This study was conducted to determine fruit quality of Satsuma mandarin Citrus unshiu, Marc. `Owari' grown on the northern coast of the Gulf of Mexico. Soluble solids increased linearly and titratable acidity decreased quadratically during October and November for the four sampling years. There was no significant interaction between sampling date and year. There was a significant year effect for titratable acidity, but not soluble solids or their ratio. A 10:1 soluble solids to titratable acidity ratio was observed on 10 Nov. Variation in fruit weight corresponded with cropload. Fruit weight increased during the sampling period due to an increase in fruit length since there was no change in width. Peel color was yellow-orange by 10 Nov., with many fruit still exhibiting patches of green color. Because of some green color present in the peel, the fruit would have to be degreened for successful marketing in U.S. retail chain stores.
R.C. Ebel, W.A. Dozier, B. Hockema, F.M. Woods, R. Thomas, B.S. Wilkins, M. Nesbitt and R. McDaniel
T.E. Thompson, W.D. Goff, M.L. Nesbitt, R.E. Worley, R.D. O'Barr and B.W. Wood
Floyd M. Woods, William A. Dozier, Robert C. Ebel, Raymond Thomas, Monte Nesbitt, Bryan S. Wilkins and David G. Himelrick
Changes in fruit quality attributes and antioxidative properties from six cultivars of thornless blackberries (Rubus sp.) (`Apache', `Arapaho', `Chester', `Loch Ness', `Navaho', and `Triple Crown') during four different ripening stages (red, mottled, shiny-black, and dull-black) were determined under Alabama growing conditions. Berry fruit samples were evaluated for pH, titratable acidity, total soluble solids, TSS/TA ratio, soluble sugars, vitamin C (reduced, oxidized and total), and antioxidant capacity (measured as trolox equivalent antioxidant capacity, TEAC). Significant variation among cultivars were noted in fruit quality attributes and antioxidative properties, which were influenced by maturity at harvest. An increase in fruit pH concomitant with a decline in titratable acidity (TA) was observed during ripening for all cultivars. Total soluble solids (TSS) values increased from 5.7% to 11.6%, with associated TSS/TA ratio values ranging from 11.92 to 63.56 in ripening fruit. Highest reducing and total sugar content were contained in dull-black fruit. Vitamin C content either declined or remained unchanged with ripening, and the pattern was dependent on cultivar, maturity at harvest and form determined. In general, antioxidant activity declined between red and dull-black ripening stages. The results suggest that the TSS/TA ratio may provide the best maturity index in determining optimal eating quality and antioxidant capacity in terms of TEAC value the best indicator of optimal nutritional quality as influenced by maturity at harvest.
R.C. Ebel, B.L. Campbell, M.L. Nesbitt, W.A. Dozier, J.K. Lindsey and B.S. Wilkins
Estimates of long-term freeze-risk aid decisions regarding crop, cultivar, and rootstock selection, cultural management practices that promote cold hardiness, and methods of freeze protection. Citrus cold hardiness is mostly a function of air temperature, but historical weather records typically contain only daily maximum (Tmax) and minimum (Tmin) air temperatures. A mathematical model was developed that used Tmax and Tmin to estimate air temperature every hour during the diurnal cycle; a cold-hardiness index (CHI500) was calculated by summing the hours ≤10°C for the 500 h before each day; and the CHI500 was regressed against critical temperatures (Tc) that cause injury. The CHI500 was calculated from a weather station located within 0.1 km of an experimental grove and in the middle of the satsuma mandarin (Citrus unshiu Marc.) industry in southern Alabama. Calculation of CHI500 was verified by regressing a predicted CHI500 using Tmax and Tmin, to a measured CHI500 calculated using air temperatures measured every hour for 4 winter seasons (1999-2003). Predicted CHI500 was linearly related to measured CHI500 (r 2 = 0.982). However, the slope was a little low such that trees with a CHI500 = 400, near the maximum cold-hardiness level achieved in this study, had predicted Tc that was 0.5 °C lower than measured Tc. Predicted and measured Tc were similar for nonhardened trees (CHI500 = 0). The ability of predicted Tc to estimate freeze injury was determined in 18 winter seasons where freeze injury was recorded. During injurious freeze events, predicted Tc was higher than Tmin except for a freeze on 8 Mar. 1996. In some freezes where the difference in Tc and Tmin was <0.5 °C there were no visible injury symptoms. Injury by the freeze on 8 Mar. 1996 was due, in part, to abnormally rapid deacclimation because of defoliation by an earlier freeze on 4-6 Feb. the same year. A freeze rating scale was developed that related the difference in Tc and Tmin to the extent of injury. Severe freezes were characterized by tree death (Tc - Tmin > 3.0 °C), moderate freezes by foliage kill and some stem dieback (1.0 °C ≤ Tc - Tmin ≤ 3.0 °C), and slight freezes by slight to no visible leaf injury (Tc - Tmin < 1.0 °C). The model was applied to Tmax and Tmin recorded daily from 1948 through 2004 to estimate long-term freeze-risk for economically damaging freezes (severe and moderate freeze ratings). Economically damaging freezes occurred 1 out of 4 years in the 56-year study, although 8 of the 14 freeze years occurred in two clusters, the first 5 years in the 1960s and 1980s. Potential modification of freeze-risk using within-tree microsprinkler irrigation and more cold-hardy cultivars was discussed.
R.C. Ebel, P.A. Carter, W.A. Dozier, D.A. Findley, M.L. Nesbitt, B.R. Hockema and J.L. Sibley
The current study was conducted to relate ice formation to the pattern and rate of leaf and stem injury of Satsuma mandarins on trifoliate orange rootstock. Potted trees were unacclimated, moderately acclimated or fully acclimated by exposing trees to 32/21 °C, 15/7 °C or 10/4 °C, respectively. Freezing treatments consisted of decreasing air temperature at 2 °C·h-1 until ice formed as evidenced by exotherms determined using differential thermal analysis of stems. Air temperature was then decreased, held constant, or increased and held constant to simulate severe, moderate and mild freeze conditions, respectively. All treatment exhibited exotherms at -2 to -4 °C, which were smaller with milder freezing treatments. Only the fully acclimated trees exhibited multiple exotherms. Leaf watersoaking, an indication of ice formation, occurred concurrently with stem exotherms except for fully acclimated trees where there was up to a 30-min delay and which corresponded with the second exotherm. Electrolyte leakage of leaves began to increase near the peak of the stem exotherm, but increased more slowly with milder freezing temperature treatments. In some treatments, electrolyte leakage reached a plateau near 50% but leaves survived. Leaves died when whole-leaf electrolyte leakage exceeded 50%. These data are discussed within the framework of a proposed mechanism of injury of Satsuma mandarin leaves by subfreezing temperatures, especially multiple exotherms of fully acclimated trees, and the plateau of electrolyte leakage of leaves at the critical level for survival.
Raymond H. Thomas, Floyd M. Woods*, William A. Dozier Jr., Robert C. Ebel, Monte Nesbitt, Brian S. Wilkins and David G. Himelrick
Blackberries are an excellent source of natural antioxidants. Fully ripened fruit of `Apache', `Arapaho', `Chester', `Loch Ness', `Navaho', and `Triple Crown' thornless blackberries were evaluated for their physicochemical and antioxidative activity. Differences in initial pH, titratable acidity (TA), total soluble solids (TSS), TSS/TA ratio and soluble sugars (reducing sugar, sucrose, and total sugars) differed among cultivars. Differences among cultivars with respect to reduced ascorbic acid (AA) were established, but there were no differences in either oxidized ascorbic acid (DHA) or total ascorbic acid (TAA) content. Antioxidant activity was determined by ABTS radical cation procedure for fractionated crude fruit extracts and the cultivars varied in the parameters evaluated. Hydrophilic antioxidant activity (HAA) was not different among cultivars evaluated. In contrast, lipophilic antioxidant activity (LAA) and total antioxidant activity (TAA) differed. The results obtained in this study indicate that Alabama-grown blackberries vary in their quality indices and are an excellent source of natural antioxidants. Information compiled will assist in marketing, handling, postharvest storage of these fruit and serve as a guide to partial fulfillment of recommended daily dietary requirements.
R.C. Ebel, W.A. Dozier Jr., M.L. Nesbitt, N.R. McDaniel, A.A. Powell, A. W. Caylor and W.R. Okie
There are a limited number of peach and nectarine cultivars available with chilling requirements that perform well in the Gulf Coast area of Alabama. A test planting of 40 peach and 13 nectarine cultivars was established in 1985 at the Gulf Coast Substation at Fairhope, Ala. The plot was prepared and trees grown according to commercial procedures. Blocks of four trees of each cultivar were planted on a 6 x 6-m spacing. Chill hours were calculated each year based on number of hours at or below 7.3 °C; starting from and including the first 10 consecutive days a total of 50 hours were accumulated to 15 Feb. Data collected included date of full bloom, first harvest date, and total yield. Fruit were measured or rated for skin color, attractiveness, firmness, stone freeness, pubescence, flesh color, dessert quality, shape, weight, percentage with split pits, and occurrence of malformed sutures and extended tips. All cultivars were evaluated for 9 years (1987–95). The best performing varieties are discussed.