Evaluation of Citrus Cultivars Resistance to Alternaria alternata, the Causal Agent of Brown Spot Disease, Using RAPD-PCR

ارزيابي مقاومت ارقام مختلف مركبات نسبت به Alternaria alternata عامل بيماري لكه قهوهاي مركبات با استفاده از RAPD-PCR

ABSTRACT Alternaria brown spot is one of the most important worldwide diseases of citrus. This disease caused by Alternaria alternata (Fr.:Fr.) Kessl, and causing serious economical losses in citrus yield. Citrus cultivars vary genetically in their degree of brown spot resistance. In this research, susceptibility of 13 citrus cultivars including "Orlando tangelo, Minneloa tangelo, Clementine mandarin, Fortune, Page, Unesi, Kino, Local tangerine, Sweet orange (Thomson and Local orange), Sweet lemon, Lime and Sour orange to Alternaria brown spot was analyzed. The results revealed that Page, Orlando tangelo and Mineola tangelo were highly susceptible to A. alternata and showed severe brown spot symptoms on leaves. Based on Disease rating Index (DRI) these cultivars were placed in sensitive class (S). However, Sour orange and Clementine with the least DRI were designated as resistance varieties (R). In molecular method, the total DNA was extracted from leaves with CTAB-phenol chloroform method and DNA fragments were amplified by RAPD-PCR using 2 single, random 10mer oligonucleotide primers; AL3 and P12. In sour orange and Clementine mandarin an 850 bp fragment by P12 and a 1250 bp fragment by AL3 primer were amplified and there was not observed any fragment in these regions in other citrus cultivars. Based on results of molecular marker and pathogenicity test, sour orange and Clementine are resistance to Alternaria brown spot and have resistant gene (amplified by P12 and AL3 primers). This is the first report of resistant gene in citrus cultivars to Alternaria alternata in Iran. Keywords: Alternaria alternata, Resistance gene, Citrus cultivars, Sour orange, RAPD-PCR