Seed Life Expectancy: The Spermosphere, Defense Chemistry, and Weed Recruitment

Open Access
Author:
Burnham, Mark B
Graduate Program:
Agronomy
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 05, 2011
Committee Members:
  • Robert Paul Gallagher Iii, Thesis Advisor
Keywords:
  • induced defense
  • Avena fatua
  • spermosphere
  • phenolics
  • seed bank
Abstract:
Plant seeds may remain dormant in the soil for extended periods of time, creating soil seed banks that contribute to the perpetuation of plant species. Weed seed banks can create weed management challenges for farmers, and reduction of these seed banks could become an important piece of an effective weed management strategy. A better understanding of the seed-soil-microbe interactions in the soil could help develop effective seed bank management tools. This study focuses on phenolic acid, short aliphatic organic acid, and long-chain fatty acid changes within dormant wild oat (Avena fatua L.) seeds and the surrounding soil (spermosphere) as the seed imbibes, and on seed defense mechanisms used to protect against harmful soil microorganisms. It is hypothesized that during imbibition, the seed will experience a loss of compounds from soluble chemical fractions, and this loss will be quantifiable in the seed and surrounding soil. In addition, it is hypothesized that during fungal attack, the seed will elevate the levels of defense compounds, especially those bound to the cell wall. During imbibition, wild oat hull chemical composition and short aliphatic concentration were most affected, with soluble short aliphatic concentration decreasing 69% in the hulls and 62% in the caryopses. Free phenolic concentration decreased 77% in concentration in the hulls. The spermosphere is likely composed of phenolics and short aliphatics, which may have varying effects on the surrounding soil ecology. When exposed for 3d to Fusarium avenaceum and F. culmorum, the greatest defense response observed in wild oat seeds was a substantial accumulation (40%-650%) of soluble-fraction phenolics in the caryopses. Soluble-fraction short aliphatics also increased substantially (up to 1800%) in caryopses. Some increase in phenolic concentration occurred in the seed hulls. Insoluble cell wall-bound fractions exhibited no change, and treatments at little effect on long-chain fatty acid concentration. Implications for seed survival in the soil and potential management options are considered.