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Abscisic acid (ABA) has a key role in some plant species under low-temperature stress (LTS). In this study the effects of ABA at four concentrations (0, 50, 100 and 200 lL) on electrolyte leakage (EL), visual damage index, soluble carbohydrate, proline, total phenolic compound and relative water content (RWC) of leaves of 'Sultana' grapevines were studied under LTS (0, 4 and -4°C). Moreover, to further elucidate the efficiency of foliar ABA on freezing tolerance, some relevant morphophysiological changes were evaluated at three sampling dates: September, October and November. The increase in cane and leaf EL and the visible symptoms of leaf damage caused by LTS were minimized by the application of ABA. Moreover, in ABA-treated vines, specifically at 200 lM, the contents of soluble carbohydrate, proline and total phenolic increased and the RWC decreased. These alterations in ABA-induced metabolism alleviated the deleterious effects of LTS on 'Sultana' grapevine. Freezing tolerance of ABA-treated vines improved within each sampling date in autumn. Foliar application of ABA at 200 lM decreased LT50 in September, October and November by -2.6, -3.6 and -3.9°C, respectively, as compared to those of control vines. This study also demonstrated that ABA was effective in shoot growth inhibition, leaf abscission and periderm development, indicating that ABA treatments advanced cold acclimation in grapevines. Increased fall freezing tolerance induced by foliar ABA application may be beneficial in nurseries, new established vineyards and for late-bearing cultivars in regions with fall frost events.

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The genetic structure and diversity of natural populations of Juglans regia L. in Iran were characterized using 11 microsatellite loci. A total of 105 individuals from seven populations were sampled. A high level of genetic diversity was observed within populations with the number of alleles per locus (A) ranging from three to 11 (average = 5.73), the proportion of polymorphic loci was 100%, and the expected heterozygosity ranged from 0.598 to 0.848 (average = 0.707). The proportion of genetic differentiation present among populations accounted for 12% of the total variation. Such considerable interpopulation differentiation detected in J. regia L. could have resulted from several factors, including restricted gene flow between populations. Significant departures from Hardy-Weinberg equilibrium were observed for WGA276, WGA32, and WGA321 loci. The deviations were primarily the result of the surplus of heterozygotes. The unweighted pair group method with arithmetic mean cluster analyses based on Nei's unbiased genetic distances separated the seven populations into two main groups.