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John R. Clark, Tony K. Wolf, and M. Kay Warren

Thermal analysis was used to determine if muscadine grape (Vitis rotundifolia Michx.) buds supercool and to determine the seasonal cold hardiness of several grape cultivars grown in Arkansas. Buds of the muscadine cultivars Carlos and Summit, sampled from vines grown at Clarksville, Ark., produced low-temperature exotherms consistent with the number of buds tested. Apparent hardiness of the buds increased from 5 Nov. 1993 through 7 Jan. 1994. Mean low-temperature exotherms (MLTE) were lowest on 7 Jan. and were –21.5C for `Carlos' and –23.4C for `Summit'. `Mars' buds, sampled at Clarksville, Ark., and Winchester, Va., were included in the study and increased in hardiness during the same period. MLTE for `Mars' from Arkansas were similar to those of the muscadine cultivars on 7 Jan.; however, `Mars' attained lower MLTE temperatures with vines grown in Virginia than with those in Arkansas. Location differences in hardiness of `Mars' are conjectural.

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B.T. Scully, R.L. Beiriger, and E.A. Wolf

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John R. Clark, Tony K. Wolf, and M. Kay Cook

Thermal analysis was used to determine if muscadine grape (Vitis rotundifolia Michx.) buds supercooled and to determine the seasonal cold hardiness of several grape cultivars. Buds of the muscadine cultivars `Carlos' and `Summit', sampled from vines grown at Clarksville, Ark., produced low-temperature exotherms consistent with the number of buds tested. Apparent hardiness of the buds increased from 5 Nov. 1993 through 7 Jan. 1994. Mean low-temperature exotherms (MLTE) were lowest on 7 Jan. and were –21.5C for `Carlos' and –23.4C for `Summit'. Mars (V. labrusca L.) buds, sampled at Clarksville and Winchester, Va., were included in the study, and increased in hardiness during the same period. MLTE temperatures for `Mars' from Arkansas were similar to those of the muscadine cultivars on 7 Jan.; however, `Mars' attained lower MLTE temperatures with vines grown in Virginia compared to those in Arkansas. Location differences may be due to cultural conditions, sample handling, environment or other reasons.

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E.A. Wolf, J.M. White, R.S. Stubblefield, and B. Scully

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B.T. Scully, R.N. Raid, G.N. Nuessly, and E.A. Wolf

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W. Rademacher, J.B. Speakman, G. Krack, M. Scholtissek, R. Wolf, J.R. Evans, S. Roemmelt, and D. Treutter

Prohexadione-Ca (BAS 125 W) is currently developed as an inhibitor of excessive vegetative growth in apple. In addition to the control of shoot growth, pronounced effects on the incidence of scab (Venturia inaequalis) and fire blight (Erwinia amylovora) are observed that are not due to any fungicidal or bactericidal effect of the compound. Prohexadione-Ca induces marked changes in the metabolism of phenylpropanoids most likely by inhibiting distinct dioxygenases, such as flavanone 3-hydroxylase, which require 2-oxoglutarate as a co-substrate. The content of flavonoids such as luteoliflavan (which does not normally occur in apple tissue) and eriodyctiol is drastically increased reaching levels in the range of 50 mg per gram of dried young shoot tissue. Simple phenols, the identity of which is still unknown, also undergo intense changes. Since phenylpropanoids have often been found to be involved in defense mechanisms of higher plants, further studies on their role in pathogen resistance in apple are justified from these results.

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D.M. Olszyk, G. Kats, C.L. Morrison, P.J. Dawson, I. Gocka, J. Wolf, and C.R. Thompson

Three-year-old `Valencia' orange [Citrus sinensis (L.) Osbeck] trees were exposed to air pollutants for 4. years in open-top field chambers to determine the chronic effects of ambient oxidants (primarily ozone) or sulfur dioxide (SO2) on fruit yield and quality and tree growth. Ozone concentrations averaged 0.012,0.040, and 0.075 ppm for 0800 to 2000 hr during April to October for filtered, half-ambient, and full ambient oxidant chambers. Sulfur dioxide was applied continuously at 0.09 ppm. Oxidant and SO2 effects were only marginally significant, as there was considerable variability in response among individual trees and between years. Across two “on” production years, yields were 31% lower with ambient oxidants, 11% lower with half-ambient oxidants, and 29% lower with sulfur dioxide compared to filtered air. Number of fruit per tree was reduced by ambient oxidants and SO2. Individual fruit weights were reduced by ambient oxidants, but no other fruit quality characteristics showed definite responses to ambient oxidants or SO2. Ambient oxidants had no effect on yield or quality of fruit during one “off' production year. Neither ambient oxidants nor SO, affected tree growth.