Differences in development of common bean ( Phaseolus vulgaris L.) crops and pod fractions within a crop : II. Seed viability and vigour

Abstract

Two field experiments with common bean cultivars Rosecoco and Mwezi Moja aimed at increasing insight into differences in development with time of viability and vigour in seeds from different pod earliness classes (early, medium, late pods), and in seeds from the overall crop. Viability was determined by the tetrazolium test. Maximum viability was achieved at moisture contents of 31–37% in seeds from all pod classes, which is well beyond physiological maturity (58% moisture content) and closer to harvest maturity (20% moisture content). No differences were found in the day at which maximum viability was achieved in different pod classes in Season 1, but in Season 2 maximum viability was achieved earlier in seeds from early (cv. Rosecoco) or medium (cv. Mwezi Moja) pods than in seeds from late pods. Seeds from the overall crop achieved the same maximum viability during the season as seeds from different pod earliness classes. Vigour was measured by seed electrical conductivity divided by seed weight (EC). Maximum seed vigour (minimum EC) was achieved around the physiological maturity in all pod classes. Minimum EC tended to be achieved earlier in seeds from earlier pods than in seeds from later pods. Early seeds showed a better vigour than later seeds, especially in Season 2. The vigour of seeds from selected pods at their optimum time of harvesting was higher than the vigour of seeds from all pods combined.