An evaluation Heat unit of potato genotypes for determining different maturity groups in Gorgan region

In order to create different environmental conditions and to estimate the required growth degree days (GDD) and heat units (CHU), fourteen foreign and Iranian potato genotypes were evaluated in three different maturity groups in two regions, Shako Mountain, and plain region for three cropping seasons (2007-2010). The results revealed that both systems, i.e. GDD and CHU changed maturity group of some of the genotypes based on heat requirement during emergence and flowering. Some genotypes such as 397007-11 and Sante were grouped late matured compared to the previous grouping based on IBPGR. The effect of year and year by genotype interaction were significant in both locations. Years with higher air average temperature increased the heat index 1200 (GDD) and 4000 (CHU) in the mountain region of Shahkooh whereas in the plain region of Gorgan GDD and CHU increased 1000 and 2000, respectively Genotypes 397009-3 could be considered the best genotype because of producing the highest tuber yield of 27003 kgha-1 in autumn and 28446 kgha-1 in spring planting and for producing 12.5 and 11.9 tuber plant-1 in autumn and spring planting, respectively. Based on the information available about the maturing groups according to IBPGR and the time of the phonological stages during evaluation of these genotypes, the grouping based on GDD seemed more logical.Based on duration to maturity grouping based on GDD was more reliable and conformed with grouping based on estimation of duration from planting to flowering.