Tepary with varying doses (0.0, 0.5, 1.0, 1.5
Tepary bean (Phaseolus acutifolius) is an important food legume originating from SouthAmerica and the South-western parts of the United States.
The crop is produced in manycountries worldwide including South Africa. It is highly tolerant to drought and the seedcontains a wide range of vitamins, minerals and protein of high nutritional quality. The geneticbase of tepary bean is narrow but can be widened by chemical mutagenesis.
However, thereare no reports on the impact of chemical mutagenesis on the root nodulation and seed storageproteins in tepary bean. Therefore, this study was designed to examine root nodulationattributes and seed storage proteins of three tepary bean genotypes in the early mutagenicgenerations (M2 to M4) derived through treatment with varying doses (0.0, 0.5, 1.0, 1.5 and 2.
0v/v) of ethyl methanesulfonate (EMS). The experiment on root nodulation attributes was laidout as a 3 x 5 x 3 (genotypes x EMS doses x mutant generations) factorial design replicatedthree times. At harvest, shoot height (SHT), primary root length (PRL), dry weights (shoot, rootand nodule), number of nodules per plant (NNP) and grain yield components such as thenumber of pods per plant (NPP) and number of seeds per pod (NSP) were measured. Highlysignificant (P?0.01) dose effects were observed for SHT, PRL, shoot dry weight (SDW) androot dry weight (RDW). Highly significant (P?0.
01) interaction effects of mutant generation xgenotype x dose were observed for NSP. A highly significant (P?0.01) positive linearrelationship was observed between the NNP and nodule dry weight (NDW). Increase in thePRL suggested that tepary bean mutants could be important in drought tolerance. EMStreatment led to an enhanced partitioning of dry matter (assimilates) to the shoots and roots.There was a three fold increase in most of the root nodulation traits at the 0.
5% EMS dose.TheKjeldahl method was used for crude protein determination whereas the sodium dodecylsulphate – polyacrylamide gel electrophoresis (SDS PAGE) was utilized in determining theprotein banding patterns of the bean. There were highly significant (P?0.01) differencesamong the genotypes in crude protein accumulation.
Highly significant (P?0.01) mutantgeneration x genotype x dose were observed for seed protein accumulation. ‘Genotype 3’attained the highest protein content (24.23%) at 1.5% EMS dose in the M4 generation.
EMSdoses ?0.5% positively stimulated protein accumulation in all genotypes but high EMS doses(2.0%) depressed protein content. There were significant variations in seed storage proteinprofiles among the genotypes and mutant generations. ‘Genotype 6’ showed a distinct15.
0kDa protein fragment which was absent in the majority of the remaining genotypes. Thepresence of distinct protein subunits in the three genotypes could be used in varietalidentification. The results demonstrated that chemical mutagenesis using EMS could inducesignificant variations in both the agronomic and nutritional traits of tepary bean.