The effectiveness of selection for a character depends upon the amount of genetic variation present in a variable population. The variability of a biological population is an outcome of genetic contribution of individuals making of that population in relation to prevailing environment. A survey of genetic variability with helps of suitable parameters such a genotypic coefficient variation, heritability, genetic advance are absolutely necessary to start an efficient breeding programme. The coefficient of correlation between yield and its contributing traits shows a complex relationship; Path coefficient analysis partitions the component of correlation coefficient into direct and indirect effects and visualizes the relationship in more meaningful way (Rahim et al. 2010). Genetic diversity is one of the criteria of parent selection in hybridization programme.

 

Secondly, knowledge of association of yield with its components, especially at the genotypic level, is of considerable importance in selection for yield. Information about the interrelationship among these yield components themselves is also equally important for selection of an optimum combination of the characters which would improve yield. Thirdly, in a system of closely associated characters, such as yields and its component, it is of use to study the cause and effect relationships in terms of nature and relative contribution of the characters component to yield. Keeping the above point in view, the present mutation breeding project in green gram was under taken for micro-mutational improvement of yield of two varieties namely Sujata and OBGG-52. The mutagenic treatment included three doses of physical mutagen i.e. gamma ray and three chemical mutagen i.e. EMS, Nitroso guanidine (NG) and Malic Hydrazide (MH) and three combination of physical and chemical mutagen at the intermediate dose of such mutagen. The population was advance to M₇ generation and the present study was undertaken with 22 numbers of induced mutants, 02 parents, 04 locals and 02 high yielding standard varieties of diverse geographic and genetic origin.

 

The mutant cultures of these two varieties showed wide range of variation for all the 12 quantitative characters studied. The genetic parameters like phenotypic coefficient of variation (PCV), genotypic coefficient of variation (GCV), heritability and genetic advance for these twelve characters are presented in the Table 1. The range of the variation of the characters that the highest limit of variation was about 20-40% higher than the lower limit for days to flowering and Clusters plant^-1 40-60% for plant height, pods plant^-1, pod length, seeds pod^-1 and 100-seed weight and yield plant^-1 and for other characters it about 70-100%. These indicated that the strains possess tremendous potential differences for the characters. Variability in greengram for different traits have been studied earlier by many workers Idress et al.(2006), Tabasum et al.(2010), Rahim et al.(2010), Tabasum et al.(2010), Abna et al.(2012), Roy and Chowdhury et al.(2012).

The extent of variability among the mutant cultures, parents, standards and locals genotypes with respect to different quantitative characters was estimated in terms of PCV and GCV. The PCV and GCV ranged from 4.00 to 48.65 and 3.34 to 48.03 respectively in days to 50% flowering and survival of 10 days old seed ling at 10 ºC. Both the PCV and GCV estimates were high (more than 10%) for Plant height, Clusters plant^-1, Seeds pod^-1, 100-seed weight, Yield plant^-1 in the mutant cultures/genotypes of the experimental material. The PCV and GCV estimates revealed precise trend and their relative magnitude would indicate that the coefficient of variation were high for survival of 10, 30, 40 days old seedling at 10 ºC, pods per plant. GCV for character were smaller than that of PCV, indicating some influence of environment on them  These variability estimates for the traits under study in mutant lines of both varieties were in close agreement with earlier findings in greengram Momin and Misra (2004); Kumar et al. (2008), Rahim et al. (2010), and Roychowdhury et al. (2012).

 

The heritability (broad sense) estimates for different characters of the mutant cultures, parents, standards and locals ranged from 69.43% (for days to 50% flowering) to 98.59% (for survival of 30 days old seedling at 10 ºC). The heritability estimates were high (more than 90%) for 100-seed weight, plant height and pods plant^-1. The heritability estimates were low (less than 70%) for days to 50% flowering. The expected genetic advance (GA) for different characters of the mutant cultures, parents, standards and locals was estimated at 5% selection intensity and was expressed as percentage of population mean. The estimated GA (% of mean) under selection for characters varied from 5.73% for days to 50% flowering to 45.75% for pods plant^-1. The expected genetic advance was high (more than 30%) for plant height, pods plant^-1 and yield plant^-1 in the population in addition to their response to cold at different growth stage. High heritability and high GA was observed for plant height, pods plant^-1, survival of 10 days old seedling at 10 ºC, survival of 20 days old seedling at 10 ºC, survival of 30 days old seedling at 10 ºC and survival of 40 days old seedling at 10 ºC indicating additive gene action where selection will be effective. Low heritability and low GA was found for character days to 50% flowering indicating the character to be highly influenced by environmental effect and selection will not be effective. The heritability estimates for different characters in greengram were in broad agreement with reports of Momin and Misra (2004), Idress et al. (2006), Babu et al. (2007), Tabasum et al.(2010), Rahim et al. (2010), Reddy et al. (2011), Makeen et al. (2007) and Roychowdhury et al. (2012).

 

The phenotypic correlation (rp) estimates among the 12 characters are presented in Table 2. The rp estimates ranged from 0.739 between pods plant^-1 and yield plant^-1 to maturity to -0.409 between pod length and 100-seed weight. Of these 66 rp estimates, 12 were significant. The genotypic correlation (rg) estimates (Table 3) ranged from 0.860 between plant height and yield to -0.666 between days to flowering and 100 seed-weights. Fifteen of 66 rg estimates were found to be significant. In general the rp and rg estimates followed almost similar trend for all the characters under study. The magnitude of rg was greater than rp in almost all cases indicating higher genotypic correlation in case of positive association and lower in case of negative association would reinforce selections based on phenotype.

Of the association of character components plant height, cluster plant^-1, and pods plant^-1, pod length and seeds pod^-1 showed highly significant positive correlation with yield plant^-1 both at phenotypic and genotypic level. Similar high positive correlation was reported by many workers [Rahim et al. (2010) for pods plant^-1, number of seeds pod^-1. Reddy et al. (2011) for plant height, pods plant^-1, seeds pod^-1, 100 seed weight. Khajudparn and Tantasawat (2011) for pods plant^-1, clusters plant^-1, seeds pod^-1. Makeen et al. (2007) for pods plant^-1, plant height]. Hundred seed weight, survival of 30 days old seedling at 10 ºC exhibited moderate positive correlation with yield at both phenotypic and genotypic level.

 

Thirty one out of 55 phenotypic correlation among the yield components were positive out of which six were significant where as only one phenotypic correlation was negatively significant. In general the phenotypic and genotypic correlation estimates followed almost similar trend. The characters seeds pod^-1, pods plant^-1, pod length showed high positive correlation among themselves both at genotypic and phenotypic level which is in close agreement with the report of Rahim et al. (2010), Makeen et al. (2007), Begum et al., (2012) and Sahu et al.(2014). Plant height showed moderate but significant positive association with seeds pod^-1, and pods plant^-1. Clusters plant^-1 also had moderate positive association with pods plant^-1 where as pods plant^-1 also have moderate non- significant positive correlation with survival of 30 days old seedling at 10 ºC. Pod length had a moderate but negative correlation with survival of seedling at different stage of their growth at 10 ºC and moderate but positive correlation with all other character. Seeds pod^-1 showed highly significant positive correlation with pods plant^-1 and pod length but low non-significant positive correlation with survival of 30 and 40 days old seedling at 10 ºC. Survival of seedling at their different growth stage at 10 ºC almost had a negative and negligible correlation with all other yield traits. Correlation of 100-seed weight was significantly negative correlated with days to 50% flowering and pod length where as in all other cases it was negligible. Correlation study in greengram for different biometrical traits have been reported by earlier scientist Reddy D. et al. (2011), Makeen et al., (2007), Begum et al. (2012) Thippani et al. (2013) and Lalinial et al. (2014). Thus the significant association of plant height, pod length, pods plant^-1 and seeds pod^-1 with yield and among them indicated that selection of genotype based on these characters will be effective for yield improvement.

 

In order to study the cause and effect relationship between component traits on seed yield, path coefficient analysis was used. Through this, the correlation of the component traits with yield were partitioned into direct and indirect effect that would reflect on the nature of these associations and the relative importance of the component traits in determining the yield. The phenotypic correlation coefficients were used for carrying out path coefficient analysis in 30 genotypes (Table 4) and the analyzed had high R² value of 85.360% and low residual effect of 0.383.

Considering the direct effect of the component traits on seed yield in the genotypes it was observed that pod per plant had the highest direct effect (0.595) followed by plant height (0.3663) and 100-seed weight (0.3249). The direct effect of seeds pod^-1, survival of 40 days old seedling at 10 ºC on yield were positive but of very low magnitude (less than 0.05) whereas clusters plant^-1, pod length, survival of 10 days old seedling at 10 ºC showed positive and moderate (>0.05 to < 0.30) direct effect. Direct effect of days to 50% flowering and survival of 30 days old seedling at 10 ºC was negative. In present investigation, path analysis revealed that pods per plant, plant height, 100-seed weight had the highest positive direct effect on seed yield, whereas direct effects of other traits on yield were very low to moderate having positive magnitude except days to 50% flowering and survival of 20 and 30 days old seedling at 10 ºC. This indicated that selection for higher yield on the basis pods/plant, plant height and 100-seed weight be most effective. This is in broad conformity with path analysis studies in greengram as reported by Mishra and Pradhan (2006), Tabasum et al. (2010), Reddy et al. (2011), Mondal et al. (2011), Khajudparn and Tantasawat (2011) Gokulakrishnan et al. (2012), Garje et al. (2013) and Gadakh et al. (2013).

 

The present investigation on “Estimation of genetic variability and character association in micro mutant lines of greengram [Vigna radiata (L.) Wilczek] for yield attributes and cold tolerance” was taken up in the Department of Plant Breeding and Genetics, College of Agriculture, OUAT, Bhubaneswar. The field experiment was conducted at the EB-II Section of OUAT and laboratory work was taken up in S.K. Sinha Molecular Breeding Laboratory of the department. The materials consisted of 30 cultures/varieties of greengram (Vigna radiata (L.) Wilczek). Twenty two of these were induced mutants (now in M7 generation) of Sujata and OBGG-52, 02 were parents and other 06 were standard genotypes including 04 locals. The induced genetic variants were developed at OUAT. The mutants were developed through selection for higher yield than the parental material by applying selection pressure from M2 - M6. Finally, the selected cultures were tried in yield trial in present investigation. The source of the materials and their pedigree are given in Table 5.

The field experiment was laid out in a randomized block design (RBD) with 3 replications with 30 entries. The crop was shown on 25.09 2011. Each entry was represented by 3 rows of 3 m length. The intra and inter rows distances were 10 cm and 30 cm respectively. Fertilizers were applied at the rate of 20:40:20 kg of N:P2O5:K2O with 300 cft. of farm yard manure per hectare. All the FYM, phosphatic, potasic and half of the nitrogenous fertilizers were applied as basal dose and rest half of the nitrogenous fertilizers were applied at 21 days after sowing. Hoeing and hand weeding were done at the time of top dressing. No plant protection measure was taken as there was no incidence of diseases and insect pest.

 

Phenotypic correlation is estimated as –

rp =

Where,

rp = Phenotypic correlation coefficient

P Cov (x, y) = Phenotypic covariance between variable x and yPV(x) = Phenotypic variance for the variable x

PV(y) = Phenotypic variance for the variable y

 

Genotypic correlation co-efficient is estimated according to the following formula:

rg =

Where,

rg = Genotypic correlation coefficient

G Cov (x, y) = Genotypic covariance between variable x and y

GV(x) = Genotypic variance for the variable x

GV(y) = Genotypic variance for the variable y

 

The path coefficient analysis is a type of cause and effect relationship among the various correlated characters. Path coefficients are standardized partial regression coefficients, which individually provide a measure of the direct effect of a causal factor on the effect variable. These permit partitioning of the correlation between a causal factor and the effect variable into components of direct and indirect effects, and thus give a better picture of the associations of the causal factors with the effect variables.

 

In the present investigation, yield per plant was taken as the 'effect' with other characters related to yield as the causal factors.

 

The path coefficients were obtained by solving the following simultaneous equations, which give the basic relationship between correlation and path coefficients in a system of correlated causes. (Wright, 1921; Dewey and Lu, 1959).

 

r1.14 = p1.14 + r1.2 p2.14 + r1.3 p3.14 +..... + r1.13 p13.14

r2.14 = r2.1 p1.14 + p2.14 +r2.3 p3.14 +..... + r2.13 p13.14

r3.14 = r3.1 p1.14 + r3.2 p2.14 + p3.14 +.... + r3.13 p13.14

..............................................................................

R13.14 = r13.1 p1.14 + r13.2 p2.14 + r13.3 p3.14 + ... + p13.14

Where,

rij = the coefficient of correlation between ith and jth characters

pqi = the path coefficient (direct effect of ith character on yield)

 

The study of variability parameters among 30 greengram genotypes in 12 traits including yield has provided valuable information regarding the genetic variability, heritability and genetic advance for the characters and efficacy of different mutagenic treatment. Genetic parameters of traits, correlation among traits and path analysis revealed that selection for pods/plant, plant height; 100-seed weight would be effective in isolation of high yielding genotypes.

 

KKP and SS carried out the overall experiment, AM and TRD prepared the manuscript. BB supervised the experiment as Chairman and member of the advisory committee for the Master degree thesis work.

 

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