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A METHODOLOGY FOR STUDIES OF DORMANCY AND
WATER CONTENT OF FLORAL BUDS IN SOUR CHERRY
CV. STEVNSBÆR
Ivar Dencker, KVL, Agrovej 10, 2630 Taastrup, Danmark
Torben Toldam Andersen, KVL, Agrovej 10, 2630 Taastrup, Danmark
The sour cherry ’Stevnsbær’ suffers severely from bud damages during winter in both
Denmark and Sweden. The floral mortality may exceed 90 percent on annual shoots. It is now
known that this bud damage can occur already in December, being caused by night frosts of
only –6 to –9 0 C in both year 1999 and 2000. It is also known that there is a strong negative
relationship between the water content of the flower bud and the actual frost hardiness. This
experiment was carried out to study the water content and dormancy of flower buds in
‘Stevnsbær’ during autumn and early winter year 2000-2001. In the period August-January,
lateral flower buds were sampled from the base and tip of annual shoots of trees from
different irrigation and fertilizer treatments. The buds were put into sealed plastic tubes,
placed on ice and immediately brought to the lab for fresh and dry matter determinations.
Furthermore, in September-January shoot pieces from the same dates and trees as above were
forced for six days at +20 0 C in a climate chamber, whereafter the buds were broken off and
weighed as in the field samplings. During autumn a major decrease in the water content of
flower buds was recorded in all treatments. Lateral buds near the shoot tip had a markedly
higher water content than buds at the shoot base, and this difference persisted throughout the
sampling period. The forcing of buds under optimized growing conditions showed that buds
remained dormant only until the middle of November. From late November and throughout
the rest of the sampling period forced buds turned green and swelled distinctly, and
simultaneously such forced buds had a sharp increase in water content. Bud dormancy was
gone in late November in all treatments. The lack of bud dormancy in December may explain
the comprehensive bud damages occurring in Stevnsbær: A warm period in the beginning of
December (as in year 2000) may force the buds, increasing their water content and
subsequently a sudden but not very severe freeze (as in year 2000) would cause frost
damages. The usability of water content measurements in floral buds to predict frost hardiness
is discussed.
Poster