Enriching Iodine and Regulating Grain Aroma, Appearance Quality, and Yield in Aromatic Rice by Foliar Application of Sodium Iodide

doi:10.1016/j.rsci.2024.02.005

Abstract

Abstract:

Applying iodine fertilizers to cultivate iodine-rich crops for daily intake is an effective approach for iodine supplementation, especially for aromatic rice. Field experiments were conducted during the early growing seasons of 2021 and 2022 to evaluate the impacts of foliar application of iodine fertilizer on aromatic rice and to explore the optimal iodine fertilizer concentration. At the full heading stage, six different concentrations of sodium iodide solutions of 0% (CK), 0.010% (T1), 0.025% (T2), 0.050% (T3), 0.075% (T4), and 0.100% (T5) were applied to indica aromatic rice cultivars Meixiangzhan 2 and Xiangyaxiangzhan. The results showed that sodium iodide treatments significantly increased the iodine and sodium contents in both leaves and grains. Compared with the CK, the T1 and T2 treatments increased the 2-acetyl-1-pyrroline (2-AP) content in mature grains by 8.41%‒101.66% and 13.58%‒ 74.60%, respectively. Improvements in the contents of 1-pyrroline-5-carboxylic acid, proline, 1-pyrroline, and methylglyoxal, as well as the activity of proline dehydrogenase were also detected. Additionally, sodium iodide treatments remarkably decreased the chalky grain rate, chalkiness area, and chalkiness degree of aromatic rice, with the T2 treatment exhibiting a 17.79%‒47.42% decrease in chalkiness degree compared with the CK. Meanwhile, T1 and T2 treatments showed beneficial impacts on chlorophyll content, photosynthetic characteristics, and yield components, while T3, T4, and T5 treatments exhibited adverse effects on leaf and grain yields. The linear discriminant analysis revealed significant differences between treatments. The correlation analysis and piecewise structural equation modeling showed that the iodine and sodium influenced the photosynthetic characteristics and chlorophyll content of the leaves, thereby regulating the 2-AP biosynthesis and yield components, ultimately affecting the 2-AP content and yield. Overall, this study suggests that foliar application of 0.025% sodium iodide is an effective method to enrich the iodine content in rice grains, improve the grain aroma and appearance quality of aromatic rice, without detrimental effects on grain yield.

Key words: 2-acetyl-1-pyrroline, appearance quality, aromatic rice, foliar application, grain yield, iodine

Hong Weiyuan, Duan Meiyang, Wang Yifei, Chen Yongjian, Mo Zhaowen, Qi Jianying, Pan Shenggang, Tang Xiangru. Enriching Iodine and Regulating Grain Aroma, Appearance Quality, and Yield in Aromatic Rice by Foliar Application of Sodium Iodide[J]. Rice Science, 2024, 31(3): 328-342.

Figures/Tables 8

Fig. 1. Effects of foliar application of sodium iodide on iodine and sodium contents in leaves (A, B, E and F) and grains (C, D, G and H) of aromatic rice at different stages in 2021 and 2022. CK, Foliar spray with distilled water; T1‒T5, Foliar spray with 0.010%, 0.025%, 0.050%, 0.075%, and 0.100% sodium iodide, respectively; 7 DAS, 7 d after spraying; 14 DAS, 14 d after spraying; 21 DAS, 21 d after spraying. Bars that share the same lowercase letters for a given parameter do not differ significantly at P < 0.05 based on the least significant difference test. Error bars represent standard errors of means.

Fig. 2. Effects of foliar application of sodium iodide on 2-AP content in leaves (A and B) and grains (C and D) of aromatic rice at different stages in 2021 and 2022. 2-AP, 2-Acetyl-1-pyrroline; CK, Foliar spray with distilled water; T1‒T5, Foliar spray with 0.010%, 0.025%, 0.050%, 0.075%, and 0.100% sodium iodide, respectively; 7 DAS, 7 d after spraying; 14 DAS, 14 d after spraying; 21 DAS, 21 d after spraying. Bars that share the same lowercase letters for a given parameter do not differ significantly at P < 0.05 based on the least significant difference test. Error bars represent standard errors of means.

Fig. 3. Effects of foliar application of sodium iodide on chalky grain rate (A and B), chalkiness area (C and D), and chalkiness degree (E and F) of aromatic rice in 2021 and 2022. CK, Foliar spray with distilled water; T1‒T5, Foliar spray with 0.010%, 0.025%, 0.050%, 0.075%, and 0.100% sodium iodide, respectively. Bars that share the same lowercase letters for a given parameter do not differ significantly at P < 0.05 based on the least significant difference test. Error bars represent standard errors of means.

Table 1. Effects of foliar application of sodium iodide on grain yield and yield components of aromatic rice in 2021 and 2022.

Year	Cultivar	Treatment	Panicle number per m²	Grain number per panicle	Filled-grain rate (%)	1000-grain weight (g)	Grain yield (g/m²)
2021	Meixiangzhan 2	CK	348.80 ± 18.98 a	102.00 ± 0.47 ab	57.51 ± 0.47 b	19.94 ± 0.04 c	886.67 ± 10.89 a
		T1	353.60 ± 11.16 a	97.33 ± 1.19 bc	60.02 ± 1.03 ab	20.60 ± 0.06 b	850.00 ± 23.57 a
		T2	334.40 ± 7.95 a	103.33 ± 1.19 a	68.70 ± 4.54 a	21.13 ± 0.10 a	933.33 ± 59.32 a
		T3	361.60 ± 5.69 a	101.00 ± 1.41 abc	57.35 ± 1.92 b	19.69 ± 0.10 cd	883.33 ± 13.61 a
		T4	366.40 ± 25.43 a	101.00 ± 1.70 abc	55.77 ± 3.78 b	19.51 ± 0.10 de	733.33 ± 13.61 b
		T5	339.20 ± 3.46 a	95.33 ± 2.13 c	64.39 ± 0.77 ab	19.27 ± 0.08 e	850.00 ± 4.71 a
	Xiangyaxiangzhan	CK	348.80 ± 3.46 a	108.00 ± 0.47 a	62.93 ± 1.51 a	19.54 ± 0.12 b	926.67 ± 30.31 bc
		T1	355.20 ± 15.84 a	101.67 ± 4.28 abc	68.94 ± 1.41 a	19.78 ± 0.05 b	1066.67 ± 36.00 a
		T2	339.20 ± 10.20 a	100.00 ± 4.50 abc	63.78 ± 2.55 a	20.31 ± 0.16 a	1016.67 ± 36.00 ab
		T3	355.20 ± 11.31 a	104.67 ± 1.52 ab	64.00 ± 2.90 a	19.31 ± 0.08 bc	916.67 ± 36.00 bc
		T4	331.20 ± 2.26 a	95.00 ± 0.47 bc	62.26 ± 2.35 a	19.26 ± 0.16 bc	833.33 ± 36.00 c
		T5	358.40 ± 6.91 a	92.00 ± 0.47 c	69.99 ±1.30 a	18.93 ± 0.17 c	950.00 ± 20.55 b
2022	Meixiangzhan 2	CK	305.60 ± 13.83 a	115.04 ± 7.86 ab	60.98 ± 1.30 bc	19.58 ± 0.18 bc	563.33 ± 27.32 a
		T1	310.40 ± 3.46 a	120.50 ± 5.27 ab	65.66 ± 0.55 a	19.92 ± 0.27 ab	555.00 ± 10.80 a
		T2	299.20 ± 8.57 a	113.53 ± 3.34 ab	64.07 ± 0.34 ab	20.33 ± 0.13 a	578.33 ± 15.69 a
		T3	307.20 ± 18.52 a	142.92 ± 5.47 a	65.09 ± 1.05 a	19.60 ± 0.17 bc	440.00 ± 15.46 b
		T4	286.40 ± 7.95 a	100.27 ± 16.64 b	66.97 ± 1.11 a	19.20 ± 0.02 c	443.33 ± 24.19 b
		T5	294.40 ± 13.83 a	102.93 ± 11.84 b	59.02 ± 1.21 c	19.04 ± 0.06 c	390.00 ± 18.41 b
	Xiangyaxiangzhan	CK	297.60 ± 13.76 a	100.34 ± 0.67 a	61.81 ± 0.85 ab	19.78 ± 0.05 c	588.33 ± 11.14 ab
		T1	307.20 ± 11.76 a	108.30 ± 1.96 a	64.65 ± 1.12 a	20.95 ± 0.16 b	636.67 ± 24.19 a
		T2	321.60 ± 27.15 a	103.27 ± 0.87 a	65.26 ± 1.23 a	21.74 ± 0.07 a	644.33 ± 23.51 a
		T3	315.20 ± 21.74 a	106.09 ± 0.72 a	63.66 ± 1.29 ab	19.60 ± 0.11 c	550.00 ± 20.55 b
		T4	280.00 ± 6.91 a	105.37 ± 13.91 a	63.39 ± 0.88 ab	19.80 ± 0.20 c	546.67 ± 10.89 b
		T5	289.60 ± 3.46 a	106.51 ± 0.85 a	59.12 ± 1.25 b	20.53 ± 0.16 b	556.67 ± 11.86 b

Table 1. Effects of foliar application of sodium iodide on grain yield and yield components of aromatic rice in 2021 and 2022.

Year	Cultivar	Treatment	Panicle number per m²	Grain number per panicle	Filled-grain rate (%)	1000-grain weight (g)	Grain yield (g/m²)
2021	Meixiangzhan 2	CK	348.80 ± 18.98 a	102.00 ± 0.47 ab	57.51 ± 0.47 b	19.94 ± 0.04 c	886.67 ± 10.89 a
		T1	353.60 ± 11.16 a	97.33 ± 1.19 bc	60.02 ± 1.03 ab	20.60 ± 0.06 b	850.00 ± 23.57 a
		T2	334.40 ± 7.95 a	103.33 ± 1.19 a	68.70 ± 4.54 a	21.13 ± 0.10 a	933.33 ± 59.32 a
		T3	361.60 ± 5.69 a	101.00 ± 1.41 abc	57.35 ± 1.92 b	19.69 ± 0.10 cd	883.33 ± 13.61 a
		T4	366.40 ± 25.43 a	101.00 ± 1.70 abc	55.77 ± 3.78 b	19.51 ± 0.10 de	733.33 ± 13.61 b
		T5	339.20 ± 3.46 a	95.33 ± 2.13 c	64.39 ± 0.77 ab	19.27 ± 0.08 e	850.00 ± 4.71 a
	Xiangyaxiangzhan	CK	348.80 ± 3.46 a	108.00 ± 0.47 a	62.93 ± 1.51 a	19.54 ± 0.12 b	926.67 ± 30.31 bc
		T1	355.20 ± 15.84 a	101.67 ± 4.28 abc	68.94 ± 1.41 a	19.78 ± 0.05 b	1066.67 ± 36.00 a
		T2	339.20 ± 10.20 a	100.00 ± 4.50 abc	63.78 ± 2.55 a	20.31 ± 0.16 a	1016.67 ± 36.00 ab
		T3	355.20 ± 11.31 a	104.67 ± 1.52 ab	64.00 ± 2.90 a	19.31 ± 0.08 bc	916.67 ± 36.00 bc
		T4	331.20 ± 2.26 a	95.00 ± 0.47 bc	62.26 ± 2.35 a	19.26 ± 0.16 bc	833.33 ± 36.00 c
		T5	358.40 ± 6.91 a	92.00 ± 0.47 c	69.99 ±1.30 a	18.93 ± 0.17 c	950.00 ± 20.55 b
2022	Meixiangzhan 2	CK	305.60 ± 13.83 a	115.04 ± 7.86 ab	60.98 ± 1.30 bc	19.58 ± 0.18 bc	563.33 ± 27.32 a
		T1	310.40 ± 3.46 a	120.50 ± 5.27 ab	65.66 ± 0.55 a	19.92 ± 0.27 ab	555.00 ± 10.80 a
		T2	299.20 ± 8.57 a	113.53 ± 3.34 ab	64.07 ± 0.34 ab	20.33 ± 0.13 a	578.33 ± 15.69 a
		T3	307.20 ± 18.52 a	142.92 ± 5.47 a	65.09 ± 1.05 a	19.60 ± 0.17 bc	440.00 ± 15.46 b
		T4	286.40 ± 7.95 a	100.27 ± 16.64 b	66.97 ± 1.11 a	19.20 ± 0.02 c	443.33 ± 24.19 b
		T5	294.40 ± 13.83 a	102.93 ± 11.84 b	59.02 ± 1.21 c	19.04 ± 0.06 c	390.00 ± 18.41 b
	Xiangyaxiangzhan	CK	297.60 ± 13.76 a	100.34 ± 0.67 a	61.81 ± 0.85 ab	19.78 ± 0.05 c	588.33 ± 11.14 ab
		T1	307.20 ± 11.76 a	108.30 ± 1.96 a	64.65 ± 1.12 a	20.95 ± 0.16 b	636.67 ± 24.19 a
		T2	321.60 ± 27.15 a	103.27 ± 0.87 a	65.26 ± 1.23 a	21.74 ± 0.07 a	644.33 ± 23.51 a
		T3	315.20 ± 21.74 a	106.09 ± 0.72 a	63.66 ± 1.29 ab	19.60 ± 0.11 c	550.00 ± 20.55 b
		T4	280.00 ± 6.91 a	105.37 ± 13.91 a	63.39 ± 0.88 ab	19.80 ± 0.20 c	546.67 ± 10.89 b
		T5	289.60 ± 3.46 a	106.51 ± 0.85 a	59.12 ± 1.25 b	20.53 ± 0.16 b	556.67 ± 11.86 b

Fig. 4. Effects of foliar application of sodium iodide on aromatic rice leaves in 2021 and 2022. CK, Foliar spray with distilled water; T1‒T5, Foliar spray with 0.010%, 0.025%, 0.050%, 0.075%, and 0.100% sodium iodide, respectively.

Fig. 5. Correlation analysis (A) and linear discriminant analysis (LDA) of investigated parameters in 2021 (B) and 2022 (C). I, Iodine; Na, Sodium; 2-AP, 2-Acetyl- 1-pyrroline; P5C, 1-Pyrroline-5- carboxylic acid; Pro, Proline; Pyr, 1-Pyrroline; MT, Methylglyoxal; ProDH, Proline dehydrogenase; CRR, Chalky grain rate; CA, Chalkiness area; CD, Chalkiness degree; GY, Grain yield; PN, Panicle number per m2; GN, Grain number per panicle; FGP, Filled-grain rate; GW, 1000- grain weight; NPR, Net photosynthetic rate; TR, Transpiration rate; ICO2, Intercellular CO2 concentration; SC, Stomatal conductance; Chl, Chlorophyll content; Caro, Carotenoid content; Tchl, Total chlorophyll content; 7d, 7 d after spraying; 14d, 14 d after spraying; 21d, 21 d after spraying; L, Leaves; G, Grains. The presence of color indicates a significant level of correlation (P < 0.05).

Fig. 6. Pathways of related parameters impacting 2-acetyl-1-pyrroline (2-AP) content and grain yield.

Fig. 7. Mechanism of foliar application of sodium iodide (NaI) affecting grain iodine, aroma, appearance quality, and yield. CK, Foliar spray with distilled water; T1‒T5, Foliar spray with 0.010%, 0.025%, 0.050%, 0.075%, and 0.100% odium iodide, respectively; 2-AP, 2-Acetyl-1-pyrroline; MX, Meixiangzhan 2; XY, Xiangyaxiangzhan.

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