Problems in Standardizing Methods for Evaluating the Chilling Requirements for the Breaking of Dormancy in Buds of Woody Plants

By F. G. Dennis. 2003

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Temperature requirements. Precise determination of the temperature requirements for breaking dormancy is nearly impossible under field conditions, where solar radiation, diurnal fluctuations in temperature, and other factors cannot be controlled. Diurnal changes in winter temperatures may be less pronounced in the subtropics than in the temperate zone, but they still occur. While precise determination has been attempted under laboratory conditions, the practical significance with regard to fruit trees under orchard conditions must be considered with caution because the environmental variables were constant, rather than fluctuating, i.e., “unnatural.” In contrast, producers of pot plants for the Easter market will find precise temperature requirements of considerable value (see Dole, 2001), as the temperature can be controlled relatively easily. End of rest. Investigators often speak of the “end of rest” when evaluating bud dormancy. This is usually defined as the time when 50% of the buds on excised shoots are capable of growth within a given period of time when held at an appropriate temperature with their bases in water. As pointed out by Couvillon and Erez (1985), this is not truly the end of rest, but an arbitrary point in the breaking of rest; more chilling will permit >50% of the buds to grow. Nevertheless, it is “useful for measurement ... and comparison ...” (Seeley, 1996). An additional problem, discussed in more detail below, is determining what constitutes “growth.” Greening of the bud scales is sometimes taken as evidence of “budbreak,” but whether this really represents “end of rest” in a given bud is questionable.

Subfields: Molecular Biology, Plant Science

View Paper: https://www.semanticscholar.org/paper/81ec2229b1220b890560ef0ad2e0cad768fa81b0

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