Effects of Cropping on Photosynthesis, Dark Respiration, Leaf ABA Concentration and Inflorescence Induction in Satsuma Mandarin

Abstract

Apparent photosynthesis (Pa), dark respiration (Dr), net photosynthesis (Pn) and abscisic acid concentration were measured on current shoots of 19-year-old satsuma mandarin cv. Aoshima. These new growths are spring shoots that may differentiate simple and/or mixed flower buds the following season depending on whether adjacent shoots on the same branch units are bearing or not. Morphorogical characteristics and the alternate bearing tendency of vegetative shoots on currently bearing (VS-A) and non-bearing (VS-B) branch units were compared for three successive seasons.
1. There were no significant differences in number of nodes between VS-A and VS-B, but the internode lengths of the former were shorter than those of the latter; therefore, VS-B were shorter than those of VS-A.
2. In the following spring, VS-A produced more non-bearing shoots than did VS-B;conversely, VS-B initiated more flower buds than did VS-A.
3. Both apparent and net photosynthesis rates were at maximum from September to October but those on VS-B were consistently higher than those on VS-A. Both rates diminished from October to November; Pa of VS-A and VS-B became equal in November; whereas, Pn of VS-B remained higher than that of VS-A. No significant difference in Dr between branch units was observed during the growing season until November when Dr of VS-B exceeded that of VS-A.
4. The ABA levels of the terminal three leaves from VS-B were consistently and significantly lower than those in VS-A in October.
These results suggest that the inhibition of floral initiation on vegetative shoots of small branch units is related to lower phothsynthesis and higher ABA oncentration in leaves during the previous growing season.