Evaluation of chilling and heat requirements of flower buds in three commercial apricot cultivars by using different models

Estimating chilling and heat requirement of flower buds in fruit trees is important due to predicting flowering time for approporiate site selection to escape spring frost damage. In this serearch, chilling and heat requirements of three apricot cultivars (namely ‘Noori’, ‘Nasiri’ and ‘Shahroodi’) were estimated by chilling models (Chilling Hours, Utah and Dynamic) and Anderson heat model during 4 years (2009 to 2013) under Karaj climate condition. Based on different chilling models estimations, chilling requirements in apricot cultivars were estimated about 951-1100 chilling units, 41-53 chilling portion and 696-888 chilling hours in 'Noori', 1071-1286 chilling units, 47-63 chilling portion and 768-1008 chilling hours in 'Nasiri' and 1093.5-1400 chilling units, 58-63 chilling portion and 945-1100 chilling hours in 'Shahroodi'. Heat requirements for flowering in ‘Noori’, ‘Shahroodi’ and ‘Nasiri’ were estimated about 3964.5-4216.5, 3140-3587 and 4477.7-4859.7 growing degree-hours (GDH), respectively. Based on the results, the Dynamic model was more homogeneous rather than the Utah and Chilling Hour models in different years with showing lower coefficient of variation (4.95%) among different years. Results showed a high positive correlation between chilling requirement and flowering date, but negative correlation found between chilling and heat requirements. According to results, chilling requirement is an affective factor on change of flowering date in comparison to heat requirement in apricot cultivars under Karaj condition.