EFFECT OF HIGH TEMPERATURE DRYING ON LONGEVITY OF SEEDS OF BAMBARA GROUNDNUT (VIGNA SUBTERRANEA (L.) VERDC) ACCESSIONS

Abstract

The effects of drying at high and low temperature on the subsequent longevity of bambara groundnut seeds were studied. The experiment was carried out at the genetic resources unit laboratory of the International Institute of Tropical Agriculture (IITA), Ibadan. The experiment was laid out in a completely randomized design with three replications. Freshly harvested seeds of 37 bambara groundnut accessions obtained from the genebank of IITA, Ibadan, Nigeria were divided into five samples. One sample, which served as the control sample, was dried at 17oC/15%RH and other four samples were dried at 35°C/45°C/35% RH for up to eight days, before final drying at 17°C/15%RH. The moisture content of seeds were increased to 10.9% after drying, packed in aluminium foil and placed at 45°C. Seeds samples were stored for 80 days and germination tests were carried out on seed samples at regular intervals till all seeds lost viability. For the longevity experiment, data were analyzed using GenStat Discovery Edition 4 for Probit analysis by fitting in the Ellis and Robert viability equation while for the seed quality and seed longevity traits, the mean values were subjected to analysis of variance (ANOVA) using Statistical Analysis Software (SAS), version 9.2 and significant means were separated with Turkey test at 5% level of probability. F-test was used to determine whether there was a significant (P<0.05) difference in the residual deviance using Varsastat statistical tool. Results from the analysis of variance revealed highly significant differences among the accessions for the characters studied. From the study, seed thickness, seed length, seedling vigour, speed of germination index, seedling length, seed weight, fat percentage and harvest moisture content can be said to be seed quality components of bambara groundnut while germination percentage, seedling vigour, speed of germination index and seedling length were observed to be important components of seed longevity traits. TVSu 2085 and TVSu 2031 were identified as promising accessions that could be recommended for seed quality attributes while TVSu 1825 was the best storable accessions in terms of P50 and also performed best for most of the traits in terms of seed longevity traits. For seed longevity, the accessions responded differently to low and high drying temperature. For some accessions, there were no significant differences (P ˃ 0.05) in seed longevity depending on how the seeds were dried while in others, longevity increased as the period of drying at 35°C and 45°C increased from 0 to 8 days; for some accessions, there was a negative trend or a variable response. Overall, the results suggest that initial drying at a higher temperature was beneficial for improving processing time and for some accessions drying at high temperature would be beneficial for seed longevity. The results of this study will therefore provide useful information on the improvement of seed longevity, seedling traits and seed quality traits in bambara groundnut.