Characterization of Some Walnut Genotypes Using RAPD Markers

To evaluate morphological markers linked with drought stress resistance for screening almond genotypes in the breeding programs the effect of drought stress was studied on six nominated almond genotypes seedlings. The six pre-selected water stress mimposed almond genotypes included: homozygote sweet (Butte from University of California), heterozygote sweet (Shahrood12, Shahrood18, Shahrood21 and White) and homozygote Bitter (Bitter Genotype). Moisture treatments were: well irrigated plants (?s=-0.33 MPa) vs drought stressed ones (?s=-1.8 MPa). The factorial experiment was conducted based on a randomized complete block design (2 irrigation factors, 6 genotype factors) of 3 replications. Such morphological and physiological traits as: leaf RWC and water potential, stomatal size and density, leaf and root N content, chlorophyll fluorescence, leaf size, root and shoot dry weight (DW), were assessed. Results indicated that different genotypes show varied degrees of resistance to drought stress. Analysis of leaf morphological traits and water status in plants showed genotypes, different strategies in coping up with and compensating for the effect of drought. All genotypes preserved their leaves although, having produced smaller leaves. Leaf size, root or shoot DW, stomatal density and root or leaf nitrogen content were not correlated with drought resistance in the studied seedlings. Ratio of root DW to leaf area increased with drought in White cultivar, while (by considering chlorophyll fluorescence and water relations) this genotype was the most resistant to drought among the studied cultivars. Specific leaf area (SLA) and stomatal size being the lowest in Butte led to the conclusion that it was the least resistant to drought.