Determination of the best harvesting date of white seedless grape to produce good quality raisin in Qazvin region

Qualitative and quantitative aspects of Iranian raisin, as a significant exporting material, has been declined because of several reasons in recent years. There are many factors affecting quality of raisin. Fruit harvesting date is one of these factors which is highly effective on quantitative and qualitative traits of raisin through alterating fruit characteristics and even plant yield. Therefore, this investigation was carried out to determine the best time of white seedless grape harvesting in Qazvin for obtaining a raisin uniform in color and size with suitable taste and tissue and highest in yield. For this purpose, harvesting dates with 10-day intervals including 22nd August, 1, 11, 21st September and 2nd October were used in a RCBD with four replications in one of the orchards of Takestan region. In each treatment, four plants were considered and harvesting was done form two middle plants. In each harvesting date, traits such as content of soluble solid materials(TSS), bunch length, bunch weight, volume and weight of berry, grape yield, and after production of raisin, traits such as color, size, 50-seed weight, marketing value and amount of recoverable raisin were measured. Results showed that late harvests (21st September and 2nd October) having about 23% TSS, weight of 18 grams for 50-seed of raisins and the best ratio of grape to raisin (3.5 kg grape for production of one kg golden yellow raisin) are the most suitable harvesting date for raisin production in Takestan region. Also higher TSS% lead to significant increase in quality, color, and 50-seed weight and raisin production efficiency.