Fruit, yield, and vegetative growth responses to photosynthetically active radiation during oil synthesis in olive trees

CHERBIY-HOFFMAN, S.U.; SEARLES, P.S.; HALL, A.J.; ROUSSEAUX, M.C.

SCIENTIA HORTICULTURAE

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 150 p. 110 - 116

0304-4238

Maximizing productivity in super high density and intensive olive orchards requires proper managementof illumination of the canopy walls and their interior. Currently, this is difficult to achieve due to thelimited knowledge about the responses to incident photosynthetically active radiation (PAR) of yielddeterminants and components. We determined the response functions for PAR during the oil synthesisphase of yield components (fruit dry weight and oil concentration) of fruit at a height of 2 m on thecanopy periphery by applying several radiation levels (3, 20, 40, and 70% of incident PAR) to the northside (S hemisphere) of well-illuminated trees. The experiment was initiated after endocarp hardening asfruit number had already been established at that time. This avoided possible confounding effects duecompensation between fruit number and size. Absence of differential fruit fall in response to treatmentsand of changes in (endocarp + seed) dry weight after application of treatment confirmed the achievementof this objective. Fruit dry weight, oil concentration, and, consequently, yield increased linearly with meandaily PAR receipt up to a threshold of 15 mol PAR m−2 d−1 (i.e., 40% of PAR). In treatments with irradiancelevels below this threshold the fruit became the priority sinks for assimilates, although their growth rateand oil concentration were reduced. Increments in length of non-fruiting branches and of trunk crosssectionalareas were substantially reduced in response to shading. We conclude that manipulation ofPAR levels during the oil synthesis phase can reduce final fruit dry weight and oil concentration, confirmsthe existence of upper thresholds to PAR responses for these variables, and provides evidence that fruitgrowth has priority in the partitioning of photosynthate over vegetative growth under low to moderatelevels of PAR.