Fruiting behaviour of walnut trees influences the relationship between the morphometric traits of the parent wood and nut weight

Abstract

SummaryRelationships between nut weight and the morphometric characteristics of annual shoots (1Y) and current year shoots (cY) in walnut (Juglans regia L.) were investigated to test the hypothesis that these traits are linked, and influenced by fruiting behaviour. The terminal fruiting cultivar, ‘Franquette’, the intermediate bearer ‘Zdole-59’, and two cultivars, ‘Lara’ and ‘Fernor’, with lateral bearing habits but different lateral branching densities, were studied over 3 years. Regression analysis was conducted for modelling the relationship between nut weight and 1Y shoot diameter, 1Y shoot length, cY shoot diameter, cY shoot length, cY shoot number, cY leaves, and the number of nuts per cY shoot. In ‘Franquette’, nut weight was significantly correlated with 1Y shoot diameter, 1Y shoot length, cY shoot diameter, cY leaves, and nuts per cY shoot. Nut weight was expected to increase by 0.7 g when the nuts per cY shoot increased by 1. When 1Y shoot diameter (as well as cY shoot diameter) increased by 4 mm, nuts were heavier by 1 g. In the vigorous and densely-branched, lateral-bearing cultivar ‘Lara’, nut weight was negatively correlated with nuts per cY shoot, and with cY shoot length. Each nut was lighter by 0.6 g when one additional nut was inserted on each cY shoot. In ‘Zdole-59’, nut weight was closely correlated with 1Y shoot diameter and cY shoot number. An increase in cY shoot number by 1, caused an increase in nut weight by 0.4 g. In the less vigorous, sparsely-branched and lateral fruiting cultivar ‘Fernor’, none of the measured shoot traits correlated with nut weight and, consequently, none could be used to predict nut weight. In the terminal bearers, nut weight could be reliably predicted, based on 1Y shoot diameter measurements. In the vigorous, lateral-bearing cultivars, the number of nuts per cY shoot was shown to be the most useful parameter for nut weight prediction, whereas in intermediate bearers it was cY shoot number.