Field Susceptibility of Scab-Resistant Apple Cultivars and Selections to Cedar Apple Rust, Quince Rust and Hawthorn Rust

Abstract

Apple cultivars and selections developed from the scab-resistant breeding programs in Ottawa, Ontario; Kentville, Nova Scotia; the disease-resistant breeding program at Geneva, N.Y.; and the cooperative breeding program at the universities of Purdue, Rutgers and Illinois were evaluated under field conditions for resistance to cedar apple rust (CAR), quince rust (QR) and hawthorn rust (HR). Between 1985 and 1989, percent fruit infection on the various cultivars and selections varied from 0 to 98 for CAR and from 0 to 79 for QR. Leaf lesions resulting from HR infection were smaller in diameter and fewer in number than those resulting from CAR infection. Long wetting periods during bud development from the pink to the calyx stage contributed to the infections. The scab-resistant cultivars ‘Liberty,’ ‘Macfree,’ ‘Moira,’ ‘Murray,’ ‘Nova Easygro,’ ‘Novamac,’ ‘Priscilla,’ ‘Redfree,’ and ‘Trent’ exhibited a high level of resistance to CAR. While none of the cultivars and selections were immune to QR, ‘Jonafree,’ ‘Liberty,’ ‘Redfree,’ ‘Co-op 1,’ ‘Co-op 8,’ ‘Co-op 15,’ and ‘O-634’ had lower levels of infection than did ‘McIntosh.’