STOMATAL DENSITY AND ION LEAKAGE AS INDICATORS OF COLD HARDINESS IN WALNUT

In this work, leaf samples of one-year-old walnut cultivars and elite genotypes including ‘Serr’, ‘Lara’, ‘Pedro’, ‘Hartley’, ‘Z₃₀’, ‘Z₆₃’, ‘Z₆₇’ and ‘Z₅₃’ were taken and exposed to cold temperature at the rate of drop of 4°C per h at 0, -4, -8, -12 and -16°C. The lethal freezing temperature (LT₅₀) of cultivars and genotypes was evaluated by electrolyte leakage studies and the cultivars/genotypes were grouped into hardy, semi- hardy and non-hardy using this method. The density of stomata in the leaves of cultivars and elite genotypes rated as hardy were significantly lower than those rated as semi-hardy and non-hardy. Stomatal density of the cultivars and genotypes in the intermediate class fell within the range of hardy and non-hardy cultivars and genotypes. According to these results, number of stomata could be considered as a simple and effective anatomical selection marker for screening walnut plants for cold hardiness.