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Timothy F. Bourne, J.N. Moore, and Milon F. George

Four interspecific grape hybrids (Vitis spp.) developed in Arkansas were evaluated for primary bud hardiness by differential thermal analysis. Buds from two locations were analyzed over 2 years for acclimation, midwinter hardiness, and deacclimation. In addition, effects of two training systems on cold hardiness of buds were evaluated in one location. The buds of the two genotypes with the greatest component of V. vinifera in their ancestry acclimated more slowly than did the other genotypes. Ultimate midwinter bud hardiness was greater in the genotypes possessing less V. vinifera than other parentage. No effect on cold hardiness due to training system was noted. No natural winter freeze damage was observed on any of the genotypes in the period of observation.

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Sorkel A. Kadir and Edward L. Proebsting

In Dec. 1990, sweet cherry (Prunus avium L.) selections varied in floral bud kill from 9% to 92% following exposure to severe cold. In the following winter, the hardiness of two hardy and two tender selections was analyzed by differential thermal analysis (DTA) to screen selections for hardiness. In a mild winter, when buds remained at their minimum hardiness level, the hardy selections consistently were > 2C hardier than the tender selections. About one-half of that hardiness difference was associated with differences in tissue water content, the other half with unknown factors. Buds of the tender selections began to develop earlier and bloomed earlier than the hardy selections. DTA analysis of floral bud populations separated selections that clearly differed in floral bud hardiness.

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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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Cindy L. Flinn and Edward N. Ashworth

The accumulation of total soluble sugars (TSS) and starch and their relationship to flower bud hardiness were studied in three Forsythia taxa: Forsythia ×intermedia `Spectabilis', Forsythia ×intermedia `Lynwood', and F. suspensa. Taxon hardiness was based on the mean temperature at which low temperature exotherms (LTEs) occurred during thermal analysis. Ethanol-extracted soluble sugars were quantified with anthrone, and starch was enzymatically digested and quantified with Trinder reagent. Qualitative changes in sugar content were determined with high-performance liquid chromatography and co-chromatography of authentic standards. Quantitative and qualitative changes in sugar content, similar for the three taxa, were observed in conjunction with fluctuations in flower bud hardiness, although neither TSS nor starch were correlated with mean LTE temperature. TSS was higher in acclimated than nonacclimated buds. However, after deacclimation began, sugars continued to increase with mean LTE temperature. Buds lacked starch except for a brief period during deacclimation. Galactose, stachyose, raffinose, and an unidentified carbohydrate were positively correlated with hardiness (P = 0.005, 0.001, 0.005, and 0.001, respectively).

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Cindy L. Flinn and Edward N. Ashworth

Differential thermal analysis (DTA) was used to study the freezing behavior of `Berkeley' blueberry (Vaccinium corymbosum L.) flower buds at cooling rates of 10, 5, and 2C/hour. Experiments were conducted at various stages of hardiness on excised and attached (5 cm of stem) buds. The presence and number of low-temperature exotherms (LTEs) in hardy buds generally increased when analyses were conducted using faster cooling rates with excised buds. The number of LTEs detected in individual buds did not correlate (r 2 = 0.27) with the number of injured florets. The inability to detect LTEs in buds attached to stem segments and cooled at 2C/hour indicates that DTA cannot reliably estimate blueberry flower-bud hardiness in field plantings.

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Mark K. Ehlenfeldt and Bryan T. Vinyard

deacclimation among diverse blueberry genotypes J. Amer. Soc. Hort. Sci. 137 31 37 Ehlenfeldt, M.K. Stretch, A.W. Vorsa, N. Draper, A.D. 2005 ‘Cara’s Choice’ blueberry HortScience 40 1556 1557 Flinn, C.L. Ashworth, E.N. 1994 Blueberry flower-bud hardiness is not

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Schuyler D. Seeley, Hossein Damavandy, J. LaMar Anderson, Richard Renquist, and Nancy W. Callan

Foliar applications of growth regulators (GR) in early autumn induced leaf retention (LR) on peach [Prunu,s persica (L.) Batsch.] and `Montmorency' tart cherry (Prunus cerasus L.) trees. In `Johnson Elberta' peach, the relative effectiveness of GRs on LR was NAA = Promalin (BA + GA4+7) > GA4+7 > GA3 > BA > control, and on leaf detachment pull force (PF) NAA > BA + GA4+7 > GA4+7 = GA3 > BA3 > BA > control. Relative GR-induced chlorophyll (CL) content in retained leaves was BA + GA4+7 > GA4+7 > GA3 > BA > control > NAA. Relative xanthophyll (XN) content of retained leaves was NAA > control > BA > GA3 = GA4+7 = BA + GA4+7. Treating only half of a peach tree with NAA did not affect LR on the untreated side. NAA decreased subsequent bud and flower size in peach. Bud hardiness was enhanced by NAA in `Johnson Elberta' peach but not in `Redhaven' peach or in `Montmorency' tart cherry. NAA increased hardening on both the leafy treated (foliated) and untreated (defoliated) sides of half-treated `Johnson Elberta' trees. Increased endodormancy duration, as measured by GA3 forcing of terminal leaf buds, was proportional to LR. Chemical names used: N-(phenylmethyl)- 1H-purin-6-amine (BA); (1a,2ß,4bß,10ß)-2,4a,7-trihydroxy-l-methyl-8-methylenegibb-3-ene-l,lO-dicarboxylic acid,l,4a-lactone (GA3, GA4+7); l-naphthaleneacetic acid (NAA).

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John R. Clark and Robert Bourne

The southern highbush blueberry (Vaccinium spp.) `Blueridge', `Cape Fear', `Cooper', `Georgiagem', `Gulf Coast', and `O'Neal'; the rabbiteye (V. ashei Reade) `Climax'; and the highbush (V. corymbosum L.) `Bluecrop' were evaluated for ovary damage following exposure of flower buds to 0 to 30C in a programmable freezer in Dec. 1993 and Jan. and Feb. 1994. The plants sampled were growing at the Univ. of Arkansas Fruit Substation, Clarksville. Damage was based on oxidative browning of the ovaries following an incubation period after removal from the freezer. With the exception of `Climax', a minimum temperature of –15C was required before bud damage was sufficient enough to differentiate among cultivars. All southern highbush cultivars and `Bluecrop' had superior hardiness compared to `Climax' at –15C in December, –20C in January, and –15C in February. Maximum hardiness of all cultivars was found in January. The hardier southern highbush cultivars were `Cape Fear' and `Blue Ridge'. Less hardy cultivars were `Gulf Coast, `Cooper', `Georgiagem', and `O'Neal', although the date of sampling affected the ranking of these clones for hardiness, especially for the February sample date. `Bluecrop' was not consistently hardier than the hardier southern highbush cultivars, except at the February sample date.

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Sorkel A. Kadir and Edward L. Proebsting

Flower buds of 20 Prunus species showed quite different strategies to cope with low temperatures. Buds of most species deep supercooled. The two hardiest species, both from the subgenus Padus (P. padus L. and P. virginiana L.), did not supercool and survived -33C with no bud kill. Prunus serotina J.F. Ehrh., also in Padus, did supercool. Prunus nigra Ait., P. americana Marsh, P. fruticosa Pall., and P. besseyi L.H. Bailey had a low minimum hardiness level (MHL), small buds, and a low water content. Exotherms were no longer detectable from the buds of these species after 2 days at -7C and some buds survived -33C. Prunus triloba Lindl. and P. japonica Thunb. were similar to that group, but no buds survived -33C. Prunus davidiana (Carriere) Franch., P. avium L., and P. domestica L. had a relatively high MHL but hardened rapidly when the buds were frozen. Prunus persica (L.) Batsch., P. subhirtella Miq., P. dulcis (Mill) D. A. Webb, and P. emarginata (Dougl. ex Hook) Walp. deep supercooled, had large flower buds and a high MHL, and were killed in the Dec. 1990 freeze. Prunus salicina Lindl., P. hortulana L.H. Bailey, P. armeniaca L., and P. tomentosa Thunb. were in an intermediate group with a moderately low MHL and a moderate rate of hardiness increase while frozen. Prunus dulcis and P. davidiana had a low chilling requirement and bloomed early, whereas P. virginiana, P. fruticosa, P. nigra, and P. domestica had high chilling requirements and bloomed late.

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Edward F. Durner, Thomas J. Gianfagna, Francis X. Rooney, Gale S. Teiger, Martin J. Seiler, and Mark J. Cantarella

Ethephon was applied at 100 mg·liter-1 to peach [Prunus persica (L.) Batsch., cvs. Jerseydawn and Cresthaven] trees in Oct. 1987 and 1988 to increase flower bud hardiness and delay bloom the following spring. Flower bud survival after exposure to -26C in Jan. 1988 was enhanced with fall ethephon application in both cultivars. Ethephon delayed bloom by 7 (1988) and 3 (1989) days in `Jerseydawn' and by 10 (1988) and 4 (1989) days in `Cresthaven'. Total fruit production per tree for `Jersey-dawn' was not affected by ethephon treatment in 1988; however, yield was enhanced with ethephon treatment in 1989. For `Cresthaven', yield was enhanced by ethephon treatment in both years. Most fruit from the untreated trees were harvested on the first harvest dates and were in the largest size categories, while most fruit from the treated trees were harvested on the last harvest dates and were in the smaller size categories both years in both cultivars. Smaller pistils and heavier prethinning crop loads lead to smaller fruit and a later harvest date. Chemical names used: 2-chloroethylphosphonic acid (ethephon).