Stability of the annual shoot diameter in Persian walnut: a case study of different morphotypes and years

Abstract

The basal diameter of the annual shoot (1YD) affects vegetative growth and fruiting of the walnut trees. In order to determine interdependency between the 1YD and the older parent wood, 64 walnut genotypes belonging to four different branching and fruiting habits (morphotypes M-I, M-II, M-III and M-IV) were investigated. Year-to-year stability of 1YD was tested with the architectural analysis of a 3-year-old fruiting branch and its constituents (a 3-year-old bearer + corresponding 2-year-old + annual shoots) during 3 successive years. Based on Pearson's correlation coefficients and the multiple regression analysis of 12 quantitative traits, 12 models (four morphotype in 3 successive years) of 1YD were formed. They were compared with the standard model which was calculated on the basis of 1-year measurements of 1Y with no respect to the branching and fruiting type and comprises three quantitative traits, i.e. basal diameter of a 2-year-old parent shoot (2YD), the length of 2Y shoot (2YL), and the length of annual shoot (1YL). In a single year, the 1YD was influenced by two–five parameters. Five out of 12 models agreed with the standard model: in the lateral fruiting genotypes (M-IV), 1YD was always under the influence of the 2Y diameter, and the 1Y length. In addition, the number of nodes of the 2Y parent shoot had an important influence on 1Y diameter. In the terminal bearers (M-I), the impact of 2YD on the 1YD slightly increased with the tree age, and some other parameters, like 1Ynumber and 1Ynodes, which became to be important for 1YD. In the intermediate genotypes with mezotonic ramification (M-II), the number of vegetative buds per 1Y and angles of 1Y had significant effects on 1YD. In the intermediate bearers with acrotonic ramification (M-III), one to four other parameters were included into the model each year beside the 1Y number. Since the traits of a 2-year-old parent shoot have a great influence on the 1YD, the information from the year N can be used for the prediction of the annual shoot development in the year N+1. Such a prediction is more reliable in M-I and M-IV than in M-II and M-III. When we deal with the intermediate fruiting cultivars, 1Y number has to be considered in prediction of 1Y diameter beside 2YD and 1YL.