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Arthur Villordon, Christopher Clark, Don Ferrin, and Don LaBonte

; Jenni et al., 1998 ; Perry and Wehner, 1996 ; Viator et al., 2005 ). Heat unit summations or growing degree days (GDD) for vegetable production has been used for many years on crops with limited life span of quality in the field ( Dufault, 1997 ). Heat

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Gil Simmons and Bill B. Dean

Carrot (Daucus carota) L.) seed quality is affected by the environment in which it matures. Substantial differences in germination from year to year and from field to field have been recognized for many years for umbelliferae seed. Part of the explanation for low germination appears to be the harvest of immature seed. Data was collected for two years, from fields of the cultivars Chantenay and Nantes. Approximately 550 growing degree days were accumulated from anthesis until maturity for seed from the primary umbel. Growing degree days were calculated using a 10°C base temperature and without truncating for temperatures in excess of 35°C. Secondary, tertiary, and quaternary umbel seed maturity sequentially followed primary umbel seed. Secondary and tertiary umbels produced approximately 80 percent of the total seed yield while the primary and quaternary umbels produced approximately 20 percent. Seed maturity was determined by measuring the germination rate. Immature seed germinate at a slower rate than mature seed. The implications of these results for obtaining high quality carrot seed will be discussed.

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Arthur Villordon, Christopher Clark, Tara Smith, Don Ferrin, and Don LaBonte

radiation, relative humidity, wind (direction and speed), and rainfall. Means (total for rainfall) for all variables were calculated for 5 d before and after transplanting (DAT). Accumulated heat units, expressed as growing degree-days (base = 15.5 °C

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James A. Schrader, Diana R. Cochran, Paul A. Domoto, and Gail R. Nonnecke

each vine was used in combination with weather data to calculate growing degree days at base 50 °F (GDD 50). The GDD 50 units were calculated by subtracting the threshold temperature of 50 °F from the mean hourly temperatures in °F, dividing each hourly

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S. Severmutlu, N. Mutlu, R.C. Shearman, E. Gurbuz, O. Gulsen, M. Hocagil, O. Karaguzel, T. Heng-Moss, T.P. Riordan, and R.E. Gaussoin

Warm-season turfgrasses are grown throughout the warm humid, sub-humid, and semiarid regions. The objective of this study was to determine the adaptation of six warm-season turfgrass species and several of their cultivars to Mediterranean growing conditions of Turkey by evaluating turfgrass establishment rate, quality, color, and percentage of turfgrass cover. Information of this nature is lacking and would be helpful to turfgrass managers and advisers working in the region. A study was conducted over a 2-year period in two locations of the Mediterranean region of Turkey. The warm-season turfgrass species studied were bermudagrass (Cynodon dactylon), buffalograss (Buchloë dactyloides), zoysiagrass (Zoysia japonica), bahiagrass (Paspalum notatum), seashore paspalum (Paspalum vaginatum), and centipedegrass (Eremochloa ophiurioides). Tall fescue (Festuca arundinacea) was included as a cool-season turfgrass species for comparison. Twenty cultivars belonging to these species were evaluated for their establishment, turfgrass color and quality, spring green-up, and fall color retention. Bermudagrass, bahiagrass, and seashore paspalum established 95% or better coverage at 1095 growing degree days [GDD (5 °C base temperature)], buffalograss and centipedegrass at 1436 GDD, and ‘Zenith’ and ‘Companion’ Zoysiagrass had 90% and 84% coverage at Antalya after accumulating 2031 GDD. ‘Sea Spray’ seashore paspalum; ‘SWI-1044’, ‘SWI-1045’, ‘Princess 77’, and ‘Riviera’ bermudagrass; ‘Cody’ buffalograss; and ‘Zenith’ zoysiagrass exhibited acceptable turfgrass quality for 7 months throughout the growing season. ‘Argentine’ and ‘Pensacola’ bahiagrass; ‘Sea Spray’ seashore paspalum; and ‘SWI-1044’ and ‘SWI-1045’ bermudagrass extended their growing season by retaining their green color 15 days or longer than the rest of the warm-season cultivars and/or species in the fall. The warm-season species stayed fully dormant throughout January and February. Zoysiagrass and buffalograss cultivars showed early spring green-up compared to the other warm-season species studied. Results from this study support the use of warm-season turfgrass species in this Mediterranean region, especially when heat stress and water limitations exist. Tall fescue did not survive summer heat stress necessitating reseeding in fall.

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Cassandra M. Plank, Edward W. Hellman, and Thayne Montague

Methoxypyrazines (MPs) are fruit-derived extractable compounds that contribute to cultivar-specific aroma traits in wine, and greater concentrations can contribute to unpleasant vegetative aromas. Both light exposure and temperature have been reported to influence MP content in developing wine grapes, but individual effects of light and temperature are confounded. A novel method of manipulating light exposure with light-emitting diodes (LEDs) was used to impose light treatments with little or no effect on cluster temperature. Three treatments were imposed on developing fruit of Vitis vinifera (cv. Cabernet Sauvignon): 1) clusters exposed to direct sunlight, 2) clusters shaded by the grapevine canopy, and 3) clusters shaded by the canopy and exposed to supplemental LED light. Experiments were conducted over 3 years across pre- and postveraison periods of fruit development. A second experiment imposed the same light exposure treatments to ripening clusters on vines experiencing continual shoot growth during the postveraison period. Light exposure reduced 3-isobutyl-2-methoxypyrazine (IBMP) concentration of developing grape berries in the preveraison period independently of berry heating from solar radiation. Berry IBMP responded less to postveraison light levels, except on vines with active shoot growth, suggesting IBMP synthesis was continued during active vine growth but was suppressed by light. An inverse relationship of growing degree days (GDDs) with berry IBMP was observed, indicating high temperatures also reduce berry IBMP concentration. Response to temperature could result from either radiant heating of light-exposed clusters or from high ambient air temperature. Canopy management should consider the impact of both light and temperature on IBMP, and vine management practices should be adjusted appropriately to regional growing conditions and grape cultivars.

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A.J. Both, E. Reiss, J.F. Sudal, K.E. Holmstrom, C.A. Wyenandt, W.L. Kline, and S.A. Garrison

continuously recorded through both growing seasons at both locations. The accumulated values for growing degree days (GDD) and light integral were determined starting on the day of transplanting. To calculate the GDD, the following equation was used ( McMaster

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Natalie R. Bumgarner, Mark A. Bennett, Peter P. Ling, Robert W. Mullen, and Matthew D. Kleinhenz

growing degree days (GDDs) were analyzed and described using Pearson correlation coefficients from Proc Corr. Environmental data. Total solar radiation was measured continuously at the OARDC weather station ≈3000 ft from the experimental site. Additionally

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Timothy Coolong

, minimum, and total accumulated values [University of Georgia Weather Network, Tifton Station, Tifton, GA ( University of Georgia, 2016 )]. The following formula was used to estimate growing degree days (GDD); GDD = [(T max + T min )/2] − T base . GDD were

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Alisson P. Kovaleski, Jeffrey G. Williamson, James W. Olmstead, and Rebecca L. Darnell

–(β0 + β1 × GDD) , where GDD stands for growing degree-days and parameters β 0 and β 1 are the intercept and slope of the linear combination of the logit function, respectively, generated by PROC NLIN. Accumulated GDD {ΣGDD = [(T max – T min