Browsing by Author "Byers, Ross E."
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- Anatomical Developments and the Role of Carbohydrate or Mineral Nutrient Deficiency in Bud Necrosis of 'Riesling' grapevines (Vitis Vinifera L.)Vasudevan, Lakshmi (Virginia Tech, 1997-02-26)Bud necrosis (BN) is observed as an abortion and death of one or more primordia of the developing compound winter bud. Anatomical developments during the onset of BN in 'Riesling' and 'Chardonnay' grapevines were characterized. Examination of ultrathin (1micro m) sections of 'Riesling' buds under a light microscope revealed a zone of compressed cells immediately beneath the primary bud axis within 60 days after budbreak. Cell rupture occurred in that zone within 90 days after budbreak. Scanning electron microscopy revealed a similar pattern of tissue destruction. Based on the hypothesis that BN was caused by essential substrate deficiency, localized carbohydrate deprivaton was attempted by shading of 'Riesling' grapevines and by shoot tip removal. In one experiment, 92% shade was applied for a three-week period at 20, 40, or 60 days after budbreak in one vineyard and at 40 days after budbreak in another vineyard. In another experiment, 92% shade was applied for a 40-day period at 25 or 65 days after budbreak. Shade reduced photosynthetic photon flux (PPF) in the fruit zone of canopies to <2% of ambient PPF. The first experiment did not increase BN. However, the second experiment increased BN in the distal nodes of the shaded vines compared to the control vines. Shoot vigor, measured as shoot diameter and internode length at season1s end, was positively correlated with BN in shaded as well as unshaded vines. The frequency of necrotic buds was greater at nodes 5 through 16 than at nodes 1 to 4 in both shaded and unshaded vines. Levels of total nonstructural carbohydrates (TNC) measured spectrophotometrically, were not significantly affected by shade treatment. Levels of sucrose, glucose, fructose, and starch in bud, leaf, and stem tissues determined by HPLC, were lower in shaded vines at the point of shade removal than in unshaded vines. Therefore, although three-week periods of shade did not affect BN in 'Riesling', 40-day periods of shade increased BN in distal nodes. Shoot tip removal increased BN at nodes distal to node 12. Bud tissues of shoot-tipped vines had lower levels of sucrose, glucose, fructose, and starch than did the control vines. Carbohydrate analysis of bud, leaf, and stem tissues indicated that 'Riesling' vines (BN-prone) had lower levels of sucrose compared to 'Chardonnay' vines (BN-insensitive). Role of mineral nutrient deprivation was examined in 'Riesling' and 'Chardonnay' buds and the results indicated that BN is unlikely caused by essential nutrient deficiency. 'Chardonnay', the BN-insensitive cultivar had greater levels of starch deposits at 50, 60, 70, and 80 days after budbreak than did the BN-susceptible cultivars, 'Riesling1', Syrah', and 'Viognier'. Starch deposits in grape buds were negatively correlated with BN incidence. From these experiments it can be concluded that a negative correlation between carbohydrate levels of grape buds and BN incidence exists.
- Chemical, cultural, and physiological factors influencing 'Stayman' fruit crackingByers, Ross E.; Carbaugh, D. H. (David H.), 1949- (Virginia Agricultural Experiment Station, 1995)
- Effects of Light Availability and Canopy Position on Peach Fruit QualityLewallen, Kara (Virginia Tech, 2000-04-10)Two experiments were conducted to determine the influence of light on 'Norman' and 'Cresthaven' peach fruit quality characteristics. Of primary interest was the relationship between ground color and flesh firmness. Light levels were manipulated by use of shade cloth, reflective mulch, and aluminum foil. 'Norman' trees, with a randomly chosen half of the canopy covered with 73% shade cloth, had fruit with lower levels of red color, soluble solids concentration (SSC), specific leaf weight, and average photosynthetic photon flux (PPF) than did non-shaded trees. Foil-covered 'Cresthaven' fruit were larger, less firm, and had lower SSC than non-covered fruit. Covered fruit developed yellow but not red color. Position of the fruit within the canopy of the tree also affected fruit quality characteristics. Inside fruit on both 'Norman' and 'Cresthaven' trees were smaller and firmer, had lower SSC, and were less red than fruit from the canopy exterior. The position effect was probably due to the degree of light exposure and not to the distance from the roots. Fruit on the inside of the tree canopies received much lower average PPF than outside fruit. Relationships were evaluated between ground color and firmness for both cultivars. At a given hue angle, fruit developing in high-light environments were firmer than fruit from low-light environments for 'Cresthaven', but the opposite was true for 'Norman'. Therefore, canopy position or the light environment in the vicinity of the developing fruit does not consistently influence the relationship between hue angle on the non-blush side of the fruit, and flesh firmness.
- Factors Affecting Preharvest Fruit Drop of AppleWard, Daniel Lee (Virginia Tech, 2004-08-31)Apple preharvest fruit drop frequently results in severe economic losses. Cultural control of preharvest drop has relied upon plant growth regulators (PGRs), but the loss of daminozide (Alar) and 2,4,5-TP has severely limited the choices of effective stop-drop compounds. A more complete understanding of factors involved in preharvest drop is therefore imperative. Experiments were conducted to provide information about cellulase activity in the abscission zone, effects of applied auxin and ethylene biosynthesis inhibition on drop, changing sensitivity to abscission induction during the season, and relationships among seed number, fruit weight, and day of drop. Observational studies were used to study effects of fruit maturity, canopy positions, and morphology of stem attachment on time of fruit drop as well as characterizing the natural timing of late-season fruit drop. Increased activity of cellulase, but not polygalacturonase, in the abscission zone was detected within 4 days of cutting fruit to induce abscission. Both aminoethoxyvinyl glycine (AVG) and naphthaleneacetic acid (NAA) applied 2 or 4 days after cutting delayed drop, but NAA delayed drop 1.6 days longer than did AVG. Fruit of "RedChief Delicious"(D) exhibited a significantly reduced sensitivity to abscission-inducing treatments from mid-June until early July compared to earlier orr later in the season. Application of plant growth regulators to cut fruit revealed a significant interaction of NAA treatment with AVG treatment such that NAA delayed drop when applied with AVG but not without AVG. Fallen fruit had lower starch and higher soluble solids than fruit on the tree on the day of collection. The highest fruit in the canopy fell an average of 4.4d earlier than the lowest fruit. Day of drop was not different for fruit from king blooms vs. side blooms within an inflorescence. There was a trend for fruit from first year wood to drop later than fruit from older wood on "Delicious", but not "Smoothee Golden Delicious" trees. There was no detectable effect of angle of orientation of the subtending spur on the limb, the pedicel:spur abscission zone, or fruit axis of symmetry on time of fruit drop. No difference was detected in time of fruit drop between East and West or North and South sides of the trees. No substantial variation in day of drop of individual fruit was explained by number of seed in the fruit. Daily drop was recorded for three cultivars ("RedChief Delicious", "Smoothee Golden Delicious", and "Commander York") for three years. Variance of average day of drop from year to year was 40.1, while variance among cultivars within a year was 51.8. Variance from tree to tree within each cultivar, within each year, was only 18.6. Multiple regression modeling to identify relationships between weather factors and daily fruit drop revealed that much of the variability in time of drop was due to factors other than the weather events modeled. The best regression models developed explained only 8% to 35% of the variability in time of drop. The most important weather factors were daily minimum temperatures and precipitation. Rain events of greater than 5.0 mm following a drier period appeared to cause increased drop of all three cultivars in one out of the three years investigated.
- Inhibition of Flower Bud Initiation and Development in Apple by Defoliation, Gibberellic Acid and Crop Load ManipulationDavis, David Evan (Virginia Tech, 2002-09-24)Biennial bearing has been investigated longer and more extensively in apple than in any other fruit tree; however, it remains a serious problem in commercial apple production all over the world. Trees that have become biennial flower profusely and carry a heavy crop in the "on" year, and flower sparsely or not at all and carry little or no crop the following year, the "off" year. Fruit in the "on" year tend to be small, poorly colored, and of low quality, while the few fruit in the "off" year are usually too large, become susceptible to physiological disorders, and also are of poor quality. Without intervention, the crops in both the "on" and "off" years are undesirable and uneconomical. The most common method used by commercial apple growers to try to prevent biennial bearing is chemical fruit thinning, which is an "on" year method of removing a part of the crop before it matures on the tree. In general, growers don't do anything in the "off" year to prevent biennial bearing with the exceptions of fertilizing and pruning lightly. In this study, several experiments were conducted with the cultivars "Braeburn", "Golden Delicious", "Ramey York", and "Fuji" in the "off" year to try and suppress FBI and thus prevent a biennial bearing situation in the following year. The first set of experiments studied the effect of whole-tree and partial-tree defoliation on suppressing spur and lateral flowering and fruit set. Flowering and fruit set were suppressed with defoliation in most cases. Defoliation in early July caused the least amount of flowering the following year and in some cases it was zero. As the defoliation timing and severity was delayed, there was less suppression of flowering and fruit set. Ammonium thiosulfate and Endothal increased flowering but decreased fruit set compared to a control. Gramoxone suppressed flowering and fruit set. In another set of experiments, gibberellic acid (GA) treatments were evaluated to suppress FBI in "off" or light crop years. The GA4+7 treatments suppressed return bloom of both spur and lateral flowers more than the GA3 treatments. The effectiveness of GA declined with delayed application. Both GA treatments reduced lateral flowering the most on the basal 1/3 of the shoot. In a four year study, apple trees were thinned to one fruit per flowering cluster every year from 1997 to 2000. Other trees were thinned to zero fruit or two fruit per flowering cluster in alternate years from 1997 to 2000. Trees thinned to one fruit per flowering cluster had moderate flowering and fruit set the following year. Trees thinned to two fruit per flowering cluster had very little to no flowering the following year. Trees thinned to zero fruit per flowering cluster had a "snowball" bloom the following year. Trees that were alternately thinned to two or zero fruit per flowering cluster were in a biennial bearing situation.
- Photosynthate production and partitioning in apple leavesElkner, Timothy Edward (Virginia Tech, 1990-05-01)Mature field-grown apple trees were used to gain a better understanding of the influences of light and fruit on leaf physiology. Light effects on net photosynthesis (Pn), specific leaf weight (SLW), leaf N content (Weight/area) (Nw), and leaf N concentration (% dry weight) (Np) of spur leaves from two canopy locations were evaluated on four dates in 1987. Interior leaves had lower Pn, SLW, Nw, and Np than exterior leaves. In 1988 the influence of %available photosynthetic photon flux (PPF) on the same parameters was examined throughout the season. On most measurement dates both Pn and SLW increased quadratically while Nw increased linearly with increasing PPF. In both years positive linear relationships existed between Pn and Nw, SLW and Nw, and Pn and SLW.
- Wildlife damage control in Virginia. Controlling volesBromley, Peter T.; Byers, Ross E.; MacPherson, Sandra L., 1959- (Virginia Cooperative Extension Service, 1987-06)Recommends ways to control voles and diminish their damage on plants and crops.