|Author: ||F. Takishita|
|Keywords: ||citrange, accumulative hours below 7°C, 'Flying Dragon', sprout, trifoliate orange|
Satsuma mandarin, the most important citrus in Japan, is usually grafted onto trifoliate orange.
Satsuma mandarin on trifoliate orange is considered to enter dormancy in autumn in year-round cultivation.
With global warming, winter temperature would increase, and there is concern that dormancy would not be released.
The objective of this experiment was to grasp how long low temperature would be required to release dormancy in citrus rootstocks, and the influence of grafting on this process.
Trifoliate oranges, normal type and 'Flying Dragon', 'Carrizo' citrange, as well as their mutually grafted seedlings were used as materials.
After each plant was exposed outdoors, whole pots were incubated at 25°C. The buds started sprouting in December after incubating a week, so the rate of sprouted buds one and two weeks after the beginning of incubation was researched for all genotypes and grafted plants.
Normal and 'Flying Dragon' trifoliate oranges were released from dormancy in mid-February in 2005-2006 and 2006-2007 seasons.
At this time, the accumulative hours below 7°C (AH7) reached 1000 h.
On the other hand, 'Carrizo' citrange sprouted in late December or during January At this time, AH7 was 600-800 h.
Grafting influenced dormancy, i.e. trifoliate orange rootstock extended the period of dormancy of citrange.
Conversely, citrange rootstock shortened the period of dormancy of trifoliate orange.
Winter temperature, genetic character and grafting greatly influenced the time of dormancy release in citrus rootstocks, so further research is desired in other citrus species.
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