Population structure of Armillaria species in several forest types

Abstract

Population structure of Armillaria calvescens, A. gemina, A. gallica and A. ostoyae in New York was studied in plots established at six sites and transects at three others. No significant differences among species in size or density of genets (identified by somatic incompatibility) was detected. The size distribution of genets revealed a high frequency of very small genets (mostly associated with single sample points) and a uniformly lower frequency of larger genets ranging up to 670 m² (44 m long). Density of genets (including all Armillaria species) was higher in plots with more species of Armillaria. There was little spatial overlap between genets regardless of species. Five of 33 pairs of isolates from within roots and from superficial, associated rhizomorphs consisted of different species; the other 28 pairs were comprised of single genets. The data suggest that expansion beyond the initial resource unit is a critical phase in the development of genets and are consistent with patchwise distribution of niches that differentiate Armillaria species in these stands. Evidence from two plots, in which A. ostoyae apparently colonized planted stands of conifers on sites previously unforested or supporting hardwoods, supports the concept that basidiospores are important in the population structure of Armillaria species and the epidemiology of the diseases they cause.

Key Words:

• basidiospores
• clone
• epidemiology
• root rot
• somatic incompatibility