| Evaluation of wheat mutants for inproved physiological
efficiency A.S. LARIK, H.M.1. HAFIZ1 and M.B. KUMBHAR Department of Plant Breeding and Genetics, Sind Agricultural University, Tandojam, Pakistan Modern crop improvement approaches involve modification and control of factors which determine crop productivity. The factors dealt with this study are visible plant attributes such as productivity per day, sink capacity (grains per spike, 100-grain weight and yield per plant ) and harvest index which contribute to high productivity. Phenotypically stable wheat mutants (Mutant-7, 28, 38, 13 and 39) and their mother cultivars (C-591 and Indus-66) were evaluated for the above physiological parameters. Productivity per day takes into consideration both plant yield and maturity. Modern agriculture not only strives for high productivity, but also for harvesting a good crop in shorter time so that the net productivity per unit area of land per unit time can be boosted up. Productivity per day was studied in all the mutants and their mother cultivars (Table 1). It may be noted that the major cause of the variation in mother cultivars was the variation in single plant yield rather than the maturity period, the variation observed in mutants arose from an interplay of these two components. A desirable significant shift was observed in the mean of all the mutants. The increase in the mean productivity per day in some of them was substantial. While EMS-derived M-7 showed maximum productivity per day. In crops like wheat, where grain is the economic end product, the number of grains per plant often becomes a limiting factor in enhancing plant yield even at higher photosynthetic rate. The number of grains per plant, which serves as the sink to receive the translocated photosynthate is, therefore an important criterion in identifyig potential high yielders. Hence the data on these traits (Table 1) clearly indicate that irrespective of the increase 100-grain weight in all the mutants, the increase in yield per plant was invariably associated with the number of grains per spike Harvest index represents the ratio between the grain yield and total biological yield. In present investigation harvest index was used to evaluate the physiological efficiency of wheat mutants for this useful plant breeding parameter. The alteration in harvest index was manifested in all the mutants with increase in the mean values (Table 1). However, they were not significantly different from their mother cultivars. Gamma rays originated mutant -39 displayed siguificant improvemenet in harvest index as compared to its mother cultivar. The physiological cause of variation in harvest index of these mutants is not well understood. However, it seems that lower number of grains per spike was due to accumulation of large amount of carbohydrate in culm has contributed to decreased harvest index (YOSHIDA 1972). For further increase in yield potential of wheat mutants, however, the number of grains per plant is obviously the limiting factor because of the physiological limitation on grain size. From this study, it may be concluded that mutagenesis may offer scope for isolating mutants with increased harvest index. It is possible that the increased grain yield observed in these mutants cound partly have resulted from an increased allocation of dry matter to the grains. It is now widely recognised that the substantial increase attained in the yields of wheat in recent times with the introduction of dwarfing genes is partly due to an increase in the harvest index of these new dwarf varieties (YOSHIDA 1972 ; JAIN et al, 1973). Hence the improvement of plant type associated with higher harvest index in wheat is more likely to be associated with larger spikes carrying more number of grains, high grain weight per ear and high 100-grain weight as well. A similar situation was observed by SIMS (1963) and CHOWDHURY (1978) in Australian grain variety of oats and wheat respectively. EMS -derived mutants displayed high degree of variation for productivity per day (WATSON 1952 ; ASANA 1968 ; CHOWDHURY 1978) as compared to gamma rays induced mutants. From present study, there is fairly a good ground to suggest that wheat plant could be reconstructed in terms of high harvest index and better sink capacity and that the mutation breeding can be exploited to evolve mutants with improved physiological efficiency. References ASANA, R.D. 1968. In quest of yield. Indian J. Pl. Physiolo. 11 : 1-10 CHOWDHURY, S. 1978. Proc. 5th Int. Wheat Cenet. Symp. 524-532. JAIN, H.K., S.K. SINHA, V.P. KULSHRETHA, & V.S. MATHUR. 1973. In Proc. 4th Int. Wheat Genet. Symp. Columbia U.S.A. SIMS, H.J. 1963. Aust. J.Exp. Agri. -Anim Husbe. 3 : 198-210. WATSON, D.J. 1952. Advance Agron. 9 : 101-145. YOSHIDA, S. 1972. Ann. Rev. Pl. Physiol. 23 : 434-468. |
| 1 Department of Botany. New Campus, Punjab University, Lahore, Pakistan. |