Architectural traits of fruiting shoots in Juglans regia (Juglandaceae) related to fruiting habit and environmental conditions

Abstract

The objective of the present study was to compare some basic architectural traits of annual shoots (1YS) in common walnut (Juglans regia L.), and to evaluate the impact of extreme drought and heat on the fruiting and growing response of the annual shoots. Measurements were conducted on three cultivars that have a terminal-bearing fruiting habit (Franquette), intermediate fruiting behaviour (Zdole-59) and a lateral-bearing fruiting habit (Fernor). Across 3 years, the mean 1YS of Franquette were one-third longer than those of the other two cultivars and their mean basal diameter was larger than that in Fernor and almost equal to that in Zdole-59. For Franquette, the length : diameter ratio showed a slender shoot morphology, whereas the shoot morphology was more compact in Fernor and Zdole-59. The 1YS of Franquette and Fernor had equal fruiting potential, with 2.8 and 2.7 fruits per shoot, respectively. Short but thick 1YS with the highest number of vegetative buds indicated dense branching and the good growing capacity of Zdole-59. The number of vegetative buds per 1YS changed during the 3 years in all cultivars, whereas the number of flowering buds per 1YS did not change in Franquette. Extreme dry and hot weather during the spring and summer of 2003 caused a reduction of 35–58% in length and a reduction of 2–16% in the basal diameter of the 1YS, regardless of fruiting behaviour. In the less vigorous, but highly productive lateral-bearer Fernor, unsuitable weather conditions in 2003 affected flower differentiation and resulted in significantly fewer fruits in 2004. The mean daily temperature in the period March–August was negatively correlated with the 1YS diameter and the number of vegetative buds per 1YS, whereas the mean precipitation during the same period showed a positive relationship with the length and diameter of the 1YS. Information obtained through shoot-architecture analysis could be useful in cultivar choice for new orchards, especially at a time of great climatic changes. Simple predictions for further development of the annual shoots could also be made.