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Physiology of the terminal bud of Vaccinium macrocarpon Ait. cultivar McFarlin in relation to winter dormancy Eady, Francis Charles

Abstract

A study of the relationship between the winter dormant period and subsequent growth and development in Vaccinium macrocarpon Ait. cultivar McFarlin was carried out. The main objectives of the study were to obtain data on this relationship, to investigate the possible role of gibberellins in the induction of flowering, to correlate the data with development of the terminal bud under field conditions, and to provide basic information relating to the problem of frost injury. Controlled environment facilities were used to investigate the effect of chilling on the subsequent growth and development of the terminal bud. Exposure to an accumulation of chilling temperatures below 7°C was required to break dormancy of the terminal bud. Longer periods of chilling were needed to induce flower development. The faster rate of vegetative response was apparently due to development of the plant during the warmer portion of the daily temperature cycle. The best responses were obtained when the chilling conditions included a period of approximately 10°C during the day. The floral primordia of terminal buds in the field recommenced development in late February or early March, and were well differentiated by the end of April under British Columbia conditions. Application of gibberellic acid to dormant, unchilled terminal buds stimulated only vegetative growth. Gibberellin is probably not involved in the induction of floral development. Cold methanol extraction of gibberellin-like substances and subsequent purification was carried out on the leaves and terminal buds of V. macrocarpon grown in the field. Fractions of R[sub f] 0.1 were scraped from thin-layer chromatography sheets and bioassayed for gibberellin-like activity using a lettuce hypocotyl bioassay. An increase in such activity on March 9, 1970 was observed for both buds and leaves. On April 6, the activity in the leaves was considerably reduced but the bud level was increased, thus suggesting a translocation of gibberellin-like substances from the leaves to the terminal buds. Some possible implications of the study in relation to frost injury were discussed. The chilling requirement may be a factor in determining both the southern and northern limits of the geographic range of the species.

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