Testing Verticillium Wilt Resistance in Urban Norway Maples

Abstract

Wilt symptoms in Norway maple half-sib families from open-pollinated seed from a random of street trees in Rochester and Syracuse, N.Y. inoculated with Verticillium dahliae were analyzed for the reliability in predicting disease, variability in the parent population, and heritability. Inoculum was prepared from 11 isolates of diverse origin from maples and reisolates from Norway maple previously inoculated with these stocks. Two replications were inoculated with two inoculum concentrations (2.5 X 106 and 0.5 X 106 propagules/ ml) and a distilled water control by dunking wounded roots of 2-0 nursery stock. Disease was verified by isolating the pathogen from stems. Thirteen families averaging 3.5 trees/family/treatment/rep (274 total) were tested in 1979, and 40 families averaging 7.8 trees/family/treatment/rep (1875 total) in 1980. Vascular streaking (dark greenish lesions) and two measures of foliage necrosis (% Crown Necrotic and % Necrosis, Worst Leaf) proved most reliable for predicting infection. These traits are recommended for screening for resistance. Three height growth measures did not prove reliable. Considerable variability is present in the parent populations, but estimates of heritabilities for each trait are quite variable, requiring further study. Increasing the incidence of infection is also important.