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Department of Genetics and Plant Breeding, S.V. Agricultural College, ANGRAU, Tirupati-517 502.
The field experiment was conducted during the Rabi 2024–2025 season at the Agricultural Research Station, Nellore, India to study the genetic variability, heritability, and genetic advance for lodging resistance and yield-related traits in a panel of 100 rice genotypes. Eleven key traits were evaluated viz., plant height, number of tillers per plant, culm thickness, culm diameter, panicle length, panicle weight, number of grains per panicle, grain yield per plant, section modulus, bending stress, and bending moment. Statistical analysis revealed significant genetic variation among the genotypes for all the studied traits. Traits such as panicle weight, number of grains per panicle, grain yield, section modulus, bending stress, and bending moment exhibited high genotypic and phenotypic coefficients of variation, indicating a broad range of variability. High heritability coupled with high genetic advance were observed for all the traits under study, suggesting the predominance of additive gene effects and the potential for effective improvement through pedigree method. These results highlight the importance of prioritizing high-heritability traits to accelerate genetic gains in breeding programs focused on enhancing lodging resistance and yield performance in rice.
KEYWORDS: Lodging resistance, variability, genetic advance, Rice, Bending moment.
Rice (Oryza sativa L.) is the second most significant staple grain crop in the world after wheat. Rice serves as a primary source of calories for nearly half of the global population and holds a dominant position in terms of cultivation area and production, particularly in South and South-East Asian regions. However, yield losses due to various stresses, shrinking arable land, and rising population pose serious challenges. Climate change, with unseasonal rains and strong winds, further aggravates the problem by causing lodging, affecting both yield and quality. Proactive measures are needed to address these climate-induced stresses. Lodging is not only influenced by natural environmental factors but also by agronomic practices viz., Excessive nitrogen application, inappropriate sowing dates and plant density, as well as factors like soil compaction and diseases such as sheath rot, significantly contribute to the risk of lodging (Zhang et al. 2014, 2016; Pan et al. 2019). Lodging can be categorized into three major types i.e., root lodging, bending type lodging, and breaking type lodging (Grafius and Brown 1954; Hirano et al. 2017). Upland-cultivated rice develops a weak root system leading to root lodging (Laosut m strength and for further improvement, knowledge of the genetic control of mechanisms that regulate culm strength is a prerequisite” (Badri et al. 2024).
The presence of adequate genetic variability is the fundamental pre-requisite to conduct any crop improvement programme. Therefore, it is essential to analyze the extent of variability within the species, understand the relationships among traits, and determine the contribution of each trait to enhancing rice productivity through breeding efforts (Khan et al. 2020). The genotypic coefficient of variation (GCV) indicates the extent of genetic variability and represents the inheritable component of trait variation. Genetic variability along with heritability estimates would provide the amount of genetic gain expected out of selection”. Therefore, assessing variability is vital for establishing effective selection criteria aimed at enhancing culm strength and improving yield potential.
A set of 100 rice genotypes were evaluated during 2024-25 rabi season at Agricultural Research Station (ARS), ANGRAU, Nellore, Andhra Pradesh, India. The genotypes were sown in the raised bed and transplanted into the main field 27 days after sowing with the spacing of 20 x 15 cm in Aplha Lattice Design. All the package of practices were followed for the good establishment of the crop. The genotypes were evaluated and observations were recorded on five randomly selected plants in each replication for morphological traits viz., plant height (PH) (cm), tiller number (TN), culm thickness (CT) (mm), culm diameter (CD) (mm), section modulus (mm3), bending stress (BS) (Kg mm-2), bending moment (BM) (g stem-1), panicle length (PL) (cm), panicle weight (PW), number of grains per panicle (NGP), grain yield (GY). The genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) were computed following the procedure outlined by Burton et al. 1952. The magnitude of variability was classified based on the criteria suggested by Sivasubramanian and Madhavamenon (1973). Broad-sense heritability (h²) and genetic advance as a percentage of the mean (GAM) were estimated using the methods described by Lush 1940 and Johnson et al. 1955 respectively.
The following traits were determined as per Ookawa et al. 2010 and Badri et al. 2024
Culm diameter (CD) = (a1+b1)/2
Culm thickness (CT) = [(a1+b1)/2] – [(a2+b2)/2]
Section modulus (SM) = π/32 × (a1 3b1-a2 3b2)/a1
Where, a1is the outer diameter of the minor axis in an oval cross-section,
b1is the outer diameter of the major axis in an oval cross-section.
a2 is the inner diameter of the minor axis in an oval cross-section,
b2 is the inner diameter of the major axis in an oval cross-section.
Bending stress (BS) = (TR÷40) × (1000÷TN)
Bending moment at breaking (M) = Section modulus
(SM) × Bending stress (BS)
Where; TR is the prostrate tester reading value (measure of pushing resistance) and TN is the tiller number. The prostrate tester (DIK-7400, Daiki Rika Kogyo Co. Ltd., Tokyo, Japan) was used to measure
the pushing resistance of the culm.
The identification of the key traits that can be used in crop improvement through various breeding techniques is extremely important. The observed variability, heritability estimates, and the strength and direction of trait associations, provide a clear understanding of the underlying genetic architecture. These findings form a robust basis for selecting desirable traits to enhance culm strength in rice breeding programs.
Analysis of variance for 11 lodging resistance and yield related traits revealed significant differences among the genotypes for all the traits under study, indicating the existence of greater variability among the genotypes. Such variability forms the foundation for effective selection in breeding programs.
The variability analysis indicated that PCV was consistently higher than GCV for all traits (Table 1), suggesting that phenotypic variation was influenced by both genetic and environmental factors. Plant height exhibited moderate variability (GCV: 19.37%, PCV: 19.52%), with very high heritability (98.50%) and high genetic advance as percent of mean (GAM: 39.61%), implying strong additive gene action and effective selection potential, in agreement with Srilakshmi et al. (2018), and Sahu et al. (2024). Similarly, number of tillers per plant showed moderate GCV (17.92%) and PCV (18.57%), high heritability (93.13%), and GAM (35.63%), supporting its improvement through selection, as observed by Akshay et al. (2022) and Arun et al. (2023). Culm thickness and culm diameter both recorded high genetic variability (GCV: 16.98% and 17.35%) and heritability (92.79% and 98.61%), with GAM values of 33.68% and 35.49%, respectively suggesting reasonable scope for improvement, as supported by Nomura et al. (2021), Silva et al. (2022) and Arun et al. (2023). The section modulus also showed high GCV (30.57%), heritability (99.16%), and GAM (62.70%), indicating the effectiveness of selection, which is in line with the observations of Akshay et al. (2024). Bending stress and bending moment exhibited high variability and heritability (95.34% and 98.14%), with respective GAM values of 51.23% and 104.16%, indicating potential for significant genetic gains, as reported by Akshay et al. (2024). Panicle length showed moderate GCV (12.59%),
high heritability (90.84%), and GAM (24.71%), while Panicle weight and number of grains per panicle displayed high variability, with heritability estimates of 98.01% and 98.54%, and genetic advance as percent of mean values of 76.81% and 78.07%, respectively, suggesting considerable potential for selection gains. These results corroborate the findings of Hasan et al. (2022), Arun et al. (2023), and Harsharaj et al. (2024)Notably, grain yield per plant had the highest GCV (40.06%), PCV (40.54%), heritability (97.64%), and GAM (81.55%), indicating that it is largely controlled by additive gene action and can be improved efficiently through direct selection, accordance with Demeke et al. (2023) and Harsharaj et al. (2024). Overall, the combination of high heritability and high genetic advance observed for all the studied traits, indicates predominance of additive gene action, suggesting that direct selection would be highly effective in achieving genetic improvement, enhance genetic gain and accelerate progress in rice breeding programs.
The present study revealed substantial genetic variability, along with high heritability and notable genetic advance for several important lodging resistance and yield-related traits in rice. Traits such as culm thickness, culm diameter, section modulus, bending stress, bending moment, panicle weight, number of grains per panicle, and grain yield per plant were found to be under strong genetic control, indicating the effectiveness of direct selection for these traits in breeding programs. These findings offer valuable guidance for rice breeders in developing lodging-resistant and high-yielding varieties, thereby supporting sustainable rice cultivation and addressing the growing challenges of global food demand and resource limitations.
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