Rest Prediction Model for Low-chilling ‘Sungold’ Nectarine1

Abstract

Floral bud break of 1-year-old rooted cuttings of ‘Sungold’ nectarine (Prunus persica (L.) Batsch) was observed following chilling at constant and diurnal temperature regimes. Continuous exposure to 10°C was as effective as 7°. Rate of bud break increased as chilling increased up to 750 hours. Floral bud break of plants exposed to 14 days at 30° during the middle of the chilling period was more rapid but failed to reach the level of activity of plants exposed to constant temperatures. A chill unit model developed for ‘Sungold’ nectarine which has a chilling requirement of 550 hours indicated a broader range of effective temperatures and a higher optimum for rest completion as compared to the Utah model and predicted rest completion more accurately than other methods when applied to orchard temperature data.

Modeling Temperature Requirements for Rest Development in Cornus sericea1

“…Chill unit models to predict the completion of rest (5,11,16) are based on the hypothesis that " chilling" temperatures break or overcome rest in temperate zone plants. These models assume that 1) " chilling" temperatures are only important in overcoming rest; 2) temperature effects are the same throughout the rest period (11); and 3) the starting date for accumulating chill units can be arbitrarily selected without consideration of the physiological stage of the plant (5,11,16,21). These assumptions have probably reduced the accuracy of the various chill unit models (5,11,21).…”

“…These models assume that 1) " chilling" temperatures are only important in overcoming rest; 2) temperature effects are the same throughout the rest period (11); and 3) the starting date for accumulating chill units can be arbitrarily selected without consideration of the physiological stage of the plant (5,11,16,21). These assumptions have probably reduced the accuracy of the various chill unit models (5,11,21). The identification of vegetative maturity as the starting point of " chilling" may help improve the accuracy of the chill unit models.…”

Characterization of the Influence of Moderate Temperatures on Rest Completion in Peach

“…The striking similarity in optimum temperature between our data, obtained with high-chilling cultivars, and that of Gilreath and Buchanan, obtained with low-chilling nectarines, suggests that optimum temperature does not differ for lowvs. high-chilling cultivars (10).…”

Prediction of Bulk Density of Pine Bark and/or Sand Potting Media from Laboratory Analyses of Individual Components

“…Prediction of plant development is based mainly on heat unit accumulation (3,4,11,12,13). The common method of calculating heat units is by means of the daily mean method, in which a day is the time unit and each degree above a base temperature has a linear effect on plant growth and on the accumulation of heat units.…”

“…In all predictive methods, it is assumed that the plant must accumulate a certain number of heat units in order to complete a developmental stage. Reports differ, however, with regard to the base temperature required for predicting the harvesting date of processing tomatoes (4,13). None of these methods shows any significant advantage over the actual counting of days.…”