Screening for Drought-tolerant Genotypes of Persian Walnuts (Juglans regia L.) During Seed Germination

Abstract

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).