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In Egypt, Citrus represents one of the main fruit tree crops for both local and export potentials. In this study, leaf and vegetative bud samples were studied for cultivars of sour orange (seedless, sweet seeded, Brazilian and Spanish), common sweet orange (Florida, Fsido, Shamoty, and Valencia) and navel orange B29 from four different areas in Egypt (El-Qalubaiya governorate, Wadi El-Mollak; Ismailia governorate, El-Salheia; Sharqaia governorate, and El-Minya; South Egypt). Cluster analysis generated by random amplified polymorphic DNA (RAPD) molecular marker showed close similarities of the four sour orange accessions, used as rootstocks, where they were grouped in one cluster. The four cultivars of sweet common orange and sweet navel orange was linked together in a separate cluster. Navel orange cultivated at El-Minya and El-Salheia showed drop in yield due to substantial flower and young fruit abscission, whereas trees of the same cultivar did not suffer from abscission and yielded enhanced crop. Comparison of the four previously mentioned localities speculated that the navel orange accessions at El-Minya and El-Salheia are subjected to drought stress. This could be further verified by the substantially enhanced levels of abscisic acid in the plants showing abscission, as compared to those exhibiting normal flowering and enhanced fruiting at El-Qalubaiya and Wadi El-Mollak.
Key words: Abscisic acid, abscission, Citrus, cluster analysis, deoxyribonucleic acid (DNA) random amplified polymorphic DNAs (RAPDs), drought, rootstock, scions.