Patterns of starch reserves in healthy and diseased American elms

Abstract

Healthy American elms stored starch all year in 12–18 growth rings. Starch reserves in healthy elms were lowest at the time of leaf expansion, which was also the time of spring vessel formation and the time of highest susceptibility to Ceratocystisulmi. Nonconductive barrier zones separated infected wood from wood that normally stored starch. The new wood cells that formed after the barrier zone was completed did not store starch until the end of the growth period. When additional infections occurred the same growth period or the next growth period, the tree had only a single functioning growth ring to maintain starch reserves. Trees inoculated with C. ulmi in June had significantly less starch reserves than controls in August of the same year. All trees in one study that died during the end of 1984 had trace amounts of starch at the end of 1983, while trees that were still alive at the end of 1984 had high amounts of starch at the end of 1983. The data suggest that depletion in trunk starch reserves is a manifestation of the host–pathogen interaction that is correlated with tree death.