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  • Author or Editor: Thomas Gianfagna x
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Fall-applied ethephon (100 ppm) delayed bloom by 6 days the following spring in peach [Prunis persica (L.) Batsch]. Whitewashing entire trees in January added 1 to 2 additional days of bloom delay to that provided by ethephon. Whitewashing delayed pistil elongation in quiescent buds from control trees, but did not significantly delay pistil elongation in buds from trees treated with ethephon. Pistils from ethephon-treated trees were significantly smaller than those from control trees from just before bud swell through bloom. Flower bud survival after freezes during bloom was enhanced for whitewashed compared to control buds as measured by fruit set. Chemical name used: 2-chloroethylphosphonic acid (ethephon).

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Growth and flowering of Freesia hybrida Bailey for the container-plant market can be controlled chemically using growth retardants and environmentally by cold storage of corms at 5C for 2 to 6 weeks before planting. Corms stored at 5C for 4 weeks flowered 20 days earlier than corms not stored at 5C. Preplant 5C storage of corms also reduced leaf and flower height. An ancymidol soil drench (3 mg) reduced leaf height and flower height by more than 50% and delayed flowering by 9 days. Combining growth regulator application with cold storage of corms produced the greatest reduction in leaf height and flower height. Moreover, plants flowered earlier than controls when corms were stored for at least 4 weeks, regardless of growth regulator treatment. Chemical name used: α-cyclopropyl-α- (4-methoxyphenyl) -5-pyrimidine methanol (ancymidol).

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Six-year-old peach trees [Prunus persica (L.) Batsch] were sprayed with ethephon (100 mg·liter–1) in Oct. 1989, whitewashed in Jan. 1990, and sprayed with dormant oil on one or two dates in Mar. 1990 to study possible interactive effects on flower bud hardiness, pistil growth, time of bloom, and yield. Flower buds from ethephon-treated trees supercooled to a lower temperature [mean low temperature exotherm (MLTE) of –18.5C] than buds from nontreated trees (MLTE of –17.7C) in February; there was no main effect of whitewashing or any interaction with ethephon. No treatment effects on hardiness were detected in March. Ethephon-treated pistils were smaller than nontreated pistils, and pistils from buds on whitewashed trees were smaller than those on nonwhitewashed trees. No main effects or interactions of dormant oil on pistil size were detected. Ethephon and whitewashing delayed bud development during bloom, but prebloom oil application(s) had no effect. Buds from ethephon-treated and whitewashed trees were more tolerant of freezes during bloom than buds from oil-sprayed trees, and yield was enhanced by ethephon and whitewashing. Prebloom oil sprays reduced yield compared with controls. Chemical name used: 2-chloroethylphosphonic acid (ethephon).

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Peach (Prunus persica (L.) Batsch cv Jerseydawn and Jerseyglo) flower bud hardiness was studied using exotherm analysis following application of ethephon ((2-chloroethyl) phosphoric acid, 0.7mM) in October. Rehardening varied with temperature (7 or 21C), cultivar, ethephon treatment, and sampling date. Buds were more susceptible to injury in March compared to January or February. Buds rehardened more rapidly at 21C than at 7C. `Jerseyglo' rehardened more rapidly than `Jerseydawn'. Untreated buds were less hardy and also rehardened more rapidly than treated buds. Ethephon enhanced flower bud hardiness by (1) decreasing the mean low temperature exotherm of pistils, (2) increasing the number of buds which supercooled after rehardening, and (3) it decreased the rate of rehardening.

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The heat requirement for flower bud growth of container-grown peach trees [Prunus persica (L.) Batsch. cvs. Redhaven and Springold] in the greenhouse varied inversely and linearly with the length of the cold-storage period (SC) provided to break bud dormancy. Ethephon reduced the rest-breaking effectiveness of the 5C treatment. Buds from ethephon-treated trees grew more slowly than buds from untreated trees upon exposure to 20 to 25C, resulting in later bloom dates. The effect of ethephon on flower bud hardiness in field-grown trees of `Jerseydawn' and `Jerseyglo' was studied using exotherm analysis after deacclimation treatments. Bud deacclimation varied with reacclimating temperature (7 or 21 C), cultivar, ethephon treatment, and sampling date. All buds were more susceptible to injury in March than in January or February. Buds reacclimated more rapidly at 21C than at 7C. `Jerseyglo' reacclimated more rapidly than `Jerseydawn'. Untreated buds were less hardy and also reacclimated more rapidly than treated buds. Ethephon enhanced flower bud hardiness in three distinct ways: 1) it decreased the mean low-temperature exotherm of pistils, 2) it increased the number of buds that supercooled after exposure to reacclimating temperatures, and 3) it decreased the rate of deacclimation, especially at 21C. Ethephon prolongs flower bud dormancy by increasing the chilling requirement. The rate at which flower buds become increasingly sensitive to moderate temperatures in late winter and spring is thus reduced by ethephon. Thus, ethephon delays deacclimation during winter and delays bloom in the spring. Chemical name used: (2-chloroethyl) phosphoric acid (ethephon).

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Flower bud growth and carbohydrate content of pistils of two peach cultivars [Prunus persica (L.) Batsch. cvs. Jerseydawn and Jerseyglo] was studied during controlled postrest deacclimation in February and March at 7 and 21C following an application of ethephon (100 mg·liter-1, in October. Ethephon-treated pistils contained more sorbitol and sucrose than untreated pistils, and levels of both sugars decreased during deacclimation. Sorbitol content decreased more rapidly at 21C than at 7C in February, but no difference was detected in March. Fructose content increased during deacclimation in February and was not affected by cultivar, ethephon treatment, or deacclimation temperature. In March, fructose increased in untreated `Jerseydawn' pistils during deacclimation, but not in ethephontreated pistils. In `Jerseyglo', fructose was detected in all samples and declined during deacclimation. Glucose was not detected in treated pistils in February. In untreated pistils, glucose increased during deacclimation. In March, glucose was not detected in `Jerseydawn' pistils reacclimated at 7C. At 21C, glucose was detected only in untreated pistils after 2, 3, or 4 days of deacclimation. In `Jerseyglo', glucose was detected in all pistils. Moisture content of ethephon-treated pistils was lower than untreated pistils in both February and March. Pistil moisture content during deacclimation increased more slowly in ethephon-treated pistils than in untreated pistils in February, but not in March. Pistils sampled in March had a lower moisture content when reacclimated at 7C than at 21C. Pistil growth at 21C was slower in ethephon-treated buds than in untreated buds, but no difference was detected at 7C. The effects of a fall application of ethephon on the carbohydrate content of flower buds in relation to both winter deacclimation and growth in the spring are discussed. Chemical names used: (2-chloroethyl) phosphoric acid (ethephon).

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Abstract

Eight-year-old ‘Cresthaven’ peach (Prunus persica L. Batsch.) were sprayed to runoff in mid-October with ethephon and Dormex, two potential bloom-delaying compounds. Flower buds were evaluated for differences in hardiness after field exposure to < −23°C for 4 hr in Jan. 1987. Buds treated with ethephon were significantly hardier than control buds or buds treated with Dormex. Controlled freezing tests just before bloom, continuing through full bloom, indicated the same difference. In addition, ethephon-treated buds had an estimated LT50 of −1.6° at full bloom compared to an estimated LT50 <0°, but greater than −0.5° for controls. Ethephon-treated buds also attained full bloom ≈7 days later than control buds. Yield also was enhanced by ethephon compared to all other treatments. Results confirm the bloom-delaying phenomenon associated with fall ethephon application and also indicate that ethephon increases the intrinsic hardiness of peach flower buds when applied in the fall. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon); calcium cyanamid (Dormex).

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Cacao (Theobroma cacao L.) contains self-compatible and self-incompatible genotypes. In the greenhouse, pollen germination and fruit set failed to occur after self-pollination of an incompatible genotype (IMC 30); however, if the self-pollinated flowers were enclosed in plastic vials for 6 h after pollination, pollen germination was 95% The promotive effect of enclosed pollination on pollen germination was due to the accumulation of CO2 (8.9 % v/v). Despite the high rate of pollen germination, fruit set was only 45%. Seeds produced from self-pollinations using this technique were viable, with 95% germination. Cross-pollination with `Amelonado' pollen resulted in 100% pollen germination and 46% fruit set. Enclosure of cross-pollinated flowers did not improve the percentage of fruit set. Sections made through the ovary 48 h after enclosed self-pollination indicated that the majority of ovules contained a zygote; however, some ovules still contained unfused male and female gametes and polar nuclei. Self-incompatibility in this genotype is expressed at two stages in the process leading to fruit set. The first is at the pollen germination stage and can be overcome by CO2 treatment; the second is at the gametic fusion stage.

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The causes of poor fruit set of cocoa (Theobroma cacao L.) in the greenhouse were studied by examining factors that may influence pollen germination. Hand pollination of cocoa flowers resulted in 45.8% fruit set when flowers were pollinated within 3 hours of anthesis. Pollen germination did not occur until about 6 hours after pollination. Later pollinations (7 to 9 hours after anthesis) or earlier pollinations (16 to 18 hours before anthesis) did not lead to fruit set. Cocoa pollen did not germinate in vitro unless the excised flowers were incubated for 6 hours at 25C in closed vials. During the incubation period, CO2accumulated to a final concentration of about 85 ml·liter-1 as a result of respiration. Ethylene production was not detectable. Incubation of flowers with a NaOH-saturated wick, to absorb CO2, prevented pollen germination in vitro. Incubation of flowers at 15C also prevented pollen germination in vitro at 25C. Hand pollination of flowers 7 to 9 hours after anthesis or 16 to 18 hours before anthesis using CO2-incubated pollen resulted in about 10% fruit set. Enclosed pollinations in vivo, in which CO2 was allowed to accumulate, resulted in nearly 100% fruit set. The initial failure to set fruit from hand pollinations may result from poor or slow pollen germination. Moreover, CO,-incubated pollen might be used to increase fruit set in cocoa by extending the effective pollination period.

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Drought stress is a widespread abiotic stress that causes a decline in plant growth. Drought injury symptoms have been associated with an inhibition in cytokinin (CK) synthesis. The objectives of this study were to investigate whether expression of a gene (ipt) encoding the enzyme adenine isopentenyl phosphotransferase for CK synthesis ligated to a senescence-activated promoter (SAG12) or a heat shock promoter (HSP18.2) would improve drought tolerance in creeping bentgrass (Agrostis stolonifera) and to examine shoot and root growth responses to drought stress associated with changes in endogenous production of CK, and the proportional change in CK and abscisic acid (ABA) due to ipt transformation. Most SAG12-ipt and HSP18.2-ipt transgenic lines exhibited significantly higher turf quality, photochemical efficiency, chlorophyll content, leaf relative water content, and root:shoot ratio under drought stress than the null transformant or the wild-type ‘Penncross’ plants. Transgenic lines that had better growth and turf performance generally had higher CK content and a higher CK-to-ABA ratio, although the direct correlation of CK and ABA content with individual physiological parameters in individual lines was not clear. Our results demonstrated that expressing ipt resulted in the improvement of turf performance under drought stress in creeping bentgrass in some of the transgenic plants with SAG12-ipt or HSP18.2-ipt, which could be associated with the suppression of leaf senescence and promoting root growth relative to shoot growth due to the maintenance of higher CK level and a higher ratio of CK to ABA.

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