Abstract: The application of growth regulators Gibberellic Acid (GA3) and lndole Acetic Acid (IAA) at panicle emergence stage/just at flowering stage affected the plant height, number of tillers per pot, sterility (%), number of spikelets per panicle and paddy yield significantly. Maximum reductions in sterility (%) was recorded in IAA and GA3 applied at panicle emergence stage as compared to check (control). The reason for this might be the delayed senescence and prolonged functionality plant leaves, allowing the vital physiological processes of the plant like photosynthesis and translocating to carbohydrate for a longer period of time as compared to the pots where no growth regulator was applied.
Introduction
Rice (Oryza sativa L.) is the most important food crop of the world. Due to large number of people subsisting on rice, its annual out put must increase by over 5 million tones a year just to keep pace with population growth (IRRI, 1985). The major role played by rice as food is unlikely to diminish in the foreseeable future. At present its role in the world trade seems to be certain and its demand in the international market would be well sustained for many years to come. Its role will be more positive and conspicuous if the quality of kernel is further improved to attract the international as well as the national customers.
In this light the need is felt to focus attention on the research activities relating to improving the filling of the spikelets and quality of kernel without lowering the yield. Ill ripening, including sterility, abortiveness, opaqueness and many other types of chalkiness are undesirable characteristics of kernel which extremely impair and deteriorate its quality. Some research work relating to the problem has been reported (Nagato and Chaudhry, 1969; Nagato et al., 1971) but many of the related ill-ripening and chalkiness of kernel were not well understood. It was therefore, contemplated to tackle the problem of ill-ripening and chalkiness through a multidimensional approach laying out some most appropriate experiments which could have exerted some influence and help decrease the severity of the problem.
The plant characteristics can be modified to a certain degree by the application of growth regulators. The appropriate concentration of growth regulators like gibberellin (GA3) can stimulate the activity of key chemical substances and physiological processes which are reflected by increased growth and ultimate increased yields of high quality (Huffaker, 1965). Different plant growth regulators were therefore, applied to rice plant to see their effect on enhancing the photosynthetic activities of the leaves and other growth characters (Jones, 1973) which may exert a favourable effect on the yield and quality of rice kernel.
Materials and Methods
The trial was conducted at Gomal University, D.I. Khan during 1994-95, in the soil filled pots each having 240 m diameter and 300 mm depth. The experiment was carried in a Completely Randomized Design with four replication before filling the pot, the soil mixed thoroughly with 0.5 N, 0.4 g P2O5 and 0.27 g K20 per pot for coarse rice varied IR-6. Similarly 0.4 g N, 0.27 g P2O5 and 0.27 g K20 per pot were applied to fine rice variety Basmati-370. The source of fertilizers were urea, single supper phosphate potassium sulphate for both varieties. Three seedling was transplanted in each pot. Aqueous solution of GA3 and IAA were sprayed at the rate of 3 ml/plant at panicle initiation stage.
The data was analysed statistically using Analysis Variance Techniques (Steel and Torrie, 1980) and Duncan multiple Range Test was used to see the significance treatment means at 5% level of probability (Duncan, 1955).
Results and Discussion
Plant height at maturity (cm): The data regarding the plant height are given in Table 1. It is clear from the data that plant height was affected by the growth regulators as well as variety during both the years. Fine rice variety, Basmati-370 produced plants of substantially more height than coarse rice variety, IR-6. As regards application of growth regulators, the plants of more height were produced in (GA3) and T3 (1AA) over control, during the years. The intact cells elongation, resulted in elongated intern of the plant stem (Dey, 1980).
Number of tillers per plant: The data given in Table 1 indicated that variety IR-6 produced more number of tillers than the than fine rice variety Basmati-370, during both the year Among the treatments, T2 (GA3) and T3 (IAA) result 12.41 and 12.47 tillers per hill during 1994 and 13.08, 12.75 tillers per hill during 1995 respectively, as compare to 9.89 and 9.97 obtained in T1 (Control) during the same years.
| Table 1: | Effect of plant growth regulators during the year 1994 and 1995 |
| Means sharing a letter in common are statistically non-significant at 5% level of probability | |
The differences among the varieties and treatments however, could not reach the level of significance when compared with each other. Results agreed with those of Harda et al. (1986) who reported that GA3 increased the number of tillers per plant.
Number of spikelets per panicle: It is evident from the data down in Table 1 that the rice variety, Basmati-370 produced more number of spikelets per panicle (132.34 and 133.49) as compared to coarse rice variety, IR-6 (111.14 and 112.09) respectively. The mean values show that both the GA3 and IAA produced more number of spikelets per panicle as compared to check (control) during both the years. The auxin (IAA) exerts influence on plant growth in many ways, including cell enlargement or elongation, flower initiation and development and fruit setting. The gibberellin hormones have many regulatory functions. The most obvious is the stimulatory effects on stem growth and flowering. Gibberellin may stimulate cell division, cell elongation and can control enzyme secretion. Debate and Murty (1981) and Singh and Singh (1982) claimed that the application. of IAA delayed leaf senescence, in terms of enhanced functional leaf area, and increased the number of spikelets per panicle.
Sterility percentage: It is clear from the data given in Table 1 that Basmati-370 resulted in more sterility (9.70 and 8.90%) as compared to 1R-6 (8.11 and 7.97%) during both the years. It is very interesting to note that the sterility which is a serious problem, reducing the rice yield and deteriorating its quality, can be controlled to a considerable extent with the use of appropriate growth regulators applied at appropriate time. The minimum sterility (2.59 and 7.28%) was recorded in treatments T3(IAA) and T2(GA3) (8.85 and 8.30%) during the years. Both the growth regulators GA3 and IAA exerted an influence on plant growth and development. They caused the cell enlargement and helped in flowering and consequent grain development, and also reduced the sterility percentage by improving fertilization. Similar results were reported by Singh et al. (1984), who observed that GA3 and 1AA spraying at anthesis increased percentage of filled spikelets.
Normal kernels (%): Normal kernels do not stop growing in the way and attained normal dimension, normal starch compaction and full weight. The data regarding normal kernels are presented in Table 1. Coarse rice variety, IR-6 produced more normal kernels (87.62 and 87.93%) as compared to fine rice variety, Basmati-370 (85.33 and 86.34%) respectively during the both years. Among the treatments, T3(IAA) produced maximum normal kernels (88.93 and 88.26%) which do not differ statistically from T2(GA3) (87.77 and 88.03%) during both years respectively. The reason for obtaining more normal kernels incase of treated pots may be due to the fact that leaves in treated pots remained functional for a longer period of time on account of delayed senescence in these pots (Singh and Singh, 1982). The second reason might be the longer functionality of the vascular bundles in different parts of the panicle which might have resulted in an efficient translocation of photosynthates (Debata and Murty, 1981; Singh et al., 1984).
Paddy yield per pot (g): The data pertaining to paddy yield/pot are given in Table 1. The coarse rice variety, IR-6 produced more paddy yield (33.62 and 34.02 g) than the fine rice variety, Basmati-370 (21.85 and 22.06 g) respectively. The variation might be due to more breadth and thickness of the kernel of this variety which may be genetically controlled. Among the growth regulators, T3(1AA) resulted more paddy yield (32.39 and 32.70 g) followed by T2(GA3) (30.31 and 30.92 g) during the years. The control treatment produced minimum paddy yield (20.52 and 21.51 g). It may again by explained in terms of more efficient functionality of the stem, leaf sheath and leaves which might have positively helped to increase the efficiency of the plant for physiological and vital functions particularly the photosynthesis and translocation of photosynthates because of the fact that senescence of leaves was delayed in the treated pots, whereas, the leaves were dried in check pots sooner. Another reason for more paddy yield in treated pots may be the more panicles, spikelets, lesser occurrence of sterility, abortive and opaque kernels and more normal kernels obtained during 1994 and 1995 respectively. The study documented that application of lAA was absolutely necessary for having improvement final yield as evidenced by Dey (1980).
Protein content (%): The data regarding protein content are shown in Table 1. It is obvious that fine rice varied Basmati-370 produced more protein content as compared to coarse rice variety, IR-6 during both the years. The reason for obtaining more protein content in case of and IAA may be due to the fact that the leaves remain functional for longer period of time and played vital role the synthesis of protein contents. Similar responses were further documented by Hack et al. (1985) who claimed that application of plant growth regulator increased yield improved quality of rice.