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Edward F. Durner

`Redhaven' peach trees [Prunus persica (L.) Batsch.] on their own roots or budded to seven rootstock [`Bailey', `Siberian C', `Lovell', `Halford' (seedlings), GF 655.2, GF 677 (`Amandier'), or `Damas' (GF 1869) (clonal)] were evaluated for rootstock influence on flower bud hardiness, live pistils at bloom, thinning requirements, marketable yield, and production efficiency after exposure to temperatures lower than – 23C in 1987 and to - 26C in 1988. In 1987, flower bud hardiness was as great on `Siberian C' as on own-rooted `Redhaven' and greater than on the other rootstock. Fewer live pistils were observed during bloom on GF 677 than on `Siberian C', `Lovell', `Damas', or self-rooted trees in 1987. In 1988, flower bud hardiness was greater on `Siberian C' and `Bailey' than on GF 677. At bloom, `Lovell' and `Siberian C' rootstock carried more flowers with live pistils than `Damas'.`Siberian C' and `Lovell' required significantly greater fruit thinning than all other rootstock and self-rooted trees. GF 677 produced a larger marketable crop than GF 655.2 or `Damas'. In addition, `Bailey', `Lovell', and self-rooted trees produced a significantly larger crop than `Damas'. No significant rootstock effect on production efficiency was detected in either year. Tree vigor during the growing season preceding each freeze did not significantly influence flower bud survival or productivity.

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Edward F. Durner

Two- to three-week-old `Sweet Charlie' strawberry (Fragaria ×ananassa Duch.) plug plants were conditioned [seven 9-hour short days without chilling (21 °C day/21 °C night) followed by seven 9-hour short days with chilling during the nyctoperiod (21 °C/12 °C night)] in September, then planted in a vertical hydroponic system for winter greenhouse production. Conditioned plugs produced significantly more fruit than did nonconditioned control plugs in January and February, but the difference was nonsignificant in March and April. Fruit yield increased linearly with height in the column (≈40 g/plant for every 30-cm increase in column height), probably because of increasing light level. When productivity is considered on an area basis (kg·m–2) and the column height effect on yield is accounted for, productivity over a 4.5-month period was 4.8 kg·m–2 for controls and 7.8 kg·m–2 for conditioned plugs. Conditioned plug plants offer the potential for increasing strawberry productivity and therefore the profitability of a winter greenhouse production system.

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Edward F. Durner

Ethephon (100 mg·liter-1) was applied to mature peach trees [Prunus persica (L.) Batsch. cv Redhaven] on 13 Oct. 1989. Ethephon-treated and non-treated trees were pruned on 12 Dec. 1989, or left not pruned. Flower bud hardiness was assessed via exotherm analysis from Dec. through Mar. on buds taken directly from the orchard and on buds deacclimated / reacclimated under controlled conditions. Buds from ethephon-treated trees were consistently hardier than buds from non-treated trees. After a warm spell in Jan., buds from pruned trees not previously treated with ethephon were less hardy than those from non-pruned trees. Hardiness of buds from ethephon-treated trees after the warm spell was not affected by pruning. All buds rehardened with the return of low temperatures. Under controlled conditions, buds from pruned trees were less hardy than those from non-pruned trees. Pruning resulted in a rapid loss of hardiness at warm temperatures (21C). If trees had been treated with ethephon the previous fall, significant rehardening of dehardened buds from pruned trees occurred at 5 or -1C. Buds from pruned, non-treated trees did not reharden.

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Edward F. Durner

Flower bud hardiness of ethephon-treated (100 mg·liter-1 in October), dormant pruned (in December) `Redhaven' peach (Prunus persica L. Batsch.) trees was studied from December through March using exotherm analysis. In early December, buds not treated with ethephon were 0.5C hardier than ethephon-treated buds. From mid-December through March, ethephon-treated buds were 0.5 to 2.1C hardier than nontreated buds. When a main effect of pruning was detected, buds from pruned trees were 0.8 to 2.8C less hardy than buds from nonpruned trees. On several dates, a significant interaction on flower bud hardiness between ethephon treatment and pruning was detected. For trees not treated with ethephon, buds from pruned trees were 1.8 to 2.2C less hardy than those from nonpruned trees. Pruning did not affect hardiness of buds from ethephon-treated trees. Ethephon delayed bloom to the 75% fully open stage by 9 days. Pruning accelerated bloom to the 75% fully open stage by 3 days compared to nonpruned trees. Flower bud dehardening under controlled conditions was also studied. As field chilling accumulated, flower buds dehardened more rapidly and to a greater extent when exposed to heat. Pruning accelerated and intensified dehardening. Ethephon reduced the pruning effect. The percentage of buds supercooling from any ethephon or pruning treatment did not change as chilling accumulated. In trees not treated with ethepbon, fewer buds supercooled as heat accumulated, and pruning intensified this effect. In pruned, ethephon-treated trees, fewer buds supercooled after exposure to heat. The number of buds supercooling in nonpruned trees did not change with heat accumulation. Flower bud rehardening after controlled dehardening was also evaluated. After dehardening in early February, there was no difference in the bud hardiness of pruned or nonpruned trees. Buds from ethepbon-treated trees were hardier than those from nontreated trees. With reacclimation, buds from pruned trees were not as hardy as those from nonpruned trees. The percentage of buds supercooling from ethephon-treated trees did not change with deacclimation or reacclimation treatments. After deacclimation in late February, buds from pruned trees were 2.2C less hardy than those from nonpruned trees. After reacclimation, buds from pruned, ethephon-treated trees rehardened 2.6C while buds from all other treatments remained at deacclimated hardiness levels or continued to deharden. Ethephon-treated pistils were shorter than nontreated pistils. Pistils from pruned trees were longer than those from nonpruned trees. Deacclimated pistils were longer than nondeacclimated pistils. Differences in hardiness among ethephon and pruning treatments were observed, but there was no relationship between pistil moisture and hardiness.

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Edward F. Durner and Thomas J. Gianfagna

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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Edward F. Durner and Thomas J. Gianfagna

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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Edward F. Durner and Joseph C. Goffreda

Three peach [Prunus persica (L.) Batsch] rootstock plantings were monitored for date and rate of bloom during Spring 1989 and 1990 to determine if the time of scion bloom on different rootstocks is determined by the date of initiation of bud growth in the spring or by the duration of a particular bud stage. Included were a 1984 planting of `Redhaven' on eight rootstocks, a 1984 planting of `Rio-Oso-Gem' and `Loring', each on 11 rootstocks, and a 1986 planting of `Encore' on 18 rootstocks. The effect of rootstock on bud phenology was consistent within scion cultivar over two extremely different spring temperature profiles. In `Redhaven' and `Rio-Oso-Gem', rootstocks affected the dates but not the rates of bud development. Rootstocks affected both the dates and rates of `Loring' and `Encore' bud development. No consistent effect of rootstock on yield could be associated with delayed bud development in `Rio-Oso-Gem', `Redhaven', or `Loring'; however, delayed bud development of `Encore' on `Okinawa' x `Cardinal' and 62325 resulted in enhanced yield following spring frosts.

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Edward F. Durner and Thomas J. Gianfagna

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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Edward F. Durner and Thomas J. Gianfagna

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).