Abstract: Homogeneous seeds of Brassica campestris L. cv. Toria selection were treated with different doses of gamma rays (750, 1000 and 1250 Gy) to induce genetic variability for the selection of new genotypes with improved agronomic traits. After passing through different stages of selection, two promising mutants were selected for further studies. Two selected mutants along with 5 other entries including parent variety were evaluated for yield and yield components in yield trials for two consecutive years. The mutant TS96-752 was significantly (P ≤ 0.05) superior to all other entries in grain yield but at par with FSD 86028-3.
Introduction
Pakistan is overwhelmingly an agrarian economy, but it is unable to produce edible oils sufficient for domestic requirements due to which substantial amount of foreign exchange is spent on its import. There is about 3-4% increase in the import bill of edible oil every year. In order to save an average out flow of foreign exchange of about $ 700 million on account of import of edible oils, annually there is a strong and an urgent need to accelerate efforts to increase the local production of oilseeds (Rizvi, 2001).
Oleiferous Brassica (rapeseed and mustard) is an important oilseed crop of Pakistan but its production per unit area is very low i.e., 908 kg ha-1 (Anonymous, 2000). There are many factors responsible for its low yield per unit area but the most important one is the non-availability of high yielding varieties. It is, therefore, imperative to develop improved varieties of oilseed Brassica to bridge the gap between local production and import of edible oil.
Introduction of genetic variability is prerequisite for the evolution of high yielding varieties. Induced mutation has been extensively used for creating new genetic variation in crop plants. More than 2200 mutant varieties of different crops with improved agronomic traits have been developed and released to the farmers for general cultivation in the world (Maluszynski et al., 2000). Mutagenesis has also been very successfully employed in rapeseed and mustard by the plant breeders to alter the genetic architecture of plant and isolate the mutants with desired economic characters such as plant height, number of pods per plant, number of grain per pod, 1000-grain weight, grain yield, oil content and disease resistance (Javed et al., 2000; Mahla et al., 1990, 1991; Rehman et al., 1987; Rehman, 1996; Robbelen, 1990; Shah et al., 1990, 1998, 1999).
The present study was therefore, carried out to evaluate the performance of newly developed mutants of Brassica campestris L. cv. Toria selection for yield and yield components under agroclimatic conditions of Tandojam, Sindh.
Materials and Methods
The research work was conducted at Nuclear Institute of Agriculture, Tandojam for two consecutive years i.e., 1998-99 and 1999-2000. Homogeneous seeds of Brassica campestris L. cv. Toria selection were irradiated with 750, 1000 and 1250 Gy of gamma rays from cesium-137 (Cs137) at the dose rate of 30.80 Gy per minute to induce new genetic variability for the selection of improved genotypes. Selection for the desired agronomic traits were carried out in different stages. Of hundreds of mutated population, two mutants TS95-1005 and TS96-752 were selected on the basis of promising performance for grain yield and other characters.
Two promising mutants (TS95-1005 and TS96-752) along with parent variety (Toria selection) and four high yielding genotypes (SMP67, FSD 850347, FSD 86028-3 and Poorbi Raya) were evaluated in yield trial in RCBD design with three replicates. Each plot consisted of four-meter long five rows 45 cm apart. Ten plants were selected from each plot to record the data on yield and yield components while three central rows were harvested to estimate yield per unit area. The data were analyzed statistically according to Gomez and Gomez (1984) and the mean values were compared by DMR test at 5% level of significance.
Results and Discussion
Significant (P ≤ 0.05) differences were observed amongst all the entries for the traits under evaluation. The variety Toria selection and its mutants were found at par with each other in stature but significantly shorter than other genotypes. The minimum plant height was recorded in TS95-1005 (143.30) during 1998-99 (Table 1). Similar trend was observed in subsequent years (Table 2) and pooled data over the years (Table 3).
Plant height is an important yield contributing character in oleiferous Brassica. The reduction in plant height causes an increase in grain yield because of good response to higher doses of fertilizer and tolerance to lodging under unfavourable weather conditions. Moreover, the dwarfness in plant height is associated with earliness in maturity (Olejniczak and Adamska, 1999), which is a highly desirable character in crop plants. Chauhan and Kumar (1986), Das and Rahman (1988) and Shah et al. (1990) have isolated short statured mutants with high yield potential from mutagen treated populations of rapeseed and mustard. This confirmed that induced mutation through gamma rays have played a significant role in the alteration of plant architecture and selection of mutants with enhanced yield potential in rapeseed and mustard (Rahman, 1996; Shah et al., 1999).
All the genotypes were significantly superior to Toria selection in primary branches. The entries FSD 850347 (386) and TS96-752 (383) were at par with each other but significantly superior to other ones in pods per plant. Toria selection and its mutants were at par with each other but better than other genotypes in pod length. Both the mutants TS95-1005 and TS96-752 had higher number of grains per pod (16.97 and 16.97) and 1000 grain weight (3.84 and 3.82) respectively than the remaining entries. Three genotypes SMP 67 (16.16) FSD 86028-3 (16.19) and TS 96-752 (17.12) were equal to each other but superior to other ones in grain yield per plant during 1998-99 (Table 1). A little variation was observed in yield and yield components during 1999-2000 (Table 2). This phenomenon may be attributed to the prevailing environmental factors. However, the overall results indicated that the genotypes TS 96-752 (15.80), FSD 86028 (15.31) and SMP 67 (15.25) gave higher yield per plant (Table 3).
Breeding for high yield is based on the generation of new genotypes with improved yield components or the characters, which are responsible for substantial increase in yield. The genotypes FSD 86028-3 (2278) and TS 96-752 (2055) were at par with each other but significantly (P≤ 0.05) superior to other entries in grain yield (kg ha-1) during 1998-99 (Table 1). The mutant TS96-752 produced significantly high yield (1843) as compared with all other genotypes during 1999-2000 (Table 2). The same performance was observed in pooled data over experimental years (Table 3).
The most important factors responsible for an increase in the productivity in oilseed Brassica are the number of primary branches, pods per plant, number of grains per pod and an increase in seed index (weight/grain). Pods on the main stem is the most productive factor and this could be possibly increased by decreasing the number of branches (Beg, 1984). The mutant TS 96-752 and genotypes (FSD 850347, FSD 86028-3 and SMP 67) have not only produced the higher number of primary branches, but also higher pods per plant (Table 3). Genotypes with more branches and pods per plant have also been reported in oilseed Brassica (Chauhan and Kumar, 1986; Naz and Islam, 1979; Shah et al., 1990) as a consequence of mutagenesis. Yadava et al. (1973) demonstrated that seed per pod and 1000-seed weight directly influenced the seed yield in mustard. The genotype FSD 850347 showed highest 1000-grain weight (4.17) followed by mutants TS 95-1005 (3.88) and TS 96-752 (3.82). Both the mutants exhibited higher 1000-grain weight than the parent Toria selection, which probably indicates an increase in the size of grain as a result of induced mutation. This is in conformity with the findings of Chauhan and Kumar (1986) and Shah et al. (1990), who have also reported the bold-seeded mutants in oilseed Brassica.
Oil content is a primary and an important component of oilseed crops. Of all the genotypes under evaluation, the highest oil content was produced by SMP 67 (40%) followed by FSD 86028-3 (38.17%) and FSD 850347 (37.33%) during 1998-99 (Table 1). The genotype SMP67 (39.83 and 39.91) maintained its superiority during 1999-2000 (Table 2) and pooled over the years (Table 3) respectively. However, the mutant strain TS96-752 was significantly superior to its parent in oil yield per unit area (711.2 kg ha-1) but at par with other entries during 1998-99 (Table 1). Its performance for oil yield (595.3 kg ha-1) was equivalent to all other entries during 1999-2000 (Table 2). The overall average (670.5 kg ha-1) indicated its superiority over parent (Table 3).
The correlation coefficients generally highlight the pattern of association among yield components and growth attributes, depicting how yield, as a complex character is expressed. Plant height showed positive correlation with primary branches (0.512), pods/plant (0.509), grain yield per unit area (0.581) and oil content (0.740) while negatively correlated with pod length (-0.637) and grains/pod (-0.545) (Table 4).
| Table 1: | Performance of promising genotypes in yield trial during 1998-1999 |
| Table 2: | Performance of promising genotypes in yield trial during 1999-2000 |
| Table 3: | Performance of promising genotypes in yield trials (pooled over years) |
| Table 4: | Correlation coefficient ‘r’ among nine characters in oleiferous Brassica |
| Means followed by the same letters are not significantly different from each other at 0.05%, *= Significant, **= Highly significant, NS= Non significant | |
The findings indicate that pod length and grains/pod may have positive correlation with short stature varieties. Similarly, primary branches showed positive correlation with all characters, except pod length, grains/pod and 1000 grain weight. Similar findings have also been reported by Thakral (1982); Pathak et al. (1986); Singh et al. (1979) and Das et al. (1984). Pod per plant showed highly positive correlation with grain yield per unit area (0.635) whereas pod length showed significantly (P≤ 0.05) negative correlation with oil content (-0.515). Grains/pod exhibited positive correlation with 1000 grains weight (0.550) and oil content (0.571).
It was concluded that the overall performance of the genotypes for yield and yield components indicates that the mutant TS 96-752, because of its high yield potential, holds great promise to be a mutant variety. Moreover, this suggests that gamma rays irradiation with the dose range of 750 to 1000 Gy can be fruitfully applied to develop new varieties with high yield and other improved agronomic traits in oleiferous Brassica.