Studies on induced chlorophyll mutation in sesame ( Sesamum indicum L.)

: The effectiveness and efficiency of gamma rays and EMS in relation to chlorophyll mutations were studied in two varieties of sesame ( Sesamum indicum L.) viz . SVPR 1 and CO 1 in M 2 generation. Four types of chlorophyll mutants namely xantha, chlorina, striata and Xantha viridis were observed. Xantha viridis was observed in maximum proportion followed by chlorina and striata in both the varieties. Gamma rays was found to be more efficient and effective than EMS in both the varieties. The effectiveness and efficiency of both the mutagens was more in SVPR 1 than CO 1.


Introduction
Mutations are important from both, theoretical and applied points of view and mutation breeding is one of the most effective tools of plant improvement. In mutagenesis, the choice of the mutagen is most important and various methods have been developed to ascertain the most effective and efficient mutagens and mutagenic treatments for the induction of desirable characters in a cultivated crop. The chlorophyll mutation rate is conveniently being used as preliminary index of effectiveness of mutagens and mutability of the variety which in turn could be helpful to realize the spectrum of desirable mutations in the treated populations. It also serves as a good index for determining the doses of different mutagens. The present paper deals with the observations on effectiveness and efficiency in terms of seedling injury, lethality and pollen fertility in M 1 generation and chlorophyll mutations in M 2 generation in sesame (Sesamum indicum L.) induced by gamma rays and EMS.

Materials and Methods
Two sesame varieties viz. SVPR 1 and CO 1 were treated with gamma rays (30 to 70 krad) and EMS (0.8 to 1.6%). The treated seeds along with their respective controls were sown immediately in the field to raise the M 1 generation with two replications in a Randomized Block Design during Aug-Oct (2001) In CO 1, the frequency rate showed a decreasing trend with an increase in dosage of gamma rays on both M 1 plant and M 2 seedling basis and this was maximum in 30 krad on both M 1 plant and M 2 seedling basis. In case of EMS, the frequency rate was in an increasing trend upto 1.4 per cent on both M 1 plant and M 2 seedling basis. The maximum value was recorded by 1.4 per cent. When comparing the two mutagens, gamma rays induced greater magnitude of chlorophyll mutants than EMS in both the varieties. Among the two genotypes, SVPR 1 registered more frequency rate than CO 1. The frequency of chlorophyll mutants in general were low in this crop and it may be due to the fact that oil seed crops are resistant to induced chlorophyll mutations as reported by Rajan (1969) and Rangaswamy (1973). It may be further attributed to the probable reasons of the elimination of gametes carrying mutations or zygote inviability.

Spectrum of chlorophyll mutants
The relative proportion of chlorophyll mutants is furnished in Table 1. The following different kinds of chlorophyll mutations were identified in accordance with the classification of Gustafsson (1947 In CO 1, among the four chlorophyll mutants, Xantha viridis was found to be the maximum followed by chlorina and striata in gamma ray irradiated population. They appeared in all the dosages of gamma rays except 70 krad in which 100 per cent of xantha viridis was observed. Xantha occurred only at lower concen-trations/dose of EMS and gamma rays. In EMS treated population, chlorina type of mutant occurred more than other types. The reason for the appearance of greater number of xantha viridis type may be attributed to the involvement of polygenes in chlorophyll formation (Gaul, 1964).
The data on mutagenic effectiveness and efficiency are furnished in Table 2. Mutagenic effectiveness denotes the frequency of mutations induced by a unit dose of mutagen (factor mutations/ dose). Gamma rays at 40 krad (4.03%) in SVPR 1 and at 50 krad (8.90%) in CO 1 were found as the most effective doses. In case of EMS, the maximum effectiveness was observed at 0.8 and 1.4 per cent concentrations in SVPR 1 and CO 1 respectively. In general gamma rays was found as the most elective when compare to EMS in both the genotypes.

Studies on induced chlorophyll mutation in sesame (Sesamum indicum L.)
The mutagenic efficiency is a measure of the proportion of mutation inrelation to undesirable changes like sterility, injury and survival etc. In SVPR 1, the mutagenic efficiency was observed maximum at 70 krad (9.80%) on seedling survival basis and 40 krad on both injury (6.68%) and sterility basis(40.76%). In case of EMS, it was maximum at 0.8% on survival (22.2%), injury (6.86%) and sterility (78.17%) basis. In CO 1, it was found maximum at 50 krad (22.25%) on survival basis and at 30 krad on injury (11.49%) and sterility (30.33%) basis in gamma ray treatments. In EMS, the maximum efficiency was at 1.0 per cent on injury basis and at 1.2 per cent (26.72%) on sterility basis. The efficiency based on sterility basis was more than the efficiency based on lethality and injury basis. It indicated that it reduced fertility to a smaller magnitude.
Among the two mutagens, gamma rays was found to be more effective and efficient than EMS. The effectiveness and efficiency of both the mutagens were more in SVPR 1 than CO 1. The higher mutagenic effectiveness and efficiency at lower doses are due to the fact that the biological damage increased at a faster rate in higher doses than the mutations.