overcoming winter rest of grapevine grown in subtropical regions using dormancy-breaking agents

although, grapevines do not have a high chilling requirement, its fulfillment is critical for normal development of the vines. in tropical and subtropical regions such as farrashband, in the south of iran, there is no adequate winter chilling to release bud dormancy in grapevines. so it is necessary to consider the effect of chemical dormancy–breaking agents on bud dormancy. in the present research an aqueous solution of dormex (3.5 and 7% , v/v), volk oil (3.5 and 7% , v/v) and potassium nitrate (1.5 and 3% , w/v) were sprayed at two separate dates (26th jan. and 11th feb. 2007) on pruned canes of vines in farrashband region, fars province, iran. results indicated that the application of dormancy-breaking chemicals in the first spray was more effective than that of the second date with respect to advancing budbreak as well as flowering. dormex (3.5%) and kno3 (1.5%) were found to be more effective than other treatments. the highest cluster weight was obtained in dormex (3.5%) and kno3 (3%). dormancy-breaking chemicals and time of application had little effect on tss, total acid and the vitamin c of ripened fruits. in general, dormancy-breaking agents and time of application positively affected advancing budbreak as well as flowering as a result of increased yield. in warm climates where the amount of chilling is not sufficient, the application of dormancy-breaking chemicals (dormex, kno3, volk oil) at the proper time may overcome bud dormancy.