively. The addition of ethephon to KGA3 applications reduced budbreak both prior to (27 Oct) and after (8 Nov) initial CU accumulation. STS in the beaker solution increased both the extent (27 Oct) and the rate (14 Dec) of KGA-induced budbreak The interaction of ethylene, bioregulator type, and endodormancy regulation will be discussed.

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To study the effects of pollen sources on ovule and berry development in southern highbush blueberries (Vaccinium corymbosum hybrids), 5-year-old `Sharpblue' plants were moved into a greenhouse for self- and cross-pollination experiments. Cross-pollination with `Gulfcoast' and `O'Neal' as pollen sources increased fruit weight by 58.2% and 54.9%, respectively, compared to self-pollination. Cross-pollination did not affect the number of total and small ovules significantly but did double the number of fully developed ovules and increase the average ovule size by 14%. The increase in number and size of fully developed ovules correlated with the significant difference in berry fresh weight between self- and cross-pollination. Cross- and self-pollination showed good correlations between fruit fresh weight and number or cross-sectional area of fully developed ovules. There was a poor correlation between fruit fresh weight and the number or cross-sectional area of partially developed ovules. This study provides further evidence that berry size in southern highbush is influenced strongly by the development of fully developed ovules.

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Plant dormancy research has long been stifled by the lack of appropriate biochemical markers to characterize the changing physiological status of dormant vegetative or reproductive buds. Two sets of experiments were conducted in an attempt to identify changes in soluble protein profiles during endodormancy of peach and blueberry reproductive apices. Bud samples from the peach cultivars `La Festival' (low chilling requirement) and `La White' (moderate chilling requirement) were taken every 15 days in the orchard during December and January, extracted for soluble proteins, and analyzed by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Outshoots were forced at 25C in a growth chamber to determine the intensity of endodormancy. A further experiment utilized potted `Bluechip' and `Meader' (troth high chilling requirement) blueberry plants given varying periods of cold (4.5C) chamber treatment, followed by forcing at 25C in a growth chamber. Bud samples were taken following cold treatment for extraction and SDS-PAGE. The relationship of the resulting protein profiles to chilling unit accumulation and intensity of endodormancy will be discussed.

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