Enzymatic Responses of Some Pear Cultivars against Erwinia amylovora by Salicylic Acid and Bacillus subtilis Applications

Abstract

Fire blight caused by Erwinia amylovora (Ea), is a destructive and contagious disease affecting mainly pear and apple and some other members of Rosaceae family and, most of the world it is a quarantine disease. In an attempt to prevent new infections, plants are sprayed with either streptomycin, copper or both, but widespread use of their have led to antibiotic resistance in some areas. Some plant defence activators as salicylic acid (Sa) is one of the major chemicals in the regulation of the plant defense against pathogens, and additionally also beneficial bacterium Bacillus subtilis (Bs) can also prevent fire blight from infecting new trees. In this study, the efficacy of Sa and Bs and the enzymatic responses of the plants were investigated on Santa Maria and Ankara pear cultivars to prevent shoot blight of fire blight disease. Applications were performed as Bs, Bs+Ea, Sa, Sa+Ea, Bs+Sa, Bs+Sa+Ea and as positive control Ea and as negative control steril distilled water (SDW). When the new season shoot lengths of 3-year-old plants with homogeneous growth reached 20-25 cm, Sa, Bs and Bs+Sa were sprayed 2 times with 1 week intervals, and 3 days after the second applications, cutting the youngest 2 leaves on the shoot tip bacterial inoculations were carried out with a sterile scissors dipped in 10⁸ CFU^-1 of str. Ea ARDY5 solution. Leaf samples at different times from three individual plants were collected, and were homogenized for enzyme analysis. According to the results, it was determined significant differences (p<0.01) between applications, diseases severities (%) and enzymatic reactions (Peroxidase, Superoxide dismutase and Catalase) of pear cultivars. The most successful application in preventing the disease was in cv. Santa Maria Bs+Sa (57,4%) and in cv. Ankara Bs (67 %) the enzymatic responses of both pear cultivars showed compatibility with the disease severity levels. The successful results have shown that the application of B. subtilis and salicylic acid can be evaluated as new, eco-friendly and sustainable in the combat against fire blight.