Abstract: Six rice mutants along with their parents and a check variety (Super Basmati) were evaluated at eight sites to determine genetic differences and the magnitude of genotype x environment interaction (G X E) for yield potential, in Sindh province. Genotype, location, year and their interactions were highly significant. The regression coefficient (b) and deviation from regression (S2d) showed significant differences among the mutants/varieties. The mutants Bas. 20/1, Bas. 15/2, Bas. 15/14 and Sonahri Sugdasi-20 (SS-20) were superior in yield to all the entries under evaluation. On the basis of stability parameters, the mutants Basmati 20/1 and Basmati 15/14 have shown good adaptation potential under favourable as well as unfavourable environments.
Introduction
Rice (Oryza sativa L.) is one of the most important crops in Pakistan and the second largest contributor in export earnings after cotton (Qayyum et al., 2000). The province of Sindh has varied ecological zones therefore; genotypes with wide adaptability are required to be identified which can perform consistently over a range of environments. Thus, estimation of stability of a new genotype for yield is a pre-requisite for its release as a commercial variety. Performance of a genotype in diverse environments is a true evaluation of its inherent potential for adaptiveness (Pandey et al., 1981). Stability analyses on cultivar performance tests conducted under different environments have been reported by many researchers (Milligan et al., 1990; Qayyum et al., 2000 and Basford and Cooper, 1998). Crop stability, is the ability of a crop to exhibit minimum interaction with both predictable and unpredictable environments (Qayyum et al., 2000). Eberhart and Russell's Model (1966) is one of the techniques used to rank the varieties for stability. The model uses simple linear regression to describe various types of varietal adoptabilities to wide range of environment as a quantitative measure of phenotypic stability.
Finlay and Wilkinson (1963) suggested that cultivar with regression coefficient (b) around 1.0 would be stable. Eberhart and Russell (1966) proposed regression coefficient (b) as the parameter of response and deviation from regression (S2d) as the parameter of stability. The performance of crop plants varies in different environments, which indicates their adaptability to specific region or over wide areas. The objective of this study was, therefore, to estimate the stability and adaptability potential of aromatic rice mutants under different agro- climatic conditions in the province of Sindh.
Materials and Methods
Five promising aromatic rice mutants of Basmati 370 and one of Sonhari Sugdasi were developed at Nuclear Institute of Agriculture (NIA), Tandojam by using different doses of gamma rays and selected on the basis of high paddy yield. These mutants were evaluated along with their parent and check varieties viz. Basmati 370, Sonahri Sugdasi, Super Basmati in the province of Sindh at 8 different locations viz. Tandojam, Sanghar, Badin, Thatta, Dadu, RRI Dokri, Shikarpur and Jacobabad for two consecutive years. The experimental layout was RCB design with 4 replications at each site. Each genotype was sown in 15m2 plot with 25 rows, 3 meter long and 20 cm apart from each other.
Data were statistically analysed according to Steel and Torrie (1960). Stability parameters (b and S2d) were estimated by using the methods described by Eberhart and Russell (1966).
Results and Discussion
The mean squares (MS) for genotypes, locations, years, location x year, location x genotype, year x genotype and year x location x genotype interactions were significant (P≤ 0.01) for paddy yield (kg ha-1) (Table 1). Significant genotype x environment (G x E) interaction indicated the presence of genetic variability and differential response of the genotypes to varying environments (Table 2). Significant (P≤0.05) differences were recorded among mutants for paddy yield. Mutants of Basmati 370 (Basmati 20/1, Basmati 15/2 and Basmati 15/14) and Sonahri Sugdasi (SS. 20) were significantly superior to all the entries.
| Table 1: | Pooled analysis of variance for paddy yield (kg ha-1) of 9 aromatic rice mutants/varieties grown over 8 locations in Sindh during 1997 and 1998 |
| MS = Mean square; ** = Significance at 1% level | |
The highest paddy yield (kg ha-1) was observed in Basmati 20/1 followed by Basmati 15/2, S.S. 20 and Basmati 15/14. The lowest yield was recorded in both the parents i.e., Basmati 370 and Sonahri Sugdasi. The mutants of Basmati viz., Basmati 20/1, Basmati 15/2 and Basmati 15/14 showed 119.7, 91.6 and 60.6% increase over the parent, respectively. On the other hand, mutants of Sonahri Sugdasi i.e., S.S.20 showed 63.8 increase over the parent. Mutants, Basmati 20/1, Basmati 15/2, Basmati 15/14 and S.S. 20 showed 57.5, 37.4, 15.2 and 18.5% increase over check variety, Super Basmati.
Traditional analysis of variance procedures are useful in determining the presence of genotypes x environment interactions, but generally do not provide informations concerning genotypic stability (Norden et al., 1986) . Regression coefficient (b) is a measure of stability in crop plants (Finlay and Wilkinson, 1963). Other researchers (Eberhart and Russell, 1966; Paroda and Hayes, 1971; Bughio et al., 2000; Norden et al., 1986) have suggested that regression coefficient (b) and deviation from regression coefficient (S2d) may be taken into consideration in identifying a stable genotype.
| Table 2: | Pooled mean performance for paddy yield (kg/ha) of 9 aromatic rice mutants /varieties grown over 8 locations for 2 years (1997 and 1998) |
| Means with different letters differ significantly at P≤0.05 | |
| Table 3: | Regression coefficient ‘b’ and variance due to deviation from regression for paddy yield (kg ha-1) of 9 aromatic rice mutants/varieties grown over 8 locations for 2 years (1997-98) |
| Bas. Basmati | |
Regression coefficient (b) values for mutants Basmati 20/1, Basmati 15/2, Basmati 15/14 and S.S. 20 value 1.577, which indicates that Basmati 370 is not well adapted in all the environments while Sonahri Sugdasi parent showed (b) value 0.815, which exhibits that Sonahri Sugdasi parent is well adapted in all the environments. Results revealed that mutation has induced positive changes in the adaptiveness and improves the yield potential of basmati mutants (Table 2). The maximum mean paddy yield was observed in Basmati 20/1. The deviation from regression coefficient (S2d) close to zero was observed in case of Basmati 20/1 followed by the parent Basmati 370 (Table 3). The check, Super Basmati showed 0.565 (b) value and (S2d) was 0.1080, respectively. A cultivar with (b) value less than 1.0 has above average stability and is specially adapted to low-performing environments, a cultivar with (b) value greater than 1.0 has below average stability and is specially adapted to high performing environments and a cultivar with (b) value equal to 1.0 has average stability and is well or poorly adapted to all environments depending on having a high or low mean performance (Finlay and Wilkinson, 1963), but a cultivar with b = 1.00 and S2d = 0.00 may be defined as stable (Eberhart and Russell, 1966; Francis and Kannenberg, 1978; Qayyum et al., 2000). On the basis of high paddy yield performance and estimates of stability parameters, it may be concluded that mutants Basmati 20/1 and Basmati 15/14 have good adaptation potential under favourable as well as unfavourable environments and may become a part of rice varietal complex of Sindh.