|Authors: ||A.N. Azarenko, A. Chozinski, L.J. Brewer|
|Keywords: ||Prunus avium, growing degree hour, growth stage, harvest date, cherry simulation model|
Sweet cherry (Prunus avium L.) fruit diameters were measured three times weekly from shuck split to maturity for seven cultivars during 2003–2004 in Corvallis, Oregon, USA. Cumulative growing degree hours (GDH, base temperature 4°C) were calculated from peak bloom for each cultivar using an asymmetric curvilinear model.
To determine GDH accumulation at temperatures between 4°C and 25°C (optimum), the following formula was applied:
GDH = [(25°C – 4°C)/2](1 + cos(π + π(hourly temperature – 4°C)/(25°C – 4°C)))
At temperatures above optimum, a second formula was applied incorporating a critical temperature (36°C) for fruit trees:
GDH = (25°C – 4°C)(1 + cos(π/2 + π/2 (hourly temperature – 25°C)/(36°C – 25°C))).
Cumulative GDHs were calculated from peak bloom for each cultivar.
Fruit diameter data were plotted against GDH describing a double sigmoidal curve.
The second derivative was used to identify concavity changes or end points for each stage of development.
Mean slopes for each stage were calculated using ending/beginning points in the data.
Data were analyzed using general linear model and lsmeans separation of means.
The double-sigmoidal growth curve illustrates a clear separation of physiological stages: first rapid growth stage (cell division and enlargement) (I), pit hardening (II), and second rapid growth stage (cell enlargement) (III). The duration of stage II increased as fruit ripened later.
Across years, the end of Stages II and III could be predicted with the use of GDHs.
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