Chilling requirements and blooming dates of leading peach cultivars and a promising early maturing peach selection, Momo Tsukuba 127

A major goal of peach breeding programs in Japan is to develop cultivars with lower chilling requirements than the leading cultivars. Low-chill cultivars can be grown in subtropical as well as temperate regions. We investigated the chilling requirements (chill units; CU), heat requirements (growing degree hours; GDH), and blooming dates of 7 leading Japanese peach cultivars, 3 subtropical low-chill cultivars, and a promising new selection, Momo Tsukuba 127. In general, the CU of the 7 leading cultivars were higher than those of the 3 subtropical cultivars and Momo Tsukuba 127. The chilling and heat requirements were determined for the 3 leading high-chill cultivars (‘Akatsuki’, ‘Hikawahakuhou’, and ‘Kawanakajimahakutou’), the low-chill cultivar ‘Okinawa 1’, and Momo Tsukuba 127 during 4 seasons at a single location. The CU for ‘Okinawa 1’ and Momo Tsukuba 127 were significantly lower than those of the three high-chill cultivars. Because Momo Tsukuba 127 had lower chilling requirements than the 7 leading peach cultivars but higher chilling requirements than the subtropical cultivars, we classified this new selection as a mid-chill variety. We used the CU and GDH, along with local temperature data, to estimate the blooming dates of 4 cultivars and the new selection during 11 seasons at one location. Regression analyses showed high correlations between the calculated and actual blooming dates. We also compared calculated and actual blooming dates for the 3 leading cultivars and Momo Tsukuba 127 at between17 and 21 locations per genotype. A total of 25 locations were used, and these were widely spread over the temperate zones of Japan. The correlations between the calculated and actual blooming dates were close to 1:1. Our results indicated that our CU and GDH values, along with actual temperature data, could be used to reliably estimate the blooming dates of the genotypes. Because of its lower chilling requirements, the new selection, Momo Tsukuba 127, bloomed 7 or more days earlier than the leading peach cultivars in this study.