Date of Award:

1975

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Advisor/Chair:

David R. Walker

Abstract

The effects of temperature, defoliation, light, and certain fall cultural practices on rest and hardiness of Gleason Elberta peach buds were studied. The influence of these factors on abscisic acid concentration in peach buds and a possible role of ABA in rest and hardiness of peach buds were also investigated.

Peach leaf buds enter rest in early fall, reach a rest intensity peak in early winter, then break rest as a chilling requirement is met. Complete defoliation before rest has begun will cause some leaf and flower buds to grow, while defoliation after rest has begun will not cause visible bud growth.

Effective chill-unit accumulation in the fall apparently did not begin until after a certain amount of leaf abscission had occurred. A GA3 application on August 15, 1974, delayed leaf abscission, and also caused an extension of the rest period. Early fall defoliation was correlated with a reduction in rest intensity and a reduction in the rest period of leaf buds.

A result of this study indicates the possibility of the existence of a rest promoting substance that was apparently translocated from a side of a tree exposed to ambient temperatures to a warm greenhouse covered side.

Decreasing temperatures caused an increase in flower bud hardiness, however, other factors also had effects on hardiness.

An extended day-length treatment caused flower buds to acclimate more slowly than those on untreated trees during the early fall period. The light affect was not evident as colder temperatures prevailed.

Buds on trees that were kept warm, acclimated to the same level as buds on trees kept at cooler but non freezing temperatures. However, it took the warm buds approximately four months longer to acclimate. Buds on trees that were exposed to below freezing temperatures acclimated to a much lower level than those on trees not exposed to freezing temperatures.

Fall pruning and heavy fertilization with ammonium nitrate did not reduce cold hardiness enough to be measured. However, buds on vigorous, large diameter twigs were more hardy during the early winter period than buds on twigs of smaller diameter.

The August 15 and September 19 GA3 treated trees and the early defoliated trees had a delay in acclimation during the fall period, although they did eventually acclimate to the same level as the untreated buds.

Abscisic acid concentration in peach leaf and flower buds was low before rest began, increased sharply during the rest inception period, and decreased in concentration before the end of rest. ABA may be a controlling factor in the inception of rest in peach.

There was no apparent relationship between ABA concentration and cold hardiness of Gleason Elberta peach flower buds.

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