Link to home

Etiology of Bronze Leaf Disease of Populus

May 2002 , Volume 86 , Number  5
Pages  462 - 469

Jason A. Smith and R. A. Blanchette , Department of Plant Pathology, University of Minnesota, St. Paul 55108 ; M. E. Ostry , North Central Research Station, United States Forest Service, St. Paul, MN 55108 ; and N. A. Anderson , Department of Plant Pathology, University of Minnesota, St. Paul



Go to article:
Accepted for publication 20 January 2002.
ABSTRACT

Bronze leaf disease is a potentially destructive disorder of the Populus section of the genus Populus. The causal agent has been reported to be Apioplagiostoma populi (anamorph: Discula sp.). Based on etiological and symptomological studies, field observations of symptom development suggest that the pathogen moves systemically in the host. This was verified by graft experiments where symptoms progressed from the scion into the elongating stem. A bronze-pigmented vascular discoloration was observed in symptomatic leaves and branches. Dieback of affected stems also was common. Spore-trap studies elucidated the timing and necessary weather conditions of A. populi ascospore dispersal in relation to infection and symptom development. Exposure-tree experiments revealed that ascospores of A. populi are the primary inoculum and resulting infection causes distinctive disease symptoms on affected trees. Perithecia of A. populi were observed on overwintered symptomatic leaves, but were not observed on asymptomatic leaves. Acervular conidiomata were observed on symptomatic leaves during August and September. Although A. populi ascospores germinated in vitro, A. populi was not recovered from symptomatic tissue. Isolations from diseased leaves consistently yielded Epicoccum nigrum, but the role of this species is unclear. Inoculations of susceptible plants with E. nigrum conidia failed to reproduce symptoms, but inoculations with ascospores of A. populi produced symptoms typical of bronze leaf disease and Koch's postulates were performed.


Additional keywords: Ascomycetes, aspen, Diaporthales, disease resistance, Leuce section, systemic fungi

© 2002 The American Phytopathological Society