Unveiling the Science of Lodging in Rice (Oryza sativa L.)

Author: Kalaichelvi K. and Murali Sankar P.

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Abstract

Lodging, the irreversible displacement of the rice plant from its upright position, results in significant economic losses by drastically reducing both yield quality and quantity. This phenomenon is categorized into three types based on the point of failure: bending lodging, breaking lodging (culm failure), and root lodging (anchorage failure). Traditional varieties, which are characteristically taller, are highly susceptible to lodging. Genetic approaches primarily target reducing plant height through dwarfism genes, although only the Sd1 gene is widely integrated into breeding programs, as alternatives like RGA1 and OSH15 often carry a yield penalty. Beyond height, culm strength is the key determinant of resistance. This strength is conferred by anatomical traits, including greater culm diameter (governed by loci like one found on chromosome 1), thicker culm walls, and increased density of both sclerenchyma cells and vascular bundles. Biochemically, the cell wall is critical. While lignin is a key strengthening polymer, its content is complexly regulated; for instance, excessive nitrogen application reduces the expression of lignin synthesis genes (e.g., OSCAD2, OSCAD7, and OSCAD20), increasing susceptibility. However, studies on DEP1 mutants suggest that mechanical integrity can be maintained despite reduced lignin through the compensatory upregulation of cellulose and hemicellulose synthesis genes. This structural balance is further enhanced by physiological factors: high levels of Non-Structural Carbohydrates (NSC) in the culm during senescence (linked to the Pr15 locus) and the crucial contribution of Silicon to cell wall rigidity.

Keywords

Cellulose, Dwarfing genes, Lodging, Oryza sativa (L.), Silicon, Rice

Conclusion

Dwarfism genes are RGA1 (Fujisawa et al., 2022), OSH15 (Niu et al., 2022), and Sd1 (Monna et al., 2002; Sasaki et al., 2002). Since the genes RGA1 and OSH15 are detrimental to yield (Yang et al., 2024), the gene Sd1 alone has been integrated into breeding programs. Culm diameter, which is located in chromosome 1, highlights a crucial role in lodging resistance. Mechanical strength was increased by schelerenchyma cells. A thicker culm has proved to increase the rice yields (Hirose et al., 2006). Additionally, a QTL on chromosome 6 between the marker interval (RM20547–RM20557) with an R2 value of 10.39 is linked to increased culm diameter, with candidate genes identified as microtubule-related genes involved in cell expansion (LOC_0s0645900) and potassium transport (LOC_0s06g45940) (Merugumala et al., 2019). Increasing vascular bundles increases the culm diameter and wall thickness, leading to lodging resistance. Lower lignin may induce lodging. Increased nitrogen application reduces the expression of more genes involved in lignin synthesis, leading to lodging susceptibility. OSCAD 2, OSCAD 7, and OSCAD 20 show higher expression in lodging-resistant varieties compared with their susceptibility counterparts (Liu et al., 2018). DEP mutants indicate DEP 1 plays a major role in cell wall biosynthesis; they showed less lignin but were found to be resistant due to upgradation of genes involved in cellulose and hemicellulose synthesis (Wang et al., 2024). SuS3 sucrose synthase gene with transgenic plant Atcesa8 exhibits lodging resistance in rice. Reduced lignin resulted in improvement in cellulose biosynthesis, indicating a potential efficiency for improving lodging resistance in rice (Fan et al., 2017). The higher the NSCs during senescence higher the lodging resistance noted in the Pr15 locus. Silicon contributes to the mechanical strength and rigidity of the cell wall, helpful in lodging resistance (Duan et al., 2004).

References

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How to cite this article

Kalaichelvi K. and Murali Sankar P. (2025). Unveiling the Science of Lodging in Rice (Oryza sativa L.). Biological Forum, 17(11): 11-16.