Ethylmethanesulfonate mutagenesis in selected Vernonia galamensis variety ethiopica lines.

Abstract

The overriding objective of this study was to induce genetic variation in Vernonia (Vernonia galamensis variety ethiopica) using ethylmethanesulfonate (EMS) and select mutants for subsequent selective breeding. Vernonia is an underutilised, potential novel oilseed crop with multiple applications in industry mostly due to the production of naturally epoxidised vernolic acid oil. Commercial cultivation of vernonia is significantly hampered by non-uniform seed maturity, tall plant height, seed shattering and lack of appropriate technologies for mechanical harvesting, seed threshing and cleaning. Mutations of a single or few genes possessing target traits are invaluable in crop improvement programs. Chemical mutagenesis using EMS is an important, affordable and effective method to induce random useful genetic mutations in crop plants. Ethylmethanesulfonate mutagenesis has previously been reported to affect various agronomic traits, induce a wide variety of phenotypic mutations and alter both seed oil content and fatty acid profile on several crops. The objectives of this study were: (i) to determine an optimum EMS treatment combination i.e. exposure duration, temperature and dose that would enable 50-60% germination at minimum days to emergence in selected V. galamensis var. ethiopica lines (Vge-1, Vge-4, Vge-7 and Vge-10), (ii) to induce genetic variation using predetermined optimal treatment conditions and select mutants in V. galamensis variety ethiopica lines (Vge-1 and Vge-4) and (iii) to evaluate oil content and fatty acid compositions among seeds of chloroplast mutants, EMS treated seeds and untreated controls of Vge-1 and Vge-4. Before any mutation is administered in plants, it is important that the optimal mutation dose is determined. The lethal dose 50 (LD50) was the standard used in this study to find optimal treatment conditions. Significant interactions (P<0.001) existed between EMS, line, time and temperature with respect to days to 50% emergence, germination percentage and seedling height. Optimal days to 50% emergence (10-12 days) and germination (50- 58%) was achieved for Vge-1, Vge-7 and Vge-10 when treated with 0.372% EMS at 350C for 1 hour treatment. The optimal treatment combination for Vge-4 was 0.372% EMS at 32.50C for 2hr. The treatment combinations that yielded optimum results in the tested lines were utilized to induce large scale mutations in V. galamensis to select target mutants in the field. Large scale mutation was conducted using the observed optimal treatment conditions. Ethylmethanesulfonate mutagenesis significantly delayed days to head formation, days to flowering and days to maturity on both lines. Delays in days to emergence were only significant in Vge-4. EMS treatment also significantly reduced germination percentage, number of seeds per head, number of fertile plants, plant height and plot yield for both Vge-1 and Vge-4. Thousand seed weight significantly increased in treated seeds of the two lines. Chlorophyll mutants were observed for tested lines associated with high count of sterility for both lines. Ethylmethanesulfonate successfully induced phenotypic mutation in selected vernonia lines, however at this stage the effect of mutation on vernonia seed oil content and fatty acid was unknown. Liquid gas chromatography method was employed for oil and fatty acids analysis. In Vge-1, significant differences were observed in composition of linoleic and oleic acid due to the mutagenesis. Significant increases in linoleic and oleic acid composition were found in chloroplast mutants due to EMS mutagenesis. No significant differences were detected in fatty acid compositions in Vge-4 after the EMS treatment. Differential responses were observed when lines were compared at various EMS mutation levels showing significant effect on vernolic, linoleic and oleic acids compositions. In both lines no differences were detected on seed oil content, palmitic acid, steraic acid and arachidic acid compositions after the treatment. Oil content significantly and positively correlated with vernolic acid for Vge-1 (P<0.001; r= 0.898) and Vge-4 (P<0.05; r= 0.65). Vernolic acid significantly and negatively correlated with other fatty acids. The study found that EMS mutagenesis significantly changed the oleic acid and linoleic acid compositions in vernonia. However, the oil content and vernolic acid composition were not significantly affected by EMS treatment. This study established that EMS was successful in inducing genetic variation (in agronomic traits, seed oil content and fatty acid composition) in the two tested lines of V. galamensis. Data from a single planting generation is insufficient to conclude fully on the effect of EMS on V. galamensis; therefore it is highly recommended that further multigenerational studies should be conducted with an increased number of testing lines from a wide range of environmental backgrounds.