Anatomical Developments and the Role of Carbohydrate or Mineral Nutrient Deficiency in Bud Necrosis of 'Riesling' grapevines (Vitis Vinifera L.)

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 '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.