Influence of temperature and moisture content on the viability and vigour of eleusine coracana L. and amaranthus hybridus L. seeds during storage.

Abstract

The present study was carried out at the National Genebank of Kenya-KARl, Muguga between September 1996 and August 1997. The study aimed at determining the progress and extent of deterioration in seeds of two traditional crops at various combinations of constant storage temperature and moisture content, and to quantify the resultant viability decline, with a view to predicting longevity at alternative storage conditions. Seeds of finger millet (Eleusine coracana L. Gaertn. Var. KATIFM-1) and those of Amaranth (Amaranthus hybridus L. Ssp. cruentus) were stored in hermetically sealed laminated aluminium foil packets, for up to 252 days at different constant environments, which included combinations of temperatures ranging from 15°C to 40°C and moisture contents ranging from 5.3% to 17.3% (fresh weight basis). To determine the progress and extent of seed deterioration at each of the different combinations of temperature and moisture content, seeds were sampled periodically from storage for vigour and viability determination. Two procedures were used to evaluate vigour. These were; percentage normal (first count); germination and electrical conductivity of seed leachate. Viability was expressed as a percentage of the total germinated normal seedlings at final count. At most of the storage combinations, both viability and vigour declined during storage, for the two species. At relatively higher storage temperatures (>_ 25°C) and moisture contents ( >_11.3%), depending on the species, viab,ility and vigour declined completely during storage, at rates dependent on the treatment combinations. The decline was generally rapid at higher temperature and! or moisture content combinations. For both species, the electrical conductivity test was unable to detect significant deterioration of seeds dtu!ng storage. The effect of storage conditions on viability was quantified using the simple viability equations. Seed survival curves (percentage normal germination, plotted against storage period) were fairly described by negative cumulative normal distribution. For each of the two species, the estimated periods for viability to fall to 50% (Pso period) was shorter the higher the storage temperature and lor moisture content. Simple viability constants were"for each of the two species obtained, and used to predict longevity at various non-extreme hypothetical storage conditions. At relatively low moisture content (<_10%) and temperaturers >_ 15C) combinations, seeds of A. hybridus were predicted to store much longer than those of E. coracana. At storage combination of 5% moisture content and a temperature of 5°C for example, seeds of the former are predicted to have a 28-fold greater longevity than the latter. The constants obtained in the present study could be applied in predicting storage life of seeds of the two species, especially in the short- and medium-term storage conditions.