Morphological characterization and assessment of genetic parameters of NERICA mutant rice lines under rainfed condition

An experiment was conducted to evaluate thirty one NERICA mutant rice genotypes (twenty eight NERICA mutant lines along with three parental lines) of advanced (M4 and M5)generations for morphological characters and genetic parameters assessment in aus season, 2014 at the experimental field of Biotechnology division, BINA, BAU Campus, Mymensingh-2202 following Randomized Complete Block Design (RCBD) with three replications. The genotypes differed significantly for all the traits viz., days to flowering (1 st , 50%, 80%), days to maturity, plant height, total tillers and effective tillers hill -1 , filled and unfilled grains panicle -1 , 100-seed weight (g) and yield plant -1 (g).N1/300/P-9-5 had maximum yield plant -1 and N4 parent had minimum yield plant -1 . All the parental lines showed less yield compared to other mutant lines. The phenotypic coefficient of variations (PCV) were higher than genotypic co-efficient of variations (GCV) for all the traits studied indicating that they all interacted with the environment to some extent. All the traits studied expressed moderate to high heritability estimates ranging from 43.68 to 92.87%. High heritability along with high genetic advance was noticed for the traits, number of filled grains panicle -1 , number of unfilled grains panicle -1 and plant height.


Introduction
NERICA is a new drought tolerant rice variety introduced by the ministry of agriculture for growing in drought prone areas of Bangladesh.The term NERICA stands for New Rice for Africa, an extended family of some 3000 siblings.NERICA is the product of interspecific hybridization between the cultivated rice species of Africa (O.glaberrima) and Asia (Oryza sativa).Rice grain yield is a quantitative polygenic character and highly influenced by environment.Extent and significance of association of yield with yield components should be considered, while determining the selection criteria of germplasm on the basis of available genetic variation.The success of breeding program also depends on the amount of genetic variability present in the population and extent to which the desirable traits are heritable.Different morphological traits play very important role for more rice production with new plant type characteristics associated with the plant yield.Phenologicalproperities of rice also associated with the yield potential of the different rice varieties that further involved in rice breeding program (Shahidullah et al., 2009).Study of genetic divergence among the plant materials is an important tool to the plant breeders for an efficient selection of the diverse parents for their potential use in a rice breeding program for the improvement of the rice production.The term rainfed is used to describe farming practises that rely on rainfall for water without any artificial irrigation.Development of improved rice varieties with stress tolerance traits from introduced varieties could significantly increase productivity (Mzengeza, 2010).NERICA varieties have high yield potential and short growth cycle.Several of them possess early vigor during the vegetative growth phase and this is a potentially useful trait for weed competitiveness.Likewise, a number of them are resistant to African pests and diseases, such as the devastating blast, to rice stem borers and termites.They also have higher protein content and amino acid balance than most of the imported rice varieties (WARDA, 2008).Though its cause of low productivity in Bangladesh is still unrevealed, the farmers found low tiller number, weak and fragile stem could be the important morphological characters that compromised the yield (reported in a discussion meeting organized by UBINIG, 28 September 2012).Moreover, the scientists in the discussion meeting assumed that the low productivity could be due to climatic change and soil variation compared to its origin.For this reason mutation is applied to produce mutant lines to improve yield of NERICA lines in Bangladesh.
Mutants have made it possible to identify critical elements for developing high yield potential varieties exhibiting desirable traits such as semi-dwarfism, early maturity, greater number of panicles plant -1 and increased fertility.The technique has been successfully utilized by Bangladesh Institute of Nuclear Agriculture (BINA) and many other research institutes on different crops (Das et al., 1999;Azad et al., 2012).Therefore, the present experiment was conducted to evaluate thirty one mutant rice lines for morphological traits and to assess the genetic parameters of the NERICA lines to screen out best performing lines and traits with high heritability and genetic advance for developing high yielding new rice varieties.

Experimental materials
Thirty one NERICA rice genotypes (twenty eight mutant lines along with three parents) of advanced generations (M 4 and M 5 ) were used.Seeds of the rice genotypes were obtained from Bangladesh Institute of Nuclear Agriculture (BINA), BAU Campus, Mymensingh-2202.The experiment was conducted in aus season 2014.The list of the genotypes is present in the Table 1.

Field experimentation and management 2.2.1. Seedbed preparation and sowing of pre-germinated seeds
Seed bed was prepared by raising soil up to 5-10 cm from the field surfaces followed by puddling.Before puddling cow dung was applied @ 2kgm -2 .The entire seed bed was than divided into three seed beds and small plots (50 cm X 50 cm) were prepared considering the 31 rice genotypes.Between the plots 10 cm distance was maintained.Drainage channels (30 cm) were prepared between seed beds to drain out excess water whenever needed.The seeds were soaked into water for 24 hours and incubated in moist cloth sacks for 48 hours for quick germination.The pre-germinated seeds were sown in seedbed on 29 th March, 2014.

Experimental design
Field experiments were conducted following randomized complete block design (RCBD) with three replications.Row to row and plant to plant distance were 20 cm and 15 cm respectively.

Transplanting
One seedling per hill was transplanted to the main plot on the 18 th April, 2014.Row to row and plant to plant distance were 20cm and 15cm respectively.

Intercultural operations
Gap filling was done within seven days after transplanting with the seedlings from same source to obtain uniform plant population.Drainage and weeding were done as and when required.Insecticides and fungicides were sprayed only once.No artificial irrigation was given.

Harvesting
Different genotypes were matured at different times.Harvesting was done when 90% of the plant populations of each plot reached to maturity.

Estimation of genetic parameters 2.3.1. Estimation of genotypic and phenotypic variances
Genotypic and phenotypic variances were estimated according to the formula given by Johnson et al., (1995).

Estimation of heritability
Heritability in broad sense (h 2 b ) was estimated according to the formula suggested by Johnson et al., (1955) and Hanson et al., (1956).

Estimation of genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV)
Genotypic and phenotypic coefficient of variations were estimated according to Burton (1952) and Singh and Chaudhury (1985).

Estimation of genetic advance
Estimation of genetic advance was done following formula given by Johnson et al., (1955) and Allard (1960).Genetic advance, GA = h 2 b .K.σ p Where, h 2 b = Heritability in broad sense, K= Selection differential, the value of which is 2.06 at 5% selection intensity and σ p = Phenotypic standard deviation.

Estimation of genetic advance in percentage of mean, GA (%)
Genetic advance in per cent of mean was calculated by the formula of Comstock and Robinson (1952) as follows:

̅
Where, GA = Genetic advance and ̅ = Population mean

Results and Discussion
The analyses of variance of different NERICA mutant lines indicated that the difference among genotypes for all the quantitativetraits under study viz., days to flowering (1 st , 50%, 80%), days to maturity, plant height (cm), total tillers hill -1 , panicle length (cm), effective tillers hill -1 , filled and unfilled grains panicle -1 ,100 seed weight (g) and yield plant -1 (g) were highly significant (Table .2). Yaqoob et al. (2012) observed significant variation among genotypes for days to maturity, total tillers hill -1 , effective tillers hill -1 , plant height, panicle length, 100grain weight and yield plant -1 .Tiwari et al. (2011) also observed significant variation among genotypes for days to 50% flowering, effective tillers plant -1 , panicle length, and grain yield plant -1 .These results suggest that all the genotypes under study had significant variation with each other.The mean performances of 31 rice genotypes for their morphological characters are shown in Table 3.

Days to flowering (1 st , 50% and 80%)
Being an important character to assess early maturity, days to flowering was taken to an account for the genotypes.Days to 1 st flowering among the genotypes ranged from 61.33 to 90.56 days with a mean value of 77.67 days.N 4 /250/P-9-5-3 took the lowest days to 1 st flowering (61.33 days) and N 1 parent took the highest days to 1 st flowering (90.56 days).The average range of days to50% flowering among the genotypes was 65.61 to 95.27days with a mean value of 82.96 days.N 4 /250/P-9-5-3 took the lowest days to 50% flowering (65.61 days) and N 1 parent took the highest days to 50% flowering (95.27days).Days to80% flowering among the genotypes ranged from 70.43 to 101.7 days with a mean value of 88.53 days.N 4 /250/P-9-5-3 took the lowest days to 80% flowering (70.43 days) and N 1 parent took the highest days to 80% flowering (101.7 days).

Plant height (cm)
Lower plant height is desirable in rice breeding.The average range of plant height among the genotypes was 73.43cm to 114.77cm with a mean value of 97.12cm.N 4 parent had the lowest plant height(73.43cm) and N 1 /300/P-9-5-12 had the highest plant height(114.77cm).Plant height in rice is a complex character and is the end product of several genetically controlled factors (Cheema et al., 1987).Reduction in plant height may improve their resistance to lodging and reduce substantial yield losses associated with this trait (Abbasi et al. 1995).

Panicle length (cm)
Panicle length is also an important yield contributing character since higher panicle length could provide higher grain numbers.Panicle length among the genotypes ranged from 20.60 to 31.13 cm with a mean value of 25.05 cm.N 1 /250/P-7-3-11 had the longest panicle (31.13 cm) and N 4 parent had the lowest panicle length (20.60 cm).

Number of filled grains panicle -1
The yield of the plant is related to number of filled grains panicle -1 and it differed significantly among the lines.In this study the number of filled grain panicle -1 ranged from 61.0 to 127.0 with a mean value of 95.91.N 4/ 350/P-2 (1)-32-11 had the highest number of filled grain panicle -1 (127.0) and N 1 /350/P-2-2-4 had the lowest number filled grain panicle -1 (61.0).

100 seed weight (g)
There was a significant difference in 100 seed weight among the lines depending on the size and shape of grains.100 seed weight ranged from 1.73g to 3.03 g with a mean value of 2.47g.The highest 100 seed weight was recorded in N 1 /250/P-7-3-12 (3.03 g) andN 1 /350/P-2-2-4 had minimum 100 seed weight (1.73g).

Estimation of genetic parameters of NERICA mutant lines along with their parents
Genotypic variances, phenotypic variances, heritability, genotypic co-efficient of variation (GCV), phenotypic co-efficient of variation (PCV), genetic advance and genetic advance as percent of mean, GA (%) for all the yield contributing traits are presented in Table 4.

Variability parameters
A wide range of variation was observed among thirty one rice genotypes for eleven yield contributing traits.The perusal of data revealed that variance due to treatment was highly significant for all the traits (Table 2).This suggested that there were inherent genetic differences among the genotypes.Coefficient of variation studied indicated that phenotypic coefficient of variation (PCV) were higher than the corresponding genotypic coefficient of variation (GCV) for all the traits (Table 3) indicating that they all interacted with the environment to some extent.That means the studied traits are influenced by the environment.Among the all traits total tillers hill -1 (26.20% and 28.64%) exhibited high estimates of genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) respectively.On the other hand, Days to 1 st flowering (8.13% and 8.46%), days to 50% flowering (7.67% and 7.99%), days to 80% flowering (7.34% and 7.62%), days to maturity (4.20% and 5.12%) and plant height (10.48% and 11.68%) exhibited low genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV).The high values of genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) for these traits suggested the possibility of yield improvement through selection of these traits.Tiwari et al. (2011) also observed the higher magnitude of PCV and GCV for grain yield plant -1 , number of fertile spikelets, effective tillers hill -1 , panicle length and number of spikelets panicle -1 .

Genetic advance
The genetic advance is a useful indicator of the progress that can be expected as result of exercising selection on the pertinent population.Heritability in conjunction with genetic advance would give a more reliable index of selection value (Johnson et al., 1955).In the present study genetic advance was highest for number of filled grains panicle -1 (28.07) and lowest for 100 seed weight (0.619) among yield contributing traits (Table 4).The genetic advance as percent of mean was highest in case of number of total tillers hill -1 (49.37%), while lowest recorded by days to maturity (7.10%).Babu et al. (2012) also found highest genetic advance for number of filled grains panicle -1 and highest genetic advance as per cent of mean in case of number of unfilled grains panicle -1 .

Conclusions
A total of 31 NERICA rice genotypes were evaluated for morphological characters and various genetic parameters were assessed.Considering the traits days to flowering and days to maturity, the genotype N 4 /250/P-9-5-3 was earliest (104.6 days) and N 1 parent took highest days (126.7 days).All parents took the highest days to maturity than different lines.In terms of yield plant -1 genotypeN 1 /300/P-9-5 was superior (33.02g) and N 4 parent had minimum yield plant -1 (6.15g).All the traits are highly influenced by the environment as PCV were higher than GCV and a little scope for genetic improvement.Days to 80%, days to 1 st flowering, days to 50% flowering, number of unfilled grain panicle -1 and 100 seed weight are less influenced by environment in their expression.The lowest heritability value was recorded for panicle length.In the present study, high heritability along with high genetic advance was noticed for the traits, number of filled grain per panicle, plant height and days to 50% flowering.These traits can be improved through simple or progeny selection methods.Other traits showed high heritability along with moderate or low genetic advance which can be improved inter mating superior genotypes of segregating population developed from combination breeding.So, while taking breeding program using this genotype, higher emphasize should be given to environmental factors as well as agronomic practices.
variance and ̅ = Population mean

Notes:
PCV= Phenotypic coefficient of variation, GCV= Genotypic coefficient of variation, GA= Genetic advance, GA (%) = Genetic advance as percent of mean