Bryan S. Wilkins

Mineral nutrition during establishment of golden delicious ‘smoothee’ apples on dwarfing rootstocks and interstems

Abstract This study was conducted to determine the influence of 4 interstems (EM.27 EMLA, Mark, M.9 EMLA, and EM.26 EMLA) and 8 rootstocks (EM.27 EMLA, Mark, M.9 EMLA, EM.26 EMLA, M.7A, MM. 106 EMLA, MM. 111 EMLA, and seedling) with and without interstems on foliar element concentrations [nitrogen (N,) phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), zinc (Zn), boron (B)] of the Golden Delicious ‘Smoothee’ (Malus domestica, Borkh). The trees were planted in 1990 and the experiment was conducted until 1996. Soil pH was low (pH=5.9) before planting but liming raised the pH to 6.5 by the 4th year after planting. Soil P was adequate, K and Mg were high, and Ca was low based on local recommendations for apples. The year by year variation in foliar element concentrations was much higher than rootstock and interstem effects. Differences among interstems and rootstocks were important as foliar element concentrations approached those of deficiency or toxicity. In this study, K decreased to deficiency concentrations by the end of the experiment except for seedling rootstocks, which slightly increased. Foliar Ca was deficient for all interstems and rootstocks at the start of the experiment, but increased extensively for M.9 EMLA and EM.26 EMLA rootstocks across years. Foliar Mn increased to nearly toxic concentrations (300 μg g‐1) in EM.27 EMLA and Mark rootstocks, whereas the other rootstocks did not. No deficiency or toxicity symptoms were noted for any elements during this study. These results indicate that a single range of foliar nutrient concentrations can be used as an aid for determining fertilization rates for the apple rootstocks and interstems used in this study. However, individual rootstocks vary in the rate at which they approach toxicity and deficiency concentrations, which needs to be known to prevent mineral nutritional related problems in commercial apple orchards.

Cultivar Variation in Physicochemical and Antioxidant Activity of Alabama-Grown Blackberries

Abstract 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. There were no consistent differences for variation in initial pH, titratable acidity (TA), total soluble sugar (TSS) and TSS/TA ratio values determined. 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. The antioxidant activity as determined by ABTS radical cation procedure for fractionated crude fruit extracts varied in response to parameters evaluated. Hydrophilic antioxidant activity (HAA) was not different among cultivars evaluated. In contrast, differences were found in lipophilic antioxidant activity (LAA) and total antioxidant activity (TAA).

Fruit Quality and Antioxidant Properties in Alabama-Grown Blackberries During Fruit Maturation

Abstract 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, motded, 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 and maturity of harvest were in fruit quality attributes and antioxidative properties found. 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%, and TSS/TA ratio ranged from 11.9 to 63.6. 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. In general, antioxidant activity declined between red and dull-black ripening stages. The results indicate that TSS/TA ratio and TEAC were good indicators of fruit maturity and nutritional quality, respectively.

Effect of Maturity at Harvest in Relation to Changes in Antioxidant Properties and Ethylene in ‘Chandler’ Strawberry Fruit

Abstract The relationship between fruit maturation and accumulation of hydrogen peroxide (H202), lipid peroxidation, ethylene (C2H4) production, antioxidant activity (hydrophilic, lipophilic and total) and the antioxidant enzyme ascorbate peroxidase (APX, EC 1.11.1.11) in fruit pericarp tissue of ‘Chandler’ (Fragaria xananassa Duch.) strawberry were measured. ‘Chandler’ fruit pericarp maturation and ripening were accompanied by a decline in H202 content early in fruit development followed by a rapid accumulation. An increase in membrane lipid peroxidation (thiobarbituric acid reactive substances, TBARS) coincided with accumulation of H202, which preceded a rise in C2H4 production. In general, antioxidant activity declined as fruit matured and ripened. APX enzyme activity increased by 2-fold and peaked at the pink stage of development and then gradually declined with ripening. H202 may serve as a signal molecule to initiate the cascade of oxidative processes during maturation and ripening. APX enzyme activity during maturation and ripening was not substantial and thus, may not have a role in alleviating accumulation of H202 and subsequent events related to oxidative senescence in fruit pericarp. To our knowledge, this is the first study to present fractionated antioxidant activities (HAA, LAA and TAA) from strawberry pericarp as assessed by the ABTS*+ radical cation assay. A fundamental understanding of the mechanisms involved in the senescent related-oxidative changes during strawberry fruit ontogeny in relation to quality and nutrition is discussed.

Effect of Primocane Topping Height and Lateral Length on Yield of ‘Navaho’ Blackberry

Abstract ‘Navaho’ erect thornless blackberry plants were subjected to a combination of three primocane summer topping heights and two lateral length pruning treatments. Plants were topped at 91, 122, 152 cm tall, and laterals were shortened to either 30 or 61 cm in length. Treatment effects on yield and plant structure were examined for four growing seasons. Lateral length had little effect on yield and any pruning height. Yield generally increased with increasing plant height. The 122-cm height appeared to optimize yield while still allowing for manageable floricane architecture.

Use of Floating Row Covers in Annual Hill Plasticulture Strawberries

Abstract The response of strawberry plants in the annual hill plasti-culture system to the use of lightweight nonwoven rowcovers (17g/square meter) during the fall establishment period, winter and early spring was investigated. These fabrics can provide some cold and wind dessication protection and can also increase soil and air temperatures around the plant. The increased temperatures under the cover may simulate increased flower bud formation during the short day induction cycles in the fall and spring. Additionally, the covers may provide a protective environment where leaves remain functional for longer periods and crown and root development may be stimulated. In this study, row covers were installed and removed at various intervals from October through March. In addition to the uncovered control plants, the following row cover timings were imposed: Oct.-Mar., Oct.-Feb., Oct.- Dec., Oct.-Nov., Nov.-Mar., Oct.-Feb., Oct.-Jan., Oct.-Dec., Oct.-Nov., Nov.-Mar., Dec.-Mar., Jan.-Mar., and Feb.-Mar. Treatments were reduced from 8 to 6 in the last year of the study. The weight of marketable berries was affected by year and by treatment. Average performance for the four year period showed the Oct.-Feb. treatment to have the highest yields followed by Oct.-Nov. and Feb.-Mar. The Jan.-Mar. performed worse than the control in terms of both yield and berry size. Average berry weight was improved in the Oct.-Feb. and Oct.-Nov. treatment. Row covers in the best treatment (Oct.-Feb.) improved marketable yield by an average of 35% over the control.

A comparison of organic fungicides: alternatives for reducing scab on pecan

In the southeastern USA, the most widespread and damaging disease of pecan is scab, caused by Venturia effusa. Although scab can be controlled using conventional chemical methods, organic pecans that attract a premium price mandate the use of organic fungicides. Also, organic production is an environmentally sustainable method. However, where susceptible pecan cultivars are grown, there are limited options for organic management of scab. We conducted experiments to compare organic fungicides to control scab on the susceptible cv. Desirable in 2011, 2012, 2014, 2015, and 2016. The alternatives compared included Bordeaux mixture, compost tea, sodium bicarbonate, Bacillus subtilis, sulfur, cuprous oxide, and extract of the Giant Knotweed (Reynoutria sachalinensis). Rainfall and scab severity differed between seasons. There was consistently low severity on foliage, with little or no difference between treatments. Similarly at the time of the first fruit assessment, the severity was low and the differences in severity small and inconsistent between seasons and treatments. However, by the time of the second fruit assessment, severity of scab had increased and consistent differences among treatments existed (except in the drought year of 2011, when scab severities were very low and similar to the control). In all other years, the control treatment had significantly more severe scab compared to some (2012 and 2014) or all other treatments (2015 and 2016). Extract of the Giant Knotweed as a fungicide was included in 2012, 2014, 2015, and 2016, and fruit on those trees had less severe scab in all years compared to that on fruit of the control trees. In three seasons (2012, 2015, and 2016), applications of Bordeaux mixture resulted in a reduction in scab severity. Compost tea, Sodium bicarbonate, B. subtilis, sulfur, and cuprous oxide significantly reduced scab compared to the control in one or two seasons, but were not consistent among seasons, and were never more efficacious compared to the extract of the Giant Knotweed. Extract of the Giant Knotweed and Bordeaux mixture appear to offer the greatest potential as organic approaches for managing scab in pecan. However, wherever possible, planting of scab resistant cultivars should be considered as a first line of defense.