Effect of storage temperature and time on viability of rhizobia on lime-coated alsike clover (Trifolium hybridum) seed

Abstract

SUMMARYSeed is often stored in warehouses where the temperature may drop below freezing or increase to 40°C depending on the time of year. Survival of rhizobia on lime-coated alsike clover (Trifolium hybridumL.) seed stored in polypropylene bags was monitored under various temperature regimes ranging from –10 to 35 °C at Agriculture Canada Range Research Station, Kamloops, British Columbia, Canada during 1990 and 1991. Rhizobia were applied ata range of initial concentrations. Seed was inoculated with a peat-based clover inoculant (‘B’ inoculant, Nitragin Ltd, Milwaukee, Wisconsin, USA), and then given a commercial polymer-based lime coat (GNR™, Grow Tec Ltd, Nisku, Alberta, Canada). Rhizobia died continuously at all temperatures within the range —10 to 35°C. The dependence of Iog10(number of viable rhizobia/seed) on storage time was best described by a linear equation: Iog10(viable rhizobia/seed) =a+b(time). Coefficientaprovidedan estimate of the initial concentration of rhizobia. Coefficientbprovided a measure of how rapidly rhizobia died. The death rate of rhizobia was the same during storage at 5 or 20 °C, but increased at a storage temperature of 35 °C. Storage at freezing temperatures did not increase the rate of rhizobial death but repeated freezing and thawing resulted in an increase. As the rate of rhizobial death was similar at constant temperatures from — 10 to 20 °C, temperature requirements are not stringent. Nevertheless, some temperature control is required to maximize the legal storage life of preinoculated coated seed, which in this study was estimated to be 96 days.