Abstract: Three short statured rice mutants (B-370-32, J-77-30 and SS-6) were developed through mutation breeding from three aromatic, fine grained, but tall and low yielding local varieties (Basmati-370, Jajai-77 and Sonahri Sugdasi, respectively). The mutants exhibited superiority in grain yield and quality over their parents. The number of panicles per hill, grain weight per hill and fertile grains per panicle made significant contribution to grain yield per unit area. Among the mutants, the grain yield of J-77-30 was significantly higher as compared to its parent/check varieties.
Introduction
Rice (Oryza sativa L.) is grown on 2.42 million hectares in Pakistan, covering approximate 1.22 million hectares under aromatic and 1.20 million hectares under non-aromatic cultivars (Anonymous, 1998-99). The excellent grain quality of aromatic rice cultivars such as Basmati-370, Jajai-77 and Sonahri Sugdasi fetch two to three times higher than those of the coarse grain varieties in the national and international markets. However, the major drawback of these local aromatic cultivars is that they grow very tall and consequently lodge on fertile soils at the time of grain formation resulting in serious yield losses. The use of induced mutation has been considered as an appropriate approach for developing short statured mutants accompanied by high yield and excellent grain quality. (Bari et al., 1981; Micke et al., 1990; Hu, 1991; Maluszynske et al., 1991; Baloch et al., 1999).
Materials and Methods
Seeds of three varieties of rice viz; Basmati-370, Jajai-77 and Sonahri Sugdasi were treated with 150, 200 and 250 Gy of gamma rays from 60Co and 15, 20 and 25 Gy of neutrons fast, to raise M1 generation. Selection was carried out in M2 generation which was raised from the seeds of first formed panicle of each plant in each treatment. M3 generation was raised to confirm the mutated traits selected from M2 generation. These mutant lines, after subsequent morphogenetic evaluation, were tested for yield performance in replicated yield trial in M4 generation at Experimental Farm, Tandojam. A high yielding variety Basmati-385 was also included in the trial as a check for comparison. The yield trial was laid out in Randomized Complete Block Design. The size of the plot was 3 x 4 m2. The seedlings were transplanted at a distance of 20 cm between rows and hills with three seedlings per hill. The fertilizer was applied at the rate of 80N:40P (kg/ha) in the form of urea and triple super phosphate. The basal dose of fertilizer 40N: 40P (kg/ha) was applied before transplanting and the remaining quantity of nitrogen fertilizer was applied as top dressing after 40 days of transplanting. The paddy yield and yield components were recorded at the time of harvesting, except days to heading date, which was recorded from seedling transplantation to 50 % flowering and data were analyzed following Gomez and Gomez (1984).
Results
The data of M3 generation revealed that the mutants B-370-32, J-77-30 and SS-6 were about 22 to 32 days earlier and had 20 to 43 cm short culm length than their respective parents. These mutants had 6 to 7 more panicles per hill, 14 to 21 more fertile grains per panicle and 242 to 543 grams higher grain yield per m2 than their parents (Table 1). The mean values for all the traits were significantly different from each other in M4 generation. Variations categorically were observed within parameters and sparse ranges existed from 94 to 131 days for seeding to 50 % flowering, 127 to 167 cm for plant height, 10.33 to 15.45 for number of panicles per hill, 18.5 to 41.15 gm for grain yield per hill, 85 to 109 for total grains per panicle, 42 to 81.75 for fertile grains per panicle, 21.43 to 24.43 (gm) for 1000 grain weight and 2.42 to 4.78 (kg) for grain yield per plot.
| Table 1: | Performance of promising mutants for yield and yield components in M3 generation |
| Table 2: | Performance of promising mutants for yield and yield components in M4 generation |
| Means followed by the same letter are not significantly different from each other at 5 % level of significance. | |
The less heading days were 94 in B-370-32 and Basmati-385 as compared to 131 days in Sonahri Sugdasi. Plant height was lowest in mutant strain SS-6 (127 cm) whereas, it was highest in a parent variety Jajai-77 (167 cm). The mutant strain J-77-30 produced higher number of viable panicles per hill (15.45), higher grain yield per hill (41.15gm), more grains per panicle (109), more fertile grains per panicle (81.75) and higher grain yield per plot (4.78 kg). Whereas, these parameters were consistently lower in other entries of the experiment. Comparatively, number of viable panicles were low in variety Sonahri Sugdasi (10.33), while variety Basmati-370 exhibited low grain yield per hill (18.5gm), low number of grain per panicle (85) and low fertile grains per panicle (42). Variables of 1000 grains (21.43gm) and grain yield per plot (2.42 kg) were low in variety Jajai-77 (Table 2).
Discussion
The results eventually impart that mutagen have induced changes providing classical criteria for isolation of useful mutants. In three mutants, there was a substantial decrease in plant height, while an increase in other quantative parameters in accordance with a shift in the mean away from the direction from the previous selection (Brock, 1965). Presently, it is a universally recognized fact that plant architecture has evolutionary significance and practically reduced plant height has contributed a lot in numerous crops to potentiate the grain yields. Therefore, the increased plant yield of our mutants may be linked to the altered plant morphology associated with increased grain yield per hill, total grains per panicle, fertile grains per panicle and 1000 grain weight. The plant morphology accompanying with such modifications in quantitative traits has achieved great importance to make the plants fit in the mathematical models for increasing the plant yield. It is identified that reduced plant height in rice has a positive relation ship with increased yield due to increased response to higher doses of fertilizer associated with increased lodging resistance and increased panicle number per unit area (Dat et al., 1978) and increased spikelets per unit area (Takeda et al., 1984). Semi-dwarfism has been reported to give 15 to 25 % more grain yield (Rutger, 1983). In the context of the improved quantitative characters, it is observed that the plot yield of all semi-dwarf mutants was significantly higher as compared to their parents. The mutant J-77-30 produced significantly highest grain yield (4.78 kg/plot) followed by SS-6 (4.02 kg/plot).
Acknowledgment
We are indebted to Mr. Muhammad Afzal Arain, PSO NIA, Tandojam for the critical review of manuscript and valuable comments.