Abstract

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 ŒRieslingı and ŒChardonnayı grapevines were characterized. Examination of ultrathin (1micro m) sections of ŒRieslingı 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 ŒRieslingı 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 seasonıs 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 ŒRieslingı, 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 ŒRieslingı vines (BN-prone) had lower levels of sucrose compared to ŒChardonnayı vines (BN-insensitive). Role of mineral nutrient deprivation was examined in ŒRieslingı and ŒChardonnayı buds and the results indicated that BN is unlikely caused by essential nutrient deficiency. ŒChardonnayı, 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, ŒRieslingı, Syrahı, and ŒViognierı. 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.

---

List of attached files

File Name	Size (Bytes)
abstract.pdf	11,479 Bytes
acknowlg.pdf	5,844 Bytes
ch1.pdf	11,636 Bytes
ch2.pdf	39,301 Bytes
ch3.pdf	43,315 Bytes
ch4.pdf	160,198 Bytes
ch5.pdf	8,342 Bytes
contents.pdf	23,464 Bytes
fig31.pdf	356,969 Bytes
fig32.pdf	181,067 Bytes
fig33.pdf	224,735 Bytes
fig34.pdf	296,365 Bytes
fig35.pdf	322,515 Bytes
fig36.pdf	196,761 Bytes
fig37.pdf	266,138 Bytes
fig38.pdf	83,024 Bytes
tab41.pdf	96,329 Bytes
vita.pdf	4,683 Bytes

---

The author grants to Virginia Tech or its agents the right to archive and display their thesis or dissertation in whole or in part in the University Libraries in all forms of media, now or hereafter known. The author retains all proprietary rights, such as patent rights. The author also retains the right to use in future works (such as articles or books) all or part of this thesis or dissertation.

---

Send Suggestions or Comments to webmaster@scholar.lib.vt.edu