The germination of wild rice seed in response to diurnally fluctuating temperatures and after-ripening period

Abstract

The germination response of wild rice ( Zizania palustris L.) seed to 100 combinations of day and night temperatures was investigated following 5,6 and 7 1 2 months of after-ripening. Percentage germination and germination rate both increased with a lengthened period of after-ripening. Germination rate was greatest in mean daily temperatures of 27.5–30°C, regardless of the length of the after-ripening period. The range of mean daily temperatures optimal for germination increased with a lengthened period of after-ripening from 17.5–22.5°C (5 months) to 12.5–32.5°C ( 7 1 2 months ). Percentage germination and germination rate were higher in diurnally fluctuating temperatures than in constant temperatures for any given mean daily temperature. The effect of diurnally fluctuating temperatures diminished with a lengthened period of after-ripening. Wild rice seed germination was intolerant of temperatures in excess of 40°C. Results indicate that germination may begin prior to or at the time of break-up of the ice in spring, and that wild rice seed can remain in the seed bank through prolonged primary dormancy and possibly through the induction of secondary dormancy.