Influence of age structure of plant populations on damping-off epidemics.

Germination synchrony may facilitate damping-off epidemics by creating a high density of uniformly susceptible individuals. We tested the hypothesis that synchronous germination causes increased seed and seedling mortality from damping-off in two legume species attacked by the fungal pathogen, Pythium aphanidermatum. Glycine max exhibited rapid, synchronous germination compared to its progenitor, G. soja, and suffered greater mortality from both pre-and postemergent damping-off in controlled environment experiments. However, when mixed-aged populations of G. max were created experimentally by staggering planting times, a significant increase in damping-off mortality occurred. In G. soja, which typically has mixed-aged populations due to asynchronous germination, experimental populations with an even-aged distribution also suffered increased damping-off mortality. Hence, the relationship between population age structure and damping-off mortality was species-specific. We propose that species differences in the duration of individual seedling susceptibility to disbase interact with population age structure to control the cutcome of damping-off epidemics.