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10 July 2008, Volume 22 Issue 4 Previous Issue    Next Issue
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研究报告
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研究报告

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Molecular-Cytological Identification and Chromosome Behavior Analysis of Telotetrasomic in Rice GONG Zhi-yun,GAO Qing-song,YU Heng-xiu,YI Chuan-deng,GU Ming-hong 2008, 22(4): 335-339 .  Abstract ( )   PDF (236KB) ( )   From the progenies of telotrisomic chromosome 9 of an indica variety, Zhongxian 3037, a phenotypical mutant was selected. Cytological and molecular cytological investigations revealed two extra chromosomes, which were the shortest in somatic cells of the mutant. Fluorescent in situ hybridization (FISH) using a rice centromere specific DNA(RCS2) and DNA sequence specific for chromosome 9 on premetaphase and pachytene chromosomes showed that these two chromosomes were the short arms of chromosome 9. That is to say, the mutant was a telotetrasomic of chromosome 9. Among the 25 pachytene cells, two telosomic chromosomes paired each other as bivalents and didn’t pair with other normal chromosome 9 as multivalents in 96% cells. However, the bivalent was easy to disassociate in advance.

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Pyramiding Effects of Three Quantitative Trait Loci for Resistance to Sheath Blight Using Near-Isogenic Lines of Rice YIN Yue-jun,ZUO Shi-min,WANG Hui,CHEN Zong-xiang,MA Yu-yin,ZHANG Ya-fang,GU Shi-liang,PAN Xue-biao* 2008, 22(4): 340-346 .  Abstract ( )   PDF (1115KB) ( )   A rice sheath blight resistance QTL qSB7(superscript Tq) on rice chromosome 7 of Teqing was confirmed by using the backcross between Teqing and Lemont. The effects and pyramiding effects of qSB7(superscript Tq), qSB9(superscript Tq) (a rice sheath blight resistance QTL mapped on chromosome 9 of Teqing) and qSB11(superscript Le) (a rice sheath blight resistance QTL mapped on chromosome 11 of Lemont) were studied by using a set of near-isogenic lines (NILs) under the background of Lemont. The results indicated that the three resistance QTLs could significantly improve the resistance to rice sheath blight separately or jointly. However. there might exist certain negative interactions among these three resistance QTLs. The importance of a uniform genetic background for studying QTL, and the significance of pyramiding and interacting effects among different QTLs in rice breeding were discussed.

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Development of a Functional Marker for Fragrance Gene in Rice WANG-Feng,LI Jin-hua,LIU Ge-wu,LIAO Yi-long,ZHU Man-shan,LIU Zhen-rong,HUANG Hui-jun,HUANG De-juan 2008, 22(4): 347-352 .  Abstract ( )   PDF (1270KB) ( )   In order to improve the precision of marker-assisted selection for fragrance gene in rice, a functional marker GRFM04 has been developed based on the deletion of 8 bp in DNA sequence of BAD2 gene, namely the fragrance gene, in the fragrant rice varieties. The F2 segregation population derived from a cross of fragrant rice variety Yuefeng B and non-fragrant rice variety Zhenfeng B, and 16 fragrant as well as 6 non-fragrant varieties were analyzed by using the marker GRFM04. The results showed that, the homozygous genotype with fragrance, the heterozygous genotype. and the homozygous non-fragrant genotype could be clearly distinguished and the band types were in completely accordance with the phenotypes of fragrance for all the individual plants in the F2 population and the 22 fragrant and non-fragrant rice varieties. The development of the functional marker GRFM04 will be of practical significance in enhancing the efficiency in genetically improving fragrant traits and fragrant rice breeding.

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Breeding and Characteristic Analysis of a Rice Restorer Line with Bt-Resistance Gene GAO Fang-yuan,LU Xian-jun,HE Shu-lin,CHEN Xiao-juan,LU Dai-hua,SUN Shu-xia,LI Zhi-hua,LIU Guang-chun,ZHANG Yi-zheng,REN Guang-jun* 2008, 22(4): 353-358 .  Abstract ( )   PDF (267KB) ( )   Bt5198, a new rice restorer line with Bt-resistance gene, was developed from the cross and backcross of the elite restorer line Chenghui 177 with rice blast resistance and Bt Minghui 63, a Bt transgenic restorer line. The inbred lines were evaluated by using PCR amplification, test paper evaluation, insect resistance evaluation in greenhouse and paddy fields, nursery evaluation of rice blast resistance and pedigree selection of agronomic traits. Larval mortalities on Bt5198 and Bt Minghui 63 were both 100% when the eggs of the striped stemborer (SSB) were inoculated on rice culms in laboratory, and Bt5198 was highly resistant against SSB and the yellow stemborers (YSB) under field conditions. The F1 hybrids derived from Bt5198 and four cytoplasmic male sterile lines were also highly resistant against SSB and YSB, and had a significant heterosis. Two-year evaluation of rice blast resistance confirmed that the resistance levels to leaf blast and neck blast in Bt5198 were similar to those in Chenghui 177 and significantly higher than those in Bt Minghui 63. The ability of seed germination and pollen yield of Bt5198 were similar with Chenghui 177, suggesting that the introduction of Bt gene into the new restorer line had no significant influence on seed vigor and seed production yield. To identify the Bt gene, it is effective to combine test paper examination with the evaluation of insect-resistance in laboratory and under field conditions.

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Breakdown or Avoidance of Genetic Drag between Blast Resistance and Spikelet Fertility Based on Genotype Selection against Heading Date in Rice LIU Wen-qiang,FAN Ye-yang,CHEN Jie,SHI Yong-feng,WU Jian-li* 2008, 22(4): 359-364 .  Abstract ( )   PDF (1486KB) ( )   Previous study showed that genetic drag between a blast resistance gene Pi25 (t) and QTLs conditioning spikelet fertility (qSF-6) and number of filled grains per panicle (qNFGP-6) were detected on the short arm of rice chromosome 6. To further verify, a larger population was used for analysis and the results confirmed the genetic drag between the blast resistance and spikelet fertility (SF) but no genetic drag was detected between the blast resistance and number of filled grains per panicle (NFGP). Breakdown or avoidance of the genetic drag could be achieved by selection against the background genotype of a heading-date gene (qHD-7) that resided in the region between RM2 and RM214 on chromosome 7. To further validate, two lines with almost identical genotypes on all chromosomal regions except the Pi25 (t) region on chromosome 6 were chosen to develop a new population. The results showed that qSF-6 could be further subdivided into qSF-6-1 and qSF-6-2. When the genotype of RM2-RM214 region was from rice variety Zhong 156, genetic drag between Pi25 (t) and SF (qSF-6-2) was detected, and the allele of qSF-6-2 from rice variety Gumei 2 reduced SF. When genotype of the region between RM2-RM214 was from Gumei 2, no genetic drag was detected. The results indicated that genetic drag between the blast resistance and spikelet fertility could be broken down or avoided under a certain background genotype based on the selection against heading-date and provided a marker aided solution for high level of blast resistance and yield breeding in rice and other crops as well.

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SSR Diversity and Genetic Structure of Main Male Sterile Lines of Three-Line Hybrid Rice in China PENG Suo-tang,WANG Hai-gang,WEI Xing-hua*,LU Jian-zhen,ZHANG Xiao-li,YUAN Xiao-ping,YANG Wu-de 2008, 22(4): 365-369 .  Abstract ( )   PDF (496KB) ( )   A total of 28 male sterile lines for major three-line hybrid rice in China were investigated by SSR assay with 48 pair primers distributed on 12 chromosomes of rice. The results revealed that 41 loci were polymorphic, with a polymorphic rate of 85.4%. The number of alleles per locus (A) ranged from 2 to 6 with an average value of 3.5. Nei’s genetic diversity index (He) and the values of polymorphism information content (PIC) were 0.40 and 0.36, respectively. Analysis of molecular variance (AMOVA) showed that the genetic differentiation among the breeding periods was rather small (Fst=0.033) and not significant (P>0.05). However, the differentiation within the breeding periods was very high. Model-based analysis showed that it contained similar ancestry for main male sterile lines of three-line hybrid rice in China, implying that enriching genetic diversity in male sterile lines should be important in hybrid rice breeding program.

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Dissection of QTLs in Two Years for Yield Component Traits in Rice (Oryza sativa) XU Ling,ZHANG Ya-dong,ZHU Zhen,ZHAO ling,ZHAO Qing-yong,ZHANG Qiao-feng,WANG Cai-lin* 2008, 22(4): 370-376 .  Abstract ( )   PDF (751KB) ( )   QTLs for six traits including number of spikelets per panicle, number of filled grains per panicle, seed setting rate, number of panicles per plant, 1000-grain weight and grain yield per plant were identified in 2005 and 2006 using a set of 111 recombinant inbred line (RIL) population derived from Nikken 2 and Milyang 23 through consecutive selfing for six or seven generations. A total of 19 QTLs distributed on seven chromosomes were detected, including 10 QTLs in 2005 and 14 QTLs in 2006, and five QTLs in both 2005 and 2006. Some QTLs controlling different traits shared the same marker interval on the chromosome with each other. which was consistent with their significant phcnotypic correlations. Three pleiotropic or tightly linked QTL regions controlling yield and its component traits were identified. The QTLs on chromosome 8 (between markers RM5556 and RM331J were found to be the co-localized regions for number of spikelets per panicle. number of filled grains per panicle and grain yield per plant in the two years. These QTLs provide useful information for high-yield rice breeding through marker-assisted selection.

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Degradation of Amyloplast Envelope and Discussion on the Concept of Compound Starch Granule in Rice Endosperm WEI Cun-xu,ZHANG Jun,ZHOU Wei-dong,CHEN Yi-fang,LIU Qiao-quan* 2008, 22(4): 377-384 .  Abstract ( )   PDF (8387KB) ( )   The development of starch granule, degradation of amyloplast envelope and morphology of compound starch granule were observed with the transmission electron microscopy and scanning electron microscopy. Many starch granules formed and developed in one amyloplast. The morphology of starch granules changed from spheroid to ellipsoid with development. Starch granules became polyhedral when they contacted to each other in amyloplast. The amyloplast envelope began to degrade after amyloplast was full of starch granules. Degraded membrane fragments surrounded cytoplasmic matrix to form ring membrane structure. Well developed starch granules were polyhedral with compact arrangement in amyloplast, and these starch granules kept the outline of amyloplast after amyloplast envelope degraded. Mature grain with well developed starch granules showed transparence where the fracture surface was suggested to he between endospcrm cells. Poorly developed starch granules were round or elliptic with loose arrangement in amyloplast, and these starch granules did not keep the outline of amyloplast after amyloplast envelope degraded. Mature grain with poorly developed starch granules showed chalkiness where thefracture surface was suggested to be through endosperm cells. In addition, the concept of compound starch granules was discussed.

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Comparatively Embryological Observations on Interspecific Hybridizations between Oryza sativa with Different Ploidy Levels and O. officinalis FU Xue-lin,LU Yong-gen*,LIU Xiang-dong,LI Jin-quan,ZHAO Xing-juan 2008, 22(4): 385-391 .  Abstract ( )   PDF (7033KB) ( )   As maternal parents, diploid and autotetraploid plants of Oryza sativa cv. L202 were crossed with O. officinalis. Fertilization and embryo development in these two crosses were comparatively studied. There were no matured hybrid seeds obtained because all the hybridized spikelets died at 30 days after pollination (DAP). The main reasons for non-seed set were abnormal fertilization and developments of the embryos and endosperms of interspecific hybrids. There were double fertilization, egg cell single fertilization and non-fertilization in these crosses. Although 59.15% and 54.87% hybrid embryos produced in the crosses of L202-2x/O. officinalis and L202-4x/O. officinalis, respectively, hybrid embryos ceased to develop or degenerated and plenty of free endosperm nuclei were in disaggregating state without developing cellular endosperms at 3 DAP. Otherwise, some embryological differences in these two crosses were found, that is, the rate of double fertilization and total rate of double and single fertilization in L202-2x/O. officinulis were higher than those in L202-4x/O. officinalis. The embryo and endosperm of hybrids developed more slowly, and embryos and free endosperm nuclei were more severely degenerated in L202-4x/O. officinalis, Till 5 DAP, a few of embryos in L202 2x/O. officinalis developed into pear-shaped ones, however, embryos in L202-4x/O. officinalis were all degenerated. It was considered that obtaining interspecific hybrids by wide crosses between autotetraploid of O sativa and O. officinalis was more difficult.

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Analysis on Anti-Fissuring Character among Early Rice Varieties in Zhejiang Province, China WANG Yue-xing,YANG Jun,NI Shen,CHEN Hong-qi,ZHU Xu-dong* 2008, 22(4): 392-398 .  Abstract ( )   PDF (7471KB) ( )   A standard treatment was designed for hygroscopic grain fissure, and the anti-fissuring character among early rice varieties in Zhejiang Province, China was analyzed and classified. There was significant difference in the percentage of fissure grain among varieties (P=4.23×10^(-16)<0.01). The highest percentage of fissure grain was 73%, and the lowest was 0.5%. The average percentages of fissure grain were 34.19% for 45 indica rice, 55.44% for 8 japonica rice, and 2.25% for 2 japonica rice with long grain. The correlation analysis showed that there was a significant correlation between anti-fissuring character and grain shape [r=0.46(superscript **)].

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Effects of Cadmium Stress on Seed Germination, Seedling Growth, and Amylase Activities in Rice HE Jun-yu,REN Yan-fang,ZHU Cheng*,JIANG De-an* 2008, 22(4): 399-404 .  Abstract ( )   PDF (1987KB) ( )   Two rice varieties, Xiushui 110 with high Cd tolerance and Xiushui 11 with low Cd tolerance were used to study the effects of cadmium (Cd) stress on seed germination, seedling growth and amylase activities. The low cadmium concentration had little effect on germination rate. However, cadmium stress could significantly inhibit plumule and radicle growth, especially for radicle growth. Germination index, vigour index, radicle length and amylase activities of Xiushui 11 decreased more significantly with the rising cadmium level compared with Xiushui 110. And the cadmium content in seedlings of Xiushui 11 was higher than that in Xiushui 110 when the cadmium concentration exceeded 5 μmol/L, which caused lower mitotic index in root tips and amylase activities, and more serious cadmium toxicity in Xiushui 11.

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Effects of Different Nitrogen Forms on Growth and Nutrient Absorption of Rice under Non-flooded Cultivation YUE Ya-peng,LI Yong,XUE Lin,ZHOU Yi,XU Yang-chun,SHEN Qi-rong,GUO Shi-wei* 2008, 22(4): 405-410 .  Abstract ( )   PDF (2794KB) ( )   In order to study the effects of different nitrogen forms (ammonium, as A; nitrate, as N; ammonium and nitrification inhibitor dicyandiamide, as A+DCD) on growth and nutrient absorption of rice plants under non-flooded cultivation at the tillering and booting stages, a pot experiment with different forms of nitrogen fertilizer was conducted in greenhouse. The results showed that at the tillering and booting stages, biomass, number of tillers and the area of newly expanded leaves of rice plants under A and A+DCD treatments were higher than those under N treatment; The highest net photosynthetic rate occurred in rice plants under A+DCD treatment, and the lowest under N treatment; The proportion of potassium distributing in leaves of rice plants under A and A+DCD treatments was higher than that under N treatment, while the proportion of potassium distributing in stems of rice plants under N treatment was higher than that under A and A+DCD treatments.

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Increasing Resistance of Rice to Low Temperature Photoinhibition by Spraying 5-Aminolevulinic Acid was Associated with Activities of Anti-oxidant Enzymes LIU Fang,GUO Jing-jing,GONG Li-li,XU Xiao-ming* 2008, 22(4): 411-415 .  Abstract ( )   PDF (1426KB) ( )   The primary mechanism of significant increase in resistance of rice to low temperature photoinhibition was studied by foliar spray with 250 mg/L aqueous solution of 5-aminolevulinic acid (ALA). Low concentration ALA-treatment enhanced the resistance of rice to low temperature photoinhibition, for the significant enhancement of the ascorbate peroxidase (APX) and glutathione reductase (GR) activities as well as the less decline superoxide dismutase (SOD) activity which alleviates the photoinhibition of photosystem Ⅱ by reducing the accumulation of the hydrogen peroxide (H2O2) rather than strengthing the thermal energy dissipation through xanthophyll cycle. Moreover, the increased activity of APX was probably resulted in the accumulation of heme.

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Influence of High Temperature on Yeast-like Endosymbiotes and Pesticide Resistance of Small Brown Planthopper, Laodelphax striatellus ZHANG Xiao-jie,YU Xiao-ping*,CHEN Jian-ming 2008, 22(4): 416-420 .  Abstract ( )   PDF (1725KB) ( )   Newly-hatched nymphs of the small brown planthopper (SBPH, Laodelphax striatellus), including field and sensitive populations, were subjected to high-temperature (35℃) for 1 d, 2 d and 3 d, respectively. The number of yeast-like endosymbiotes in the 3rd instar SBPH reduced by 23.47%-34.23%, 57.86%-61.51% and 88.96%-90.71% after treated with high temperature for 1 d, 2 d, and 3 d, respectively. However, the size of yeast-like endosymbiotes was not obviously affected. Resistance of SBPH to three insecticides (midacloprid, chlorpyrifos and fipronil) decreased with increasing treatment time, with the order of resistance as follows: 1 d>2 d>3 d.

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Spatial and Temporal Variations in Susceptibility to Imidacloprid and Its Realized Heritability in Brown Planthopper, Nilaparvata lugens WANG Yan-hua,LI Yong-ping,CHEN Jin,SHEN Jin-liang*,LI Wen-hong,GAO Cong-fen,ZHUANG Yong-lin,DAI De-jiang,ZHOU Wei-jun,LIANG Gui-mei,SHAO Zhen-run 2008, 22(4): 421-426 .  Abstract ( )   PDF (248KB) ( )   To provide a scientific basis for application of insecticides, spatial and temporal variations in susceptibility of N. lugens to imidacloprid were monitored by rice-stem dipping method from 42 field populations in seven provinces (autonomous region) in China from 1996 to 2006. Most field populations remained susceptible from 1996 to 2003 except for a population from Guilin, Guangxi in 1997, which showed a low level of resistance. However, the surveys in 2005 indicated that 16 populations from six provinces quickly developed the resistance to imidacloprid with resistance ratios ranged from 79-to 811-fold. The data collected in 2006 revealed that the resistance levels in 11 populations from seven different provinces decreased slightly (resistance ratios ranged from 150- to 322-fold), except Tongzhou population (Jiangsu province) which developed 627-fold resistance ratio. This phenomenon might be attributed to the temporal suspension of imidacloprid for N. lugens control. After selection for 18 generations with imidacloprid against a laboratory population of N. lugens, the resistance level of N. lugens to imidacloprid increased from 208.3- to 1110.8-fold and the realized heritability (h^2) of the resistance was estimated as 0.1414. It implied that continuous use of imidacloprid would cause further increase in the resistance level of N. lugens to imidacloprid after the high resistance level was developed. Discussion on strategies of N. lugens resistance management was also included.

实验技术

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A General Method for QTL Mapping in Multiple Related Populations Derived from Multiple Parents AO Yan,HU Zhi-qiu,TANG Zai-xiang,WANG Xue-feng,XU Chen-wu* 2008, 22(4): 427-431 .  Abstract ( )   PDF (41KB) ( )   It’s well-known that incorporating some existing populations derived from multiple parents may improve QTL mapping and QTL-based breeding programs. However, no general maximum likelihood method has been available for this strategy. Based on the QTL mapping in multiple related populations derived from two parents, an maximum likelihood estimation method that can incorporate several populations derived from three or more parents and can be used to handle different mating designs was proposed. Taking the circle design as an example, simulation studies were performed to study the impact of QTL heritability and sample size upon the proposed method. The results showed that under the same heritability, higher QTL detection power and more exact and accurate estimation of parameters could be obtained when three F2 populations were analyzed jointly than when only any two F2 populations were analyzed simultaneously; and higher heritability, especially with larger sample sizes would increase the ability of QTL detection and improve the estimation of parameters. Potential advantages of the method are as follows: firstly, the existing results of QTL mapping in single population can be compared and integrated with each other using this proposed method, so the ability of QTL detection and precision of QTL mapping can be improved. Secondly, owing to multiple alleles in multiple parents, the method can exploit gene resource more adequately, which will lay an important genetic groundwork for plant improvement.

研究简报

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Genetic Mapping of a Gold Hull and Internode Gene in Rice (Oryza sativa) LI Liang-jie,ZHOU Hai-peng,ZHAN Xiao-deng,CHU Zong-li,CHENG Shi-hua*,CAO Li-yong* 2008, 22(4): 432-434 .  Abstract ( )   PDF (4208KB) ( )   Genetic analyses were carried out for an F2 population derived from the cross between a cytoplasmic male sterile line Zhong 9A and R68, an indica restorer line with a gold hull and internode marker. The results indicated that the gold hull and internode trait was controlled by one recessive gene. Relying on simple sequence repeat (SSR) markers and recessive class analysis method, the gold hull and internode gene (gh) was mapped at an interval on rice chromosome 3 flanked by RM1230 and RM7000 on one side, as well as RM227 and RM514 on the otherside, at distances of 8.7, 3.3, 2.7 and 4.7 cM, respectively. The newly mapped gene was tentatively designated to be gh-5.

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QTLs Mapping for Lysine Content of Rice Using Backcross Inbred Lines TANG Shao-qing,HU Pei-song,LUO Ju,JIAO Gui-ai,WAN Jian-min,SHI Chun-hai* 2008, 22(4): 435-438 .  Abstract ( )   PDF (666KB) ( )   A backcross inbred lines (BILs) population consisting of 98 lines derived from a cross of Nipponbare (japonica)/Kasalath (indica) Nipponbare was used to detect QTLs controlling the lysine content of milled rice in two distinct environments, Zhejiang and Hainan Provinces, China. The lysine content of BILs ranged from 2.19 mg/g to 4.03 mg/g in Zhejiang and 2.39 mg/g to 4.29 mg/g in Hainan, with continuous variation and transgressive segregation. Two putative QTLs (qLYS6-1 and qLYS6-2) with genetic main effects were detected on chromosome 6, which contributed to 27.08 % and 47.56% of the total phenotypic variations, respectively. qLYS6-1 was also detected to have significant genotype X environment interaction effects. The additive effect of qLYS6-1 came from Kasalath, while qLYS6-2 from Nipponbare. In addition, no additive additive epistasis for QTLs was detected.

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Effects of Acid Stimulation and Glutamate Treatments on γ-Aminobutyric Acid Accumulation in Different Japonica Rice Varieties ZHAO Yan 2008, 22(4): 439-442 .  Abstract ( )   PDF (238KB) ( )   The effects of germinating duration, acid stimulation and L-glutamate (L-Glu) supplying treatments on γ-aminobutyric acid (GABA) accumulation in different rice varieties were compared, using six japonica rice varieties including Changyou 94-1, Zhehu 9423, R717, Zhongchao 123, Zhuanqian 1 and Nipponbare as materials. The GABA content in rice could be increased notably by germinating activation for 4-6 days, soaking the germinating rice samples in pH 6.0 buffer for 2 hours and in the solution supplied with 50 mmol/L L-Glu for 12 hours. The above treatments increased the GABA content in germinating rice by 0.8-5.9 times than that in the non-germinated rice. The promoting effects of germination activation, acid stimulation and L-Glu supplying treatments on GABA accumulation in germinating rice were significantly different among varieties. The highest GABA contents were noted in Zhongchao 123 and Nipponbare after treatments, amounting to 1.1236 mg/g and 0.9064 mg/g, respectively, 5.6- and 2.2-fold as those in their non-germinated controls.

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Inducing Effect of Plant Growth Substance Coronatine on Drought Tolerance of Upland and Lowland Rice Seedlings and Its Physiological Mechanism AI Lin,LI Zhao-hu,LI Jian-min,TIAN Xiao-li,WANG Bao-min,ZHAO Zhi-xi,DUAN Liu-sheng* 2008, 22(4): 443-446 .  Abstract ( )   PDF (3578KB) ( )   Two rice varieties Handao 297 (upland rice) and Koshiyutaka (lowland rice) seedlings were employed to study the effect of plant growth substance coronatine on leaf water content, membrane permeability, osmotic adjustment substances (proline, soluble sugar and soluble protein) and endogenous hormones (ABA, IAA and GA3) contents under 20% PEG-simulated drought stress. The results showed that coronatine treatment could maintain leaf relative water content of Handao 297 (0.01 μmol/L) and Koshiyutaka (0.1 μmol/L) at a higher level, enhance the accumulation of proline, soluble sugar and soluble protein, decrease the membrane permeability and maintain the integrity of their plasma membrane structure under drought stress. Coronatine treatments (0.01 and 0.1 μmol/L) also significantly promoted the accumulation of ABA and changed the content and proportion of IAA and GA, in Handao 297 and Koshiyutaka under drought stress. This proved that the coronatine treatments could improve the capacity of the drought tolerance of upland and lowland rice seedlings, with the optimal concentrations in tolerance induction at 0.01 μmol/L and 0.1 μmol/L for upland and lowland rice varieties, respectively.