Submitted to: Allelopathy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/12/2008
Publication Date: 4/1/2009
Citation: Williams, R.D., Bartholomew, P.W. 2009. Effects of accelerated aging and p-coumaric on crimson clover (Trifolium incarnatium L.) seed germination.Allelopathy Journal. 23(1):269-276. Interpretive Summary: Several phenolic acids, including p-coumaric acid, have been identified as allelochemicals that inhibit seed germination or seedling growth. In the soil these compounds are often found at the 10-3 M to 10-5 M concentrations. In laboratory bioassays these levels will delay germination. To invoke these compounds in allelopathic interactions, the inhibition of one plant by another plant through the release of a chemical, we either suggest that several of these compounds act cooperatively in the soil or these compounds have greater inhibitory properties under certain environmental conditions (water stress or temperature). However, in the bioassays fresh seed with good germination and seedling vigor are used. In the field, seed in the soil are of various ages, ranging from newly deposited seed to seed that have been in the soil for several years. Here we use a technique referred to as accelerated aging where seed are subjected to high temperature (41 C) and humidity (100%) for various time periods. The longer seed are held under these conditions, the greater the decline in germination and vigor. Using accelerated aged seed we were able to demonstrate that 10-3 M and 10-5 M p-coumaric acid reduced germination to a greater extent than aging or allelochemical alone. These results lead us to believe that older seed in the soil would be inhibited more than younger seed, thus affecting germination and subsequent seedling establishment.
Technical Abstract: Several phenolic acids, including p-coumaric acid, have been described as allelochemicals that may inhibit seed germination or seedling growth. Whether these effects are exacerbated in forage species by environmental stressors is unknown. Accelerated seed aging (high temperature (41 C) and high humidity (100%)) reduces germination and seedling vigor, and provides some indication of seed germination and seedling performance under stress conditions (eg., temperature and water stress). Thus, accelerated aging provides a means to determine how seed "age" might affect germination or seedling vigor in response to a stressor. Here we compare responses of aged and non-aged seed of crimson clover to p-coumaric acid at 10-5 and 10-3 M concentrations. Accelerated aging delayed and reduced crimson clover seed germination. The mean germination for the 0, 24, 48, and 72 h aging treatment was 93%, 73%, 40%, and 15%, respectively, and by 96 h most of the germination had occurred. Un-aged seed germination appeared to be slightly stimulated by 10-3 M p-coumaric acid concentration, while the 10-5 M p-coumaric acid concentration reduced seed germination. When accelerated aging was combined with the p-coumaric acid treatments there were significant differences as to accelerated aging by p-coumaric acid treatment interactions. Accelerated aging for 24 h followed by p-coumaric acid further reduced germination. At 48 h accelerated aging, there was no significant difference as to p-coumaric acid, probably due to the overwhelming effect of accelerated aging. These results show that accelerated aging, as a proxy for increased physiological age, could make seed more susceptible to an allelochemical at concentration levels generally found in the soil.