Chilling and heat requirements of almond cultivars for flowering

Chilling and heat requirements for breaking dormancy and flowering were studied in ten almond cultivars which spanned the range of flowering times in this species. The cultivars showed a wide range of chilling requirements for flowering (chill units, CU), i.e. Achaak (266), Desmayo Largueta (309), Ramillete (326), S2332 (417), Marcona (435), Marta (478), Anto (n) over tilde eta (514), Ferragnes (558), 55133 (973), 81000 (996), with a narrower range of heat requirements, between 5942 and 7577 (growing degree hours, GDH). Extra-late-flowering cultivars, S5133 and 81000, finished the dormancy more than 40 days after the earliest cultivar Achaak. The results indicated that flowering time in almond is mainly a consequence of the chilling requirements of the different genotypes, with the heat requirements contributing a smaller effect. The choice of parents in a breeding programme for late flowering must be focused mainly on genotypes with high chilling requirements. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.