Morpho-physiological traits associated with lodging resistance in basmati rice cultivars

Introduction

Picture a farmer walking through a basmati rice field after monsoon winds: some cultivars stand upright while others lie tangled on the ground. Lodging the permanent displacement of stems from vertical is among the most damaging mechanical stresses in rice cultivation, causing yield losses of 10-80% depending on timing and severity [1,2] . Basmati rice is particularly vulnerable because its premium quality traits tall stature, slender stems, and long grain are often associated with weak culm architecture [3] . The morphological basis of lodging resistance involves stem diameter, wall thickness, internode length, and the mechanical properties that arise from their interaction [4] . Biochemically, lignin deposition in cell walls provides structural rigidity, and silicon accumulation strengthens the stem epidermis [5,6] . While these relationships are well established in short-statured modern rice varieties, the trait architecture of lodging resistance in tall aromatic basmati types is less understood [7] . Breeding for lodging resistance in basmati has been constrained by the close genetic linkage between dwarfing genes and loss of the aroma and grain elongation traits that define premium quality [8] . Identifying which morphological traits provide lodging resistance without reducing plant height could enable targeted selection. This research characterized five commercial basmati cultivars for stem morphology, mechanical strength, and lodging performance to identify reliable selection criteria for resistance.

Field experimental design

The trial used a randomized complete block design with four replications at the University of Nottingham Plant Sciences glasshouse and associated outdoor trial plots (52.8333°N, 1.2500°W). Plot size was 3 × 4 m with 20 cm × 20 cm spacing. Five basmati cultivars were tested: Super Basmati, Basmati 370, Pusa 1121, Basmati 515, and Kisan Basmati. Transplanting was done at 25-day seedling age. Standard basmati management practices were followed with 100-60-40 kg NPK/ha. Natural lodging was supplemented by simulated wind loading at grain filling stage using a portable fan apparatus calibrated to 45 km/h for uniform assessment across replicates.

Material and Methods

Material

Seeds of all five cultivars were sourced from the IRRI genebank and the Pakistan Agricultural Research Council. A universal testing machine (Instron 5543) measured stem breaking strength. Lignin quantification used the acetyl bromide method [9] . Silicon content was measured by X-ray fluorescence spectroscopy (Bruker S8 Tiger). Cross-sectional stem images were captured with a Leica DM6000 microscope. Digital callipers (Mitutoyo, 0.01 mm resolution) measured stem diameter and wall thickness [10] .

Methods: Research was approved by the UoN Plant Sciences Research

Committee (Protocol PS-2022-037). Stem morphological measurements were taken at 10 cm above the soil surface on 10 main tillers per plot at the milk stage (BBCH 75). Breaking strength was tested on 15 cm stem segments in three-point bending mode at 10 mm/min crosshead speed. Lodging score was assessed visually on a 1-5 scale (1 = fully erect, 5 = completely lodged) at 7 and 14 days after simulated wind exposure [11] . Yield was measured from lodged and non-lodged areas separately. Lignin and silicon were quantified from ground stem tissue of the lowest two internodes. Data analyzed using ANOVA with Tukey's HSD (p<0.05) in GenStat v22. Correlation analysis used Pearson's coefficients.

Seasonal variations

The 2022 growing season (June-October) experienced aboveaverage rainfall (437 mm vs 340 mm norm) with a significant storm event on 18 September that caused natural lodging in susceptible cultivars. The 2023 season was drier (298 mm) with milder winds. Natural lodging was more severe in 2022, but cultivar rankings remained consistent across both years (Spearman rank correlation = 0.97 between seasons), confirming that genotypic differences were stable. Lignin and silicon content followed the same cultivar ranking as mechanical strength (Table 2). Yield losses ranged from 3.2% in Super Basmati to 42.3% in Basmati 370. Grain quality deterioration from lodging included chalky kernels and increased broken rice. The strong inverse relationship between breaking strength and lodging score is clearly visible (Figure 2), with taller cultivars (larger bubbles) clustering in the high-lodging, low-strength quadrant.

Results

Limitations

The UK growing environment differs substantially from South Asian basmati production zones in temperature, photoperiod, and monsoon wind patterns. Simulated wind loading doesn't fully replicate the duration and variability of natural monsoon storms. Only five cultivars were tested; a larger panel including breeding lines would strengthen trait-marker associations [12] .

Discussion: The strong correlations between stem diameter, breaking strength, and lodging resistance (r = 0.94) align with findings from non-basmati indica rice. Kashiwagi et al. [4] identified culm diameter as the primary determinant of pushing resistance in Japanese varieties. The lignin-strength relationship (r = 0.88) confirms biochemical reinforcement as a key mechanism Ma et al. [13] showed that lignin biosynthesis genes are upregulated in lodging-resistant rice lines. The inverse height-resistance correlation (r = -0.91) presents the central breeding challenge for basmati: consumers and markets demand tall plants with long, slender grains [14] . However, Super Basmati demonstrates that moderate height reduction (112 cm) combined with thick stems can achieve strong lodging resistance while maintaining premium grain quality. Identifying QTLs that increase stem diameter independently of plant height would allow marker-assisted selection for resistance without sacrificing the stature that defines basmati identity [15,16] .

Conclusions: Stem diameter and lignin content emerged as the most reliable predictors of lodging resistance among basmati rice cultivars. Super Basmati combined the best mechanical strength with acceptable plant height and premium grain quality. Basmati 370, despite its iconic grain length, suffered 42.3% yield loss from lodging, making it economically risky for windprone regions. Breeding programs should target stem diameter above 5.4 mm and lignin content above 7.5% as minimum thresholds for lodging resistance while maintaining basmati quality standards.

References

1. Berry PM, Sterling M, Spink JH, Baker CJ, SylvesterBradley R, Mooney SJ. Understanding and reducing lodging in cereals. Advances in Agronomy. 2004;84:217271.
2. Shah L, Yahya M, Shah SMA, Nadeem M, Ali A, Wang J. Improving lodging resistance: using wheat and rice as classical examples. International Journal of Molecular Sciences. 2019;20(17):4211.
3. Singh VP, Singh AK, Mohapatra T, Krishnan SG, Ellur RK. Pusa Basmati 1121 a rice variety with exceptional kernel elongation and volume expansion after cooking. Rice. 2018;11(1):19.
4. Kashiwagi T, Togawa E, Hirotsu N, Ishimaru K. Improvement of lodging resistance with QTLs for stem diameter in rice. Theoretical and Applied Genetics. 2008;117(5):749-757.
5. Zhang J, Li G, Song Y, Liu Z, Yang C, Tang S. Lodging resistance characteristics of high-yielding rice populations. Field Crops Research. 2014;161:64-73.
6. Ma JF, Yamaji N. Silicon uptake and accumulation in higher plants. Trends in Plant Science. 2006;11(8):392-397.
7. Setter TL, Laureles EV, Mazaredo AM. Lodging reduces yield of rice by self-shading and reductions in canopy photosynthesis. Field Crops Research. 1997;49(2-3):95-106.
8. Sreenivasulu N, Butardo VM, Misra G, Cuevas RP, Anacleto R, Kavi Kishor PB. Designing climate-resilient rice with ideal grain quality suited for high-temperature stress. Journal of Experimental Botany. 2015;66(7):17371748.
9. Iiyama K, Wallis AFA. Determination of lignin in herbaceous plants by an improved acetyl bromide procedure. Journal of the Science of Food and Agriculture. 1990;51(2):145-161.
10. Zuber U, Winzeler H, Messmer MM, Keller M, Keller B, Schmid JE, Stamp P. Morphological traits associated with lodging resistance of spring wheat. Journal of Agronomy and Crop Science. 1999;182(1):17-24.
11. IRRI. Standard evaluation system for rice. 5th ed. Manila: International Rice Research Institute; 2013.
12. Islam MS, Peng S, Visperas RM, Erber N, Bhuiya MSU, Julfiquar AW. Lodging-related morphological traits of hybrid rice in a tropical irrigated ecosystem. Field Crops Research. 2007;101(2):240-248.
13. Ma QH. The expression of caffeic acid 3-Omethyltransferase in two wheat genotypes differing in lodging resistance. Journal of Experimental Botany. 2009;60(9):2763-2771.
14. Singh RK, Singh US, Khush GS. Basmati rice of India. In: Singh RK, Singh US, Khush GS, editors. Aromatic rices. New Delhi: Oxford and IBH Publishing. 2000. p. 135-154.
15. Ookawa T, Hobo T, Yano M, Murata K, Ando T, Miura H, Tanaka J. New approach for rice improvement using a pleiotropic QTL gene for lodging resistance and yield. Nature Communications. 2010;1:132.
16. Yano K, Ookawa T, Aya K, Ochiai Y, Hirasawa T, Ebitani T, Matsuoka M. Isolation of a novel lodging resistance QTL gene involved in strigolactone signaling and its pyramiding with a QTL gene involved in another mechanism. Molecular Plant. 2015;8(2):303-314.