effect of planting date on dry matter content and agronomical characteristics of potato cultivars influenced by natural frost in field conditions

frost occurrence during plant growth created special conditions to evaluate the effects of planting date on dry matter content and agronomical characteristics of potato cultivars influenced by natural frost in field conditions. a split-plot experiment with three replications was carried out to compare three planting dates, as main plot, from 1 to 21 november with 10 day intervals and four cultivars (sante, savalan, santana and elmera) as sub plot for one year (2011-2011) at behbahan agriculture research station. treatments were arranged in a randomized complete block design. all haulms of plants in planting dates of 1 and 11 nov., in vegetative growth and tuber initiation stages all haulms were killed due to frost. however plants in planting date of 21 nov didn’t emerge. one week before harvest, haulms were defoliated. tubers were harvested at mid-may. the haulm and tuber dry matter content of all cultivars decreased in the first sampling date after frost. the recovery rate of savalan cultivar was higher than other cultivars. plants in planting date of 11 nov. were recovered faster than the plants in planting date of 1 nov. savalan cultivar produced the maximum dry matter content in planting dates of 1 and 11 nov. due to higher dry matter content of plants in planting date of 11 nov., the yield of mentioned planting date was higher than planting date of 1 nov. comparison of characteristics showed that frost influenced the total and marketable yield, marketable yield percentage and mean tuber weight of 1 and 11 nov planting dates, which were higher than 21 nov planting date. however, the effect of frost on mean tuber number and tuber dry matter content did not differe significantly. regarding to results, planting of winter potato should be avoided before late january in khuzestan province to minimize the risk of yield damage by frost and savalan cultivar is recommended for winter potato planting in this province.