Effects of Sheet-mulching and Rootstock on Flowering in Satsuma Mandarin ‘Sasebo Unshiu’

Abstract

In this study, the effects of sheet-mulching and rootstock on expression of Citrus FLOWERING LOCUS T (CiFT), number of flowers, and yield were investigated in satsuma mandarin ‘Sasebo Unshiu’ grafted on trifoliate orange (Poncirus trifoliata (L.) Raf.) or ‘Hiryu’ (Flying Dragon) for several years. In the analysis of data from a plural year, rootstock and sheet-mulching had no influence on CiFT expression or the number of flowers. On the other hand, in the analysis of data from a respective single year, significant differences were detected in CiFT expression and the number of flowers in some years. Trees both with and without sheet-mulching tended to flower in alternate years, and the pattern in trees with sheet-mulching were opposite to those without sheet-mulching. In the year when trees with sheet-mulching produced more flowers than the average number, those without sheet-mulching had fewer than the average number of flowers, and vice versa. The alternate bearing index in each tree showed that the annual change in the CiFT mRNA level was significantly greater in trees with than without sheet-mulching. These results suggest that sheet-mulching cultivation makes annual floral induction unstable in ‘Sasebo unshiu’ although this instability has no effect on the number of flowers or yield.