Molecular tagging of a gene for resistance to brown planthopper in rice (Oryza sativa L.)

An introgression line derived from an interspecific cross between Oryzasativa and Oryza officinalis, IR54741-3-21-22 was found to beresistant to an Indian biotype of brown planthopper (BPH). Genetic analysisof 95 F₃ progeny rows of a cross between the resistant lineIR54741-3-21-22 and a BPH susceptible line revealed that resistance wascontrolled by a single dominant gene. A comprehensive RAPD analysisusing 275 decamer primers revealed a low level of (7.1%) polymorphismbetween the parents.RAPD polymorphisms were either co-dominant (6.9%), dominant forresistant parental fragments (9.1%) or dominant for susceptible parentalfragments (11.6%). Of the 19 co-dominant markers, one primer,OPA16, amplified a resistant parental band in the resistant bulk and asusceptible parental band in the susceptible bulk by bulked segregantanalysis. RAPD analysis of individual F₂ plants with the primerOPA16 showed marker-phenotype co-segregation for all, with only onerecombinant being identified. The linkage between the RAPD markerOPA16₉₃₈ and the BPH resistance gene was 0.52 cM in couplingphase. The 938 bp RAPD amplicon was cloned and used as a probe on122 Cla I digested doubled haploid (DH) plants from aIR64xAzucena mapping population for RFLP inheritance analysis and wasmapped onto rice chromosome 11. The OPA16₉₃₈ RAPD markercould be used in a cost effective way for marker-assisted selection of BPHresistant rice genotypes in rice breeding programs.     

Detection of quantitative trait loci (QTL) associated with resistance to whitebacked planthopper (Sogatella furcifera) in rice (Oryza sativa)

Whitebacked planthopper (WBPH) is an important insect pest of rice. In this study, we report quantitative trait loci (QTL) associated with resistance to WBPH using a doubled‐haploid (DH) mapping population derived from the cross IR64/Azucena. We evaluated a set of 91 DH lines using various screening tests which measure seedling resistance, antibiosis and tolerance to WBPH. QTL analysis involving a RFLP map of 175 markers detected a significant QTL on chromosome 7 (RG511‐RG477) associated with seedling resistance to WBPH. In addition, QTL analysis involving available defence related candidate genes as markers on a sub set of 60 DH lines showed significant association of genomic regions on chromosome 1 (W1‐pMRF1), 2 (XLRfrI7‐RG157) and 7 (RG711‐CDO418) with resistance to WBPH. Several suggestive QTL were detected on chromosomes 2, 3, 6, 7, 8 and 11 showing the possibility of their association with resistance to WBPH. The phenotypic contribution of the QTL ranged from 8.4% to 32.1%. Some of the WBPH resistance QTL detected in this study showed similar map positions with the QTL reported for resistance to brown planthopper (BPH) in the same mapping population. These results would be useful for attempts to trace the genes associated with resistance to planthoppers in rice.     

RFLP/AFLP mapping of a brown planthopper (Nilaparvata lugens Stål) resistance gene Bph1 in rice

We have constructed a linkage map of the rice brown planthopper (BPH)resistance gene, Bph1. RFLP and AFLP markers were selected by thebulked segregant analysis and used in the mapping study of 262 F₂sthat were derived from a cross of `Tsukushibare', a susceptible japonica cultivar, and `Norin-PL3', an authentic japonicaBph1-introgression line. Twenty markers were mapped within a 28.9-cMregion containing the Bph1 locus on the long arm of rice chromosome12. Combining the result of segregation analysis of BPH resistance by themass seedling test and that of the markers, the Bph1 locus wasmapped within a 5.8-cM region between two flanking markers. The closestAFLP markers, em5814N and em2802N, was at 2.7 cM proximal to theBph1 locus. Together with the previously constructed high-resolutionmap of bph2 locating the locus at ca. 10 cM proximal to the Bph1 locus, this improved version of the linkage map would facilitatepyramiding these two important BPH resistance genes.     

节水抗旱稻恢复系的抗褐飞虱分子标记辅助选育及抗性评价

褐飞虱是水稻的主要害虫之一,利用水稻抗褐飞虱基因培育抗虫品种是目前公认最经济有效、环境友好的策略。本研究利用水稻功能基因组已克隆的抗褐飞虱基因,通过分子标记辅助选择和常规回交育种相结合的方法,将抗褐飞虱基因Bph6、Bph9、Bph14和Bph15单独和聚合导入到节水抗旱稻恢复系旱恢3号,获得了一系列含有单基因、双基因、三基因和四基因的改良系。采用标准苗期集团筛选法进行褐飞虱抗性鉴定,评价这些基因在旱恢3号背景下的效应及相互作用。表明单基因改良系中, Bph9的抗性最强,且Bph9 Bph6 Bph15 Bph14;在聚合改良系中,抗性均优于单基因改良系,四基因聚合改良系的抗性最强,不同基因型组合的抗性效应是Bph6+Bph9+Bph14+Bph15Bph6+Bph9 Bph6+Bph9+Bph14 Bph6+Bph9+Bph15 Bph6+Bph14+Bph15 Bph9+Bph14+Bph15 Bph14+Bph15。在自然条件下,改良系与旱恢3号在株高、有效穗和千粒重等农艺性状上差异不显著,其他性状与旱恢3号相仿或略差。本试验表明单独和聚合导入Bph6、Bph9、Bph14和Bph15基因能显著提高节水抗旱稻恢复系的褐飞虱抗性,这4个基因的加性效应明显,可为今后节水抗旱稻抗褐飞虱育种提供理论依据和材料基础。     

Substitution mapping and characterization of brown planthopper resistance genes from indica rice variety, ‘PTB33’ (Oryza sativa L.)

Rice (Oryza sativa L.) yield is severely reduced by the brown planthopper (BPH), Nilaparvata lugens Stål, in Asian countries. Increasing resistance in rice against BPH can mitigate yield loss. Previous reports indicated the presence of three BPH resistance genes, BPH2, BPH17-ptb, and BPH32, in durable resistant indica rice cultivar ‘PTB33’. However, several important questions remain unclear; the genetic locations of BPH resistance genes on rice chromosomes and how these genes confer resistance, especially with relationship to three major categories of resistance mechanisms; antibiosis, antixenosis or tolerance. In this study, locations of BPH2, BPH17-ptb, and BPH32 were delimited using chromosome segment substitution lines derived from crosses between ‘Taichung 65’ and near-isogenic lines for BPH2 (BPH2-NIL), BPH17-ptb (BPH17-ptb-NIL), and BPH32 (BPH32-NIL). BPH2 was delimited as approximately 247.5 kbp between RM28449 and ID-161-2 on chromosome 12. BPH17-ptb and BPH32 were located between RM1305 and RM6156 on chromosome 4 and RM508 and RM19341 on chromosome 6, respectively. The antibiosis, antixenosis, and tolerance were estimated by several tests using BPH2-NIL, BPH17-ptb-NIL, and BPH32-NIL. BPH2 and BPH17-ptb showed resistance to antibiosis and antixenosis, while BPH17-ptb and BPH32 showed tolerance. These results contribute to the development of durable BPH resistance lines using three resistance genes from ‘PTB33’.     

QTL analysis for the resistance to small brown planthopper (Laodelphax striatellus Fallén) in rice using backcross inbred lines

Small brown planthopper (SBPH) is a serious pest of rice ( Oryza sativa L.) in China. An indica variety 'Kasalath' is highly resistant to SBPH. A mapping population consisting of 98 BC₁F₉ lines, derived from a backcross of 'Nipponbare'/'Kasalath'//'Nipponbare', was applied to detect quantitative trait loci (QTL) for resistance to SBPH. In the modified seedbox screening test, three QTLs for SBPH resistance were mapped on chromosomes 3 and 11, explaining 49.9% of the phenotypic variance. In the antixenosis test, a total of three QTLs conferring antixenosis against SBPH were detected on chromosomes 3, 8 and 11, which accounted for 36.4% of the total phenotypic variance. In addition, two QTLs expressing antibiosis to SBPH were detected on chromosomes 2 and 11, explaining 13.8% and 14.7% of the phenotypic variance, respectively. Qsbph11e , Qsbph11f and Qsbph11g were located in the region between S2260 and G257 on chromosome 11, indicating that the locus is significant in conferring resistance to SBPH in 'Kasalath'. The molecular markers linked to these QTLs should be useful in the development of varieties with horizontal resistance to SBPH.     

A new locus for resistance to brown planthopper identified in the indica rice variety DV85

The brown planthopper (BPH) is one of the most destructive insect pests of rice. Resistant varieties have proved to be one of the most economic and effective measures for BPH management. In this study, an indica rice ‘DV85’ showed resistance to biotype 2 of BPH by bulked seedling test, and a recombinant inbred line (RIL) population derived from a cross between a susceptible rice ‘Kinmaze’ and ‘DV85’ was phenotyped to map genetic factors conferring BPH resistance in ‘DV85′. Composite interval mapping revealed that one quantitative trait locus (QTL) with a LOD score of 10.1 was detected between XNpb202 and C1172 on chromosome 11. This QTL was designated as Qbph11. Qbph11 explained 68.4% of the phenotypic variance of BPH resistance in this population. The allele from the resistant parent ‘DV85’ at Qbph11 reduced the damage caused by BPH feeding and would be very useful in breeding resistant rice varieties via marker‐assisted selection.     

浙江天台晚稻褐飞虱长期运动规律与ARIMA模型研究

根据天台1969-2008年田间褐飞虱发生监测情况,阐述了褐飞虱长期运动规律及其运行周期,分析造成褐飞虱种群周期性变化的周期特性与主要影响因素,分析表明褐飞虱种群数量变化符合多项式函数模型, Y（t）= X2=C0+C1×X+C2×X2+C3×X3+...+C15×X15, X={1,2,3,┅┅,n},并创建了褐飞虱种群数量变动的时间序列ARIMA(2,1,1)模型：Y(t+l)=0.0659+0.0616851Z(t+l-2)+ e(t+l) + 0.3802611e(t+l-1) ,应用此模型回测,吻合率达98.6%,具有很高的精度;从而预示今后1段时期褐飞虱仍处高位运行状态,应加大防控力度,保障生产安全。     

Role of the rice blast resistance gene Pi-cd in rice (Oryza sativa) breeding programmes

A series of DNA markers for various agronomic traits may accelerate the success of marker-assisted selection in practical plant breeding programmes. Here, we developed DNA markers for the blast resistance gene Pi-cd. In this study, we examined the effects of the Pi-cd locus on not only blast resistance but also agronomic traits in agriculture. We developed three pyramiding lines (PLs) coupling Pi-cd with three blast resistance genes, pi21, Pi35 and Pi39. The effect of Pi-cd on blast resistance was dependent on the coupled resistance genes. Then, we evaluated the effects of Pi-cd on 13 agronomic traits. Amylose content and 1,000-grain weight showed significant differences between the PLs and current commercial varieties, which had no negative effects on agronomic trait values. Furthermore, we investigated the distribution of genotype for the Pi-cd locus among varieties of upland rice. The KT genotype specific to rice blast resistance may be predominant in the varieties. The results suggested that Pi-cd has the potential to be useful for improving blast resistance in rice breeding programmes.     

Faba bean breeding for resistance against biotic stresses: Towards application of marker technology

Summary Faba beans are adversely affected by numerous fungal diseases leading to a steady reduction in the cultivated area in many countries. Major diseases such as Ascochyta blight (Ascochyta fabae), rust (Uromyces viciae-fabae), chocolate spot (Botrytis fabae), downy mildew (Peornospora viciae) and foot rots (Fusarium spp.) are considered to be the major constraints to the crop. Importantly, broomrape (Orobanche crenata), a very aggressive parasitic angiosperm, is the most damaging and widespread enemy along the Mediterranean basin and Northern Africa. Recent mapping studies have allowed the identification of genes and QTLs controlling resistance to some of these diseases. In case of broomrape, 3 QTLs explained more than 70% of the phenotypic variance of the trait. Concerning Ascochyta, two QTLs located in chromosomes 2 and 3 explained 45% of variation. A second population sharing the susceptible parental line also revealed two QTLs, one of them likely sharing chromosomal location and jointly contributing with a similar percentage of the total phenotypic variance. Finally, several RAPD markers linked to a gene determining hypersensitive resistance to race 1 of the rust fungus U. viciae-fabae have also been reported. The aim of this paper is to review the state of the art of gene technology for genetic improvement of faba bean against several important biotic stresses. Special emphasis is given on the application of marker technology, and Quantitative Trait Loci (QTL) analysis for Marker-Assisted Selection (MAS) in the species. Finally, the potential use of genomic tools to facilitate breeding in the species is discussed. The combined approach should expedite the future development of lines and cultivars with multiple disease resistance, one of the top priorities in faba bean research programs.     

利用Mudgo/武育粳3号F2群体分析水稻抗灰飞虱QTL

灰飞虱是我国水稻生产上的重要害虫。Mudgo是一个高抗灰飞虱的籼稻品种,对灰飞虱具有强的排驱性和抗生性抗性。利用Mudgo/武育粳3号F₂群体,构建了含有177个单株的F₂群体的遗传连锁图谱。该连锁图包含104个SSR标记和3个Indel标记,覆盖整个水稻基因组1 409.9 cM,每两个标记之间的平均距离为13.2 cM。采用改进的苗期集团筛选法对177个F_2:3家系进行了抗性鉴定,通过Windows QTL Cartographer 2.5进行复合区间作图分析,在第2、3、12染色体上分别检测到抗灰飞虱QTL Qsbph2b、Qsbph3d和Qsbph12a,分别位于标记RM5791~RM29、RM3199~RM5442和I12-17~RM333 1之间,单个LOD值分别为3.25、3.11和6.82,贡献率分别为17.3%、15.6%和35.8%,各QTL增强抗性的等位基因效应均来自Mudgo。其中Qsbph12a与标记RM3331和I12-17紧密连锁。结合表型鉴定的结果,Qsbph12a应为抗灰飞虱主效QTL,与该位点紧密连锁的标记可用于抗灰飞虱快速选择辅助育种。     

Exploring genetic diversity of rice cultivars for the presence of brown planthopper (BPH) resistance genes and development of SNP marker for Bph18

Brown planthopper (BPH) is the most devastating insect pest in rice‐growing areas. Information on availability of BPH resistance alleles and their sources enhances BPH‐resistant breeding programmes. In this study, 260 highly diversified rice cultivars or breeding lines were screened for the presence of five major BPH resistance genes (Bph10, Bph13, Bph18, Bph20 and Bph21) using gene‐specific markers. The analysis revealed that 137 of the 260 cultivars possess at least one BPH resistance gene. Bph10 was predominant while Bph20 was the least distributed. Moreover, two and three different resistance gene combinations were found in the cultivars. Molecular markers play an important role in molecular breeding programmes. A tightly linked PCR‐based co‐dominant Bph18 marker was developed, which is cost effective and time effective and simpler than available Bph18 CAPS marker (7312.T4A). We strongly believe that the identified BPH‐resistant cultivars can be used as alternative resistance gene sources and also as resource for novel BPH resistance genes. The developed Bph18 marker will be highly useful in molecular breeding applications of BPH‐resistant breeding programmes.     

Evaluation of 'quick and dirty' DNA extraction methods for marker-assisted selection in rice (Oryza sativa L.)

Six simple methods for extracting DNA from rice seedlings were evaluated for marker‐assisted selection (MAS). The assessment of each method was based on PCR amplification of SSR markers, DNA yield and purity, time and cost. Based on these criteria, two methods were selected as being superior to other methods. The best two methods included the standard method developed at the International Rice Research Institute (IRRI), which utilizes a sodium dodecyl sulfate extraction buffer followed by chloroform/isoamyl alcohol extraction and a previously published method using sodium hydroxide and Tris. These two methods produced nearly identical PCR amplification results. The sodium hydroxide method is considerably simpler, quicker and cheaper than the standard IRRI method, and may be particularly useful for many applications of MAS or high‐resolution mapping. This method was also adapted into an effective high throughput method utilizing 96‐well plates emphasizing its versatility.     

水稻单片段替换系群体的建立及QTL分析

农作物大多数性状都是由多基因控制的数量性状，对数量性状基因座(quantitative trait loci，QTL)进行鉴定和定位对作物遗传育种具有重要意义。单片段替换系(single segment substitlationulines，SSSI。)消除了遗传背景的干扰，是用于QTL分析的重要试验材料。本研究以6个水稻品种为供体，利用回交和微卫星标记辅助选择相结合的方法，建立了以华粳籼74为遗传背景的水稻单片段替换系群体，并选用其中的59个单片段替换系对水稻24个重要农艺性状的QTL进行了鉴定；还利用一个单片段替换系的次级分离群体对抽穗期基因Hd-3-1进行了定位。主要试验结果如下：1 对供体亲本苏御糯、IR64、IRAT261、成龙水晶米、Lemont和IAPAR9与华粳籼74之间的微卫星标记多态性进行了检测，6个供体亲本与华粳籼74之间的多态率分别为56．33％、34．93％、59．31％、33．19％、55．90％和56．55％。2 对回交的遗传效应进行了分析，在BC2F1和BC3F1单株中检出替换片段的平均数分别为8．93个和4．37个，在BC2F1和BC3F1单株中检出替换片段的平均长度分别为32．23cM和27．63cM，BG2F1和BC3F1受体亲本基因组的回复率分别为81．55％和92．32％。3 建立了118个以华粳籼74为遗传背景的单片段替换系，其中包括86个不同的单片段替换系。这些单片段替换系分布于水稻12条染色体上，10号染色体上的单片段替换系最多，有16个。单片段替换系中替换片段的平均长度为23．0cM，全部单片段替换系对水稻基因组的覆盖率为57．11％。4 利用59个单片段替换系对水稻24个重要农艺性状的QTL进行了鉴定，总共鉴定出了248个QTL，分别为25个抽穗期QTL、1个有效穗数QTL、13个穗颈长QTL、16个株高QTL、5个穗长QTL、7个倒一节间长QTL、8个倒二节间长QTL、4个倒三节间长QTL、7个倒四节间长QTL、12个剑叶长QTL、22个剑叶宽QTL、13个倒二叶长QTL、14个倒二叶宽QTL、4个倒三叶长QTL、12个倒三叶宽QTL、14个一次枝梗数QTL、2个二次枝梗数QTL、5个总粒数QTL、10个结实率QTL、6个着粒密度QTL、11个粒长QTL、13个粒宽QTL、11个粒形QTL、13个粒重QTL。5 利用替换作图法对一些QTL进行了定位，将其中22个QTL定位在10cM的区段以内。6 利用一个单片段替换系的次级分离群体，将完全显性早熟基因Hd-3-1定位在3号染色体短臂上，微卫星标记PSM304、PSM305和PSM306位于Hd-3-1靠近短臂末端的一侧，与Hd-3-1的遗传距离分别为2．4cM、2．7cM和3．3cM；RM569和RM231位于另一侧，与Hd-3-1的遗传距离分别为5．1cM和8．9cM。本研究建立了单片段替换系的构建和QTL鉴定的试验技术体系，为分子标记技术应用于作物遗传育种提供了新的思路和途径。     

Application of marker‐assisted backcross to introgress Bph3, Bph14 and Bph15 into an elite indica rice variety for improving its resistance to brown planthopper

To improve brown planthopper (Nilaparvata lugens Stål; BPH) resistance of an elite indica cultivar of South China, Hemeizhan (HMZ), we applied marker‐assisted backcross (MABC) to incorporate three BPH‐resistance genes (Bph3, Bph14 and Bph15) into the genetic background of HMZ. In the third backcross (BC₃) generation, we obtained near‐isogenic lines (Bph3‐NIL, Bph14‐NIL, Bph15‐NIL and Bph14 + Bph15‐NIL) with more than 96% recovery of recurrent parent genome, and pyramided lines (Bph3 + Bph14‐PYL, Bph3 + Bph15‐PYL and Bph3 + Bph14 + Bph15‐PYL) with more than 89% recovery of recurrent parent genome. These lines showed stronger resistance against BPH than HMZ at seedling and booting stages. The rank of resistance gene effect was Bph3 + Bph14 + Bph15 ≥ Bph3 + Bph15 ≥ Bph3 +Bph14 ≥ Bph14 + Bph15 ≥ Bph3 ≥ Bph15 ≥ Bph14 > none. Compared with HMZ, only Bph3 + Bph14 + Bph15‐PYL had a significant difference in yield per plant, and the lines carrying Bph3 had higher amylose contents, indicating that Bph3 was tightly linked to Wx^a allele. These improved lines are good intermediate sources of broad‐spectrum and durable BPH resistance to improve other indica cultivars. Our results demonstrate that MABC is a very efficient approach to improve BPH resistance of elite rice cultivar.     

Identification of a RAPD marker linked to a brown planthopper resistance gene in rice

We report the tagging of a brown planthopper (BPH) resistance gene (Bph–1) in rice using RAPD and RFLP markers. The Korean rice variety ‘Gayabyeo’ has dominant duplicate genes including Bph–1 conferring resistance to biotype 1 of BPH. Bulked segregant RAPD analysis was employed for rapid identification of DNA markers linked to resistance genes. For tagging these two genes, an F2F3 population from a ‘Gayabyeo’ × ‘Nagdongbyeo’ cross was developed and evaluated for BPH resistance. Three bulked DNAs from two groups of homozygous BPH resistant (each for Bph–1 and the other unknown gene) and homozygous susceptible F2 plants were analyzed by RAPD using 140 random oligomers. One primer, OPD–7 yielded a 700-bp fragment that was present in Gayabyeo and resistant F2 plants (homozygous for Bph-1 locus) but absent in Nagdongbyeo and susceptible F2 plants. Cosegregation of this marker with Bph-1 was verified using an F2 population segregating for Bph-1. Chromosomal regions surrounding the Bph-1 were examined with additional RFLP and microsatellite markers on chromosome 12 to define the location of the RAPD marker and Bph-1. Use of this RAPD marker could facilitate early selection of resistant lines for BPH. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mapping of quantitative trait loci associated with rice black‐streaked dwarf virus disease and its insect vector in rice (Oryza sativa L.)

Rice black‐streaked dwarf virus disease (RBSDVD), transmitted by small brown planthopper (SBPH, Laodelphax striatellus), causes serious loss in rice production. Breeding resistant cultivars are one of the most effective strategies to control the virus disease and its vector. By both natural inoculations in the field and modified seedling‐box screening test in the glasshouse, an indica variety WR24 showed high resistance to RBSDVD and SBPH. An F_2:3 population consisting of 153 lines derived from a cross between WR24 and a susceptible japonica variety Suyunuo was used for quantitative trait loci (QTL) analysis of RBSDVD and SBPH resistance. The linkage map consisting of 130 SSR markers was constructed with an average marker interval of 13.90 cM, spanning a total of 1890.9 cM. Totally, five QTLs for RBSDV resistance, viz. qRBSDV3^WR24, qRBSDV6^WR24, qRBSDV7^WR24, qRBSDV9^WR24 and qRBSDV11^WR24, were detected on chromosomes 3, 6, 7, 9 and 11, with LOD scores of 2.7, 3.08, 3.13, 5.28 and 3.7, respectively. Meanwhile, three QTLs for SBPH resistance, including qSBPH5^WR24, qSBPH7^WR24 and qSBPH10^WR24, were mapped on chromosomes 5, 7 and 10, with LOD scores of 2.18, 3.5 and 3.57, respectively. All resistant alleles were from WR24. Among these QTLs, qRBSDV7^WR24, qSBPH5^WR24 and qSBPH10^WR24 were newly reported, and qSBPH10^WR24 showed major effect that explained 17.9% of total phenotypic variance. The RBSDVD and SBPH resistance QTLs and the tightly linked DNA markers can be utilized in RBSDV and SBPH resistance breeding in rice.     

Genetic progress of upland rice (Oryza sativa L.) lines for disease resistance

The rice crop is affected by diseases throughout its cycle, impacting negatively on grain yield and quality. The control of the disease impact can be accomplished via crop breeding, using highly multiple resistant genotypes. This study aimed to evaluate the efficiency of multiple-character and specific selection of multiple resistance to major culture-associated diseases (neck blast, leaf scald and grain discoloration) in rice lines of the Upland Rice Genetic Breeding Program. The experiments were conducted in 35 sites during 12 agricultural years, where 124 lines were evaluated for the severity of fungal diseases, under natural field conditions. Multiple parameters were calculated based on the diseases´ scores: genetic, phenotypic and environmental variances, heritability, selection gain, renewal rate, and genetic and renewal progress. Genetic variance for the disease resistance was identified in the population, and the selection gain for multiple-character selection was of 3.16 year⁻¹ throughout the breeding process with a renewal rate of over 35%. The programme has showed efficiency in selecting multiple resistant genotypes to the mentioned diseases, highlighting genotypes with high potential for market release.     

QTL analysis for resistance to preharvest sprouting in rice (Oryza sativa)

Preharvest sprouting (PHS) is caused by early breaking of seed dormancy. In Sichuan, a major hybrid rice seed production area of China, PHS in hybrid seeds originated from ‘G46A’ parent may lead to severe yield loss, causing serious damage to agricultural production. To detect quantitative trait loci (QTLs) governing PHS, we developed an F₂ population of 164 plants derived from ‘G46B’ and ‘K81’, a near‐isogenic introgression line of G46B, with high level of resistance to PHS. PHS was evaluated under controlled field and laboratory conditions. Using simple sequence repeat markers, we constructed a linkage map from this population and identified three QTLs for PHS, namely qPSR2, qPSR5 and qPSR8, which were located on chromosomes 2, 5 and 8, respectively. Among these QTLs, qPSR8, residing in the interval between RM447 and RM3754 on chromosome 8, was the major QTL controlling PHS, for it had a relative high logarithm of the odds (LOD) score and explained 43.04% of the phenotypic variation. These results were correspondent to those identified in extreme low germination rate plants (ELGP) using linkage and linkage disequilibrium. At all loci, ‘K81’ was responsible for enhancing the resistance to PHS.     

Mutation of DEP1 facilitates the improvement of plant architecture in Xian rice (Oryza sativa)

Plant architecture is a complex trait and has a profound impact on crop performance and productivity. We applied the CRISPR/Cas9 system to mutate the DEP1 gene, which has been reported to function as regulator of plant architecture, in elite Xian cultivar ‘Huhan1509’. Sequencing analysis of T₀ transformed plants showed that the CRISPR/Cas9 system was highly efficient in mutagenesis of targeted DEP1 gene, with 30% of the homozygous mutations and 70% of the heterozygous mutations. T₂ homozygous mutants without T-DNA were further examined for the agronomic traits. The DEP1 mutants exhibited an altered plant architecture along with a shorter plant height and grain size and increased spikelets and grain density. Furthermore, phenotypes of raising primary branches and stem diameters were observed in the DEP1 mutants. Our results demonstrate that favourable alleles of the DEP1 gene, developed by CRISPR/Cas9 system, could be used to improve plant architecture in Xian rice.