Field Susceptibility of Scab-Resistant Apple Cultivars and Selections to Cedar Apple Rust, Quince Rust, and Frogeye Leaf Spot

Abstract

Thirty-seven scab-resistant apple cultivars and selections were evaluated in the field for level of susceptibility to cedar apple rust (CAR), Gymnosporangium juniperi-virginianaeSchw., quince rust (QR), G. clavipesCke. and Pk., and frogeye leaf spot (FLS), Botryosphaeria obtusa(Schw.) Shoemaker. Between 1994 and 1996, fruit infection from CAR varied from 0 to 40% for the various cultivars and selections. The selections originating from the Geneva, N.Y. breeding program were resistant to CAR or had low levels of fruit infection (0-3%). They also had low leaf rust ratings (0 to 0.3) except for NY 74828-12 which had leaf rust ratings of 0.2 to 1.3 (1-25 lesions per leaf) over the three years. The Quebec apple selections (QAS) from Agriculture and Agri-Food Canada, St. Jean, Quebec also had low levels of fruit infection from CAR (0 to 3%). However, several selections did have leaf rust lesions. Other cultivars and selections with field resistance to CAR included ‘Moira,’ ‘Novamac,’ ‘Redfree,’ ‘William's Pride,’ Co-op 26, O-637 and 547-25-52. QR infection varied from 0 to 31% with ‘Moira,’ CBR4T29, Co-op 24, QAS-04, QAS-11 and O-661 being most susceptible with fruit infection of 10% or higher. FLS occurred on all cultivars. Those with 5 or fewer lesions per leaf over the three years included ‘Dayton,’ ‘Jonafree,’ ‘Novaspy,’ CBR4T29, Co-op 12, Co-op 15, Co-op 19, Co-op 20, Co-op 24, QAS-01, QAS-03, NY 75414-1 and O-661. In this trial, QAS-01 and NY 75414-1 had combined resistance to all three diseases.