Iron Toxicity Tolerance of Rice Genotypes in Relation to Growth, Yield and Physiochemical Characters

doi:10.1016/j.rsci.2023.02.002

Abstract

Abstract:

Iron (Fe) toxicity, generated from excess reduced ferrous Fe (Fe²⁺) ion formation within the soil under submerged condition, is a potent environmental stress that limits lowland rice production. Total 11 diverse Thai rice genotypes, including a recognized tolerant genotype Azucena and a susceptible genotype IR64, were evaluated against 5 Fe²⁺ levels [0 (control), 150, 300, 600 and 900 mg/L] to screen the tested genotypes for their Fe-toxicity tolerance and to classify them as a sensitive/tolerant category. The evaluation was conducted by a germination study, followed by a polyhouse study on growth, yield and physiochemical performances. Results showed significant variations in Fe²⁺-tolerance across genotypes. Increasing Fe²⁺ level beyond 300 mg/L was detrimental for germination and growth of all the tested genotypes, although germination responses were negatively affected at Fe²⁺ ≥ 300 mg/L. Physiochemical responses in the form of leaf greenness, net photosynthetic rate, membrane stability index and Fe contents in leaf and root were the most representative of Fe²⁺-toxicity-mediated impairments on overall growth and yield. Difference in physiochemical responses was effectively correlated with the contrasting ability of the genotypes on lowering excess Fe²⁺ in tissues. Analysis of average tolerance and stress tolerance index unveiled that the genotypes RD85 and RD31 were the closest to the tolerant check Azucena and the sensitive check IR64, respectively. The unweighted pair group method with arithmetic means clustering revealed three major clusters, with cluster II (four genotypes) being Fe²⁺ tolerant and cluster I (four genotypes) being Fe²⁺ sensitive. Principal component (PC) analysis and genotype by trait-biplot analysis showed that the first two components explained 90.5% of the total variation, with PC1 accounting for 56.6% and PC2 for 33.9% of the total variation. The identified tolerant rice genotypes show potentials for cultivation in Fe²⁺-toxic lowlands for increased productivity. The findings contribute to the present understanding on Fe²⁺-toxicity response and provide a basis for future genotype selection or rice crop improvement programs against Fe²⁺-toxicity.

Key words: iron toxicity, Oryza sativa L., submerged soil, principal component analysis, stress tolerance index

Sheikh Faruk Ahmed, Hayat Ullah, May Zun Aung, Rujira Tisarum, Suriyan Cha-Um, Avishek Datta. Iron Toxicity Tolerance of Rice Genotypes in Relation to Growth, Yield and Physiochemical Characters[J]. Rice Science, 2023, 30(4): 321-334.

Figures/Tables 6

References 62

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Factor	Final germination (%)	Germination energy (%)	Mean germination time (d)	Germination rate index (seed/d)	Root length (cm)	Shoot length (cm)	Seedling vigor index
Genotype (G)
RD31	82.1 ± 1.4 f	64.8 ± 1.4 f	4.8 ± 0.03 a	55.0 ± 1.0 g	2.5 ± 0.1 b	5.3 ± 0.2 d	679.1 ± 23.9 ef
RD41	83.9 ± 1.4 ef	72.2 ± 1.7 de	4.8 ± 0.02 b	58.4 ± 1.0 ef	1.9 ± 0.1 de	5.5 ± 0.1 cd	644.8 ± 20.7 f
RD57	85.4 ± 1.4 de	71.7 ± 1.4 de	4.6 ± 0.03 ef	61.7 ± 1.1 d	2.7 ± 0.2 ab	5.6 ± 0.2 bc	733.0 ± 17.1 cd
RD71	85.4 ± 1.5 de	67.4 ± 1.2 f	4.8 ± 0.03 bc	57.5 ± 1.1 f	2.0 ± 0.1 cd	4.9 ± 0.1 e	603.3 ± 18.1 g
RD77	86.9 ± 1.3 cd	74.1 ± 1.3 cd	4.7 ± 0.01 de	61.3 ± 0.8 d	2.1 ± 0.1 cd	5.8 ± 0.1 b	702.3 ± 17.5 de
RD79	83.6 ± 1.1 ef	70.7 ± 1.3 e	4.7 ± 0.03 cd	58.7 ± 1.0 ef	2.2 ± 0.1 c	5.3 ± 0.1 d	651.2 ± 14.0 f
RD85	91.9 ± 0.9 a	88.0 ± 0.9 a	4.5 ± 0.01 h	73.6 ± 0.6 a	2.7 ± 0.1 ab	6.5 ± 0.1 a	851.0 ± 11.4 a
RD87	88.5 ± 1.1 bc	81.0 ± 1.0 b	4.5 ± 0.02 h	69.4 ± 0.6 b	2.8 ± 0.1 a	5.9 ± 0.1 b	771.6 ± 17.7 b
RD35	89.7 ± 1.0 ab	83.6 ± 1.3 b	4.6 ± 0.03 fg	66.8 ± 0.9 c	1.9 ± 0.1 de	6.3 ± 0.1 a	750.7 ± 12.4 bc
Azucena	85.9 ± 1.4 cde	75.0 ± 1.5 c	4.7 ± 0.02 cd	59.1 ± 0.9 ef	2.8 ± 0.1 ab	5.5 ± 0.1 cd	728.7 ± 15.1 cd
IR64	78.3 ± 1.3 g	73.2 ± 1.3 cde	4.6 ± 0.02 g	60.4 ± 1.0 de	1.8 ± 0.1 e	4.8 ± 0.1 e	554.7 ± 13.2 h
Fe level (Fe, mg/L)
0 (control)	92.9 ± 1.2 a	92.9 ± 1.3 a	4.4 ± 0.01 d	78.8 ± 0.9 a	3.2 ± 0.1 b	7.0 ± 0.1 b	950.5 ± 21.9 b
150	90.6 ± 1.4 b	90.6 ± 1.4 b	4.4 ± 0.01 d	76.5 ± 1.1 b	3.7 ± 0.1 a	7.5 ± 0.1 a	1 014.0 ± 24.2 a
300	88.4 ± 1.1 c	75.9 ± 1.2 c	4.6 ± 0.02 c	62.9 ± 0.8 c	2.2 ± 0.1 c	5.5 ± 0.1 c	684.9 ± 14.1 c
600	84.0 ± 1.1 d	65.5 ± 1.2 d	4.8 ± 0.03 b	53.4 ± 0.8 d	1.4 ± 0.1 d	4.6 ± 0.1 d	516.1 ± 11.6 d
900	72.1 ± 1.4 e	48.6 ± 1.4 e	5.1 ± 0.04 a	38.3 ± 0.9 e	1.1 ± 0.1 e	3.3 ± 0.1 e	321.0 ± 10.6 e
G	**	**	**	**	**	**	**
Fe	**	**	**	**	**	**	**
G × Fe	**	**	**	**	**	**	**

Factor	Final germination (%)	Germination energy (%)	Mean germination time (d)	Germination rate index (seed/d)	Root length (cm)	Shoot length (cm)	Seedling vigor index
Genotype (G)
RD31	82.1 ± 1.4 f	64.8 ± 1.4 f	4.8 ± 0.03 a	55.0 ± 1.0 g	2.5 ± 0.1 b	5.3 ± 0.2 d	679.1 ± 23.9 ef
RD41	83.9 ± 1.4 ef	72.2 ± 1.7 de	4.8 ± 0.02 b	58.4 ± 1.0 ef	1.9 ± 0.1 de	5.5 ± 0.1 cd	644.8 ± 20.7 f
RD57	85.4 ± 1.4 de	71.7 ± 1.4 de	4.6 ± 0.03 ef	61.7 ± 1.1 d	2.7 ± 0.2 ab	5.6 ± 0.2 bc	733.0 ± 17.1 cd
RD71	85.4 ± 1.5 de	67.4 ± 1.2 f	4.8 ± 0.03 bc	57.5 ± 1.1 f	2.0 ± 0.1 cd	4.9 ± 0.1 e	603.3 ± 18.1 g
RD77	86.9 ± 1.3 cd	74.1 ± 1.3 cd	4.7 ± 0.01 de	61.3 ± 0.8 d	2.1 ± 0.1 cd	5.8 ± 0.1 b	702.3 ± 17.5 de
RD79	83.6 ± 1.1 ef	70.7 ± 1.3 e	4.7 ± 0.03 cd	58.7 ± 1.0 ef	2.2 ± 0.1 c	5.3 ± 0.1 d	651.2 ± 14.0 f
RD85	91.9 ± 0.9 a	88.0 ± 0.9 a	4.5 ± 0.01 h	73.6 ± 0.6 a	2.7 ± 0.1 ab	6.5 ± 0.1 a	851.0 ± 11.4 a
RD87	88.5 ± 1.1 bc	81.0 ± 1.0 b	4.5 ± 0.02 h	69.4 ± 0.6 b	2.8 ± 0.1 a	5.9 ± 0.1 b	771.6 ± 17.7 b
RD35	89.7 ± 1.0 ab	83.6 ± 1.3 b	4.6 ± 0.03 fg	66.8 ± 0.9 c	1.9 ± 0.1 de	6.3 ± 0.1 a	750.7 ± 12.4 bc
Azucena	85.9 ± 1.4 cde	75.0 ± 1.5 c	4.7 ± 0.02 cd	59.1 ± 0.9 ef	2.8 ± 0.1 ab	5.5 ± 0.1 cd	728.7 ± 15.1 cd
IR64	78.3 ± 1.3 g	73.2 ± 1.3 cde	4.6 ± 0.02 g	60.4 ± 1.0 de	1.8 ± 0.1 e	4.8 ± 0.1 e	554.7 ± 13.2 h
Fe level (Fe, mg/L)
0 (control)	92.9 ± 1.2 a	92.9 ± 1.3 a	4.4 ± 0.01 d	78.8 ± 0.9 a	3.2 ± 0.1 b	7.0 ± 0.1 b	950.5 ± 21.9 b
150	90.6 ± 1.4 b	90.6 ± 1.4 b	4.4 ± 0.01 d	76.5 ± 1.1 b	3.7 ± 0.1 a	7.5 ± 0.1 a	1 014.0 ± 24.2 a
300	88.4 ± 1.1 c	75.9 ± 1.2 c	4.6 ± 0.02 c	62.9 ± 0.8 c	2.2 ± 0.1 c	5.5 ± 0.1 c	684.9 ± 14.1 c
600	84.0 ± 1.1 d	65.5 ± 1.2 d	4.8 ± 0.03 b	53.4 ± 0.8 d	1.4 ± 0.1 d	4.6 ± 0.1 d	516.1 ± 11.6 d
900	72.1 ± 1.4 e	48.6 ± 1.4 e	5.1 ± 0.04 a	38.3 ± 0.9 e	1.1 ± 0.1 e	3.3 ± 0.1 e	321.0 ± 10.6 e
G	**	**	**	**	**	**	**
Fe	**	**	**	**	**	**	**
G × Fe	**	**	**	**	**	**	**

Factor	Plant height (cm)		Root length (m)		Shoot dry matter (g/plant)	Root dry matter (g/plant)		Tiller number per plant	Panicle number per plant		Filled grain ratio (%)	1000-grain weight (g)		Grain yield (g/plant)
Genotype (G)
RD31	92.1 ± 1.9 bc		128.9 ± 6.4 a		86.5 ± 3.0 bc	13.3 ± 0.5 cd		23.6 ± 0.6 ab	16.6 ± 0.7 ab		78.6 ± 0.2 gh	16.8 ± 0.7 cd		19.1 ± 1.1 c
RD41	90.6 ± 3.6 bc		129.1 ± 6.2 a		71.9 ± 1.8 d	13.4 ± 0.7 cd		19.7 ± 0.5 d	14.1 ± 0.8 cd		81.6 ± 0.1 cde	19.0 ± 0.8 ab		19.4 ± 1.2 c
RD57	93.5 ± 2.0 b		127.2 ± 7.7 a		84.3 ± 1.4 c	12.0 ± 1.2 d		22.4 ± 0.5 bc	16.5 ± 0.8 ab		79.2 ± 0.1 fgh	18.3 ± 0.3 b		18.8 ± 1.0 c
RD71	91.7 ± 1.7 bc		125.4 ± 7.7 a		73.3 ± 1.3 d	13.0 ± 0.5 cd		21.4 ± 0.5 bcd	14.8 ± 0.9 bcd		81.2 ± 0.1 def	19.2 ± 0.7 ab		20.5 ± 0.8 bc
RD77	90.1 ± 2.7 bcd		121.4 ± 6.7 a		69.1 ± 2.3 de	11.6 ± 0.7 d		22.1 ± 0.8 bc	16.4 ± 0.8 ab		78.9 ± 0.2 gh	18.8 ± 0.4 ab		20.6 ± 0.8 bc
RD79	90.9 ± 2.4 bc		121.4 ± 6.8 a		90.1 ± 2.0 b	13.8 ± 0.6 bcd		21.7 ± 0.8 bcd	16.1 ± 1.2 abc		80.3 ± 0.4 efg	18.8 ± 0.4 b		20.9 ± 0.8 bc
RD85	84.8 ± 1.0 d		125.9 ± 4.4 a		68.5 ± 2.1 de	17.2 ± 1.1 a		22.2 ± 0.7 bc	17.1 ± 0.7 a		84.9 ± 0.3 b	20.3 ± 0.5 a		23.5 ± 0.8 a
RD87	87.9 ± 2.8 cd		120.1 ± 6.9 a		73.5 ± 1.8 d	15.9 ± 1.4 ab		21.0 ± 0.7 cd	15.0 ± 1.1 bc		82.9 ± 0.1 bcd	19.5 ± 0.8 ab		21.8 ± 0.5 ab
RD35	88.4 ± 3.4 bcd		128.9 ± 8.0 a		69.9 ± 1.0 de	16.2 ± 0.5 a		23.3 ± 0.8 zb	15.2 ± 0.9 abc		83.6 ± 0.3 bc	18.2 ± 0.5 bc		22.4 ± 0.8 ab
Azucena	129.3 ± 2.7 a		120.3 ± 10.2 a		106.3 ± 1.8 a	15.0 ± 0.6 abc		11.3 ± 0.5 e	7.0 ± 0.3 e		93.7 ± 0.1 a	18.8 ± 0.6 ab		16.4 ± 0.6 d
IR64	76.0 ± 1.6 e		126.7 ± 7.0 a		64.6 ± 4.0 e	16.5 ± 0.9 a		24.7 ± 1.0 a	13.0 ± 1.1 d		78.0 ± 0.2 h	16.5 ± 0.5 d		19.0 ± 1.0 c
Fe level (Fe, mg/L)
0 (control)	92.1 ± 2.2 ab		121.1 ± 8.8 c		80.9 ± 1.6 c	13.7 ± 0.8 c		21.5 ± 0.7 bc	15.5 ± 0.8 b		81.3 ± 0.8 bc	18.8 ± 0.4 c		21.0 ± 0.9 c
150	94.3 ± 2.8 a		134.6 ± 5.6 b		89.6 ± 1.5 b	17.5 ± 0.7 b		22.5 ± 0.7 ab	16.9 ± 0.9 a		83.0 ± 1.2 ab	19.9 ± 0.6 b		23.6 ± 1.2 b
300	94.9 ± 2.7 a		149.7 ± 7.1 a		97.7 ± 2.4 a	21.0 ± 1.0 a		23.3 ± 0.7 a	16.5 ± 1.0 ab		83.2 ± 0.8 a	20.8 ± 0.9 a		25.2 ± 1.3 a
600	91.1 ± 1.6 b		115.2 ± 7.5 c		69.5 ± 2.2 d	11.6 ± 0.9 d		20.6 ± 0.6 c	13.2 ± 0.8 c		81.9 ± 1.0 c	17.7 ± 0.4 d		18.8 ± 0.4 d
900	89.1 ± 2.3 b		104.6 ± 6.5 d		52.3 ± 2.5 e	7.9 ± 0.5 e		18.2 ± 0.6 d	11.3 ± 0.8 d		81.0 ± 0.9 c	15.6 ± 0.5 e		12.5 ± 0.5 e
G	**		ns		**	**		**	**		**	**		**
Fe	**		**		**	**		**	**		**	**		**
G × Fe	ns		ns		**	**		*	*		**	**		**
Factor		SPAD value		Net photosynthetic rate [μmol/(m²∙s)]			Membrane stability index (%)			Leaf Fe content (mg/g)			Root Fe content (mg/g)
Genotype (G)
RD31		36.9 ± 0.4 cd		18.6 ± 0.6 b			72.8 ± 0.5 cd			7.2 ± 0.2 b			11.8 ± 0.4 b
RD41		37.8 ± 0.5 abcd		18.2 ± 0.7 b			75.2 ± 0.5 abcd			3.7 ± 0.1 f			10.9 ± 0.4 f
RD57		38.3 ± 0.3 abc		18.8 ± 1.0 b			77.1 ± 0.5 abc			5.7 ± 0.1 e			11.0 ± 0.2 d
RD71		38.1 ± 0.4 abc		19.6 ± 0.8 b			75.3 ± 0.6 abcd			5.3 ± 0.1 d			11.4 ± 0.3 e
RD77		35.7 ± 0.4 d		19.3 ± 0.6 b			74.5 ± 0.5 bcd			6.2 ± 0.1 c			11.6 ± 0.5 c
RD79		39.1 ± 0.2 abc		19.4 ± 0.8 b			77.2 ± 0.5 abc			3.9 ± 0.1 f			11.0 ± 0.3 e
RD85		39.2 ± 0.5 abc		23.0 ± 0.9 a			80.4 ± 0.2 ab			2.3 ± 0.1 h			10.1 ± 0.3 i
RD87		40.1 ± 0.3 a		22.4 ± 1.2 a			78.5 ± 0.4 abc			3.1 ± 0.1 g			10.6 ± 0.4 g
RD35		39.3 ± 0.5 ab		21.8 ± 0.8 a			78.4 ± 0.4 abc			2.6 ± 0.1 h			10.4 ± 0.2 h
Azucena		39.2 ± 0.6 ab		19.8 ± 0.7 b			81.3 ± 0.6 a			2.5 ± 0.1 h			9.9 ± 0.5 j
IR64		37.6 ± 0.5 bcd		19.2 ± 0.8 b			70.0 ± 0.4 d			8.7 ± 0.3 a			12.3 ± 0.5 a
Fe level (Fe, mg/L)
0 (control)		38.4 ± 0.4 bc		20.5 ± 0.7 c			84.1 ± 0.4 a			0.7 ± 0.0 e			4.1 ± 0.5 e
150		39.3 ± 0.4 ab		22.4 ± 0.5 b			83.9 ± 0.5 a			1.2 ± 0.0 d			8.0 ± 0.2 d
300		40.1 ± 0.4 a		25.0 ± 1.2 a			77.9 ± 0.4 b			2.0 ± 0.1 c			10.8 ± 0.2 c
600		37.5 ± 0.4 c		18.4 ± 0.5 d			71.4 ± 0.5 c			6.5 ± 0.1 b			13.3 ± 0.2 b
900		36.1 ± 0.4 d		13.7 ± 1.1 e			64.7 ± 0.6 d			12.8 ± 0.4 a			18.7 ± 0.5 a
G		**		**			**			**			**
Fe		**		**			**			**			**
G × Fe		**		**			**			**			**

Factor	Plant height (cm)		Root length (m)		Shoot dry matter (g/plant)	Root dry matter (g/plant)		Tiller number per plant	Panicle number per plant		Filled grain ratio (%)	1000-grain weight (g)		Grain yield (g/plant)
Genotype (G)
RD31	92.1 ± 1.9 bc		128.9 ± 6.4 a		86.5 ± 3.0 bc	13.3 ± 0.5 cd		23.6 ± 0.6 ab	16.6 ± 0.7 ab		78.6 ± 0.2 gh	16.8 ± 0.7 cd		19.1 ± 1.1 c
RD41	90.6 ± 3.6 bc		129.1 ± 6.2 a		71.9 ± 1.8 d	13.4 ± 0.7 cd		19.7 ± 0.5 d	14.1 ± 0.8 cd		81.6 ± 0.1 cde	19.0 ± 0.8 ab		19.4 ± 1.2 c
RD57	93.5 ± 2.0 b		127.2 ± 7.7 a		84.3 ± 1.4 c	12.0 ± 1.2 d		22.4 ± 0.5 bc	16.5 ± 0.8 ab		79.2 ± 0.1 fgh	18.3 ± 0.3 b		18.8 ± 1.0 c
RD71	91.7 ± 1.7 bc		125.4 ± 7.7 a		73.3 ± 1.3 d	13.0 ± 0.5 cd		21.4 ± 0.5 bcd	14.8 ± 0.9 bcd		81.2 ± 0.1 def	19.2 ± 0.7 ab		20.5 ± 0.8 bc
RD77	90.1 ± 2.7 bcd		121.4 ± 6.7 a		69.1 ± 2.3 de	11.6 ± 0.7 d		22.1 ± 0.8 bc	16.4 ± 0.8 ab		78.9 ± 0.2 gh	18.8 ± 0.4 ab		20.6 ± 0.8 bc
RD79	90.9 ± 2.4 bc		121.4 ± 6.8 a		90.1 ± 2.0 b	13.8 ± 0.6 bcd		21.7 ± 0.8 bcd	16.1 ± 1.2 abc		80.3 ± 0.4 efg	18.8 ± 0.4 b		20.9 ± 0.8 bc
RD85	84.8 ± 1.0 d		125.9 ± 4.4 a		68.5 ± 2.1 de	17.2 ± 1.1 a		22.2 ± 0.7 bc	17.1 ± 0.7 a		84.9 ± 0.3 b	20.3 ± 0.5 a		23.5 ± 0.8 a
RD87	87.9 ± 2.8 cd		120.1 ± 6.9 a		73.5 ± 1.8 d	15.9 ± 1.4 ab		21.0 ± 0.7 cd	15.0 ± 1.1 bc		82.9 ± 0.1 bcd	19.5 ± 0.8 ab		21.8 ± 0.5 ab
RD35	88.4 ± 3.4 bcd		128.9 ± 8.0 a		69.9 ± 1.0 de	16.2 ± 0.5 a		23.3 ± 0.8 zb	15.2 ± 0.9 abc		83.6 ± 0.3 bc	18.2 ± 0.5 bc		22.4 ± 0.8 ab
Azucena	129.3 ± 2.7 a		120.3 ± 10.2 a		106.3 ± 1.8 a	15.0 ± 0.6 abc		11.3 ± 0.5 e	7.0 ± 0.3 e		93.7 ± 0.1 a	18.8 ± 0.6 ab		16.4 ± 0.6 d
IR64	76.0 ± 1.6 e		126.7 ± 7.0 a		64.6 ± 4.0 e	16.5 ± 0.9 a		24.7 ± 1.0 a	13.0 ± 1.1 d		78.0 ± 0.2 h	16.5 ± 0.5 d		19.0 ± 1.0 c
Fe level (Fe, mg/L)
0 (control)	92.1 ± 2.2 ab		121.1 ± 8.8 c		80.9 ± 1.6 c	13.7 ± 0.8 c		21.5 ± 0.7 bc	15.5 ± 0.8 b		81.3 ± 0.8 bc	18.8 ± 0.4 c		21.0 ± 0.9 c
150	94.3 ± 2.8 a		134.6 ± 5.6 b		89.6 ± 1.5 b	17.5 ± 0.7 b		22.5 ± 0.7 ab	16.9 ± 0.9 a		83.0 ± 1.2 ab	19.9 ± 0.6 b		23.6 ± 1.2 b
300	94.9 ± 2.7 a		149.7 ± 7.1 a		97.7 ± 2.4 a	21.0 ± 1.0 a		23.3 ± 0.7 a	16.5 ± 1.0 ab		83.2 ± 0.8 a	20.8 ± 0.9 a		25.2 ± 1.3 a
600	91.1 ± 1.6 b		115.2 ± 7.5 c		69.5 ± 2.2 d	11.6 ± 0.9 d		20.6 ± 0.6 c	13.2 ± 0.8 c		81.9 ± 1.0 c	17.7 ± 0.4 d		18.8 ± 0.4 d
900	89.1 ± 2.3 b		104.6 ± 6.5 d		52.3 ± 2.5 e	7.9 ± 0.5 e		18.2 ± 0.6 d	11.3 ± 0.8 d		81.0 ± 0.9 c	15.6 ± 0.5 e		12.5 ± 0.5 e
G	**		ns		**	**		**	**		**	**		**
Fe	**		**		**	**		**	**		**	**		**
G × Fe	ns		ns		**	**		*	*		**	**		**
Factor		SPAD value		Net photosynthetic rate [μmol/(m²∙s)]			Membrane stability index (%)			Leaf Fe content (mg/g)			Root Fe content (mg/g)
Genotype (G)
RD31		36.9 ± 0.4 cd		18.6 ± 0.6 b			72.8 ± 0.5 cd			7.2 ± 0.2 b			11.8 ± 0.4 b
RD41		37.8 ± 0.5 abcd		18.2 ± 0.7 b			75.2 ± 0.5 abcd			3.7 ± 0.1 f			10.9 ± 0.4 f
RD57		38.3 ± 0.3 abc		18.8 ± 1.0 b			77.1 ± 0.5 abc			5.7 ± 0.1 e			11.0 ± 0.2 d
RD71		38.1 ± 0.4 abc		19.6 ± 0.8 b			75.3 ± 0.6 abcd			5.3 ± 0.1 d			11.4 ± 0.3 e
RD77		35.7 ± 0.4 d		19.3 ± 0.6 b			74.5 ± 0.5 bcd			6.2 ± 0.1 c			11.6 ± 0.5 c
RD79		39.1 ± 0.2 abc		19.4 ± 0.8 b			77.2 ± 0.5 abc			3.9 ± 0.1 f			11.0 ± 0.3 e
RD85		39.2 ± 0.5 abc		23.0 ± 0.9 a			80.4 ± 0.2 ab			2.3 ± 0.1 h			10.1 ± 0.3 i
RD87		40.1 ± 0.3 a		22.4 ± 1.2 a			78.5 ± 0.4 abc			3.1 ± 0.1 g			10.6 ± 0.4 g
RD35		39.3 ± 0.5 ab		21.8 ± 0.8 a			78.4 ± 0.4 abc			2.6 ± 0.1 h			10.4 ± 0.2 h
Azucena		39.2 ± 0.6 ab		19.8 ± 0.7 b			81.3 ± 0.6 a			2.5 ± 0.1 h			9.9 ± 0.5 j
IR64		37.6 ± 0.5 bcd		19.2 ± 0.8 b			70.0 ± 0.4 d			8.7 ± 0.3 a			12.3 ± 0.5 a
Fe level (Fe, mg/L)
0 (control)		38.4 ± 0.4 bc		20.5 ± 0.7 c			84.1 ± 0.4 a			0.7 ± 0.0 e			4.1 ± 0.5 e
150		39.3 ± 0.4 ab		22.4 ± 0.5 b			83.9 ± 0.5 a			1.2 ± 0.0 d			8.0 ± 0.2 d
300		40.1 ± 0.4 a		25.0 ± 1.2 a			77.9 ± 0.4 b			2.0 ± 0.1 c			10.8 ± 0.2 c
600		37.5 ± 0.4 c		18.4 ± 0.5 d			71.4 ± 0.5 c			6.5 ± 0.1 b			13.3 ± 0.2 b
900		36.1 ± 0.4 d		13.7 ± 1.1 e			64.7 ± 0.6 d			12.8 ± 0.4 a			18.7 ± 0.5 a
G		**		**			**			**			**
Fe		**		**			**			**			**
G × Fe		**		**			**			**			**

Genotype	Tolerance (TOL)					Stress tolerance index (STI)
Genotype	150 mg/L	300 mg/L	600 mg/L	900 mg/L	Mean^#	150 mg/L	300 mg/L	600 mg/L	900 mg/L	Mean^#
RD31	-2.92 ± 0.26 g	-5.24 ± 0.69 i	1.83 ± 0.62 e	10.16 ± 1.75 b	5.99 ± 1.19 c	1.00 ± 0.01 b	1.03 ± 0.01 d	0.83 ± 0.01 g	0.66 ± 0.01 g	0.75 ± 0.01 f
RD41	-3.79 ± 0.15 i	-5.32 ± 0.29 j	1.31 ± 0.38 f	7.23 ± 1.08 i	4.27 ± 0.78 h	1.04 ± 0.00 a	1.10 ± 0.01 a	0.85 ± 0.01 f	0.81 ± 0.01 c	0.83 ± 0.01 d
RD57	-4.10 ± 0.51 j	-5.68 ± 0.61 k	2.73 ± 0.68 b	8.34 ± 1.13 e	5.54 ± 0.91 d	1.01 ± 0.02 b	1.11 ± 0.00 a	0.88 ± 0.02 de	0.77 ± 0.01 e	0.83 ± 0.02 d
RD71	-2.66 ± 0.19 e	-4.88 ± 0.25 f	2.32 ± 0.60 c	8.16 ± 1.24 g	5.24 ± 0.92 f	1.01 ± 0.01 b	1.08 ± 0.01 c	0.87 ± 0.00 ef	0.77 ± 0.02 e	0.82 ± 0.01 d
RD77	-2.19 ± 0.11 c	-4.91 ± 0.82 g	2.29 ± 0.81 d	8.32 ± 1.38 f	5.30 ± 1.10 e	1.01 ± 0.01 b	1.10 ± 0.02 ab	0.85 ± 0.01 f	0.75 ± 0.01 f	0.80 ± 0.01 e
RD79	-3.04 ± 0.28 h	-5.01 ± 0.26 h	2.28 ± 0.75 d	9.77 ± 1.13 c	6.03 ± 0.94 b	1.02 ± 0.01 ab	1.10 ± 0.00 ab	0.90 ± 0.01 d	0.79 ± 0.01 cd	0.84 ± 0.01 c
RD85	-2.46 ± 0.12 d	-3.79 ± 0.82 b	1.21 ± 0.39 g	6.93 ± 1.20 j	4.07 ± 0.80 j	1.01 ± 0.03 b	1.12 ± 0.02 a	0.94 ± 0.02 ab	0.83 ± 0.02 b	0.88 ± 0.02 b
RD87	-1.03 ± 0.09 a	-4.06 ± 0.71 d	0.86 ± 0.57 h	9.48 ± 1.79 d	5.17 ± 1.18 g	1.01 ± 0.02 b	1.08 ± 0.01 bc	0.91 ± 0.01 c	0.78 ± 0.02 de	0.85 ± 0.02 c
RD35	-2.77 ± 0.14 f	-4.29 ± 0.95 e	0.73 ± 0.90 i	7.78 ± 1.67 h	4.26 ± 1.29 i	1.01 ± 0.01 b	1.11 ± 0.00 a	0.92 ± 0.01 bc	0.83 ± 0.01 b	0.87 ± 0.01 b
Azucena	-1.19 ± 0.17 b	-3.87 ± 0.43 c	0.45 ± 0.45 j	4.36 ± 0.98 k	2.40 ± 0.72 k	1.02 ± 0.01 ab	1.10 ± 0.00 ab	0.95 ± 0.02 a	0.85 ± 0.02 a	0.90 ± 0.02 a
IR64	-3.02 ± 0.35 h	1.16 ± 0.67 a	8.15 ± 1.79 a	12.95 ± 1.34 a	10.55 ± 1.57 a	1.00 ± 0.01 b	0.91 ± 0.01 e	0.70 ± 0.01 h	0.58 ± 0.01 h	0.64 ± 0.01 g