ARS | Publication request: A Survey of Watermelon Germplasm for Inhibitory Seed Exudates

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 14, 2008
Publication Date: February 1, 2008
Citation: Harrison Jr, H.F., Levi, A., Kousik, C.S. 2008. A survey of watermelon germplasm for inhibitory seed exudates. HortScience. 42(1):138-142.

Interpretive Summary: Germinating watermelon seeds release substances (seed exudates) that inhibit the growth of weed seedlings. The purpose of the research reported in this manuscript was to survey a collection of watermelon varieties and varieties of closely related species in order to identify those with the most inhibitory seed exudates. Seed exudates of most of the varieties tested were not inhibitory, but 55 of 141 reduced the growth of millet seedlings in a Petri dish test. Based on differences in concentration responses, it appears that seed exudates of inhibitory varieties may contain different inhibitory compounds. Seed exudates from some varieties inhibited spore formation by an important watermelon pathogen, Phytophthora capsici in a laboratory test. These results suggest that seeds of some watermelon varieties may contain substances that protect germinating seeds. Further studies are needed to determine the effect of the inhibitors released from germinating watermelon seeds under field conditions.

Technical Abstract: Watermelon (Citrullus lanatus v. lanatus) seed exudates are inhibitory to seedling growth of other plant species. A miniature bioassay experiment that measured proso millet radicle growth was developed to assess the inhibition caused by seed exudates, and the bioassay was used to screen 141 genotypes of watermelon and related Citrullus species. Exudates of most genotypes were not inhibitory; however, exudates of 55 accessions reduced radicle growth in comparison to the control. Seed exudates also inhibited Phythophthora capsici sporangia formation in vitro which suggests that substances in the exudates may affect pathogens in the spermosphere. Differences between genotypes in concentration response in the millet bioassay, and differences in the relative inhibition in the millet and fungus bioassays suggest that constituents contributing to inhibition by seed exudates may vary between genotypes.