evaluation of chilling requirement in four commercial grape cultivars

no sufficient of chilling is a major problem in producing temperate fruit in warm climates. so determination of chilling requirement of different cultivars of grape is important. the aim of this research was determination of chilling requirement of four grape vine commercial cultivars including: kolahdary, red rasin, yaghoti and white rasin that factorial experiment based on a completely randomized design with 12 chilling temperatures included: control, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900 and 1000 hours below 5±10c and three replications with 6 individual samples in each replicate. results showed that the effects of chilling requirement and cultivars on the studied traits including sprouting percentage, number of days to first sprouting shoot, number of days to last sprouting shoot and ratio of fresh weight to dry weight were significantly different. with increasing chilling duration from 200-1000 hour in yaghoti cultivar and from 300-1000 hour in other three cultivars, there was no significant difference in the percentage of sprouting. nevertheless at least 100 hr, of chilling is needed to get the favorable sprouting in yaghoti cultivar and 200 hr, in other three cultivars. results showed that with increasing chilling duration 0-1000 hr, the number of days for complete sprouting in kolahdary, red rasin, yaghoti, and white rasin cultivars decreased by 19, 19, 22 and 15 day, respectively. moreover, the highest ratio of fresh weight to dry weight of vegetative parts of cutting above mentioned cultivars was observed in 200-1000 hr, rang of chilling.