Heat unit evaluation 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 in three different maturity groups were evaluated 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 as the late matured compared to the previous grouping based on IBPGR. Year and year by genotype interaction effect 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 as the best genotype because of producing the highest tuber yield (27003 kg ha-1) in autumn and spring cropping (28446 kg ha-1), with production of 12.5 and 11.9 tuber plant-1 in autumn and spring cropping, 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.