Cold and heat requirements of the apricot tree (Prunus armeniaca L.)

The cold units (CU) and heat units (HU) required for the flowering of 13 ap ricot cultivars (Prunus armeniaca L.) cultivated in Abaran (Murcia) have be en established. The end of the dormancy period was determined on the basis of the dry-weight increase of the flower buds. The tests in which the dry w eight was measured after forcing the flower buds at 20 degrees C turned out to be more precise in detecting the beginning of the reactivation phase th an those in which they were not forced.