Studies on PCV, GCV, heritability and genetic advance in F2 segregating population of cross KJT-5-4-14 x Dokra-Dokri in rice (Oryza sativa L.)

Introduction

Rice (Oryza sativa L.) is an important staple food and a primary dietary intake for over half of the world population. Rice is grown on 45.15 million hectares in India, with an annual production of 123.81 million tons with an average productivity of 2742 kilograms of milled rice per hectare (Ministry of Agriculture, 2023-24) [2]. While India contributes 22% of the global rice supply, its burgeoning populace poses a significant threat to food security by 2050, increasing future rice demand (Khush 2005) [2] . Though Novel rice cultivars have produced higher yields over last few decades they have reached a yield threshold because of narrow genetic base becoming a major bottleneck for further yield improvement besides many biotic and abiotic stresses (Fiyaz et al., 2022) [3] . Identification of untapped potential of wild relates of crop species having high variability and their utilization in hybridization programs through selection of desirable traits that enhance yield is one of the best feasible solutions for achieving high productivity and nutritional security Ahmed et al.,1998 [4]. Existence of Genetic variability among yield attributes is mandatory during selection for the successful yield enhancement through breeding. Presence of high segregation and recombination in segregating populations can be taken as advantage for selection of superior progenies Priyanka et al., 2019 [5] . Presence of low genetic difference between Phenotypic Coefficient of Variation (PCV) and Genotypic Coefficient of Variation (GCV) indicate low genetic difference and high environmental effects large differences Tuhina-Khatun et al., 2015 [6] . More precise genetic gain under selection may be obtained from Heritability estimates along with genetic advance Johnson et al., 1955 [7] . Third-and fourth-degree statistics i.e., skewness and kurtosis in segregating generations can help in better understanding of genetics of the traits Savitha et al., 2015 [8] . Hence, the current study was conducted to assess variability, heritability, and genetic progress as a percentage of the mean in F2 segregating generations, which might be beneficial in selection and future yield enhancement.

Materials and Methods

The experiment was carried out at Indian Council of Agricultural Research-Indian Institute of Rice Research (ICAR-IIRR), Rajendranagar, Hyderabad, during kharif 2022. The experimental trial was laid out in ICAR-IIRR Rajendranagar Farm using Augmented Randomized Complete Block Design (ARCBD) consisting of 92 F2 segregating population derived from cross KJT-5-4-14 x Dokra-Dokri having high test weight. The experimental area contains a total of four blocks. Prior determining individuals in each block, two checks were initially randomized. Each block was contained 23 F2 ' S and 2 checks as reported earlier Bharath et al. 2023 [9] . Thirty days old seedlings were transplanted in the main field with a spacing of 20 x 15 cm. All cultural practices and plant protection measures were taken to ensure uniform and healthy crop stand. Eleven traits, namely, Plant Height (cm), Panicle length (PL) (cm), Total Number of Tillers per plant (TNT), No. of Productive Tillers per plant (NPT), Panicle weight (PW), No. of filled grains per panicle (NFG), No. of unfilled grains per panicle (NUFG), Total No. of grains per panicle (TGP), Spikelet fertility (SF) (%), 1000 grain weight (TGW)(gm), and Single plant yield (SPY) (gm) were recorded in every individual F2 plant.

Statistical analysis

The augmented ANOVA analysis was carried out in R studio (version 3.5.2) using augmented RCBD package developed by Aravind et al., 2019 [10] (https://aravind-j.github.io/augmented RCBD/). The genetic variability parameters, namely, Genotypic and Phenotypic Coefficient of Variation were calculated as per formula outlined by Singh and Chaudhary (1977) [11] and classified as described by Sivasubramanian and Madhava Menon (1973) [12] while estimates of Heritability was calculated using the formula given by Allard 1960 [13] and genetic advance as percentage of mean was calculated by adopting the formula given by Johnson et al., 1955 [7] .

Results and Discussion

Mean performance

The ANOVA analysis revealed that variance due to treatment (ignoring blocks) was highly significant for all the characters except total number of tillers per plant (TNT) and productive tillers (NPT) revealing that F2 segregating population under study had enough variation showing the inherent genetic differences between the individuals given in Table -1. The Plant height had a range of variance 87.12 cm to 194.63 cm, with an average of 148.83 cm which is in agreement with Gupta et al., 2023 [14]. The average panicle length in the F2 population studied was noticed to be 27.70 cm, the lowest panicle length was 21.56 cm and the highest was 31.81 cm, similar results were observed by Manojkumar et al., 2022 [15] . Total number of tillers per plant ranged from 7.12 to 16.50 with an average of 11.05 whereas the average number of productive tillers per plant was 9.85, with a range of 6.62 to 15.13. The average spikelet fertility was 73.89 per cent, with the lowest spikelet fertility value being 31.16 per cent and the greatest spikelet fertility value being 97.73 per cent. The average TGW was 26.22 gm, with the lowest and the highest of 13.93 and 39.85 g respectively. Similar variation in F2 was reported by Khandappagol et al., [16] . Single plant yield had a mean value of 27.01 g with minimum and maximum of 10.81 and 67.40 g respectively which is in agreement with the reports of Manojkumar et al., [15] .

PCV and GCV

The development of a plant characteristic is greatly influenced by genetic variability and heritability. Prior knowledge of population variability estimates and the heritable elements of a trait are helpful tools in any breeding programme. It would be more challenging to enhance a character through selection unless a significant amount of the variation is heritable. Breeding would benefit from knowledge of the character's heritability apart from its phenotypic and genotypic coefficient of variation. In order to compare the variability seen across various traits, the coefficient of variation expressed at the phenotypic and genotypic levels was used. The results of genotypic (GCV) and phenotypic (PCV) coefficients of variation are presented in Table 2 and Fig. 1 that varied from high to moderate. For all traits higher PCV value was observed compared to GCV value, indicating the effect of environment. Greater difference between PCV and GCV values was recorded in Total number of tillers (TNT) followed by number of productive tillers (NPT) indicating higher influence of environment on these traits, resulting in low heritability values. However, panicle weight, total grains per panicle, spikelet fertility and thousand grain weight recorded minimum variation between GCV and PCV values, indicating lesser influence of environment resulting in high heritability values. Similar results were reported by Vijayakumari et al. [17] for panicle weight and Gupta et al . [14] for thousand grain weight. Higher values of PCV and GCV were observed for panicle weight, number of filled grains, number of unfilled grains, total grains per panicle, and single plant yield. These results were consistent with Dileep Kumar et al., [18] ,Sravani et al., [19] for above traits; Borah et al., [20] , Manojkumar et al., [15] for filled grains and total grains per panicle; Kujur et al., [21] , Abdul Fiyaz et al., [22] for single plant yield suggesting possibility of yield improvement through selection of these traits. Moderate values of PCV and GCV were observed for plant height, number of productive tillers and TGW. Similar results were observed by Sravani et al., [19] for above three traits; vijayakumari et al., [17] for spikelet fertility; Abdul Fiyaz et al., [22] and Faysal et al., [23] for TGW suggesting greater influence of genetic factors on these traits and relatively less influence of the environment. Low values of PCV and GCV were observed for panicle length similar findings were obtained by Gnaneswari et al., [24] , Yumkhaibam et al. [25]

Heritability (h 2 ) and Genetic Advance (GA)

When heritability along with genetic advance are followed greater degree of accuracy in predicting the genetic gain under selection is possible than heritability estimates alone. However, it is not necessary that a character showing high heritability will also exhibit high genetic advance Johnson et al. [7] .

The traits plant height, panicle weight, number of filled grains, number of unfilled grains, total grains per panicle, spikelet fertility, thousand grain weight and single plant yield recorded high heritability (>60%) associated with high genetic advance as % of mean (>20) presented in Table 2 and Fig. 2,3. Similar results were obtained by Dileep Kumar et al., [18] , Sravani et al., [19] , vijayakumari et al., [17] for above traits; Manoj kumar et al., [15] , for panicle length, number of filled grains per panicle, total grains per panicle and test weight; Gupta et al., [14] for plant height, single plant yield; Abdul Fiyaz et al., [22] for total grains per panicle and test weight resulting in minimum environmental influence on the expression and selection for improvement of such characters could be worthwhile. High heritability coupled with moderate genetic advance as % of mean was observed for panicle length earlier reported by Lakshmi et al., [26] , Gupta et al., [14] , Borah et al., [20] showing greater role of non-additive gene action in their inheritance suggesting heterosis breeding for improving these traits. Moderate heritability and genetic advance as % of mean was observed for number of productive tillers per plant which is in conformity with the results of Singh et al., [27] indicating the presence of both additive and non-additive gene effects and considerable effect of the environment. Overall high GCV and PCV coupled with high heritability and high genetic advance as % of mean was recorded for panicle weight, number of filled grains, number of unfilled grains, total grains per panicle, and single plant yield. Similar findings were reported by Bharath et al., 2023 [9] , Shivani et al., [28] , Bagudam et al., [29] , Manojkumar et al., [15] for filled grains per panicle, total grains per panicle; Bhargava et al., [30] for total grains per panicle suggesting significant amount of variability with predominance of additive type of gene action. Hence, direct phenotypic selection would be effective for improvement of these traits even in early generations.

Conclusion

Overall, the study found that the F2 segregating population had enough diversity, which could be efficiently, managed using proper breeding procedures and programs to generate superior varieties. Most characteristics had high GCV, PCV, heritability, and genetic progress, showing that additive gene action predominated and that direct phenotypic selection may be done even in early generations.

Acknowledgement

This is part of the author's PhD Research work at Indian Institute of Rice Research. The author is highly thankful for the research facilities provided by the Indian Institute of Rice Research, Hyderabad and Professor Jayashankar Telangana Agricultural University.

Competing Interests

Authors have declared that no competing interests exist.

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