Estimating Narrow Sense Heritability from Parent Progeny Regression and Inter-generation Correlation Coefficient Analysis for Yield and Component Characters in Segregating Lines of Urdbean [Vigna mungo (L.) Hepper]

Black gram commonly called as urad bean, mungo bean or black matpe bean is a self-pollinated short duration grain legume belonging to the family Fabaceae with diploid chromosome number 2n=22. It is most extensively grown in Asia and some adjacent areas including India, Pakistan, Afghanistan, Bangladesh and Myanmar. It forms significant part of diet as it contains valuable amount of protein (25-28%), carbohydrates (62-65%), fibre (3.5-4.5%), ash (4.5-5.5%), oil (0.5-1.5%) along with some amino acids (methionine, lysine), vitamins (thiamine, niacin, riboflavin) and minerals (iron and phosphorus). Being a leguminous crop, it nourishes the soil by restoring its fertility through symbiotic nitrogen fixation and thus acts as soil ameliorant with low water requirement. It is grown annually in many parts of India and is also suitable as catch crop, mulch crop, inter crop, mixed crop and green crop. Despite of its varied significance, it doesn’t hold key position due to vulnerability to several biotic and abiotic factors, poor ideotype, narrow genetic base and their cultivation in marginal and harsh environments which makes the performance of this crop very low in terms of yield and productivity. As yield is a complex trait and is interaction of many component variables, selection cannot be done directly based on this for development of new black gram genotypes. Therefore, yield can be improved only if the breeder has the knowledge about the association among yield and related traits. Keeping in view, the prime objective was to increase efficiency of selection by using method of parent progeny regression and intergeneration correlation analysis between two generations for better crop yield predictability which determines the degree of dependence of one variate on the other for estimating the amount of genetic potential transferred from parent to progeny. These two parameters will be further helpful in working out narrow sense heritability which is a measure of additive variance and this method will directly provide better chances of improving the traits through their effective selection.

The present study was undertaken at Experimental Farm of the Department of Genetics and Plant Breeding, College of Agriculture, CSK HPKV, Palampur (H.P.) during Kharif 2018 and 2019. The experimental material comprising of 14 crosses (Table 1) derived from seven lines and two testerswas evaluated in randomized complete block design over three replications. The main objectives were determined to estimate parent-progeny regression, intergeneration correlation and from them narrow sense heritability between F₂ and F₃ populations for their genetic improvement.The observations were recorded on 20 randomly selected plants from three rows (2 m each) in F₂ and ten plants from ten progeny rows in F₃  with spacing of 30 × 10cm for each cross along with parents and checks.
 

       
Data was analysed on the basis of individual plant mean for 11 agro-morphometric traits using parent progeny regression coefficient which is calculated by regressing the mean values of a character in the progeny (F₃) upon the mean values of a character in the parent (F₂) (Rao and Saxena 1999). Intergeneration correlation coefficients (r) were calculated between selected F₂ and F₃ progenies as suggested by Lush (1940). In each case progeny means (y) of F₃ generation were regressed on the individual plants (x) of F₂ generation.
               
Based on parent progeny regression, narrow sense heritability was calculated as suggested by Smith and Kinmann (1965) i.e. h²_ns= 2 × b. But, this method was not proved to be efficient as the heritability estimates from this method was found to be more than 1 (or 100%). This weakness of the method was tackled by using correction formula (Smith and Kinmann 1965). i.e. multiplicative factor of 2/3; h2ns =2/3 * b (For F₂- F₃)  with the help of MS-Excel and OP-STAT software.

The parent progeny regression and correlation between two generations are less prone towards the influence of environment and thus is very helpful for selection of better genotypes in early segregating generationsso as to make improvements in the existing genotypes or the production of new ones and were calculated for all the crosses in selected F₃:F₂ plants for various traits.The regression and intergeneration correlation for yield and its component characters are presentedin Table 2.
 

       
Regression coefficient (b) and intergeneration correlation (r) values in cross IC-281980 × HPBU-111 were found to be positive and significant for two traits namely DTM and seeds per pod. positive and non-significant values were found for plant height andbiological yield and 100 seed weight followed by DTF, plant height and pod length respectively. In cross IC-281982 × HPBU-111 b values were positive and non-significant for biological yield per plant and pod length, while exhibited non-significant positive correlation for pod length, DTM and harvest index. Cross IC-281993 × HPBU-111 possess non-significant positive b values for pods per plant, biological yield and harvest index, whereas r values for harvest index, DTM and seeds per pod.Values of b and rin cross IC-436852 × HPBU-111 were found to be non-significant and positive for plant height, DTM and100 seed weight. Cross IC-398973 × HPBU-111 revealed high degree of non-significant positive b and r values for DTM, pod length and DTF. Cross IC-413306 × HPBU-111 showed significant positive b and r values for DTM whereas positively non-significant for seed yield and biological yield. In cross IC-413304 × HPBU-111, high positive non-significant values of b were observed for pods per plant, DTM and biological yield while DTM, pod length and DTF have high non-significant r values. In cross IC-281980 × Him Mash-1, high positive and non-significant values of b and r were observed for pod length. Cross IC-281982 × Him Mash-1 showed high degree of significant positive b and r values for DTM and non-significant for harvest index and pod length. Cross IC-281993 × Him Mash-1 exhibited significant positive b and r values for DTM and non-significant forplant height and biological yield (b) and DTF, pod length and plant height (r). Cross IC-436852 × Him Mash-1 exhibited high degree of non-significant positive r values for DTM, DTF and pod length, whereas b values for pod length, biological yield and plant height. For cross IC-398973 × Him Mash-1, band r values were significant for 100 seed weight andDTM whereas positively non-significant for biological yield. In cross IC-413306 × Him Mash-1, significant b and r values were observed for DTF and high positive non-significant for biological yield and plant height (b) and DTM, seeds per pod andharvest index (r) between parent and progeny. Cross IC-413304 × Him Mash-1exhibited high significant positive b and r values for branches per plant and non-significant for seed yield and biological yield and days to 75% maturity and 100-seed weight respectively.
       
Similar results were supported by (Muralidhara et al., 2015) for branches per plant and seeds per pod in green gram, Kumar et al., (2011) and Singh et al., (2017) for 100-grain weight in rice and wheat respectively and (Kavithamani et al., 2013; Lalitha et al., 2018) for days to 50% flowering in rice.
       
However, plant height, pods per plant, pod length, biological yield per plant, seed yield and harvest index had not shown any significant regression and intergeneration correlation values in any of the crosses between F₂ and F₃ generations indicating that direct selection for yield on the basis of phenotypic performance may not be effective during early generation or otherwise selection must be delayed in later succeeding generations. Result is in line with the findings of Barman and Borah (2012) and Manohara and Shashidhar (2018) for yield in rice and Gandi and Shunmughavalli 2017 in blackgram.
       
In terms of regression (b) and intergeneration correlation analysis(r), five crosses viz., IC-281980 × HPBU-111, IC-413306 × HPBU-111, IC-281982 × Him Mash-1, IC-281993 × Him Mash-1and IC-398973 × Him Mash-1 showed positive and significant values for days to 75% maturity, whereas IC-281980 × HPBU-111, IC-413306 × Him Mash-1, IC-413304 × Him Mash-1and IC-398973 × Him Mash-1for seeds per pod, days to 50% flowering, branches per plant and 100-seed weight in F₂-F₃ generations respectively.
 
Narrow sense heritability (NSH)
 
Narrow sense heritability for F₃ over F₂ generation by regression coefficient in all crosses for 11 traits is given in Table 3. Narrow sense heritability is measured as the ratio of additive variance to the total phenotypic variance, involving additive and additive × additive type of fixable variance. So, higher values of narrow sense heritability provide more possibility for improving the characters through selection in F₂ or later generations.
 

       
For cross IC-281980 × HPBU-111, NSH was highest for the plant height followed by DTM and biological yield. For cross IC-281982 × HPBU-111, NSH was found highest for biological yield and pod length. For cross IC-281993 × HPBU-111 pods per plant has highest NSH followed biological yield and harvest index. For cross IC-436852 × HPBU-111 plant height has highest NSH, following 100-seed weight and DTM. NSH for cross IC-398973 × HPBU-111 was maximum for pod length and DTM. Cross IC-413306 × HPBU-111 has highest NSH for seed yield followed by DTM. For cross IC-413304 × HPBU-111, pods per plant has highest NSH followed by DTM and biological yield. For cross IC-281980 × Him Mash-1, NSH was found to be highest for pod length followed by days to 50% flowering. For cross IC-281982 × Him Mash-1, harvest index has highest NSH followed by DTM. NSH for cross IC-281993 × Him Mash-1 was maximum for plant height followed by biological yield and DTM. Cross IC-436852 × Him Mash-1, has highest NSH for pod length followed by biological yield per plant and plant height. NSH for cross IC-398973 × Him Mash-1 was maximum for biological yield per plant, 100-seed weight, DTM and seeds per pod. For cross IC-413306 × Him Mash-1, biological yield per plant has highest NSH followed by plant height and seeds per pod. NSH for cross IC-413304 × Him Mash-1 was found to be highest for seed yield followed by biological yield, branches per plant and plant height.
               
The estimates of NSH were noticed higher for biological yield and days to 75% maturity while lower heritability was recorded for seeds per pod, branches per plant and seed yield in most of the crosses. Higher values of narrow sense heritability indicates effect of additive variance and provides better chances of improving the traits through their effective selection, whereas low heritable traits can be improved only through hybridization as dominance or epistatic effects may be present. Hence, in the present study, biological yield has the better chances of improvement through selection.

In any crop development effort, the ultimate goal of a plant breeder is to boost production. Because yield is a complicated feature and straightforward choices based on yield components may not always provide acceptable results, the pattern of association takes note on further importance. The data estimation for regression and intergeneration correlation for F₂-F₃ progenies revealed positive significance fordays to 75% maturity meaning that effective selection can be done during this stage based on phenotypic observations while four crosses showed the significant positive relationship for seeds per pod, days to 50% flowering, branches per plant and 100-seed weight respectively indicating to be cautious while going for direct selection on the basis of these traits or selection may be done in later generations. As narrow sense heritability is the ratio of additive variance to the total phenotypic variance, it includes additive and additive × additive component of variance, which are fixable. Higher the narrow sense heritability, higher is the chances of improving the characters through selection.The amplitude of NSH values based on the parent-offspring regression coefficient was maximum for biological yield and days to 75% maturity implying to be the reliable indicator of the performance of their progeny in subsequent generations and thus provides usefulness of selection in early generation with greater impact on blackgram breeding program.

The authors would hereby like to declare that there is no conflict of interests that could possibly arise.