Short- and long-term growth of navel orange fruit

Abstract

SummarySeasonal patterns of fruit development of young and mature `Bellamy' navel orange trees were measured from mid November to late July. Growth of whole fruit, expressed as fresh or dry weight, was best described by a fourparameter logistic curve (R2>0.99). The fresh weight growth curves of fruit from young and mature trees were not significantly different. Dry weights and fresh weights were linearly correlated (R2>0.99). The relationship between relative growth rate (RGR) of whole fruit and time was best described by two linear regressions (R2>0.98, 0.92, respectively). The two linear phases of RGR did not correspond to ontogenic phases of fruit development as described by Bain (1958). Increases in whole fruit and pulp radii, and whole fruit, pulp, rind and albedo volume during fruit development followed single sigmoidal patterns (four parameter logistic function, R2 >0.99). Relative changes in the volume of the structural parts of the fruit were small during Stage III of fruit development. Diurnal variations in growth and rind temperature of fruit from young (under continuous irrigation) and mature (under weekly irrigation) `Leng' navel orange trees were recorded during Stage II of fruit development. Inelastic growth measured by LVDTs was described better by diurnal diameter means (max 1 min)/2 than diurnal maxima or minima. Diurnal diameter means of fruit from young trees showed a significant (R2 = 0.42, P<0.0001) relationship to daily ambient temperature maxima, and the diurnal growth profiles paralleled the diurnal temperature profiles of the rind. In contrast, the diurnal growth rhythms of fruit from mature trees were insensitive to ambient temperature maxima and the diurnal rhythms appeared to reflect the water status of the tree.