Resistance Performance to Whitebacked Planthopper in Different Phenotypes of Japonica/Indica Doubled Haploid Rice Lines

Field performance of whitebacked planthopper （WBPH）-resistance of four phenotypes was evaluated in Chunjiang 06 （C J-06） / TN1 DH rice lines, which were expressed by different combinations of sucking inhibitory and ovicidal traits inherited independently from C J-06. WBPH established the highest populations in susceptible DH lines that had neither sucking inhibitorynor ovicidal resistance. Both immigration and subsequent population levels were kept below the damage-causing density in the sucking inhibitory DH lines even under a WBPH outbreak. WBPH could not build up populations in the DH lines having both the sucking inhibitory and ovicidal resistance. Although WBPH immigrated preferentially to non-sucking inhibitory DH lines with ovicidal resistance, subsequent population buildup was significantly suppressed. It was concluded that the differential performance to WBPH-resistance in CJ-06 / TN1 DH lines was primarily due to the sucking inhibitory trait, and complementarity to the ovicidal trait.     

Differential Expression of Whitebacked Planthopper Resistance in the japonicaJindica Doubled Haploid Rice Population under Field Evaluation and Seedbox Screening Test

Whitebacked planthopper (WBPH) -resistance in a japonica / indica doubled haploid (DH) rice population established from a cross between WBPH-resistant japonica Chunjiang 06 and susceptible indica TN1, was comparatively evaluated through a field experiment based on the WBPH immigrant density and standardized seedbox screening test (SSST). All the susceptible DH lines in the field experiment behaved accordingly in SSST. However, 35 of resistant 66 lines (53%) in the field, were categorized to susceptible groups in SSST. Likewise, there were no significant differences in WBPH immigrant densities among 70 DH lines that were highly resistant to susceptible in SSST. The results revealed that SSST could not evaluate properly WBPH resistance in the DH lines. Four QTLs for WBPH-resistance phenotyped by the immigrant density were detected on chromosomes 2, 3, 4, and 11. Of them, the QTL on chromosome 4 was the most effective (LOD 21.8, variance 78%). Five QTLs associated with seedling mortality were mapped on chromosomes 2, 3, 4, 5 and 6. In addition to the QTL (LOD 10.5, variance 68%) on chromosome 4, there was another major QTL (LOD 12.7, variance 71%) located on chromosome 5, which was SSST-specific but might be irrespective of the WBPH resistance traits.     

Differential Expression of Whitebacked Planthopper Resistance in the japonica/indica Doubled Haploid Rice Population under Field Evaluation and Seedbox Screening Test

Whitebacked planthopper (WBPH) -resistance in a japonica / indica doubled haploid (DH) rice population established from a cross between WBPH-resistant japonica Chun]iang 06 and susceptible indica TN1, was comparatively evaluated through a field experiment based on the WBPH immigrant density and standardized seedbox screening test (SSST). All the susceptible DH lines in the field experiment behaved accordingly in SSST. However, 35 of resistant 66 lines (53%) in the field, were categorized to susceptible groups in SSST. Likewise, there were no significant differences in WBPH immigrant densities among 70 DH lines that were highly resistant to susceptible in SSST. The results revealed that SSST could not evaluate properly WBPH resistance in the DH lines. Four QTLs for WBPH-resistance phenotyped by the immigrant density were detected on chromosomes 2, 3, 4, and 11. Of them, the QTL on chromosome 4 was the most effective (LOD 21.8, variance 78%). Five QTLs associated with seedling mortality were mapped on chromosomes 2, 3, 4, 5 and 6. In addition to the QTL (LOD 10.5, variance 68%) on chromosome 4, there was another major QTL (LOD 12.7, variance 71%) located on chromosome 5, which was SSST-specific but might be irrespective of the WBPH resistance traits.     

Mapping of putative sucking inhibitory gene to whitebacked planthopper by linkage analysis with CAPS markers

Resistance to whitebacked planthopper (WBPH) in Chinese japonica rice Chunjiang 06 (CJ-06) was mediated by sucking inhibitory and ovicidal mechanism. The ovicidal reponse was a common self-defense mechanism against WBPH in japonica. The ovicidal gene and its chromosomal position had already been identified. The sucking inhibitory nature of CJ-06 caused a define non-preference behavior of WBPH in fields. A single dominant gene governed the sucking inhibition in CJ-06.     

Quantitative Trait Loci for Resistance to Stripe Disease in Rice （Oryza sativa）

In order to map the quantitative trait loci for rice stripe resistance, a molecular linkage map was constructed based on the F2 population derived from a cross between Zhaiyeqing 8 and Wuyujing 3. Reactions of the two parents, F1 individual and 129 F2:3 lines to rice stripe were investigated by both artificial inoculation at laboratory and natural infection in the field, and the ratios of disease rating index were scored. The distribution of the ratios of disease rating index in Zhaiyeqing 8/Wuyujing 3 F2:3 population ranged from 0 to 134.08 and from 6.25 to 133.6 under artificial inoculation at laboratory and natural infection in the field, respectively, and showed a marked bias towards resistant parent (Zhaiyeqing 8), indicating that the resistance to rice stripe was controlled by quantitative trait loci (QTL). QTL analysis showed that the QTLs detected by the two inoculation methods were completely different. Only one QTL, qSTV7, was detected under artificial inoculation, at which the Zhaiyeqing 8 allele increased the resistance to rice stripe, while two QTLs, qSTV5 and qSTV1, were detected under natural infection, in which resistant alleles came from Zhaiyeqing 8 and Wuyujing 3, respectively. These results showed that resistant parent Zhaiyeqing 8 carried the alleles associated with the resistance to rice stripe virus and the small brown planthopper, and susceptible parent Wuyujing 3 also carried the resistant allele to rice stripe virus. In comparison with the results previously reported, QTLs detected in the study were new resistant genes to rice stripe disease. This will provide a new resistant resource for avoiding genetic vulnerability for single utilization of the resistant gene Stvb-i.     

Identification and Genetic Analysis of Gall Midge Resistance in Rice Germplasm 91-1A2

Resistance to rice gall midge in rice germplasm 91-1A2 was identified and genetically analyzed. F1s of rice population were derived from 91-1A2 which crossed with rice materials Jinggui, TN1, W1263 (Gm1), IET2911 (Gm2), BG404-1 (gm3), OB677 (Gm4), ARC5984 (Gm5) and Duokang 1 (Gm6) as a male parent. The resistance of all parental lines and F1, BC1F1 and F2 populations to rice gall midge was identified. The results showed that 91-1A2 and all F1s were resistant to Chinese rice gall midge biotype IV. The segregation ratio of resistant plants to susceptible ones in BC1F1 and F2 were accorded with 1:3 and 9:7 rules by χ2 test, suggesting that the resistance of 91-1A2 to Chinese rice gall midge biotype IV was controlled by two dominant genes which were new resistance genes, non-allelic to the known rice gall midge resistance genes.     

Inheritance and QTL Mapping of Salt Tolerance in Rice

An F2 population derived from the cross between Jiucaiqing (japonica) and IR36 (indica) was used to analyze the inheritance of salt tolerance in rice by genetic model of major-genes plus polygenes, and to map the corresponding QTLs by SSR molecular markers. Rice plants of P1, P2, F1 and F2 at 5- to 6- leaf stage were treated under 140 mmol/L NaCI for 10 days. Three indices representing the ability of salt tolerance of rice seedlings were measured, including salt tolerance rating (STR), Na^ /K^ ratio in roots and dry matter weight of shoots (DWS). STR, Na^ /K^ and DWS were all controlled by two major genes with modification by polygenes. Heritability of these traits from major genes was 17.8, 53.3 and 52.3%, respectively. The linkage map constructed by 62 SSR molecular markers covered a total length of about 1 142 cM. There were three QTLs detected for STR located on chromosome 1, 5 and 9, two QTLs for DWS on chromosomes 8 and 9, and two QTLs for Na^ /K^ on chromosomes 2 and 6, one on each chromosome respectively. Single QTL accounted for 6.7 to 19.3% of phenotypic variation. Identification method of salt tolerance in rice and breeding of rice varieties with salt tolerance based on molecular markers assisted selection had been discussed.     

Use of Major Quantitative Trait Loci to Improve Grain Yield of Rice

Further improvement of rice productivity remains a challenge. Breeding is perceived as an important option to increase rice yield. However, the genetic progress of grain yield in most rice breeding programs was slow in the last decades. Although great progress in rice genomics and molecular biology has been achieved, the effect of such technological innovations on rice breeding is far small. Marker-assisted selection （MAS） for a few target quantitative trait loci （QTLs） has significant effects in improving qualitative traits, such as disease resistance. The success of MAS has therefore motivated breeders to identify and use major QTLs for yield and yield component traits. In this review, we summarized the recent methods in QTL identification, including novel statistical methods for linkage and association mapping, special population types, and whole-genome sequencing. We reviewed the successful application of marker-assisted gene introgression and gene pyramiding to improve grain yield and discussed the design of efficient MAS schemes to further increase the success rate of breeding programs. The use of well-characterized major QTLs through introgression and gene pyramiding is proven effective in improving grain yield, particularly yield under abiotic stress. Major QTLs that are stable across genetic background and growing environments are often found in less adapted germplasms, such as landraces and wild relatives. Advanced backcross QTL analysis and introgression lines, which integrate QTL discovery and utilization, are important methods for exploiting major QTLs contained in such germplasms. Next-generation sequencing substantially increases mapping resolution and accelerates the identification of casual genes underlying major QTLs. Practical guidelines derived from theoretical and empirical studies are given to guide the design of efficient marker-assisted gene introgression and pyramiding schemes.     

Osa-mi R439 Negatively Regulates Rice Immunity Against Magnaporthe oryzae

Osa-miR439 is a rice-specific microRNA family. Here we showed that Osa-miR439 acted as anegative regulator in rice immunity against blast fungus Magnaporthe oryzae. Osa-miR439 differentiallyresponded to M. oryzae between susceptible and resistant rice accessions. The accumulation ofOsa-miR439 was constitutively more in the susceptible accession than in the resistant one. Transgeniclines overexpressing Osa-miR439a (OX439a) showed higher susceptibility associating with lower inductionof defense-related genes and less hydrogen peroxide (H2O2) accumulation at the infection sites than thecontrol plants. In contrast, transgenic lines expressing a target mimic of Osa-miR439 (MIM439) displayedcompromised susceptibility associating with increased H2O2 accumulation. Furthermore, we found thatthe expression of three predicted target genes was decreased in OX439a but increased in MIM439 incomparison to control plants, and this expression was differential in susceptible and resistant accessionsupon M. oryzae infection, indicating that Osa-miR439a may regulate rice blast resistance via these genes.Our results unveiled the role of Osa-miR439a in rice blast resistance and provided the potentiality toimprove the blast resistance via miRNA.     

Susceptibility to Insecticides and Ecological Fitness in Resistant Rice Varieties of Field Nilaparvata lugens Stl Population Free from Insecticides in Laboratory

A population of rice brown planthopper(BPH) Nilaparvata lugens collected from a paddy field in Hangzhou was successively reared on susceptible rice Taichung Native 1(TN1) in a laboratory free from insecticides for more than 14 generations. The changes in susceptibility to insecticides and ecological fitness on different resistant rice varieties were monitored in each generation. The resistance ratio to imidacloprid sharply declined with the succession of rearing generations without insecticides from 359.94-fold at F1 to 6.50-fold at F14 compared with the susceptible strain, and the resistance ratio to chlorpyrifos was from 9.90-fold at F1 to 5.94-fold at F14. Nymphal duration and weights of newly hatched female adults were significantly affected by rice variety, generation and their interactions, but nymphal survival was significantly affected by the generation only. The ratio of brachypterous adults in males was affected by the generation and generation × variety interaction, whereas no difference was found in females. Nymphal duration extended with increasing generations, and the female nymphal duration was shorter in the susceptible variety TN1 than those in the resistant varieties IR26 and IR36. In addition, the female adult weight in TN1 was higher than those in IR26 and IR36. These results indicated that the resistance of field BPH population to insecticides was reversed after several generations of no-exposure to insecticides, and the ecological fitness in TN1 was higher than those in IR26 and IR36. These findings suggested the rational and reduced use of insecticides in combination with the manipulation of resistant rice varieties would be effective for BPH management.     

Phenotypic Expression of Whitebacked Planthopper Resistance in the Newly Established japonica / indica Doubled Haploid Rice Population

A new doubled haploid (DH) rice population was established from a cross between WBPH-resistant japonica Chunjiang 06 (C J-06) and susceptible indica TN1. Sucking inhibitory and ovicidal resistance of the DH rice lines were evaluated on the basis of non-preference response of WBPH immigrants and honeydew excretion by WBPH females, and appearance of watery lesions in the necrotic discoloration of leaf sheaths ovipositied by WBPH,respectively. Both the major gene resistance to WBPH, sucking inhibitory and ovicidal resistance, showed 1 (resistant): 1 (susceptible) segregation ratio in the DH population. Relative density of WBPH populations and damage scores in the DH population indicated combined functions of both the major resistance genes as well as QTLs affecting the host plant response to WBPH infestations. Thus, the newly developed CJ-06/TN1 DH population could be a useful material to analyze major genes and QTLs for WBPH resistance in japonica rice.     

中国粳稻春江06抗白背飞虱的遗传

分析了高抗白背飞虱、对白背飞虱的抗性表现为拒取食性和杀卵作用的中国粳稻春江06和感虫籼稻品种TN1正反交获得的F1和F2代拒取食性和杀卵作用的遗传方式.所有的F1稻株都具有拒取食和杀卵作用.两种抗性在F2代中以3∶1的抗感比例独立分离. 具有拒取食和杀卵抗性的不同组合的4种表现型以9∶3∶3∶1分离.表型分离说明春江06中的拒取食性和杀卵抗性分别受一个显性基因控制.采用常规的杂交方法可以容易地将春江06中的拒取食抗性导入日本粳稻品种日本晴、北陆-153和越光中.     

水稻籼粳交DH群体中影响白背飞虱抗虫性QTL的检测

分析了水稻籼粳交加倍单倍体(DH)群体中影响白背飞虱抗虫性和感虫性的QTL.虽然DH株系的亲本窄叶青8号和京系17没有拒取食抗性,但是白背飞虱在6个DH株系中的取食受到了强烈的抑制,可能属超亲分离.在第3染色体的粳型片段中检测到1个影响蜜露分泌的微效QTL.粳稻亲本京系17具有杀卵抗性.DH株系中的杀卵特性是通过叶鞘上杀卵反应产生的坏死症状表现的.在DH株系分蘖早期和中期,将4个杀卵作用的QTL定位在第1、2、6和8染色体的粳型片段上.出现在分蘖中期的另一个QTL被定位在第9染色体的籼型片段上.在分蘖盛期至孕穗期,杀卵位点减少至2个.整个试验期间对每个DH株系的最高杀卵级别的分析显示,在染色体2、6和9上共有4个QTL.两个主效QTL位于近邻第6染色体的粳型片段.在第1、3和5染色体上检测到3个影响第2代白背飞虱若虫密度的QTL.第3染色体上起主要作用的QTL源自粳稻亲本;第5染色体上的微效QTL源自籼稻亲本.两个白背飞虱为害的QTL位于第8和第10染色体的籼型片段,另一个QTL位于第3染色体的粳型片段.这些QTL被认为与水稻品种对白背飞虱田间抗性表达有关.     

中国粳稻春江06抗白背飞虱的系谱分析

对中国粳稻春江06的抗白背飞虱特性进行系谱分析表明,春江06对白背飞虱的拒取食和杀卵抗性均来源于秀水620.秀水620的亲本中,只有秀水04具有较强的拒取食抗性,但没有杀卵抗性.在祥湖24中检测到明显的杀卵反应.亲本秀水04、单209和辐农709具有拒取食抗性,但测21没有.单209和辐农709的共同亲本农虎6号也具有拒取食抗性.然而,农虎6号、农垦58(日本粳稻)和老虎稻(中国粳稻地方品种)不具有拒取食抗性,在田间表现出感虫性.农虎6号、单209、辐农709和秀水04表现出稳定的田间抗性.春江06育种中的两个籼稻品种IR26和IR28高感白背飞虱,既无拒取食抗性,也无杀卵作用.     

中国粳稻品种春江06的抗白背飞虱机理

与感虫杂交稻汕优63相比较,研究了具有抗性的中国粳稻春江06对白背飞虱的抗性.结果表明,春江06高抗白背飞虱.迁入的白背飞虱拒绝在春江06上着陆,也不能在其上繁殖种群;而白背飞虱更趋向于在汕优63上定居,并繁殖良好.在自由选择的试验条件下,选择春江06的白背飞虱数量显著地低于选择汕优63的.白背飞虱在春江06上平均每天每只雌成虫分泌的蜜露量仅为4.8 mg,而在汕优63上为17.4 mg,表明春江06明显抑制白背飞虱的取食活动.如果让刚羽化的白背飞虱在春江06上连续取食和产卵的话,其产卵能力和卵孵化能力明显降低.白背飞虱在春江06和汕优63上的平均产卵量分别为每只雌成虫42.4个和133.6个,孵化率分别为20.1%和64.5%;在春江06上孵化出的若虫数量只有在汕优63上的10%左右.白背飞虱卵在春江06的水渍状产卵部位有很高的死亡率.在卵孵化之前,水渍状褐变部位迅速形成坏死症状.卵死亡出现在产卵后的1～2 d内.这样的水渍状褐变则极少发生在卵孵化正常的汕优63上.根据以上的发现,可总结出在春江06对白背飞虱的抗性中,抑制取食和杀卵作用是关键的因素.这些作用分别与对迁入白背飞虱的忌避性机理、与居留型白背飞虱产卵能力和卵孵化能力下降的抗生性机理相关.这种品种抗虫性的双抗机理使得粳稻品种春江06具有了稳定和持久的田间抗虫性.     

水稻籼粳交DH群体白叶枯病抗性的QTL定位

以中抗白叶枯病的粳稻品种春江06、感病品种TN1及其DH群体为材料,接种白叶枯病菌浙173后,考察了该DH群体的白叶枯病抗性,并进行了数量性状座位(QTL)分析。共检测到控制白叶枯病的3个QTL（qBBR1、qBBR3 1和qBBR7）,分别位于第1、3和第7染色体上,其中第3染色体上的qBBR3 1和第7染色体上的qBBR7加性效应为正值;而位于第1染色体上的qBBR1为负值,3个QTL的总效应达54.4%。春江06中不存在白叶枯病抗性主基因,它的抗性由微效多基因控制,其中在第3和第7染色体上分别有1个QTL。     

水稻抗恶苗病微效QTL的定位

对粳稻品种春江06和籼稻品种TN1以及由它们构建的加倍单倍体（DH）群体,采用芽期接菌方法接种恶苗病菌,进行抗恶苗病微效QTL的定位分析。共检测到2个QTL:qB1和qB10,分别位于第1和第10染色体上,2个QTL的抗性基因都来自春江06,贡献率相近。     

Mapping of putative sucking inhibitory gene to whitebacked planthopper by linkage analysis with CAPS markers

Resistance to whitebacked planthopper (WBPH) in Chinese japonica rice Chunjiang 06 (CJ-06) was mediated by sucking inhibitory and ovicidal mechanism.