APS Homepage

Poster: Biology & Disease Mgmt: Genetics of Resistance


Mitigating the effects of shoot blight caused by Erwinia amylovora by enhancing plant systemic resistance
B. LEHMAN (1), C. Bower (1), K. Peter (1) (1) Penn State University, U.S.A.

Fire blight, caused by Erwinia amylovora, is one of the most devastating diseases of apple and pear and continues to cause large economic losses for tree fruit producers. Antibiotics are largely used to control blossom blight where bacterial resistance is absent, but the need exists for alternative control strategies where resistance occurs, and where shoot and canker blight are prevalent. One strategy is through controlled activation of the plant immune system by the application of materials containing plant defense activating compounds. Our goal was to test the effectiveness of an experimental resistance activating compound in reducing shoot blight severity. We applied three different concentrations of the chemical as foliar sprays on potted ‘Gala’ apple trees grafted on M.26 rootstocks. Three concentrations were applied at three, two, and one week before shoot tip inoculation and three, two and one day before shoot tip inoculation; Acibenzolar-S-methyl (Actigard) was also applied at three, two, and one week before shoot tip inoculation. Evaluations of shoot severity were made at one and two weeks after inoculation. Treatments started three days before inoculation reduced severity by 9, 26, and 35% for the three concentrations tested. Treatments started three weeks before inoculation reduced severity by 27, 21, and 44%, for the concentrations tested. Acibenzolar-S-methyl applications reduced severity by 75%. The testing of other alternatives is ongoing.