The effect of ethylmethanesulfonate (EMS) on morphological characteristics and seed quality development of Vernonia (Centrapalus pauciflorus var.ethiopica Willd.)

Abstract

Vernonia (Centrapalus pauciflorus Willd.) belongs to the Asteraceae family (Compositae). The crop can produce epoxidized vernolic acid oil that can be used by industries to produce products such as paints.Crop production is significantly hampered by non-uniform seed maturity, lodging due to tall plant height, seed shattering and lack of appropriate technologies. There is need for research to address these challenges and improve productivity. Firstly, this study compared two selected vernonia mutant lines (Vge-1 and Vge-4) and untreated controls with respect to morphological traits and seed quality development. A field experiment was conducted as a factorial design with 2 lines (Vge-1 and Vge-4) and 2 treatments (ethylmehanesulphonate treated and untreated seeds) at the University of KwaZulu- Natal Research farm at Ukulinga in Pietermaritzburg. The experiment was laid out in a Randomized Complete Block design (RCBD) with four replications, thus giving 16 experimental units (plots measuring 3mx6m). Data was collected on plants height, leaf number of secondary heads, mass of heads per plant and yield. Highly significant differences (P<0.001) were observed with respect to leaf number and seed mass.Vge-1 mutants plant produced more leaves (48 leaves per plant) compared with untreated controls (40 leaves), Vge-4 treated seeds had higher mass of heads per plant (2.46g) compared untreated controls Vge-4 with (0.75g). Vge-4 had seed yields of 3.5 ton/ha compared with untreated controls (3ton/ha). The effect of EMS application on growth parameters in vernonia lines resulted in an increase in leaf number, mass of seed per heads and seed yield of Vge-4; this line could be important than Vge-1 for potential use of vernonia as a new industrial crop. Secondly, the study determined the pattern of seed quality development of Vge-1 and Vge-4 compared to untreated controls. Vernonia flowers were tagged at flowering stage and sampled at weekly intervals from seed development up to maturity. Twenty seeds from each line (both treated and untreated controls) at each developmental stage were used to determine solute leakage using conductivity meter (CM100). Percentage germination was determined using a growth chamber set at a constant temperature of 25oC. Samples of twenty seeds were used for determination of seed moisture content using Kett’s PM650 seed soil moisture meter (Kett instruments, USA). Viability tests were done using 2, 3, 4-triphenyl tetrazolium chloride (TZ) solution. Seed viability was evaluated by assessing the proportion of stained embryo according to the ISTA Rules and Methods for Seed Testing. Five seeds of each line (both treated and untreated controls) were scanned using an electron microscope to observe morphological changes during embryo development. The results showed that germination (%) was generally iv low but differed significantly (P<0.01) between the lines; Vge-1 untreated seeds had the highest germination percentage (60%) compared with Vge-1 treated with (58%). The low germination percentage in vernonia could probably be attributed to seed dormancy. Thirdly, the study investigated the effect of gibberellic acid (GA) and potassium nitrate on seed dormancy in vernonia lines. A total of 100 seeds per treatment (treated seeds of Vge-1 and Vge4 and untreated controls) were subjected to three different temperatures regimes (25/25°C; 25/17°C or 30/17°C) and 0.7mM gibberellic acid or 1mM KN03. Seeds germination was assessed on daily basis by recording seeds with a radicle protrusion of at least 2mm. Highly significant differences and interactions (P<0.001) were observed between temperatures and dormancy breaking chemicals with respect to percentage germination, mean germination time (MGT) and germination index (GI).The GI increased with GA3concentration application. The mean germination time (MGT) also improves for all treatments. Fourthly, the effect of EMS on seedling growth was investigated. Harvested seeds of the two lines Vge-1 and Vge-4 were soaked in 0.372%, 0.744% and 1.1% EMS solutions for 2 hours and rinsed in water for 30 minute. The experiment was laid out as 2x4x4x3 treatment structure using a completely randomized design with the following factors: Vernonia lines with 2levels (Vge-1 and Vge-4); EMS concentration 4 levels (0.372%, 0.744%, 1.1 % and control); duration time 4level (0.5, 1, 1.5 and 2 hour) and temperature 3 levels (30oC, 32.5oC and 35oC) replicated 3 times, giving a total of 96 treatments combinations and 288 experimental units. The treated seeds were sown in seedling trays filled with sterilized soil. The following data were collected; seedling emergence, seedling length, germination percentage and the presence of chlorophyll mutants. Highly significant differences (P<0.001) were observed between EMS treatments with respect to seedling vigor, germination percentage and seedling height. The seedling length decreased with increased EMS concentration. EMS concentration increased emergence percentage and germination index. Increasing EMS concentrations, temperature, exposure time and duration negatively affected on all the traits measured in the study. EMS had the effect of causing mutations as evidenced by the various chlorophyll mutants identified in the study. The major findings of this study suggest that EMS as mutagen was effective in inducing genetic variability in vernonia. This suggests that EMS can be used for creating new vernonia lines.