水稻叶片叶绿素和过氧化氢含量的QTL检测及上位性分析

研究水稻叶片叶绿素和过氧化氢含量的遗传规律,对探讨光合代谢产物遗传规律和开展高产育种具有重要指导意义。利用由日本晴／Kasalath∥日本晴的杂交组合衍生的98个回交重组自交家系(BC1F9)所组成的BIL(backcross inbred lines)群体,在第1、2、3和10染色体上分别检测出5个与叶绿素含量相关的QTL和2个影响剑叶过氧化氢含量的QTL,其中位于第1染色体的RFLP标记C86和C813之间的q-Chll对叶绿素含量的影响最为显著,对表型变异的贡献率达22％,其增效基因来自粳稻品种日本晴;同时在该区间检测到1个与剑叶过氧化氢含量相关的QTL:q-H2O2I,对过氧化氢含量的减效基因来自日本晴品种。上位性分析结果显示影响叶绿素含量及过氧化氢含量的非等位QTL之间存在显著的上位性效应。具有上位性效应的QTL分布于第2、6、11和12染色体上,未检测到与q-Chll或q-H2O2I互作的位点。暗示日本晴品种的RFLP标记C86和C813之间存在1个能够提高叶绿素含量,同时又能降低过氧化氢含量的主效QTL,其加性效应显著而不存在上位性效应。     

Mapping of quantitative trait loci associated with ultraviolet-B resistance in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

The detection of quantitative trait loci (QTLs) associated with UV-B resistance in rice should allow their practical application in breeding for such a complex trait, and may lead to the identification of gene characteristics and functions. Considerable variation in UV-B resistance exists within cultivated rice (Oryza sativa L.), but its detailed genetic control mechanism has not been well elucidated. We detected putative QTLs associated with the resistance to enhanced UV-B radiation in rice, using 98 BC₁F₅ (backcross inbred lines; BILs) derived from a cross between Nipponbare (a resistant japonica rice variety) and Kasalath (a sensitive indica rice variety). We used 245 RFLP markers to construct a framework linkage map. BILs and both parents were grown under visible light with or without supplemental UV-B radiation in a growth chamber. In order to evaluate UV-B resistance, we used the relative fresh weight of aerial parts (RFW) and the relative chlorophyll content of leaf blades (RCC). The BIL population exhibited a wide range of variation in RFW and RCC. Using composite interval mapping with a LOD threshold of 2.9, three putative QTLs associated with both RFW and RCC were detected on chromosomes 1, 3 and 10. Nipponbare alleles at the QTLs on chromosome 1 and 10 increased the RFW and RCC, while the Kasalath allele at the QTL on chromosome 3 increased both traits. Furthermore, the existence of both QTLs on chromosomes 1 and 10 for UV-B resistance was confirmed using chromosome segment substitution lines. Plants with Kasalath alleles at the QTL on chromosome 10 were more sensitive to UV-B radiation than plants with them on chromosome 1. These results also provide the information not only for the improvement of UV-B resistance in rice though marker-associated selection, but also for the identification of UV-B resistance mechanisms by using near-isogenic lines.Communicated by D.J. Mackill     

Response of rice to Al stress and identification of quantitative trait Loci for Al tolerance

Rice (Oryza sativa L.) shows the highest tolerance to Al toxicity among small-grain cereal crops, however, the mechanisms and genetics responsible for its high Al tolerance are not yet well understood. We investigated the response of rice to Al stress using the japonica variety Koshihikari in comparison to the indica variety Kasalath. Koshihikari showed higher tolerance at various Al concentrations than Kasalath. The Al content in root apexes was less in Koshihikari than in Kasalath, suggesting that exclusion mechanisms rather than internal detoxification are acting in Koshihikari. Al-induced secretion of citrate was observed in both Koshihikari and Kasalath, however, it is unlikely to be the mechanism for Al tolerance because there was no significant difference in the amount of citrate secreted between Koshihikari and Kasalath. Quantitative trait loci (QTLs) for Al tolerance were mapped in a population of 183 backcross inbred lines (BILs) derived from a cross of Koshihikari and Kasalath. Three putative QTLs controlling Al tolerance were detected on chromosomes 1, 2 and 6. Kasalath QTL alleles on chromosome 1 and 2 reduced Al tolerance but increased tolerance on chromosome 6. The three QTLs explained about 27% of the phenotypic variation in Al tolerance. The existence of QTLs for Al tolerance was confirmed in substitution lines for corresponding chromosomal segments.     

Identification and functional analysis of a locus for improvement of lodging resistance in rice

We identified a new locus responsible for increased pushing resistance of the lower part of rice (Oryza sativa) and analyzed its physiological function to understand how to improve lodging resistance in rice. Quantitative trait loci (QTLs) controlling pushing resistance of the lower part were analyzed in a population of backcross inbred lines of japonica Nipponbare x indica Kasalath plants cut out at 40 cm to exclude the effect of the weight of the upper parts. Five QTLs for pushing resistance were detected; only one QTL from Kasalath on chromosome 5 (prl5) had a positive effect. The likelihood odds ratio curve of prl5 echoed that for lodging resistance by typhoon. We selected three near-isogenic lines (NILs) in which the chromosomal region of prl5 was substituted with that of Kasalath in the Nipponbare background. The dry weights and densities and the contents of accumulated carbohydrate in stems below 40 cm (lower stems) in each NIL were significantly higher than those of Nipponbare. There was no difference between Nipponbare and the NILs in yield, root characteristics, or the weights of the upper parts. Pushing resistance of the lower part and lodging resistance in the NILs were up to twice as high as in Nipponbare. These results suggest that prl5 might affect the characteristics of the lower stems of the NILs, thus increasing lodging resistance.     

Identification of quantitative trait loci associated with salt tolerance at seedling stage from Oryza rufipogon

Soil salinity is one of the major abiotic stresses affecting plant growth and crop production.In the present study,salt tolerance at rice seedling stage was evaluated using 87 introgression lines (ILs),which were derived from a cross between an elite indica cultivar Teqing and an accession of common wild rice (Oryza rufipogon Griff.).Substantial variation was observed for four traits including salt tolerance score (STS),relative root dry weight (RRW),relative shoot dry weight (RSW) and relative total dry weight (RTW).STS was significantly positively correlated with all other three traits.A total of 15 putative quantitative trait loci (QTLs) associated with these four traits were detected using single-point analysis,which were located on chromosomes 1,2,3,6,7,9 and 10 with 8％-26％ explaining the phenotypic variance.The O.rufipogon-derived alleles at 13 QTLs (86.7％) could improve the salt tolerance in the Teqing background.Four QTL clusters affecting RRW,RSW and RTW were found on chromosomes 6,7,9 and 10,respectively.Among these four QTL clusters,a major cluster including three QTLs (qRRW10,qRSW10 and qRTW10) was found near the maker RM271 on the long arm of chromosome 10,and the O.rufipogon-derived alleles at these three loci increased RRW,RSW and RTW with additive effects of 22.7％,17.3％ and 18.5％,respectively,while the phenotypic variance explained by these three individual QTLs for the three traits varied from 19％ to 26％.In addition,several salt tolerant ILs were selected and could be used for identifying and utilizing favorable salt tolerant genes from common wild rice and used in the salt tolerant rice breeding program.     

利用粳稻染色体片段置换系群体检测水稻抗亚铁毒胁迫有关性状QTL

潜育性水稻田广泛分布于中国、斯里兰卡、印度、印度尼西亚、塞拉里昂、利比亚、尼日利亚、哥伦比亚和菲律宾等国,其中我国南方稻区就有近700万公顷低产潜育性水稻田。该类水稻田还原性强,矿质营养失调,尤以Fe^2 过量积累,对水稻生长发育产生不良的逆境胁迫作用。培育抗亚铁毒的水稻品种是简便、经济有效地提高稻谷产量的重要途径之一。该文利用由粳稻品种Asominori与籼稻品种IR24杂交衍生的Asominori染色体片段置换系(Chromosome Segment Substitution Lines,CSSLs)群体为材料,检测与抗亚铁毒胁迫有关性状QTL。共检测到与抗亚铁毒胁迫有关性状QTL14个,各QTL的LOD值为2．72～6．63。其中检测到与抗亚铁毒胁迫直接有关的性状叶片棕色斑点指数QTL3个,分别位于第3、9、11染色体C515～XNpb279、R2638～C1263和G1465～C950之间,对应的贡献率分别为16．45％、11．16％和28．02％;与其他已发表的定位结果比较发现,位于第三染色体C515～XNpb279间控制叶片棕色斑点指数的QTL与水稻功能图谱上控制叶绿素含量的QTL的位置一致;表明在亚铁毒胁迫条件下,水稻在其叶片表面出现棕色斑点,叶片衰老,产生一些叶绿素降解物或衍生物,以提高叶片细胞对亚铁等重金属毒害的耐受力。另外,在第11染色体G1465～C950之间检测到了控制叶片棕色斑点指数、茎干重和根干重QTL1个,为主效QTL。在第6染色体XNpb386～XNpb342之间检测到控制茎干重、株高、根长和根干重QTL1个,是否与水稻抗亚铁毒有关需要进一步研究。本研究旨在通过定位与抗亚铁毒有关的QTL,借助与之紧密连锁的分子标记有效地聚合这些QTL,培育出抗亚铁毒性强的水稻新种质材料。     

Mapping of QTLs for phosphorus-deficiency tolerance in rice (Oryza sativa L.)

 Phosphorus (P) deficiency of soils is a major yield-limiting factor in rice production. Increasing the P-deficiency tolerance of rice cultivars may represent a more cost-effective solution than relying on fertilizer application. The objective of this study was to identify putative QTLs for P-deficiency tolerance in rice, using 98 backcross inbred lines derived from a japonica×indica cross and genotyped at 245 RFLP marker loci. Lines were grown on P-deficient soil and P uptake, internal P-use efficiency, dry weight, and tiller number were determined. Three QTLs were identified for dry weight and four QTLs for P uptake, together explaining 45.4% and 54.5% of the variation for the respective traits. Peaks for both traits were in good agreement which was to be expected considering the tight correlation of r=0.96 between dry weight and P uptake. For both traits the QTL linked to marker C443 on chromosome 12 had a major effect. Two of the three QTLs detected for internal P-use efficiency, including the major one on chromosome 12, coincided with QTLs for P uptake; however, whereas indica alleles increased P uptake they reduced P-use efficiency. We concluded that this was not due to the tight linkage of two genes in repulsion but rather due to an indirect effect of P uptake on P-use efficiency. Most lines with high use efficiency were characterized by very low P uptake and dry weight and apparently experienced extreme P-deficiency stress. Their higher P-use efficiency was thus the result of highly sub-optimal tissue-P concentrations and did not represent a positive adaptation to low P availability. The number of tillers produced under P deficiency is viewed as an indirect indicator of P-deficiency tolerance in rice. In addition to the major QTL on chromosome 12 already identified for all other traits, two QTLs on chromosome 4 and 12 were identified for tiller number. Their position, however, coincided with QTLs for tiller number reported elsewhere under P-sufficient conditions and therefore appear to be not related to P-deficiency tolerance. In this study P-deficiency tolerance was mainly caused by differences in P uptake and not in P-use efficiency. Using a trait indirectly related to P-deficiency tolerance such as tiller number, we detected a major QTL but none of the minor QTLs detected for P uptake or dry weight. Received: 9 February 1998 / Accepted: 29 April 1998     

应用AFLP与RFLP标记研究水稻磷吸收与利用率的数量性状位点

To identify genetic factors underlying phosphorus (P) uptake and use efficiency under low-P stress in rice (Oryza sativa L.), 84 selected genotypes (recombinant inbred lines) and their parents (which differed in tolerance for low-P stress) “IR20” and IR55178-3B-9-3, were cultured in liquid medium supplemented with adequate and low P levels in a greenhouse. Plants were sampled after 6 weeks in culture for measurements of plant dry weight, P concentration, P uptake and P use efficiency under both P sufficient and stress conditions. A total of 179 molecular markers, including 26 RFLPs and 153 AFLPs, mapped on all 12 chromosomes of rice based on the 84 selected genotypes were used to detect the quantitative trait loci (QTLs) underlying tolerance for low-P stress. Three QTLs were detected on chromosomes 6, 7 and 12, respectively, for relative plant dry weight (RPDW) and relative P uptake (RPUP). One of the QTLs flanked by RG9 and RG241 on chromosome 12 had a major effect which explained about 50% of the variations in the two parameters across the population. The results coincided with the QTLs for low-P stress based on relative tillering ability from the same population from a cross between Nipponbare and Kasalath under soil condition. The identical major QTL for P uptake and plant growth under low-P stress in both liquid medium and soil strongly suggests that the ability of P uptake mainly controls rice tolerance for low-P stress.     

Genetic effects of major QTLs controlling low-temperature germinability in different genetic backgrounds in rice (Oryza sativa L.)

The effects of QTLs are demonstrated basically within the population used in the original QTL analysis as the difference between the alleles of the parental varieties. For the efficient use of QTLs in breeding programs, it is necessary to assess whether the QTL exhibits its genetic effect when it is introgressed into different genetic backgrounds. Extensive studies of tolerance to low temperature at the seed germination stage (called low-temperature germinability) in rice revealed that 2 major QTLs on chromosomes 3 and 11, qLTG3-1 and qLTG11, have large effects. This study assessed the effects of these 2 QTLs from an aus variety, Kasalath, in different genetic backgrounds of 3 japonica varieties, Hoshinoyume, Hayamasari, and Koshihikari. Backcrossed progenies and chromosome segment substitution lines showed that both qLTG3-1 and qLTG11 were effective in the Hoshinoyume and Koshihikari backgrounds, while only qLTG3-1 was effective in the Hayamasari background. The results in this study demonstrated that these 2 QTLs are useful for the improvement of low-temperature germinability in rice breeding programs. The results also indicated that low-temperature germinability in rice is governed by an epistatic interaction of qLTG11.     

Effects of zinc deficiency on rice growth and genetic factors contributing to tolerance

Zinc (Zn) deficiency is the most widespread micronutrient disorder in rice (Oryza sativa), but efforts to develop cultivars with improved tolerance have been hampered by insufficient understanding of genetic factors contributing to tolerance. The objective of this paper was to examine alternative evaluation methods and to identify the most informative traits that would provide realistic information for rice breeders and to map quantitative trait loci (QTLs) associated with tolerance. Screening experiments in low-Zn nutrient solution and in a Zn-deficient field did not produce similar tolerance rankings in a set of segregating lines, which suggested that rhizosphere effects were of greater importance for lowland rice than internal Zn efficiency. The most severe symptom in the field was high plant mortality. The occurrence of leaf bronzing, usually regarded as indicative of susceptibility, did not necessarily concur with high plant mortality, which implied that both were under independent genetic control. The QTL mapping experiment conducted in the field with a population derived from a cross of IR74 (intolerant) with Jalmagna (tolerant) largely confirmed this. Four QTLs associated with plant mortality were detected, and only one of those colocalized with one of the four QTLs detected for leaf bronzing. The two most influential QTLs for plant mortality were detected on chromosomes 2 and 12. They explained 16.6% and 24.2% of the variation, and alleles of the tolerant donor parent Jalmagna reduced mortality by 16.6% and 14.8%, respectively. QTLs for plant mortality acted in a purely additive manner, whereas digenic epistatic interactions were important for leaf bronzing.     

Mapping quantitative trait loci controlling seed longevity in rice ( Oryza sativa L.)

Quantitative trait loci (QTLs) controlling seed longevity in rice were identified using 98 backcross inbred lines (BILs) derived from a cross between a japonica variety Nipponbare and an indica variety Kasalath. Seeds of each BIL were kept for 12 months at 30 degrees C in dry conditions to promote loss of viability. To measure seed longevity, we performed an additional aging-processing treatment for 2 months at 30 degrees C maintaining seeds at 15% moisture content. We measured the germination percent of these treated seeds at 25 degrees C for 7 days as the degree of seed longevity. The germination of BILs ranged from 0 to 100% with continuous variation. Three putative QTLs for seed longevity, qLG-2, qLG-4 and qLG-9, were detected on chromosome 2, 4 and 9, respectively. Kasalath alleles increased the seed longevity at these QTLs. The QTL with the largest effect, qLG-9, explained 59.5% of total phenotypic variation in BILs. The other two QTLs, qLG-2 and qLG-4, explained 13.4 and 11.6% of the total phenotypic variation, respectively. We also verified the effect of the Kasalath allele of qLG-9 using chromosome segment substitution lines. Furthermore, QTLs for seed dormancy were identified on chromosomes 1, 3, 5, 7 and 11. Based on the comparison of the chromosomal location of QTLs for seed longevity and seed dormancy, these traits seem to be controlled by different genetic factors.     

Mapping quantitative trait loci controlling seed dormancy and heading date in rice, Oryza sativa L., using backcross inbred lines

 To detect quantitative trait loci (QTLs) controlling seed dormancy, 98 BC₁F₅ lines (backcross inbred lines) derived from a backcross of Nipponbare (japonica)/Kasalath (indica)//Nipponbare were analyzed genetically. We used 245 RFLP markers to construct a framework linkage map. Five putative QTLs affecting seed dormancy were detected on chromosomes 3, 5, 7 (two regions) and 8, respectively. Phenotypic variations explained by each QTL ranged from 6.7% to 22.5% and the five putative QTLs explained about 48% of the total phenotypic variation in the BC₁F₅ lines. Except for those of the QTLs on chromosome 8, the Nipponbare alleles increased the germination rate. Five putative QTLs controlling heading date were detected on chromosomes 2, 3, 4, 6 and 7, respectively. The phenotypic variation explained by each QTL for heading date ranged from 5.7% to 23.4% and the five putative QTLs explained about 52% of the total phenotypic variation. The Nipponbare alleles increased the number of days to heading, except for those of two QTLs on chromosomes 2 and 3. The map location of a putative QTL for heading date coincided with that of a major QTL for seed dormancy on chromosome 3, although two major heading-date QTLs did not coincide with any seed dormancy QTLs detected in this study. Received: 10 October 1997 / Accepted: 12 January 1998     

QTL mapping and confirmation for tolerance of anaerobic conditions during germination derived from the rice landrace Ma-Zhan Red

Wide adoption of direct-seeded rice practices has been hindered by poorly leveled fields, heavy rainfall and poor drainage, which cause accumulation of water in the fields shortly after sowing, leading to poor crop establishment. This is due to the inability of most rice varieties to germinate and reach the water surface under complete submergence. Hence, tolerance of anaerobic conditions during germination is an essential trait for direct-seeded rice cultivation in both rainfed and irrigated ecosystems. A QTL study was conducted to unravel the genetic basis of tolerance of anaerobic conditions during germination using a population derived from a cross between IR42, a susceptible variety, and Ma-Zhan Red, a tolerant landrace from China. Phenotypic data was collected based on the survival rates of the seedlings at 21 days after sowing of dry seeds under 10 cm of water. QTL analysis of the mapping population consisting of 175 F_2:3 families genotyped with 118 SSR markers identified six significant QTLs on chromosomes 2, 5, 6, and 7, and in all cases the tolerant alleles were contributed by Ma-Zhan Red. The largest QTL on chromosome 7, having a LOD score of 14.5 and an R ² of 31.7 %, was confirmed using a BC₂F₃ population. The QTLs detected in this study provide promising targets for further genetic characterization and for use in marker-assisted selection to rapidly develop varieties with improved tolerance to anaerobic condition during germination. Ultimately, this trait can be combined with other abiotic stress tolerance QTLs to provide resilient varieties for direct-seeded systems.     

The OzT8 locus in rice protects leaf carbon assimilation rate and photosynthetic capacity under ozone stress

Tropospheric ozone (O₃) is a phytotoxic air pollutant whose current background concentrations in parts of East Asia have caused estimated rice yield losses of up to 20%; currently, however, little is known about the mechanisms of O₃ tolerance in rice. We previously identified a quantitative trait locus (QTL) in rice called OzT8, which was associated with relative dry weight under ozone stress. The photosynthetic response in SL46, a Nipponbare (NB)–Kasalath chromosome segment substitution line (SL) containing the OzT8 locus, was compared to the parent NB in multiple ozone fumigation experiments (100 ppb, 8 h d^–1, 23 d). By day 23, SL46 showed significantly less reduction of photosynthetic capacity compared to NB; the maximum carboxylation rate of ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco) decreased by 24% in SL46 compared to 49% in NB, and the maximum electron transport rate decreased by 16 and 39%, respectively. The midday carbon assimilation rates also showed a similar trend, but there was no genotypic difference in stomatal conductance. These results indicate that the OzT8 locus confers ozone tolerance via biochemical acclimation, not avoidance, making it a potentially valuable target for breeding of ozone tolerance into future rice lines. The sequence of photosynthetic response of rice to ozone stress and related tolerance factors are also discussed.     

Identification of quantitative trait loci controlling heading date in rice using a high-density linkage map

 Quantitative trait locus (QTL) analysis has been carried out to identify genes conferring heading date in rice. One hundred and eighty six F₂ plants derived from a cross between a japonica variety, Nipponbare, and an indica variety, Kasalath, were used as a segregating population for QTL mapping and more than 850 markers were employed to identify QTLs. Scan-analysis revealed the existence of two QTLs with large effects, Hd-1 and Hd-2, one in the middle of chromosome 6 and one at the end of chromosome 7, respectively. For both loci, the Kasalath alleles reduced days-to-heading. In addition, three QTLs with minor effects, Hd-3, Hd-4 and Hd-5, were found to be located on chromosomes 6, 7 and 8 based on a secondary scan analysis which was carried out by removing the phenotypic effects of Hd-1 and Hd-2. For the three secondary loci, the Nipponbare alleles reduced days-to-heading. The five QTLs explained 84% of the total phenotypic variation in the F₂ population based on a multiple-QTL model. The presence of a digenic interaction between Hd-1 and Hd-2 was clearly suggested. Received: 18 March 1997 / Accepted: 24 June 1997     

Molecular mapping of quantitative trait loci for drought tolerance in maize plants

Drought tolerance is one of the most important but complex traits of crops. We looked for quantitative trait loci (QTLs) that affect drought tolerance in maize. Two maize inbreds and their advanced lines were evaluated for drought-related traits. A genetic linkage map developed using RFLP markers was used to identify QTLs associated with drought-related traits. Twenty-two QTLs were detected, with a minimum of one and a maximum of nine for drought-related traits. A single-QTL was detected for sugar concentration accounting for about 52.2% of the phenotypic variation on chromosome 6. A single-QTL was also identified for each of the traits root density, root dry weight, total biomass, relative water content, and leaf abscisic acid content, on chromosomes 1 and 7, contributing to 24, 0.2, 0.4, 7, and 19% of the phenotypic variance, respectively. Three QTLs were identified for grain yield on chromosomes 1, 5, and 9, explaining 75% of the observed phenotypic variability, whereas four QTLs were detected for osmotic potential on chromosomes 1, 3, and 9, together accounting for 50% of the phenotypic variance. Nine QTLs were detected for leaf surface area on chromosomes 3 and 9, with various degrees of phenotypic variance, ranging from 25.8 to 42.2%. Four major clusters of QTLs were identified on chromosomes 1, 3, 7, and 9. A QTL for yield on chromosome 1 was found co-locating with the QTLs for root traits, total biomass, and osmotic potential in a region of about 15 cM. A cluster of QTLs for leaf surface area were coincident with a QTL for osmotic potential on chromosome 3. The QTLs for leaf area also clustered on chromosome 9, whereas QTLs for leaf abscisic acid content and relative water content coincided on chromosome 7, 10 cM apart. Co-location of QTLs for different traits indicates potential pleiotropism or tight linkage, which may be useful for indirect selection in maize improvement for drought tolerance.     

水稻耐亚铁毒QTLs的定位

亚铁毒是潜育性水稻土中限制水稻产量的主要因子。利用龙杂8503／IR64的F2和等价的F3群体,在营养液中培养来定位耐亚铁毒的QTLs。通过构建101SSR标记的遗传连锁图谱来确定耐亚铁毒QTLs的位置和特性。借助叶片棕色斑点指数、株高和最大根长3个性状,利用营养液在水稻苗期来评价F2单株、F3群体和亲本龙杂8503、IR64,共检测到叶片棕色斑点指数、株高和最大根长的QTLs20个,分布在水稻的10条染色体上,表明这些性状受多基因控制。控制叶片棕色斑点指数的QTLs分别定位在第1染色体的RM315-RM212、第2染色体的RM6-RM240和第4染色体的RM252-RM451之间。与前人的研究结果比较发现：1）位于第4染色体RM252-RM451之间的控制叶片棕色斑点指数的QTL与水稻功能图谱上控制叶绿素含量减少的QTL的位置一致。另一个位于第1染色体的RM315-RM212之间的控制叶片棕色斑点指数的QTL与水稻功能图谱上位于C178-R2635之间控制叶绿素含量的QTL连锁。2）位于第2染色体RM6-RM240之间的第3个控制叶片棕色斑点指数的QTL与位于RZ58-CD0686的控制钾吸收的QTL连锁。     

Developing rice with high yield under phosphorus deficiency: Pup1 sequence to application

The major quantitative trait locus (QTL) Phosphorus uptake1 (Pup1) confers tolerance of phosphorus deficiency in soil and is currently one of the most promising QTLs for the development of tolerant rice (Oryza sativa) varieties. To facilitate targeted introgression of Pup1 into intolerant varieties, the gene models predicted in the Pup1 region in the donor variety Kasalath were used to develop gene-based molecular markers that are evenly distributed over the fine-mapped 278-kb QTL region. To validate the gene models and optimize the markers, gene expression analyses and partial allelic sequencing were conducted. The markers were tested in more than 80 diverse rice accessions revealing three main groups with different Pup1 allele constitution. Accessions with tolerant (group I) and intolerant (group III) Pup1 alleles were distinguished from genotypes with Kasalath alleles at some of the analyzed loci (partial Pup1; group II). A germplasm survey additionally confirmed earlier data showing that Pup1 is largely absent from irrigated rice varieties but conserved in varieties and breeding lines adapted to drought-prone environments. A core set of Pup1 markers has been defined, and sequence polymorphisms suitable for single-nucleotide polymorphism marker development for high-throughput genotyping were identified. Following a marker-assisted backcrossing approach, Pup1 was introgressed into two irrigated rice varieties and three Indonesian upland varieties. First phenotypic evaluations of the introgression lines suggest that Pup1 is effective in different genetic backgrounds and environments and that it has the potential to significantly enhance grain yield under field conditions.     

Boron toxicity in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.). I. Quantitative trait locus (QTL) analysis of tolerance to boron toxicity

Boron toxicity tolerance of rice plants was studied. Modern japonica subspecies such as Koshihikari, Nipponbare, and Sasanishiki were tolerant, whereas indica subspecies such as Kasalath and IR36 were intolerant to excessive application of boron (B), even though their shoot B contents under B toxicity were not significantly different. Recombinant inbred lines (RILs) of japonica Nekken-1 and indica IR36 were used for quantitative trait locus (QTL) analysis to identify the gene responsible for B toxicity tolerance. A major QTL that could explain 45% of the phenotypic variation was detected in chromosome 4. The QTL was confirmed using a population derived from a recombinant inbred line which is heterogenic at the QTL region. The QTL was also confirmed in other chromosome segment substitution lines (CSSLs).