Chilling and heating accumulations impact bud burst and flowering of 'KU-PP2' peach tree

Responses to chilling accumulation and heat requirement are crucial factors for peach growing in forcing culture. However, the performance of 'KU-PP2' peach trees under forcing conditions has not been elucidated. In this study, we investigated the effects of chilling accumulation and heat requirement on breaking dormancy and flower development and the correlation between these factors over two consecutive seasons. 'KU-PP2' peach trees in containers were transferred to a phytotron after being exposed to different chilling periods (250, 500 and 750 h). The air temperature in phytotron varied at 15, 20 and 25°C. Bud bursting and flowering were monitored every three days. The results show that the duration of chilling exposure reduced the time and heat required to induce bud break and flowering. At 250 chilling hours (CH), 'KU-PP2' trees required more than 10,000°C growing degree hours (GDH) for flower bloom, while at 500 and 750 CH, they required between 4,000 and 9,000°C GDH. The highest temperature accelerated budburst in peach trees with low- and mid-chilling exposure but delayed and prolonged the flowering period in trees with high chilling accumulation. Moreover, the heating temperature was also negatively correlated with the size of reproductive organs, pollen germination, and fruit set in both seasons. The interaction between chilling exposure and heating temperature affected final bud bursting, flower size and fruit set. These results suggested that inadequate chilling accumulation and excessive heat in forcing culture might have a negative effect on flowering and yield of 'KU-PP2'.