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Jianying Peng and Peter Hirst

Buds were sampled from nonflowering spurs on 1-year-old wood of 10 apple cultivars during the 2004 growing season and dissected to determine floral commitment and morphogenesis. Dissected buds were classified into five stages based on floral bud morphogenesis. The 10 cultivars differed in their patterns of floral commitment and morphogenesis. At the end of the growing season, the proportion of floral buds was 30% to 100% depending on cultivar. The probability of observing doming, indicating floral commitment, was from 5% to 50% depending on cultivar, with `NJ90' (50%), `Zestar' (30%), and `CQR10T17' (30%) rated among the highest. The lowest probability (5%) was with `Ambrosia', `Pinova', and `Silken'. The time of a peak of floral commitment was earliest in `Delblush' and `CQR10T17' and latest in `Sundance'™ and `Pinova'. Most cultivars exhibited a single peak of floral commitment, except for `Pink Lady' in which two peaks were present. The duration of the process of flower initiation was from 20 to 43 days depending on cultivar. The timing of floral commitment and morphogenesis was not related either to blooming date, or to fruit harvest time of the cultivar.

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Gary J. Keever and J. Raymond Kessler Jr.

In previous studies, night-interrupted lighting (NIL) promoted earlier flowering of summer-blooming herbaceous perennials grown under outdoor nursery conditions in the southeastern U.S. However, NIL promoted excessive plant height, thus reducing product quality. Our objective was to control plant height of Coreopsis grandiflora `Early Sunrise' (ES) and Rudbeckia fulgida `Goldsturm' (RG) grown under NIL with plant growth retardants (PGR) without offsetting earlier flowering promoted by NIL. Treatments under NIL were three rates of daminozide, daminozide plus chloromequat, flurprimidol, uniconazole, and NIL and natural controls. Plant height was reduced 3% to 38% in ES and 8% to 31% in RG and time to visible bud was unchanged by all PGR treatments compared to the NIL control. Time to visible bud was unchanged in RG by all PGR treatments and flurprimidol in ES, but the remaining PGR treatments increased time to visible bud compared to the NIL control in ES. Only ES plants treated with daminozide and daminozide plus chloromequat at the two highest rates and all rates of uniconazole were similar in height to the natural control. RG plant heights with the two highest rates of flurprimidol and uniconazole and the highest rate of daminozide plus chloromequat were less than the natural control; heights of plants in the remaining PGR treatments were similar to the natural control. Quality rating was unchanged in RG but was increased in ES by all PGR treatments compared to the NIL control.

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Ioannis C. Porlingis and Demetrios G. Voyiatzis

Anthesis of an important staminate pistachio (Pistacia vera L.) cultivar (B) in Greece was delayed by foliar paclobutrazol (PBZ) sprays applied in June or July the previous season. A September spray was ineffective. The amount of delay depended on dose (50 to 1000 mg PBZ/liter applied to incipient runoff). Using the same total amount of chemical, one spray was as effective as two sprays 1 month apart. There were no effects on inflorescence fresh weight, pollen production, and pollen germination. Stem elongation was inhibited strongly, but the number of nodes and flower buds per shoot was reduced only slightly. In Expt. 2, two other staminate cultivars (A and C) responded similarly to cultivar B. Treatment effects appeared only during the treatment year, whereas a soil drench was effective for 2 years. PBZ may be able to synchronize the blooming of staminate and distillate pistachio cultivars and result in good fruit set without artificial pollination. Chemical name used: B[(4-chlorophenyl)methyl] -α-(1,1 dimethylethyl)-l H -1,2,4-triazole-l-ethanol (paclobutrazol).

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James R. Ballington and Susan D. Rooks

Three rabbiteye blueberry selections, NC 1550, NC 1877, and NC 2305, will be released by the North Carolina Agricultural Research Service in Spring 1997. All three selections are self-fruitful, with fruit as large or larger than Tifblue, with good picking scars, aromatic flavor, and resistance to fruit cracking. NC 1877 is early-blooming and ripens a few days later than Premier, with similar color, firmness, and quality. Plants of NC 1877 are semi-upright and of only moderate vigor. Both NC 1877 and NC 1550 are resistant to the sharpnosed leafhopper which transmits blueberry stunt. NC 1550 blooms with or slightly later than Tifblue and is outstanding for consistent productivity, particularly on spring frost—prone sites. It ripens in early midseason to midseason, usually a few days ahead of Tifblue. Stemming was a problem in one year on overcropped plants. NC 1550 and NC 2305 have average to above color, and fruit firmness equal to Tifblue. NC 2305 blooms and ripens with Tifblue in most years. Fruit quality is at least equal to Premier and it fruits primarily on the tips of the branches. The names of these selections are Ira' (NC 1550), 'Montgomery' (NC 1877), and 'Yadkin' (NC 2305).

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Arlen D. Draper

The USDA blueberry breeding program was initiated in 1910 by Dr. F.V. Coville and has been continuous since that time. Plant breeders Drs. G.M. Darrow, D.H. Scott, J.N. Moore, and A.D. Draper have worked with SAES and private growers to develop the majority of cultivars presently grown for commercial production. In the South, major cooperators with the USDA include SAES in Arkansas, North Carolina, Georgia, and Texas. Recently the USDA Station at Poplarville MS, has been instrumental in blueberry cultivar development for the South. Rabbiteye blueberry cultivars make up the majority of blueberry acreage grown in the region. A new type of blueberry, the southern highbush (SHB), has been developed by interspecific hybridization with various Vaccinium species. Late-blooming SHB cultivars have been developed that offer better protection from spring frosts and ripen earlier than the earliest rabbiteye blueberry. Genes required to meet future needs reside within native Vaccinium species. Progress has been made in plant adaptation, disease resistance, fruit quality, and season of ripening. There remains a need for greater plant vigor, insect resistance, and consistent production.

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S. Pérez-González

The variability of species under local ecosystems, particularly in response to temperatures during endodormancy, permits adaptation of temperate fruit trees to subtropical climates. Information about the behavior of endodormant fruit trees and seeds is based on a narrow genetic base from higher latitudes. This work was conducted to generate information about responses of endodormant seeds from several subtropical peach (Prunus persica L.) genotypes, as a basis for breeding and selection in these regions. Samples of peach seeds were collected from genotypes originating at a range of altitudes in tropical-subtropical regions to evaluate their responses to different temperatures and lengths of stratification periods. When seeds were stratified at 7 °C, some genotypes with very low-chilling requirement registered a high percent germination in <40 days, and all accessions studied reached 95% germination before day 80. When seeds were stratified at warmer temperatures (10 and 14 °C), germination started earlier and was high at 10 °C for most accessions. Although seeds of some late-blooming accessions germinated earlier at 10 or 14 °C than at 7 °C, percent germination was lower and time-response curves were flatter. This contrasts with previous reports on genotypes with high-chilling requirement, where no germination was registered at 14 °C. These observations provide a background for screening seedlings for adaptation to local conditions, and suggest that endodormancy models should be based on information generated from local genotypes when applied in subtropical regions.

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Dan Ga'ash, Israel David, and Malka Cohen

Blossom thinning trials with AKZO Co. surfactant Armothin were carried out on fruitful peach cultivars Early Grande and Babcock during 1993–94. Effective thinning occurred before “full bloom” (40% to 90% FB) at 3% Armothin, increasing between 2% and 4%. However, an improved fruit distribution of `Early Grande' was achieved by repeated application (35% + 75% FB) at 2%. A second spray at 3%, just after FB, thinned some late-blooming flowers on `Babcock' trees, but a temporary leach scorch occurred, as well as with 4% Armothin (single spray) on both cultivars. For a single spray, the optimal stage was found within 60% to 90% FB, at 3% Armothin. Flower biology studies showed susceptibility of the petals to increasing Armothin concentrations at all stages, but pollen tube penetration into the pistils and subsequent fertilization failed only after an earlier application, before anthesis or pollination of the stigma. Within this range of concentration and timing, no damage occurred to the vital fruit set and to commercial yield, provided that weather conditions were favorable during bloom (and spray). Some corrective hand-thinning (20% to 60%) should be applied to the fruitful trees 3 to 4 weeks later to achieve optimal fruit size at harvest. Blossom hand-thinning is still practical in Israel.

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Gregory L. Reighard and Terry Guinn

An Asian pcar variety trial planted in 1989 near Columbia, South Carolina was evaluated for growth, productivity, and disease resistance for 4 years. A total of 13 cultivars were observed. The Chinese types Ya Li and Shin Li reached full bloom in mid-March 2 weeks before the Japanese types. The latest blooming cultivars were Choju and Twentieth Century. Shinsei, Shin Li, and Ya Li were the most vigorous cultivars, whereas Niitaka, Shinko, and Shinsui were the least vigorous. Most cultivars produced suckers on the Betulaefolia rootstock; however, few suckers were observed for Chojuro, Shinseiki, Shinko, and Ya Li. Fruit production began in the third year, and after the fourth year Shinseiki, Twentieth Century, Choju, Shinko, and Kosui were the most productive cultivars (8.1-18.2 kg/tree). Chinese types were not precocious but did produce the largest fruit (203-270 g). Choju ripened the earliest (early July), and the Chinese types ripened the latest (late August). Fireblight had infected few trees after 4 years and still was not a problem at this location.

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

Floral initiation (FI) was studied both in greenhouse- and field-grown plants of primocane-fruiting (PF) blackberries recently developed by the Univ. of Arkansas. Root cuttings of A-1836 and APF-13 were dug from the field and planted in a greenhouse on 1 Mar. 1997. NC 194 was included only in the field study. Terminal apices were sampled weekly starting at 0 (just before emergence) nodes of growth on 21 Mar. Floral primordia were first seen at five and six nodes of growth in greenhouse-grown A-1836 and APF-13, respectively, 35-42 days after root cuttings were planted (DAP). Under field conditions, the same event was not observed until 21 May when A-1836 and APF-13 reached at least 20 nodes; NC 194 did not show evidence of floral parts until 10 July. Once FI occurred, floral differentiation proceeded uninterrupted until completion. Blooming occurred 32-35 and 40-45 days after FI in APF-13 and A-1836, respectively; NC 194 bloomed in late August. The first fruits of APF-13 were harvested 120 DAP. These findings demonstrate that PF blackberries form flower buds soon after a short period of vegetative growth. This information should be useful for implementing horticultural practices, such as programming of the harvest date.

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Randy R. Lee, John K. Fellman, and Esmaeil Fallahi

The influence of flower bud position on bloom, fruit quality, and fruit maturity was investigated on `Rome Beauty' apple (Malus domestica Borkh.). Limbs on trees containing spur terminal flower buds and lateral flower buds were tagged and the number of blossoms counted every three days until bloom ended. At harvest, fruit from each bud type were selected and seed number, fresh weight, fruit quality characteristics, and onset of ethylene production were measured. Spur terminal flower buds began blooming earlier, blossomed for a longer period of time, and produced more blossoms than lateral flower buds. Fruit from spur terminal flower buds had more seeds, were heavier, and contained more starch than lateral bud fruit. Lateral bud fruit had higher pressure values, due to smaller size, and higher soluble solids, due to consumption of starch reserves. Fruit color and titratable acidity were not significantly different regardless of bud position. Spur terminal fruit started producing ethylene eight days later than lateral bud fruit, indicating they were maturing less quickly. Cultivars such as `Fuji', `Gala', and `Braeburn' display similar growth and fruiting habits.