Flowering and heat requirements of four olive cultivars grown in the south of Tunisia

Olive phenology is a sensitive indicator of climate change and especially the climatic warming of areas where olives are grown. Flowering occurs after being exposed to chilling and subsequent accumulation. The Mediterranean region is characterized by a changeable climate, especially in spring when temperature varies quickly from year to year. In this context, a study was carried out on local ('Meski' and 'Chemlali') and foreign ('Picholine' and 'Koroneiki') olive cultivars grown in southern Tunisia to calculate the heat requirements for flowering during the period 2008-2012. The aim of the present work is to compare flowering full bloom dates for the different cultivars and to calculate the heat requirement until flowering. Heat units were expressed in growing degree day (GDD). For the GDD accumulation, the results indicated a large inter-annual variation. The GDD began being recorded when the calculations of chilling accumulation were stopped. There were differences in flowering dates among cultivars. During the springs of 2008, 2009 and 2010, 'Chemlali' began blooming on 16 April, just after accumulation of 173.85, 100.7 and 160.65 GDD after the end of chilling respectively. 'Koroneiki' was in full bloom on 12 April in 2010-2011 after accumulation of 133.33 GDD. For the year 2011-2012, 'Meski' entered to bloom on 12 April after accumulation of 182.56 GDD while the other cultivars entered into bloom after receiving heat requirements ranging between 169.45 and 267.6 GDD.