Moisture content and the longevity of seeds of six Euphorbia species in open storage

Abstract

Seeds from six Kenyan Euphorbia species were placed into experimental storage under open conditions (i.e. not hermetically sealed) over a range of relative humidities (between 25 and 75%) at 45°C. Viability during storage was assessed at pre-determined intervals and seed viability equation constants estimated. The constants Cw, which quantifies the relative effect of change of moisture content on longevity, and KE, which quantifies inherent longevity were variant between species. Similarly the constants describing the relative effect of change in rh on longevity differed between species. The highest estimate of KE was 10.2 for E. quinquecostata followed by 10.1 for E. pseudoburuana, 8.9 for E. heterochroma, 7.4 for E. heterophylla and 7.3 for E. bussei. The reverse order of the species was observed in the estimates for CW which ranged from 3.96 for E. bussei to 8.09 for E. quinquecostata. These viability constants were used to predict seed longevity following recommended Seed Banking protocols. Longevity was also predicted for seeds stored under ambient conditions at two Kenyan cities, Nairobi and Kisumu, with and without refrigeration at 5°C. These predictions show how even basic refrigeration can improve the longevity of seed stocks destined for short-term storage, for example those required to support academic teaching in universities. Seed stocks destined for long-term conservation should be dried and stored at conditions prevailing in standard gene bank facilities.