Correlation and causal relationships among 21 horticultural traits were determined using 71 walnut genotypes selected from seven valleys in Kerman Province, Iran. Pearson's correlation coefficient was calculated. Kernel percentage and blight susceptibility were used as dependent variables in a stepwise regression model to determine predictor variables. Direct and indirect effects of each independent variable were calculated using path analysis. A highly significant correlation was observed between lateral bearing habit and yield. Lateral-bearing trees were also more susceptible to blight and winter cold than terminal bearers. Kernel and nut weights, shell thickness, and difficulty of extracting kernel halves were the most important traits accounting for kernel variation. Kernel weight and difficulty extracting kernel halves had the strongest positive direct effects and nut weight the most negative. Flowering habit, nut shape, and leafing date had positive direct effects on blight susceptibility, but the large residual effects suggest there are other important determinant traits for blight susceptibility, which were not considered in this study.

The effects of osmotic stress induced by polyethylene glycol on the seed germination of 16 walnut genotypes (‘Z30’, ‘Z53’, ‘Z67’, ‘Z60’, ‘Z63’, ‘K72’, ‘B21’, ‘V30’, ‘Panegine20’, ‘Hartley’, ‘Pedro’, ‘Vina’, ‘Lara’, ‘Serr’, ‘Ronde de Montignac’, and ‘Chandler’) of Juglans regia L. were studied. Potted seeds were kept under controlled conditions (12/12-h light/dark photoperiod and 25 ± 1 °C) during the experiments. The objective was to screen genotypes and determine the critical range of osmotic potential (ψS) for walnut seeds during germination. Decreasing the ψS of the germination solutions markedly reduced germination percentage in all genotypes, but there were variations in degree among the genotypes. The Z genotypes were the most sensitive to osmotic stress, and their germination rates were the lowest at ψS more negative than –0.75 MPa. Cluster analysis produced a dendrogram with four groups differing in their tolerance to osmotic stress. Based on factor analysis, four factors explained 90.45% of data total variance. Factor analysis showed that tissue fresh and dry weight, tissue water content, and thickness were the most important traits under drought condition. Regression analysis failed to show a significant relationship between percent germination and either seed weight (r2 = 0.0601) or kernel weight (r2 = 0.0258).

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