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

Abstract

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.

Progression of damping-off epidemics in Glycine populations of even-age and mixed-age structure

“…& Zucc. (13), but when incubated under similar conditions, the incidence of disease caused by P. aphanidermatum is greater in populations of G. mar than in populations of G. soja. Disease symptoms may develop on these plants within 4 and 9 days after planting, respectively (1 3).…”

“…Prior to emergence, seeds and seedlings were considered susceptible to preemergence damping-off. Seedlings of G. rnax and G. soja emerged 5 3 and 4.3 days after planting, respectively (13). All postemergence dampingoff occurred in < 1 and 5 days after emergence for G. mar and G. soja seedlings, respectively.…”

“…All postemergence dampingoff occurred in < 1 and 5 days after emergence for G. mar and G. soja seedlings, respectively. Therefore, we concluded that the total period of susceptibility of G. mar and G. soja seedlings to preemergence and postemergence damping-off combined were a maximum of 4 and 9 days after planting, respectively (13).…”

“…Age structures were created to mimic naturally occurring even-and mixed-age structures of G. max and G. soja (13). Mixed-age structures for both plant species were created by staggered plantings; even-aged structures of G. soja were created by scarifying seeds with 95 % sulfuric acid for 2; min and rinsing in sterile distilled water.…”

“…The period of host susceptibility to P. aphanidermaturn was determined using methods described by Neher et al (13). Prior to emergence, seeds and seedlings were considered susceptible to preemergence damping-off.…”