Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 11/5/2004
Publication Date: 12/13/2004
Citation: Davis, A.S., Renner, K.A. 2004. Seed depth placement and soil fungal pathogens affect fatal germination of velvetleaf [Abstract]. Weed Science Society of America Meeting. 44:204. Interpretive Summary:
Technical Abstract: Characterizing and manipulating weed seedling recruitment is an important goal in integrated weed management systems. One poorly understood area of weed germination biology is fatal germination, in which weed seeds germinate, but seedlings do not emerge from the soil surface. Our objective was to determine whether fatal germination of weed seedlings has a pathogenic component. Three experiments were conducted to investigate this question. First, germination bioassays were performed at 25 C in soil collected in East Lansing, MI, and velvetleaf seed fates were scored after five days as non-germinants (NG), fatal germinants (FG), and successful germinants (SG). Second, sterile agar plates containing velvetleaf seeds were inoculated with either FG or SG velvetleaf seedlings and incubated for five days at 25 C. Third, velvetleaf seeds were planted at 2, 4, 6, 8 or 10 cm depths in field soil that was steam sterilized, inoculated with seedlings from the FG-inoculated plates, or left untreated. In the germination bioassays, 15%, 2%, and 83% of velvetleaf seeds were in the NG, FG and SG classes, respectively. Velvetleaf radicle length was 200% greater in agar plates inoculated with SG seedlings (30 mm) than in agar plates inoculated with FG seedlings (14 mm). Subsequent culturing indicated that the FG-inoculated seedlings were infected with Pythium ultimum (pea root rot). Fatal germination in pot experiments increased with depth of seed placement for all soil treatments. However, fatal germination in the sterilized soil remained under 5% at all depths, whereas fatal germination in the control and inoculated soil increased from 10% at 2 cm to over 30% at 10 cm. At intermediate sowing depths (4 and 6 cm), fatal germination was greatest in the inoculated soil, intermediate in the control soil, and lowest in the sterilized soil. These results offer support for the existence of a pathogenic component to fatal germination of weed seedlings. The virulence of P. ultimum to many crops makes it unacceptable for biocontrol use, but the principle of increasing fatal germination at intermediate soil depths through fungal inoculation may help guide the development of effective, safe biocontrol programs targeted at weed seedling recruitment.