Cold hardiness in flower buds of highbush blueberry and thirteen Forsythia taxa

Cindy Leanna Cummings Flinn, Purdue University

Abstract

The relationship between low temperature exotherms (LTEs) and lethal ice formation in flower buds was evaluated as an estimator of hardiness in high bush blueberry and 13 Forsythia taxa. The relationship between physiological characteristics, LTEs, and morphological features were also examined. In blueberry buds, the number of LTEs detected was influenced by both cooling rate and amount of attached stem. Although mean LTE temperatures changed throughout the year, as did ice distribution in buds exposed to -5C, LTE temperature was not correlated with hardiness. Ice, which formed at -5C within the bracts and scales of all buds regardless of hardiness, occurred within the ovaries, pedicels, and rachises of buds that were lethally injured by the same temperature. In acclimated buds, these organs were devoid of ice even though they were connected to adjacent ice-containing tissues with strands of xylem large enough to allow ice propagation. The formation of ice within florets was associated with lethal injury even though mean LTE temperatures did not reliably estimate hardiness in blueberry. Flower buds of all 13 Forsythia taxa exhibited LTEs when examined by thermal analysis. In all but four taxa, the mean LTE temperature for each taxon closely approximated the temperature required to kill 50% of the buds (T$\sb{50}$) as determined by conventional hardiness tests. The lack of agreement in the estimates among those four taxa may have been due to the unavoidable inclusion of field injury in the T$\sb{50}$ estimate, resulting in an underestimation of hardiness. Mean LTE temperatures were not similarly affected because dead buds did not produce LTEs. Pistil size, as assessed through image analysis of either the largest longitudinal or transverse area, was positively correlated with LTE temperature among all taxa except 'Lynwood', 'Spectabilis', and F. suspensa. Among these latter three taxa, total soluble sugars, which were primarily comprised of glucose and fructose, generally increased throughout the winter. Neither total carbohydrates nor the negligible amounts of starch were correlated with hardiness. Hardiness was positively correlated with the following sugars, listed in increasing amounts: raffinose, stachyose, and an unknown sugar that eluted just before raffinose.

Degree

Ph.D.

Advisors

Ashworth, Purdue University.

Subject Area

Botany|Agronomy

COinS