The Chilling Requirements Of Kiwifruit Cultivars In China

Chilling requirements were usually refered as a minimum of chiling hours received during winter. Leaf and floral budbreak, uniformmity and density in spring were directly related to chilling requirements. Therefore, the knowledge of chiling requirements of a cultivar has significant paractical and economic impacts on the control, maintenance and breeding program of temperate fruits. To investigate the correlation between chilling requirements and Actinidia. chinensis Planchon complex, the chilling requirements of 14 kiwifruit cultivars (inculding hybrids between species) were determined by Utah model, and the main results are highlighted as follows:(a) To understand the correlation between chilling requirements and ploidy races (2x, 4x,6x), chilling requirements among nine kiwifruit cultivars of three ploidy leves were estimated by Utah model (CU) under field conditions. Cuttings were collected after a certain chilling accumulation in the field, and then were cultivated in a greenhouse maintained at 22℃. The physiological parameters were recorded every two days. The cultivars were refered as respectively, diploid cv ’Jinyu’, cv ’Donghong’, cv’Wuzhi-7’, tetraploid cv’Jintao’, cv ’Jinxia’, cv’H-15’, and hexaploid cv’Jinkui’, cv’Chuanmi-1’, cv’Bruno’. For vegetative budbreak, the mean value of diploid cvs were observed the lowest number of chilling requirements 422 CU; 722 CU and 761 CU were respectively for the mean values of tetraploid cvs and hexaploid cvs. As for floral budbreak, the mean value of diploid cvs also showed the lowest number of chilling reuirements 774 CU, the mean value of tetraploid cvs and hexaploid cvs were respectively for 935 CU and 966 CU. The ploidy showed association with chilling requirements for both vegetative and floral budbreak in this study. Significant variation was found between diploids and ploiyploids in mean values of both leaf and floral chilling requirements, while little difference was observed between tetraploids and hexaploids. The results above indicated that Acinidia. chinensis can growth and reproduce in a region with chilling accumulation above 700 CU. The diploid cvs were more suitable to warm climate conditions, and the tetraploid cvs or hexaploid cvs suited temperate climate conditions.(b) The kiwifruit cultivars studied were ’Moshan-4’(male parents)、’Maohua 6113’ (female parents)、’Mantianhong’(hybrids)、’Jinyan’(hybrids), and chilling requirements of these cultivars were estimated by Utah model (CU) under field conditions. Cuttings were collected after 100 CU、200 CU、400 CU、500 CU、700 CU、900 CU chilling accumulation, and then cultivated in a greenhouse maintained at 22℃. The cultivars showed a broad range of chilling requirements.’Mantianhong’ showed the lowest number of chilling reuirements 367 CU for leaf budbreak,’Jinyan’ with the hightest chilling requirements 814 CU,’Maohua 6113’ and Moshan-4 were respectively for 649 CU and 446 CU. The floral chilling requirements of four cultivars were ’Mantianhong’(551 CU), ’Jinyan’ (867 CU)、’Maohua 6113’(485 CU),’Jinyan’ (908 CU). In addition, cv ’Jinyan’ and cv ’Mantianhong’ showed transgressive inheritance, which implied that low chilling requirements genotypes can be selected by hybrids in kiwifruit breeding program.(c) The kiwifruit cultivars examined were diploid cv ’Wuzhi-7’, hexaploid cv ’Jinkui’. Chilling requirements of the two cultivars were estimated by Utah model (CU) under natural chilling conditions (methods as (a)) and artificial chilling conditions (4℃). As for artificial chilling conditions, all the cuttings were collected at the first 100 CU, and then were kept in artificial chilling conditions (4℃). The cuttings were cultivared in a greenhouse maintained at 22℃ each 100 CU. The results obtained in this study showed the chilling requirements of the two cltivars in different chilling methods are ’Wuzhi-7’ (261 CU),’Jinkui’(652 CU), and 959 CU,1249 CU for floral budbreak respectively. As for natural chilling conditions, the chilling requirements of ’Wuzhi-7’ and ’Jinkui were respectively 563CU、802 CU for leaf budbreak, and 893 CU、968 CU for floral budbreak. The results obtained in this study indicated that chilling requirements under artificial chilling conditions were higher than under natural chilling conditions for both of vegetative and flroal budbreak.