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。     

Assessing the importance of genotype × environment interaction for root traits in rice using a mapping population II: conventional QTL analysis

Modifying plant root systems is considered a means of crop improvement targeted to low-resource environments, particularly low nutrient and drought-prone agriculture. The identification of quantitative trait loci (QTLs) for root traits has stimulated marker-assisted breeding to this end, but different QTLs have been detected in different populations of the same species, and importantly, in the same population when grown in different experimental environments. The presence of QTL × environment interaction is implicated, and this must be characterised if the utility of the target QTLs is to be realised. Previous attempts to do this suffer from a lack of control over replicate environments and inadequate statistical rigour. The Bala × Azucena mapping population was grown in two replicate experiments of four treatment environments, a control, a low light, a low soil nitrogen and a low soil water treatment. After a 4 weeks growth, maximum root length, maximum root thickness, root mass below 50 cm, total plant dry mass, % root mass and shoot length were measured. A summary of the overall results is presented in an accompanying paper. Here, QTL analysis by composite interval mapping is presented. A total of 145 QTLs were detected, mapping to 37 discrete loci on all chromosomes. Superficial evidence of QTL × E (great difference in LOD score) was tested by single-marker analysis which confirmed QTL × E for five loci representing only five individual trait-loci interactions. Some loci appeared to be stable across environments. Some QTLs were clearly more or less active under low light, low nitrogen or drought. A few notable loci on chromosomes 1, 2, 3, 5, 7 and 9 are briefly discussed. Also discussed are some remaining statistical shortcomings that will be addressed in another companion paper.     

Mapping QTLs for root morphology of a rice population adapted to rainfed lowland conditions

In the rainfed lowlands, rice ( Oryza sativa L.) develops roots under anaerobic soil conditions with ponded water, prior to exposure to water stress and aerobic soil conditions that arise later in the season. Constitutive root system development in anaerobic soil conditions has been reported to have a positive effect on subsequent expression of adaptive root traits and water extraction during progressive water stress in aerobic soil conditions. We examined quantitative trait loci (QTLs) for constitutive root morphology traits using a mapping population derived from a cross between two rice lines which were well-adapted to rainfed lowland conditions. The effects of phenotyping environment and genetic background on QTLs identification were examined by comparing the experimental data with published results from four other populations. One hundred and eighty-four recombinant inbred lines (RILs) from a lowland indica cross (IR58821/IR52561) were grown under anaerobic conditions in two experiments. Seven traits, categorized into three groups (shoot biomass, deep root morphology, root thickness) were measured during the tillering stage. Though parental lines showed consistent differences in shoot biomass and root morphology traits across the two seasons, genotype-by-environment interaction (GxE) and QTL-by-environment interaction were significant among the progeny. Two, twelve, and eight QTLs for shoot biomass, deep root morphology, and root thickness, respectively, were identified, with LOD scores ranging from 2.0 to 12.8. Phenotypic variation explained by a single QTL ranged from 6% to 30%. Only two QTLs for deep root morphology, in RG256-RG151 in chromosome 2 and in PC75M3-PC11M4 in chromosome 4, were identified in both experiments. Comparison of positions of QTLs across five mapping populations (the current population plus populations from four other studies) revealed that these two QTLs for deep root morphology were only identified in populations that were phenotyped under anaerobic conditions. Fourteen and nine chromosome regions overlapped across different populations as putative QTLs for deep root morphology and root thickness, respectively. PC41M2-PC173M5 in chromosome 2 was identified as an interval that had QTLs for deep root morphology in four mapping populations. The PC75M3-PC11M4 interval in chromosome 4 was identified as a QTL for root thickness in three mapping populations with phenotypic variation explained by a single QTL consistently as large as 20-30%. Three QTLs for deep root morphology were found only in japonica/indica populations but not in IR58821/IR52561. The results identifying chromosome regions that had putative QTLs for deep root morphology and root thickness over different mapping populations indicate potential for marker-assisted selection for these traits.     

QTLs and epistasis for aluminum tolerance in rice (Oryza sativa L.) at different seedling stages

To investigate the genetic background for aluminum (Al) tolerance in rice, a recombinant inbred (RI) population, derived from a cross between an Al-sensitive lowland indica rice variety IR1552 and an Al-tolerant upland japonica rice variety Azucena, was used in culture solution. A molecular linkage map, together with 104 amplified fragment length polymorphism (AFLP) markers and 103 restriction fragment length polymorphism (RFLP) markers, was constructed to map quantitative trait loci (QTLs) and epistatic loci for Al tolerance based on the segregation for relative root length (RRL) in the population. RRL was measured after stress for 2 and 4 weeks at a concentration of 1mM of Al³⁺ and a control with a pH 4.0, respectively. Two QTLs were detected at both the 2nd and the 4th weeks on chromosomes 1 and 12 from unconditional mapping, while the QTL on chromosome 1 was only detected at the 2nd stress week from conditional mapping. The effect of the QTL on chromosome 12 was increased with an increase of the stress period from 2 to 4 weeks. The QTL on chromosome 1 was expressed only at the earlier stress, but its contribution to tolerance was prolonged during growth. At least one different QTL was detected at the different stress periods. Mean comparisons between marker genotypic classes indicated that the positive alleles at the QTLs were from the Al-tolerant upland rice Azucena. An important heterozygous non-allelic interaction on Al tolerance was found. The results indicated that tolerance in the younger seedlings was predominantly controlled by an additive effect, while an epistatic effect was more important to the tolerance in older seedlings; additionally the detected QTLs may be multiple allelic loci for Al tolerance and phosphorus-uptake efficiency, or for Al and Fe²⁺ tolerance. Received: 29 July 1999 / Accepted: 13 October 1999     

Mapping QTLs associated with drought avoidance in upland rice

The identification of molecular markers linked to genes controlling drought resistance factors in rice is a necessary step to improve breeding efficiency for this complex trait. QTLs controlling drought avoidance mechanisms were analyzed in a doubled-haploid population of rice. Three trials with different drought stress intensities were carried out in two sites. Leaf rolling, leaf drying, relative water content of leaves and relative growth rate under water stress were measured on 105 doubled haploid lines in two trials and on a sub-sample of 85 lines in the third one. Using composite interval mapping with a LOD threshold of 2.5, the total number of QTLs detected in all trials combined was 11 for leaf rolling, 10 for leaf drying, 11 for relative water content and 10 for relative growth rate under stress. Some of these QTLs were common across traits. Among the eleven possible QTLs for leaf rolling, three QTLs (on chromosomes 1, 5 and 9) were common across the three trials and four additional QTLs (on chromosomes 3, 4 and 9) were common across two trials. One QTL on chromosome 4 for leaf drying and one QTL on chromosome 1 for relative water content were common across two trials while no common QTL was identified for relative growth rate under stress. Some of the QTLs detected for leaf rolling, leaf drying and relative water content mapped in the same places as QTLs controlling root morphology, which were identified in a previous study involving the same population. Some QTL identified here were also located similarly with other QTLs for leaf rolling as reported from other populations. This study may help to chose the best segments for introgression into rice varieties and improvement of their drought resistance.     

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。     

Molecular mapping of genomic regions associated with wheat seedling growth under osmotic stress

A quantitative trait loci (QTL) approach was applied to dissect the genetic control of the common wheat seedling response to osmotic stress. A set of 114 recombinant inbred lines was subjected to osmotic stress from the onset of germination to the 8^th day of seedling development, induced by the presence of 12 % polyethylene glycol. Root, coleoptile and shoot length, and root/shoot length ratio were compared under stress and control conditions. In all, 35 QTL mapping to ten chromosomes, were identified. Sixteen QTL were detected in controls, 17 under stressed conditions, and two tolerance index QTL were determined. The majority of the QTL were not stress-specific. In regions on five chromosome arms (1AS, 1BL, 2DS, 5BL and 6BL) the QTL identified under stress co-mapped with QTL affecting the same trait in controls, and these were classified as seedling vigour QTL, in addition to those expressed in controls. Tolerance-related QTL were detected on four chromosome arms. A broad region on chromosome 1AL, including five QTL, with a major impact of the gene Glu-A1 (LOD 3.93) and marker locus Xksuh9d (LOD 2.91), positively affected root length under stress and tolerance index for root length, respectively. A major QTL (LOD 3.60), associated with marker locus Xcdo456a (distal part of chromosome arm 2BS) determined a tolerance index for shoot length. Three minor QTL (LOD < 3.0) for root length and root/shoot length ratio under osmotic stress were identified in the distal parts of chromosome arms 6DL (marker locus Xksud27a) and 7DL (marker locus Xksue3b). Selecting for the favourable alleles at marker loci associated with the detected QTL for growth traits may represent an efficient approach to enhance the plants’ ability to maintain the growth of roots, coleoptile and shoots in drought-prone soils at the critical early developmental stages.     

QTL mapping of grain length in rice (Oryza sativa L.) using chromosome segment substitution lines

Chromosome segment substitution (CSS) lines have the potential for use in QTL fine mapping and map-based cloning. The standard t-test used in the idealized case that each CSS line has a single segment from the donor parent is not suitable for non-idealized CSS lines carrying several substituted segments from the donor parent. In this study, we present a likelihood ratio test based on stepwise regression (RSTEP-LRT) that can be used for QTL mapping in a population consisting of non-idealized CSS lines. Stepwise regression is used to select the most important segments for the trait of interest, and the likelihood ratio test is used to calculate the LOD score of each chromosome segment. This method is statistically equivalent to the standard t-test with idealized CSS lines. To further improve the power of QTL mapping, a method is proposed to decrease multicollinearity among markers (or chromosome segments). QTL mapping with an example CSS population in rice consisting of 65 non-idealized CSS lines and 82 chromosome segments indicated that a total of 18 segments on eight of the 12 rice chromosomes harboured QTLs affecting grain length under the LOD threshold of 2.5. Three major stable QTLs were detected in all eight environments. Some minor QTLs were not detected in all environments, but they could increase or decrease the grain length constantly. These minor genes are also useful in marker-assisted gene pyramiding.     

不同供水条件下水稻幼苗根系形成的遗传分析

利用分子标记图谱对溶液培养与旱作培养（纸培养）下的水稻（Oryza sativa L.)幼苗的种子根与最长不定根长,不定根数,总根干重,根冠比等性状进行了基因定位与遗传分析。4种参数共检测到6个数量性状位点（quantitative trait loci,QTLs)与22对上位性互作位点,其中溶液培养中的最长不定根长,总根干重和旱作培养中的总根干重检测到的QTLs位点对总变异的贡献率分别为20％,23％和13％左右;旱作培养中的最长不定根长,不定根数,根冠比和溶液培养中的根冠比仅检测到上位性位点,对表型变异的贡献率在12％－61％之间,溶液培养与旱作条件下没有一个或一对检测到的QTL或互作位点完全相同,提示溶液培养和旱作条件下影响幼苗根系生长的遗传机制差异,上位性作用对旱作培养条件下的根生长具重要影响。     

Quantitative trait loci for root-penetration ability and root thickness in rice: comparison of genetic backgrounds.

Drought is the major abiotic stress limiting rice (Oryza sativa) production and yield stability in rainfed lowland and upland ecosystems. Root systems play an important role in drought resistance. Incorporation of root selection criteria in drought resistance improvement is difficult due to lack of reliable and efficient screening techniques. Using a wax-petrolatum layer system simulated to compacted soil layers, root traits were evaluated in a doubled haploid (DH) population derived from the cross between 'IR64' and 'Azucena'. Twelve putative QTLs (quantitative trait loci) were detected by interval mapping comprising four QTLs for root-penetration ability, four QTLs for root thickness, two QTLs for penetrated root number, and two QTLs for total root number. These QTLs individually explained 8.4% to 16.4% of the phenotypic variation. No QTL was detected for maximum penetrated root length by interval mapping. One QTL located between RG104 and RG348 was found to influence both root-penetration ability and root thickness. QTLs for root-penetration ability and root thickness were compared across two populations, 'IR64'-'Azucena' and 'CO39'-'Moroberekan', and different testing conditions. The identified consistent QTLs could be used for marker-assisted selection for deep and thick roots with high root-penetration ability in rice.     

QTLs and epistasis for seminal root length under a different water supply in rice (Oryza sativa L.)

To identify the genetic background of seminal root length under different water-supply conditions, a recombinant inbred (RI) population consisting of 150 lines, derived from a cross between an indica lowland rice, IR1552, and a tropical japonica upland rice, Azucena, was used in both solution culture (lowland condition) and paper culture (upland condition). Quantitative trait loci (QTLs) and epistatic loci for seminal root length were analyzed using 103 restriction fragment length polymorphism (RFLP) markers and 104 amplified fragment length polymorphism (AFLP) markers mapped on 12 chromosomes based on the RI population. One QTL for seminal root length in solution culture (SRLS) and one for seminal root length in paper culture (SRLP) were detected on chromosomes 8 and 1, and about 11% and 10% of total phenotypic variation were explained, respectively. The QTL for SRLP on chromosome 1 was very similar with the QTL for the longest nodal root referred to in a previous report; this QTL may be phenotypically selectable in a breeding program using paper culture. Five pairs of epistatic loci for SRLS were detected, but only one for SRLP, which accounted for about 60% and 20% of the total variation in SRLS and SRLP, respectively. The results indicate that epistasis is a major genetic basis for seminal root length, and there is a different genetic system responsible for seminal root growth under different water supply conditions. Received: 26 May 2000 / Accepted: 19 October 2000     

Development of Chromosome Segment Substitution Lines Derived from Backcross between Two Sequenced Rice Cultivars, <Emphasis Type="Italic">Indica</Emphasis> Recipient 93-11 and <Emphasis Type="Italic">Japonica</Emphasis> Donor Nipponbare

Chromosome segment substitution lines (CSSLs) are powerful tools for detecting and precisely mapping quantitative trait loci (QTLs) and evaluating gene action as a single factor. In this study, 103 CSSLs were produced using two sequenced rice cultivars: 93-11, an elite restorer indica cultivar as recipient, and Nipponbare, a japonica cultivar, as donor. Each CSSL carried a single chromosome substituted segment. The total length of the substituted segments in the CSSLs was 2,590.6 cM, which was 1.7 times of the rice genome. To evaluate the potential application of these CSSLs for QTL detection, phenotypic variations of seed shattering, grain length and grain width in 10 CSSLs were observed. Two QTLs for seed shattering and three for grain length and grain width were identified and mapped on rice chromosomes. The results demonstrate that CSSLs are excellent genetic materials for dissecting complex traits into a set of monogenic loci. These CSSLs are of great potential value for QTL mapping and plant marker-assisted breeding (MAB).     

Genetic mapping of gray leaf spot (GLS) resistance genes in maize

Bulked segregant analysis was used to identify amplified fragment length polymorphism markers (AFLPs) linked to quantitative trait loci (QTLs) involved in the resistance to gray leaf spot (GLS) in maize. By using ten AFLP primer combinations 11 polymorphic markers were identified and converted to sequence- specific PCR markers. Five of the 11 converted AFLPs were linked to three GLS resistance QTLs. The markers were mapped to maize chromosomes 1, 3 and 5 using existing linkage maps of two commercially available recombinant inbred-line populations. Converted restriction fragment length polymorphism markers and microsatellite markers were used to obtain a more-precise localization for the detected QTLs. The QTL on chromosome 1 was localized in bin 1.05/06 and had a LOD score of 21. A variance of 37% was explained by the QTL. Two peaks were visible on chromosome 5, one was localized in bin 5.03/04 and the other in bin 5.05/06. Both peaks had a LOD score of 5, and 11% of the variance was explained by the QTLs. A variance of 8–10% was explained by the QTL on chromosome 3 (bin 3.04). The consistency of the QTLs was tested across two F₂ populations planted in consecutive years. Received: 10.10.00 / Accepted: 26.01.01     

Genetic Analysis of Root Growth in Rice Seedlings Under Different Water Supply Conditions

To understand the genetic background of root growth of rice (Oryza sativa L.) seedlings under different water supply conditions, quantitative trait loci (QTLs) and epistatic effect on seminal root length, maximum adventitious root length, adventitious root number, total root dry weight and ratio of root to shoot were detected using molecular map including 103 restriction fragment length polymorphism (RFLP) markers and 104 amplified fragment length polymorphism (AFLP) markers mapped on a recombinant inbred line (RIL) population with 150 lines derived from a cross between an lowland rice IR1552 and an upland rice Azucena in both solution culture (lowland condition) and paper culture (upland condition). Six QTLs and twenty-two pairs of epistatic loci for the four parameters were detected. Three QTLs detected for maximum adventitious root length in solution culture (MARLS), total root dry weight in both solution culture and paper culture (TRDWS and TRDWP) accounted for about 20%, 23% and 13% of the total variations, respectively. Only epistatic loci were found for maximum adventitious root length and adventitious root number in paper culture (MARLP and ARNP), and for ratio of root to shoot in both paper and solution culture (R/SP and R/SS), which accounted for about 12%-61% of the total variations in the parameters, respectively. No identical QTL or epistatic loci were found for the parameters in both solution and paper culture. The results indicate that there is a different genetic system responsible to root growth of rice seedlings under lowland and upland conditions and epistasis might be the major genetic basis for MARLP, ARNP, R/SP and R/SS.     

Quantitative trait loci controlling resistance to cadmium rhizotoxicity in two recombinant inbred populations of Arabidopsis thaliana are partially shared by those for hydrogen peroxide resistance

To understand mechanisms of cadmium (Cd) tolerance variation associated with root elongation in Arabidopsis thaliana , quantitative trait loci (QTLs) and epistasis were analyzed using relative root length (RRL: % of the root length in +Cd to −Cd) as a tolerant index. Using the composite interval mapping method, three major QTLs ( P < 0.05) were detected on chromosomes 2, 4 and 5 in the recombinant inbred population derived from a cross between Landsberg erecta (L er −0) and Columbia (Col-4). The highest logarithm of odds (LOD) of 5.6 was detected with the QTL on chromosome 5 (QTL5), which is linked to the genetic marker CDPK9 and explained about 26% of the Cd tolerance variation. There was no significant difference in Cd-translocation ratio from roots to shoots between tolerant and sensitive recombinant inbreed lines (RILs), while greater accumulations of reactive oxygen species were observed in the roots of sensitive RILs. This suggested that accumulation of ROS would explain Cd tolerance variation of the L er /Col RILs, which is mainly controlled by the QTL on chromosome 5. The QTL5 in L er /Col population was also detected as one of the major QTLs controlling tolerances to hydrogen peroxide and to copper, which is another ROS generating rhizotoxic metal. The same chromosomal position was detected as a common major QTL for Cd and hydrogen peroxide tolerances in a different recombinant inbreed (RI) population derived from a cross of Col- gl1 and Kashmir (Kas-1). These data, along with a multitraits QTL analysis in both sets of RILs, suggest that peroxide damage depends on the genotype at a major Cd-tolerant locus on the upper part of chromosome 5.     

Identification of QTLs for Yield and Associated Traits in F₂ Population of Rice

Identification of quantitative trait loci (QTLs) controlling yield and yield-related traits in rice was performed in the F₂ mapping population derived from parental rice genotypes DHMAS and K343. A total of 30 QTLs governing nine different traits were identified using the composite interval mapping (CIM) method. Four QTLs were mapped for number of tillers per plant on chromosomes 1 (2 QTLs), 2 and 3; three QTLs for panicle number per plant on chromosomes 1 (2 QTLs) and 3; four QTLs for plant height on chromosomes 2, 4, 5 and 6; one QTL for spikelet density on chromosome 5; four QTLs for spikelet fertility percentage (SFP) on chromosomes 2, 3 and 5 (2 QTLs); two QTLs for grain length on chromosomes 1 and 8; three QTLs for grain width on chromosomes1, 3 and 8; three QTLs for 1000-grain weight (TGW) on chromosomes 1, 4 and 8 and six QTLs for yield per plant (YPP) on chromosomes 2 (3 QTLs), 4, 6 and 8. Most of the QTLs were detected on chromosome 2, so further studies on chromosome 2 could help unlock some new chapters of QTL for this cross of rice variety. Identified QTLs elucidating high phenotypic variance can be used for marker-assisted selection (MAS) breeding. Further, the exploitation of information regarding molecular markers tightly linked to QTLs governing these traits will facilitate future crop improvement strategies in rice.     

不同遗传背景及环境中水稻（Oryza sativa L.）穗长的QTLs和上位性分析

以粳稻Ａｚｕｃｅｎａ为父本与灿稻ＩＲ６４杂交发展的一双单倍体（ＤＨ） 本,与灿稻ＩＲ１５５２杂交发展的一重组自交系（ＲＩ）群体为材料,应用分子标记图说对２个群体在大田答舅栽２个环境下的穗长进行ＱＴＬｓ及上位性效应分析,ＤＨ群体中共检测６个穗长ＱＴＬｓ,位于第１、４长染色体上的３个ＱＴＬｓ,,在２个环境中稳定表达,未检测一闰性效应,加性效应为穗长遗传主效应,ＲＩ群体中,共检测到３个穗长ＱＴＬｓ及６对     

Quantitative trait loci mapping of resistance to Laodelphax striatellus (Homoptera: Delphacidae) in rice using recombinant inbred lines

Laodelphax striatellus Fallén (Homoptera: Delphacidae), is a serious pest in rice, Oryza sativa L., production. A mapping population consisting of 81 recombinant inbred lines (RILs), derived from a cross between japonica' Kinmaze' and indica' DV85' rice, was used to detect quantitative trait loci (QTLs) for the resistance to L. striatellus. Seedbox screening test (SST), antixenosis test, and antibiosis test were used to evaluate the resistance response of the two parents and 81 RILs to L. striatellus at the seedling stage, and composite interval mapping was used for QTL analysis. When the resistance was measured by SST method, two QTLs conferring resistance to L. striatellus were mapped on chromosome 11, namely, Qsbph11a and Qsbph11b, with log of odds scores 2.51 and 4.38, respectively. The two QTLs explained 16.62 and 27.78% of the phenotypic variance in this population, respectively. In total, three QTLs controlling antixenosis against L. striatellus were detected on chromosomes 3, 4, and 11, respectively, accounting for 37.5% of the total phenotypic variance. Two QTLs expressing antibiosis to L. striatellus were mapped on chromosomes 3 and 11, respectively, explaining 25.9% of the total phenotypic variance. The identified QTL located between markers XNpb202 and C1172 on chromosome 11 was detected repeatedly by three different screening methods; therefore, it may be important to confer the resistance to L. striatellus. Once confirmed in other mapping populations, these QTLs should be useful in breeding for resistance to L. striatellus by marker-assisted selection of different resistance genes in rice varieties.     

不同生长环境下水稻最上节间长度QTL定位研究

利用由98 个家系组成的 Nipponbare/Kasalath//Nipponbare 回交重组自交系(backcross inbred lines, BIL)作图群体(BC1F12和BC1F13)和复合区间作图方法(CIM), 在3种不同的生长环境下对水稻最上节间长度进行了 QTL 分析。结果表明, 3种不同的生长环境共检测到 13 个 QTL , 分布于第 1, 2, 3, 5, 6, 8, 10, 11 染色体上, 解释性状变异的 3.97%～15.21%。其中qUIL-6在3种不同生长环境中均检测到, qUIL-1a, qUIL-3a, qUIL-3b和 qUIL-10a 等4个位点在两种不同生长环境中均被检测到, 说明这些 QTL 位点受环境影响较小, 表达较为稳定。     

Locating genes associated with root morphology and drought avoidance in rice via linkage to molecular markers

This research was undertaken to identify and map quantitative trait loci (QTLs) associated with five parameters of rice root morphology and to determine if these QTLs are located in the same chromosomal regions as QTLs associated with drought avoidance/tolerance. Root thickness, root:shoot ratio, root dry weight per tiller, deep root dry weight per tiller, and maximum root length were measured in three replicated experiments (runs) of 203 recombinant inbred lines grown in a greenhouse. The lines were from a cross between indica cultivar Co39 andjaponica cultivar Moroberekan. The 203 RI lines were also grown in three replicated field experiments where they were drought-stressed at the seedling, early vegetative, and late-vegetative growth stage and assigned a visual rating based on leaf rolling as to their degree of drought avoidance/tolerance. The QTL analysis of greenhouse and field data was done using single-marker analysis (ANOVA) and interval analysis (Mapmaker QTL). Most QTLs that were identified were associated with root thickness, root/shoot ratio, and root dry weight per tiller, and only a few with deep root weight. None were reliably associated with maximum root depth due to genotype-by-experiment interaction. Root thickness and root dry weight per tiller were the characters found to be the least influenced by environmental differences between greenhouse runs. Correlations of root parameters measured in greenhouse experiments with field drought avoidance/tolerance were significant but not highly predictive. Twelve of the fourteen chromosomal regions containing putative QTLs associated with field drought avoidance/tolerance also contained QTLs associated with root morphology. Thus, selecting for Moroberekan alleles at marker loci associated with the putative root QTLs identified in this study may be an effective strategy for altering the root phenotype of rice towards that commonly associated with drought-resistant cultivars.