Robert C. Ebel

Cold acclimation induced genes of trifoliate orange (Poncirus trifoliata)

Commercial citrus varieties are sensitive to low temperature. Poncirus trifoliata is a close relative of Citrus species and has been widely used as a cold-hardy rootstock for citrus production in low-temperature environments. mRNA differential display-reverse transcription (DDRT)-PCR and quantitative relative-RT-PCR were used to study gene expression of P. trifoliata under a gradual cold-acclimation temperature regime. Eight up-regulated cDNA fragments were isolated and sequenced. These fragments showed high similarities at the amino acid level to the following genes with known functions: betaine/proline transporter, water channel protein, aldo-keto reductase, early light-induced protein, nitrate transporter, tetratricopeptide-repeat protein, F-box protein, and ribosomal protein L15. These cold-acclimation up-regulated genes in P. trifoliata are also regulated by osmotic and photo-oxidative signals in other plants.

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.

Gene expression analysis of cold treated versus cold acclimated Poncirus trifoliata

Poncirus trifoliata, a close relative of Citrus species, has been widely used as a cold hardy rootstock for citrus production in low-temperature environments. cDNA Amplified Fragment Length Polymorphism (cDNA-AFLP) and Relative Quantification (RQ-PCR) were used to study gene expression of P. trifoliata in response to 10, 24 and 55xa0h of low temperature (4°C) treatment and a gradual 3xa0weeks long cold-acclimation regime. Thirteen differentially expressed cDNA fragments were chosen for further study. These fragments show high similarities to genes with the following known functions: signal transduction and regulation of gene expression, osmotic stress response, cell skeleton reorganization, vesicle trafficking and senescence. Expression levels of genes implicated in signal transduction and regulation of gene expression (MAPK3 and bZIP TF) increased with prolonged exposure to low temperature, but were not upregulated following cold-acclimation. Others were induced following cold-acclimation, but not upon exposure to 4°C. Only the auxin-ethylene GH3-like protein showed dramatic increases during all cold treatments. These comparisons provide information on the dynamic changes in gene expression levels during different cold response regimes.

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).

Phenolic Content and Antioxidant Capacities of Alabama – Grown Thornless Blackberries

ABSTRACT Total phenolics (TPH), flavonoids (TF), monomeric anthocyanins (ACY), and Vitamin C Equivalent Antioxidant Capacities (VCEAC) utilizing ABTS and DPPH radical scavenging assays were determined for five fully ripened blackberries cultivars (‘Loch Ness’, ‘Navaho’, ‘Arapaho’, ‘Apache’, and ‘Triple Crown’) of Rubus spp. grown in Alabama. The ABTS and DPPH methods were highly correlated (Ru2009=u20090.897) and the ABTS method was better for assessing the overall antioxidant capacity. Cultivar differences were found in TPH, ACY, and VCEAC as determined by the ABTS method (P ≤ 0.05) with ‘Loch Ness’ and ‘Apache’ containing the highest levels. Based on these findings ‘Apache’, ‘Arapaho’, and ‘Navaho’ are three thornless blackberry cultivars that have potential to be used as dietary supplements and for commercial production in Alabama due to high phytonutrient content, antioxidant capacities, and yield.

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 Temperature, Photoperiod and Pretreatment Growing Condition on Floral Induction in Springbearing Strawberry

Abstract ‘Chandler’ strawberry plants (Fragaria X ananassa Duch.) were greenhouse grown under natural lighting and then placed into growth chambers at two constant temperatures of 16 °C and 26 °C and two day lengths of 9 h (SD) and 9 h photoperiod (NI) which was night interrupted with 3 h of incandescent radiation at 30-45 μmol s ∼ 1m ∼ 2 PAR. Plants were given different numbers of inductive cycles in growth chambers and then moved to the greenhouse where flowering and growth were monitored. Flowering was completely inhibited at 26 °C, regardless of pretreatment growing conditions such as pot sizes and plant ages, photoperiod and inductive cycles. At 16 °C, SD promoted floral induction compared to NI under all inductive cycles except a 7-day induction. The minimum number of inductive cycles required at 16 °C for floral induction was dependent on photoperiod and prior greenhouse treatment. Flowering rate was also affected by greenhouse treatment, photoperiod and inductive cycles. Runner production was affected by photoperiod and temperature Xinductive cycle.

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.

Kiwifruit Cultivars Differ in Response to Winter Chilling

Abstract Cuttings from five cultivars of [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa] were excised following ambient exposure to chilling temperatures in 100 hour accumulated increments. Cuttings were then placed in a thermostatically controlled greenhouse maintained at 72°F (22.2°C) for forcing to determine effects of chilling on flower buds and vegetative growth. Our data indicate ‘Matua’ and ‘AU-1M’ are better pollinizers than Tomuri based on flower uniformity per stem, the number of flowers per stem and the total number of flowers remaining at the end of the study. Stem length and leaf area, providing indicators of overall plant vigor, were always greater for males than female cultivars. Our data indicate ‘AU-1F’ could potentially set more fruit than ‘Hayward’ based on stem uniformity of flowering, flowers per stem, and flower retention.