EFFECTS OF HARPIN PROTEIN AND HUMIC ACID ON SHOOT GROWTH AND FIRE BLIGHT DISEASE (Er-winia amylovora (Burr.) Winslow et al.) ON PEARS

Abstract

Harpin protein is critical to the virulence of Erwinia amylovora in host plants. Humic acid is reported to improve plant growth and resistance to plant diseases. In vitro and in vivo conditions, effectiveness of the systemic acquired resistance (SAR) inducer harpin protein, humic acid as a fertilizer, and bactericides copper and streptomycin were evaluated on pear cultivars, on shoot blight phase of the disease. Harpin protein was applied at the rate of 50 mg.L^-1 at two shoot lengths of 15-20 cm and 30-35 cm, humic acid (200 mg.L^-1) was applied three times when the shoot lengths 6-12 cm, 15-20 cm and 30-35 cm. On cv. Ankara, harpin protein showed about 55% effectiveness,  alone and  the addition of copper had been the most effective treatments in both years, followed by streptomycin. In addition, it reduced the shoot blight phase of the disease on the inoculated seedlings and trees significantly compared to copper applications and untreated controls. None of the chemicals affected shoot lengths of plants statistically. Humic acid applications gave worse results within  all of the chemicals in controlling fire blight on pear cultivars. In the bioassay test, on the contrary of humic acid, harpin protein reduced bacterial populations compairing to control plants in the leaves. Harpin protein should be seen as a complementary action in the whole process of fire blight control measures.