| Induction of chlorophyll and viable mutations in Triticum
aestivum L. A.S. LARIK and Y.A. AL-SAHEAL Department of Agronomy and Range Science, Gassim College of Agriculture, P.O. Box. 1482, King Saud University, Saudi Arabia The main object of mutation breeding are (i) to enhance the frequency of mutations and (ii) to increase the mutation spectrum. Many reports on the induction of macromutations in diploid species have been presented earlier (AASTVEIT 1968 ; NILAN et al. 1977 ; TIWARI & SISODIA 1981), on the contrary, with polyploid species only comparatively few experiments have been conducted (LARIK & AL-SAHEAL 1986 ; WASHINGTON & SEARS 1970). With the use of chemical mutagens all sorts of chlorophyll mutations are obtained which helped in further understading of genetics of chlorophyll development. The present study deals with the frequency of chlorophyll and viable mutations induced by EMS in two bread wheat cultivars extensively grown in Saudi Arabia. Material and Methods Dormant seeds of two hexaploid bread wheat cultivars namely ; Al-Samma and Maaya were presoaked in distilled water for 20h, treated with freshly prepared 0.2%, 0.4% and 0.6% EMS solution for 7h and 9h duration at a constant room temperature 20+ or -1C. The EMS solutions were prepared using standard phosphate buffer of pH 7. The treated seeds, after thorough washing in running tap water for 30 min, were grnown in pots in replicates to obtain M1 generation. All M1 plants were harvested individually and M2 generation was raised as row progenies. M2 population was carefully screened for both chlorophyll and viable mutations throughout the life span of the crop. Results and Discussion The chlorophyll mutations in M2 generation have been proved to be most dependable indices for evaluating the genetic effect of mutagenic treatments (TSUKUDA et al. 1977 ; TIWARI & SISODIA 1981). In present study mutation frequency was calculated in terms of (i) percentage of families segregating for mutations and (ii) percentage of mutant plants in M2 population. Chlorophyll mutation frequency is summerized in Table 1. The highest and the lowest chlorophyll mutation frequency was observed under EMS 0.6% with 9 h and EMS 0.2% with 7h duration which was 23.53% and 13.63% on the basis of M1 segregating families and 5.22% and 2.9% on the basis of M2 population, recorded in cultivars Al-Samma and Maaya respectively. Four types of chlorophyll mutations were observed in the following order chlorina>tip-xantha>viridis >xantha. No chlorophyll mutants were observed in control. The chlorophyll mutations chlorina and viridis induced in hexaploid wheat with EMS are assumed to be point mutations rather than deficiencies. Evidence for this is found earlier (SHAMA RAO & SEARS 1964 ; WASHINGTON & SEARS 1970). The frequency of viable mutations with respect to various populations is depicted in Table 2. The highest frequency of viable mutations was observed in cultivar Al-Samma under EMS 0.6% with 9h duration, 41.17% on the basis of M1 segregating families and 13.04% on the basis of M2 population. The same cultivar displayed lowest frequency of viable mutations under EMS 0.2% with 7h duration on the basis of M1 segregating families, whereas the lowest frequency of viable mutations on the basis of M2 population was shown by cultivar Maaya under EMS 0.2% with 9h duration. Resistance of Maaya and sensitivity of Al-Samma in terms of recovery of viable mutations could partly be on account of their inherent genetic property. Such varietal differences in mutation yielding ability as been reported by LARIK (1985). Already there exists much evidence that genetic differences, even though they are as small as single gene difference, can produce significannt changes in mutation expression (LARIK et al. 1984 ; LARIK & AL-SAHEAL 1986). |
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