Abstract: Regulation of flower bud differentiation is one of the key ways to improve yield and quality of apple products. Flower bud differentiation was regulated by many external factors，such as latitude and altitude. In order to explore the influence of latitude and altitude on the period of apple flower bud differentiation，this research was performed in three apple producing areas，including Yangling，Shaanxi Province，Jingning，Gansu Province，and Maoxian，Sichuan Province.‘Nagafu 2’at different altitudes （1 425，1 680，and 2 050 m）from Maoxian and Jingning（1 601 m），as well as different cultivars （‘Nagafu 2’，‘Yanfu 6’，‘Gala’，‘Qinguan’）from Yangling were used to determine their flower buds physiological differentiation. De-leaves and de-fruits were used to investigate the start time of floral induction. Dissection was used to observe morphological difference during flower bud development. The results show different cultivars need different time to finish flower bud physiological differentiation：‘Nagafu 2’lasts 56 days，‘Yanfu 6’needs 49 days，‘Gala’maintains 56 days and‘Qinguan’requests 42 days. In same place，flower buds physiological differentiation lasts longer time at low altitude than that at high altitude. At the altitude of 1 425 m，it needs about 75 days，while at an altitude of 1 680 m and 2 050 m，it only lasts 70 and 65 days. In different regions，flower buds differentiation of‘Nagafu 2’from the low latitude was longer than that from the high latitude，the results showed as below：Maoxian（70 d），Yangling（56 d），Jingning（49 d）. Growing stop of current-year shoots indicates beginning of flower buds physiological differentiation. At high altitude and high latitude regions，the growth of branches stopped late and a duration of flower buds physiological differentiation became short. Flower bud morphological differentiation of‘Gala’and‘Nagafu 2’started from the beginning of June to the end of October，and they are classified into six periods with significantly marked features，and some periods are overlapped with each other.‘Nagafu 2’always shows an earlier start and a later ending when compared with‘Gala’.‘Nagafu 2’also shows a long differentiation time.‘Gala’shows a more concentrated differentiation time than that of‘Nagafu 2’，which is believed to be related to the flower formation difficulty for Fuji apple.

Key words: apple, latitude, altitude, environmental factor, flower bud differentiation, arbuscular mycorrhiza, abiotic stress, horticulture plants, transcription factor, external factors, mycorrhizal effect