Chestnut blight is a classic example of an introduced pathogen that has a severe negative influence on its host. When the main stem dies, infected trees produce multiple sprouts from their root collar. However, the effects of chestnut blight on dynamics of individual American chestnut sprout growth and survival is not well understood. Research has also focused on the biological control of chestnut blight with double-stranded RNA hypoviruses.
Analysis of more than 10 years of data on sprout numbers and diameter at breast height (DBH) and an empirical study of individual sprout growth and survival of American chestnuts in populations in MI and WI were used to evaluate differences in sprout dynamics among three population types (healthy, diseased with hypovirus [recovering], and diseased without hypovirus [epidemic]). The hypothesis that increasing DBH should be associated with fewer sprouts was investigated. For the empirical study, eight chestnut stands were selected: 2 in Wisconsin (West Salem and Rockland) and 6 in Northern Michigan (Roscommon, Leelanau, Stivers, Frankfort, Missaukee Healthy, and Missaukee Diseased). Within each site, 30 trees were selected randomly and assigned to one of three treatments for a total of 10 trees per treatment per site. The treatments were: (1) all sprouts were removed excluding the largest sprout which was measured and left behind; (2) all sprouts were counted and measured; then the largest sprout was removed; and (3) all sprouts were measured and none were removed (control). Height or DBH was measured for each stem. This experiment examined the relationship between number of sprouts and growth and survival of the largest sprout.
Analysis of the long-term data set on sprout numbers and DBH of American chestnuts in populations in MI and WI revealed significant differences among healthy (no blight), recovering and epidemic populations in sprout numbers over time. Results of this study contribute to our understanding of the dynamics of American chestnut sprout growth and survival following pathogen and hypovirus spread within the host populations. Ultimately, these results have important implications for evaluating the success of biological control efforts of chestnut blight by examining the growth and survival of trees in presence and absence of the hypovirus biological control agent.