Screening some common onion cultivars for resistance to fusarium basal rot ‎‎(Fusarium oxyosporum f. sp cepae) and assaying expression levels of the COI1 and ‎ERF1 genes in sensitive and tolerant cultivars

Onion is a major horticultural crop, which is regularly affected by substantial yield loss due to fusarium basal rot. In this research, the pathogenicity tests of eight Fusarium isolates were performed on onion bulbs of the Early Grano cultivar in vitro. Four isolates, namely HR1, HR97, HR42, and HR21, showed the highest degree of pathogenicity. The host ranges of the four pathogenic isolates were determined in the greenhouse condition. The HR1, HR42, and HR21 were isolated from the genus Allium. The TEF regions were sequenced on these isolates and the diagnosis of Fusarium oxyosporum f. sp cepae was approved based on a comparison with the sequence data of the GenBank. The screening for fusarium basal rot was performed on some Iranian onion cultivars together with the two foreign cultivars, namely the Early Grano and Sweet Spanish. The results indicated that the Ghermeze-Azarshahr cultivar and Sefide-Kashan cultivar were, respectively, sensitive and tolerant to this disease. The expressions of the COI1 transcript (Coronatine-Insensitive 1) and the ERF1 transcript (Ethylene Response Factor 1) were measured in the sensitive and tolerant cultivars after inoculation with the Fusarium isolates. The results showed no difference in the COI1 expression between the sensitive and tolerant cultivars. The ERF1 expression was higher in the Ghermeze-Azarshahr cultivar 24 hours after inoculation; whereas, an ERF1 expression decline was observed in the Sefide-Kashan cultivar. According to the results, it seems that the ERF1 plays a key role in resistance mechanisms of onions infected with fusarium basal rot disease.