No abstract

Chromosomal aberrations produced by physical and chemical mutagens are the main causes of damage in mutation studies However, recent experiments have amply revealed that a great many factors modify the chromosomal damage by affecting the biological changes induced by physical and chemical mutagens (Curtis et al., 1958, Nilan et al., 1961and Konzak et al., 1965. Hormones, e.g., indole acetic acid, along with other chemicals have been found to modify the mutagenic damage only to the extent that they influence the growth pattern in plants (Guttman and Brown 1959, Gaur and Notani 1963and Arartjan 1967.The present experiments relate to cytological changes observed in ethyl methane sulphonate (EMS) and methyl methane sulphonate (MMS) treated peas during M,, M2 and M3 generations. Further, studies were also conducted to study the modify ing effect of post-mutagenic treatments with gibberellic acid. Materials and methodsPea seeds (Pisum sativum L., 2n=14) of variety Bonnvile were used for the present studies. Two chemical mutagens namely ethyl methane sulphonate (EMS) and methyl methane sulphonate (MMS) were employed, while gibberellic acid (GA) was the only hormone tested as a post treatment during these studies. In the first instance, preliminary studies were conducted to determine the suitable dose of each of the mutagens. These preliminary studies revealed that the suitable dose for EMS was 0.25% and 0.025% for MMS (volume by volume). The mutagenic solu tions were prepared in phosphate buffer adjusted to a pH of 7.0. Only one con centration of GA of 1000 ppm was used as this was found to be the most suitable concentration (Narsinghani and Kumar 1971). The following treatments were used:-1. EMS 0.25% 4. MMS 0.025%+GA (1000 ppm) 2. EMS 0.25%+GA (1000 ppm) 5. GA (Control) 1000ppm 3. MMS 0.025% 6. Control-distilled water. The seeds were first presoaked for two hours in distilled water and then im mersed in solutions of mutagens for ten hours. At the end of the treatment the seeds were washed with distilled water and sown in the field. Plants in the M1 generation were tagged individually and chromosomal aberrations recorded. The

The chlorophyll mutations have been commonly observed after the application of mutagenic treatments and these have attracted considerable attention since they help in estimating the efficiency and effectiveness of mutagenic agents (Ehrenberg et al. 1961). On the other hand the sterility induced by mutagenic treatments impose a great barrier in practical plant breeding, but the recent studies have revealed that many factors can modify the mutagenic damage by altering the radio sensitivity of organisms (Konzak et al. 1965). The present investigations were carried out to see if the frequency of chlorophyll mutations and sterility induced by ethyl methane sulphonate and methyl methane sulphonate could be modified by gibberellic acid post-mutagenic treatments in M1, M2 and M3 generations. Materials and methodsPea seeds (Pisum sativum L.) of variety Bonnvile were treated with ethyl methane sulphonate (EMS) and methyl methane sulphonate (MMS). Only one dose of each of the two mutagens as determined from the seedling injury and mitosis was used for field studies (Narsinghani and Kumar 1971).Gibberellic acid (GA) of 1000ppm concentration was used as post-mutagenic treatments. The following treatments were given: i) EMS 0.25%+distilled water ii) EMS 0.25%+GA (1000ppm) iii) MMS 0.025%+distilled water iv) MMS 0.025%+GA(1000ppm) v) Distilled water+GA 1000ppm (Control) vi) Distilled water+distilled water (Control) Pea seeds soaked in distilled water for two hours were treated with mutagenic solutions for a period of 10 hours, thoroughly washed and resoaked in 1000ppm GA solution for 8 hours. The controls consisted of distilled water and GA soak ing for the same duration. One hundred seeds in each treatment were sown in M1 generation. The seeds of each plant were harvested separately and for subsequent M2 and M3 generations these were sown on progeny row basis. The pollen fertility was studied as per aceto-carmine method.