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Eric Young

Dormant apple trees (Malus domestics Borkh., cv. MM. 111) were chilled at SC for O, 500, 1000, or 1500 hours and then forced at 10, 20, or 30C for 21 days. Budbreak and root growth were recorded after forcing, and shoot and root respiration was measured at 5, 10, 20, and 30C to determine Q10 and energy of activation values. Budbreak, root growth, and respiration generally increased with chilling and forcing temperature. The Q10 of shoot respiration increased significantly with increasing chilling when measured before forcing; however, after forcing, Q10 decreased with chilling. Root respiration Q10 was not as influenced as shoot respiration by chilling either before or after forcing. Energy of activation for shoot and root respiration decreased significantly with chilling after forcing at each temperature.

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Eric Young

During natural leaf abscission, 2-year-old potted apple trees (Malus domestica Borkh. cv. MM.111 EMLA) were placed in a room at 6C for chilling [0,600, 900, or 1400 chilling units (CU)]. After each chilling treatment, respiration of shoot segments was measured as CO2 evolved and O2 consumed at 22C in several O2 concentrations. Respiration increased with oxygen concentration after all CU treatments. Carbon dioxide evolved at the several O2 levels did not show a pattern related to CU, but O2 consumed decreased at a decreasing rate with additional CU. Respiratory quotient was <1 at 0 and 600 CU and equal to 1 at 900 and 1400 CU, indicating a possible shift in respiratory substrate with chilling.

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Eric Young

During natural leaf abscission, two-year-old, potted apple trees (Malus domestica cv. MM.111 EMLA) were placed in a cold room at 6C for chilling. At 0, 600, 900, and 1400 chilling hours (CH), ten trees were removed and terminal shoots cut into four 15 cm sections. These sections were randomly placed in forty 10 1 test tubes at 20C and subjected to ten oxygen levels from 0.5 to 21% O2 with four reps each by flushing tubes with mixtures of air and nitrogen prior to sealing. Tubes remained sealed for 4 hr then reflushed and resealed for another 4 hr after which 1 ml gas samples were drawn and CO2 and O2 levels measured on a gas chromatograph. Respiration decreased with oxygen level at all CH. CO2 evolved did not show a pattern related to oxygen level, but O2 consumed decreased at a decreasing rate with additional CH. Respiratory quotient was below one at 0 and 600 CH and equal to one at 900 and 1400 CH, indicating a possible shift in respiration substrate with chilling.

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Eric Young

Budbreak and root and shoot extension growth of apple trees (Malus domestics Borkh. MM.111) were affected by exposure to 500 hours of higher temperatures (15, 20, or 30C) during the first, second, or third 500 hours of a 1500-hour, 5C chilling period. Exposure to 15C during the third 500 hours had a significantly positive effect on budbreak, 20C at this time had no effect, and all other treatments had a negative effect on budbreak and new root and shoot growth.

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Michael Parker and Eric Young

Controlling vegetative growth resulting from a long growing season in the southeast is difficult while trying to promote early fruiting. This study was initiated in 1990 to evaluate higher density leader training techniques, cultivar interactions, and the benefits of pre-plant fumigation on apple replant sites. Another objective was to evaluate these management parameters in four regions with very different climates and elevations. The training techniques evaluated were, weak leader renewal, bending of the leader during the growing season, and partial terminal leaf removal every 10 inches of leader growth (without injuring the apical meristem). The cultivars used were Jonagored, Spur Gala, and Red Fuji, all on Mark rootstock. First and second year branching was not significantly different between the various training techniques. Yields during the third year did not appear to differ between the leader training techniques. Pre-plant fumigation appeared to be beneficial in increasing tree growth in only two of the four sites.

Open access

Eric Young

Abstract

Fall- and spring-planted spur ‘Delicious’ trees were monitored for first-year spur and shoot development and major carbohydrate levels in 1986 and 1987. Fall planting resulted in significantly greater shoot extension growth and lower tendency to become spurbound than spring planting during both years for two strains of spur ‘Delicious’. Higher starch reserves were found following the growing season after fall planting than after spring planting. A root dip of 10,000 mg a.i. IBA/liter before spring planting in 1987 did not affect any of the characteristics measured. Chemical name used: lH-indole-3-butyric acid (IBA).

Open access

Eric Young

Abstract

Nonchilled, nursery-grown apple (Malus domestica Borkh.) trees were subjected to all combinations of root and/or shoot chilling (5°C) or nonchilling (16°) temperatures for 1500 hr. Trees then were given one of the following six plant growth regulator treatments prior to greenhouse forcing for 30 days: no plant growth regulator; 10-sec shoot dip of either 6-BA, GA4+7, or Promalin; 10-sec root dip of IBA; or IBA on root plus Promalin on shoot. Chilling either the root or shoot alone resulted in partial budbreak, while chilling the entire tree increased budbreak and dry weight of new shoots significantly. New root growth depended primarily on chilling the root. Treatment of the shoot with 6-BA, GA4+7, or Promalin increased budbreak and replaced the requirement for root chilling for this response, but did not affect new shoot dry weight or root growth. Treating the root with IBA significantly increased new root growth, budbreak, and new shoot dry weight, and replaced the requirement for root chilling for these responses. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); gibberellic acid (GA4+7); 1H-indole-3-butanoic acid (IBA); mixture of BA and GA4+7 (Promalin).

Open access

Eric Young

Abstract

Xylem sap from three apple (Malus domestica Borkh.) rootstocks was vacuum-extracted during and after artificial chilling and during forcing of chilled and unchilled trees. Sap was assayed for cytokinins by immunoassay and for soluble carbohydrates (sorbitol, glucose, fructose, and sucrose) by enzymatic assays. Xylem cytokinin increased after 10 days of forcing at 21/18C regardless of chilling treatment. Cytokinin levels decreased significantly as budbreak occurred in fully chilled trees, but not in unchilled trees with very little budbreak. Xylem sucrose, glucose, and fructose concentrations decreased upon exposure to 21/18C, then increased after 30 days in both chilled and unchilled trees. Sorbitol level remained low and unchanged throughout growth. Full chilling was not necessary in apple for adequate cytokinin and carbohydrates to be transported to the developing buds via the xylem stream. Sorbitol apparently is not used in carbohydrate transport from reserve, as it is in photosynthesis.

Open access

Eric Young and Jean Houser

Abstract

A four-year-old planting of peach (Prunus persica (L.) Batsch cvs. Cresthaven and Harken on Halford, Lovell, and Siberian C rootstocks was monitored for date of completion of chilling requirement and date of bloom, and change in xylem water potential with bloom. Siberian C rootstock delayed the completion of chilling requirement by 2 days and time of bloom by 4 days in both cultivars. Xylem water potential of fruiting shoots decreased to a minimum just after the swollen bud stage then increased sharply until petal fall. The change in water potential and all 5 bloom stages were delayed by Siberian C but not by Halford or Lovell seedling rootstocks.