Changes in photosynthesis and fruit characteristics in olive in response to assimilate availability

Abstract

The "source" level in the olive cultivar Leccino was varied by girdling at different stages of fruit growth. Afterwards, the effects on gas exchange, fruit growth, and ripening and blooming were studied. Girdling during fruit growth did not significantly influence net photosynthetic rate (P N) except in the last phase of fruit growth when the PN was reduced. In the girdled branch, PN began to decrease at the onset of starch accumulation because fruit growth ceased. In mid-November stomatal conductance (gs) and transpiration rate (E) were also reduced by girdling, whereas sub-stomatal CO2 concentration (Ci) increased in leaves from the girdled branches. The total chlorophyll content (Chl) tended to decrease in parallel with the reduced PN. Girdling did not substantially influence the leaf and shoot water contents. The large availability of assimilates seems to cause an earlier fruit ripening. In general, girdling increased fruit dry mass. Healing before the time when the majority of pulp growth occurs reduced the effect of girdling. June girdling increased the pit dry mass. Girdling at the beginning of August and September, compared to the control, increased the pulp dry mass, but the pit dry mass did not differ with respect to the control. The percentage of oil in the fruit, on a dry mass basis, increased with August and September girdlings, but the percentage of oil in the pulp did not change. Girdling reduced shoot growth, but the internode length was unchanged. Girdling slightly stimulated differentiation of flower buds.