Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/11/2006
Publication Date: 1/10/2007
Citation: Davis, A.S., Kenner, K. 2007. Seed depth and pathogens affect fatal germination of velvetleaf and giant foxtail. Weed Science. 55:30-35. Interpretive Summary: Weed seed fate in the soil seedbank is of central importance in determining the size of annual weed populations. Seeds lose viability, remain dormant, or germinate. Most germination results in seedling emergence from the soil surface. In contrast, fatal germination of weed seeds occurs when germination is initiated, but the seedling does not reach the soil surface. Controlled-environment studies indicate that both soil borne pathogens and seed depth placement affect the amount of fatal germination that takes place within the soil seedbank. Soil inoculation with selective seed pathogens and use of tillage equipment to send seeds to a precise depth in the soil are two promising methods for increasing fatal germination of weed seeds that should be studied further within a field environment.
Technical Abstract: Fatal germination of weed seeds occurs when a weed seed initiates germination, but the seedling does not reach the soil surface. Bioassays of velvetleaf and giant foxtail seed fate in Michigan field soil were used to determine the role of pathogenic fungi and seed burial depth in fatal germination of these species. Fatal germination at 2 cm seed depth was nonexistent for giant foxtail, and rare (< 10% of seeds studied) for velvetleaf. At greater depths, fatal germination remained close to zero for giant foxtail, whereas it increased to as high as 40% for velvetleaf at a 10 cm burial depth. Cultures taken from fatally germinated velvetleaf seedlings were found to contain Pythium ultimum, a soil-borne pathogen known as the causal agent for pea root rot. When samples of infected media taken from these cultures were used to inoculate field soil in pots, fatal germination of velvetleaf was increased, compared to field soil inoculated with sterile media, at depths of 4 to 6 cm. At greater seed burial depths, fatal germination of velvetleaf was the same for unsterilized soil and P. ultimum-inoculated soil, increasing to 20% and 40% at 8 and 10 cm burial depths, respectively. Given that maximal fatal germination of velvetleaf was reached in the unsterilized soil treatment at the 10 cm depth, inoculation of soil with a pathogenic agent is likely to be less important for managing fatal germination than guiding newly shed seeds to a precise depth with tillage equipment.