Cultivar and areal differences in the breaking period of bud endodormancy in pear plants

We investigated the occurrence of bud break in Japanese pear [Pyrus pyrifolia (Burm.f.) Nakai] cultivars and wild pear species to estimate the chilling requirement (CR) for breaking bud endodormancy. The leaf buds of the ‘Hosui’ and ‘Kosui’ cultivars showed a higher CR than their counterpart floral buds. Each CR values of the ‘Kosui’ and ‘Niitaka’ cultivars in three areas, namely Tottori (cold-winter area), Saga (moderate-winter area), and Kumamoto (warm-winter area), were completely dependent on the chilling accumulation in each cultivar and area. Among these areas, a chill unit (CU) value of 1566 was observed in Kumamoto in mid- or late February. The results suggest that pear cultivars showing less than 1500 CU should be selected for commercial production in that specific area, south of Kumamoto. Among the Japanese pear cultivars observed, ‘Akizuki,’ ‘Natsusoyoka,’ ‘Ryougetsu,’ and ‘Shinkansen’ showed the lowest CR, whereas ‘Syuugyoku’ showed the highest. The CR of Japanese pears ranged from 800 to 1800 CU. Among the examined wild pear plants, a bud break incidence of at least 60% was observed in 14 plants during the period from January 7 to February 4. Among these, P. calleryana (No. 12) showed the lowest CR and was thus identified as a useful rootstock for warm-winter regions.

► We investigated the occurrence of bud break in Japanese pear cultivars and wild pear species.
► Leaf buds of Japanese pear required a higher chilling requirement for breaking endodormancy than its floral buds.
► The chilling requirement of Japanese pears ranged from 800 to 1800 CU.
► P. calleryana (No. 12) showed the lowest chilling requirement among the pear plants examined.