Chilling and Heat Requirements of Some Grape Cultivars (Vitis vinifera L)

An experiment was carried out in the experimental orchard and the laboratory of fruit science (Pomology) division, Faculty of Agriculture, Assiut University, Assiut, Egypt during 2004/2005 and 2005/2006 seasons to determine the chilling and heat requirements in addition to some berry characteristics of four grape cultivars namely: Beauty Seedless, Palomino, Rish Baba and Ruby Seedless grown under warm climatic conditions. The endodormancy was considered to be broken when the percentage of bud break reached 50% or more. At endodormancy completion (50% bud break), additional chilling resulted in more increase of the bud break percentage towards the maximum value. Palomino cultivar recorded the highest chilling and heat requirements followed by Ruby Seedless while Beauty Seedless and Rish Baba cultivars showed the lowest values. The grapevines required (two seasons average) 118, 247, 89 and 180 chill units at ≤ 7.2°C and 368, 651, 300 and 497 chill units at ≤ 10°C for Beauty Seedless, Palomino, Rish Baba and Ruby Seedless cultivars, respectively, to achieve 50% bud break. Palomino and Ruby Seedless cultivars required growing degree hours (GDH) higher than that of Beauty Seedless and Rish Baba to reach the ripening stage. On the other hand, Palomino, Ruby Seedless and Rish Baba cultivars showed good berry quality while Beauty Seedless needs further studies concerning the improvement of its berry quality under warm climatic conditions.