Influence of different inoculation methods on the evaluation of the resistance to rice sheath blight(Rhizoctonia solani Kuhn)

To establish a standard system for geneticstudies on sheath blight resistance, a field testwas conducted at the experimental farm ofYangzhou University to compare several pro-cedures for inoculating rice plants with R.solani Kuhn (RH9). The varieties used wereJasmine 85, Teqing (resistant or moderatelyresistant), and Lemont (susceptible). They

Verification test on an innovated method for the studies on inheritance of resistance to rice sheath blight

We have recently developed a systematic method for the study on the inheritance of resistance to sheath blight. The key of the system is an innovated method of inoculation and investigation along with the employment of the permanent population. This paper reported the procedure of the system and the result of its verification.

Advances in Mapping Loci Conferring Resistance to Rice Sheath Blight and Mining Rhizoctonia solani Resistant Resources

Sheath blight （SB） caused by Rhizoctonia solani is one of the three major diseases of rice, and now has become the most severe disease causing rice yield loss in China. Breeding and use of varieties resistant to SB is crucial in controlling the disease, but the advances achieved have been limited due to the tack of highly SB-resistant rice germplasm. Genetic analysis revealed that the SB resistance in rice was a typical quantitative trait controlled by multi-genes. Although many QTLs conferring resistance to SB have been identified in recent years, most of the QTLs only showed small effects and few of them have been evaluated for utilization potential. Many R. solani-resistant resources have been found in wild rice species, microorganisms and other plant species. It is already known that the SB-resistance could be improved in transgenic rice plants by genetic transformation. This paper reviewed the genetic mapping of loci associated with resistance to rice SB, the evaluation of the potential of resistance QTLs, and the resistant resources found in various organisms besides rice. To develop SB-resistant rice varieties, it is important to develop and explore new resistant rice germplasms, fine map and evaluate resistance QTLs, and also to pay attention to various bio-resources showing resistance to R. solani.

Characteristics of Resistance to Rice Sheath Blight of Zhongda 2,a Transgenic Rice Line as Modified by Gene “RC24”

The transgenic rice, Zhongda 2, which was genetically modified from an indica rice line Zhuxian B by rice chitinase gene (RC24), had high resistance to rice sheath blight (Rhizoctonia solan!) in laboratory and a two-year field experiment. The pathogen could invade sheath of Zhongda 2 and induce symptoms of the disease. No difference was noted in time of penetration or incubation period between Zhongda 2 and non-transgenic rice control, Zhuxian B, but the hyphae lysate could be observed earlier than control. Its resistance expressed as to inhibit the growth of mycelium in host tissue. Fis from Zhongda 2(4) crossed with other five non-transgenic rice lines showed higher resistance than donor non-transgenic parents, but the resistance was different along with the different maternal parents.

Effect of Morphological Traits on Sheath Blight Resistance in Rice

Sheath blight, caused by the Rhizoctonia solani Kuhn, is one of the most serious diseases of rice (Oryza sativa L.). The relationship between morphological traits and sheath blight resistance was investigated in 1999 and 2000 by using a segregant population consisting of 240 inbred recombination lines, derived from an elite combination of Zhenshan 97 X Minghui 63. Partial correlation analysis between phenotypic data (morphological characteristics and heading date (HD)) and sheath blight ratings (SBR) showed that only one trait, plant compactness, was significantly correlated with resistance to sheath blight in both 1999 and 2000, eight traits, such as plant height, heading date, and penultimate leaf angle, were significantly correlated with SBR in either of the two years, and the remaining 10 morphological traits were not consistently associated with SBR in the two years. A major quantitative trait locus (QTL) controlling plant compactness was found to be in the site on chromosome 9 adjacent to the region responsible for qSB9, a major QTLs conferring sheath blight resistance. One out of the three QTLs contributing to a penultimate leaf angle was mapped approximately on the same region as another sheath blight resistance QTL, qSB5, located on chromosome 5. Whereas, no QTLs underlying most other traits was detected on the chromosomal region correlated with sheath blight resistance QTL. The results in the present study suggested that the morphological traits were not the main factors responsible for the SBR separation among the recombinant inbred lines (RILs) population. Nevertheless, some morphological characteristics had some indirect influence on expression of sheath blight resistance genes through altering a microclimate on paddy field so as to influence the infection of the pathogen and development of the disease. An efficient approach in resistance breeding to sheath blight was recommended by pyramiding major QTLs for sheath blight resistance and selecting those morphological traits that favor resistance gene expression.

Mapping QTLs Associated with Sheath Blight Resistance Using Chromosome Segment Substitution Lines of Rice(Oryza sativa L.)

In this study, a population of 119 chromosome segment substitution lines （CSSLs） derived from backcross between indica 9311 and japonica Nipponbare was employed to map quantitative trait loci （QTL） associated with sheath blight resis-tance in rice with toothpick inoculation method. A total of three sheath blight resis-tance-associated QTLs （qsb8-1, qsb8-2 and qsb8-3） were identified, which were lo-cated on adjacent molecular markers RM3262, RM5485 and RM3496 of chromo-some 8; the genetic interval was 81.7cM-91.7cM, 91.7cM-108.1cM and 108.1cM-119.6cM, respectively. The additive effect of qsb8-2 was negative, indicating that sheath blight resistance of susceptible parent harboring qsb8-2 fragment was en-hanced; additive effects of qsb8-1 and qsb8-3 were positive, indicating that sheath blight resistance of susceptible parent harboring qsb8-1 and qsb8-3 fragments was reduced.

Resistance Evaluation to Sheath Blight in Transgenic Rice Lines

Resistance of forty-one homozygous rice lines transformed with chitinase gene (RC24) and β-1,3 -glucanse gene β-1,3-Glu) to sheath blight was analyzed by inoculation. Among different lines, the resistance had significant differences according to the result by cluster analysis. The lines could be categorized into resistant, moderately resistant, moderately susceptible and susceptible types, while 92.1% of which belonging to moderately resistant or moderately susceptible type. For different resistant or susceptible lines, the resistance to rice sheath blight was remarkable correlated with the chitinase activity of transgenic lines except resistant type lines, in which enzyme activity coded by target gene was lower than moderately resistant type. The chitinase activity of transgenic lines tested at different time after inoculation or different organs of the same plant was uniform, which suggested that the expression of chitinase gene was constitutive in nature. Check varieties chitinase activity would change at different time after inoculation and reach a peak at sometime, but it had no difference at various pans of the same plant.

Breeding of Selectable Marker-Free Transgenic Rice Lines Containing AP1 Gene with Enhanced Disease Resistance

In order to obtain marker-free transgenic rice with improved disease resistance, the AP1 gene of Capsicum annuum and hygromycin-resistance gene （HPT） were cloned into the two separate T-DNA regions of the binary vector pSB130, respectively, and introduced into the calli derived from the immature seeds of two elite japonica rice varieties, Guangling Xiangjing and Wuxiangjing 9, mediated by Agrobacterium-mediated transformation. Many cotransgenic rice lines containing both the AP1 gene and the marker gene were regenerated and the integration of both transgenes in the transgenic rice plants was confirmed by either PCR or Southern blotting technique. Several selectable marker-free transgenic rice plants were subsequently obtained from the progeny of the cotransformants, and confirmed by both PCR and Southern blotting analysis. These transgenic rice lines were tested in the field and their resistance to disease was carefully investigated, the results showed that after inoculation the resistance to either bacterial blight or sheath blight of the selected transgenic lines was improved when compared with those of wild type.

Identification of Stable Quantitative Trait Loci for Sheath Blight Resistance Using Recombinant Inbred Line

To identify stable quantitative trait loci(QTLs)responsible for sheath blight resistance,a recombinant inbred line mapping population consisting of 219 lines was developed by crossing Lemont and Yangdao 4.Average disease rating,average lesion length,maximum disease rating and maximum lesion length were assayed in six different environments.A total of 128 minor effect QTLs were detected by multiple interval mapping.These QTLs explained less than 11.2%of the phenotypic variations individually,and 106 QTLs were clustered in 20 QTL-rich regions/putative loci.Significant QTL×environment interactions were detected at three putative loci(qSBR11.1,qSBR11.2 and qSBR11.3),indicating that these three loci were not stable.The other 17 stable loci(qSBR1.1,qSBR1.2,qSBR2.1,qSBR2.3,qSBR3.1,qSBR3.2,qSBR3.5,qSBR3.6,qSBR5.1,qSBR7.1,qSBR8.1,qSBR9.1,qSBR9.2,qSBR9.3,qSBR12.1,qSBR12.2 and qSBR12.4)provided a foundation for marker-assisted selection in breeding.Analysis of allelic effect on the 20 putative loci identified 7 highly stable loci,including qSBR3.2,qSBR7.1,qSBR8.1,qSBR9.2,qSBR9.3,qSBR12.1 and qSBR12.2.

Study on Exogenous Ethylene Induced Rice Resistance to Rhizoctonia solani

Rice sheath blight is one of the main diseases in rice production in China,which can make rice unable to absorb and utilize nutrients,and has a serious impact on rice yield and quality.In this study,exogenous ethylene was used to induce rice resistance against rice sheath blight,aiming at exploring a new environment-friendly control method of rice sheath blight.The results showed that within a range of certain concentrations,ethylene had no significant effects on mycelium growth,but it could induce resistance to sheath blight in rice.The optimum concentration was 0.2 mmol•L^(-1) and the relative control was 86.17%.It was found that ethylene could effectively increase the activities of peroxidase(POD),phenylalanine ammonia-lyase(PAL),β-1,3-glucanase and reduce the contents of malondialdehyde(MDA),which could enhance the resistance of rice against Rhizoctonia solani.In addition,qRT-PCR detected the expressions of rice defense genes,which indicated that the expressions of the POX,PAL and OsPR1b genes were up-regulated.

Prospect of the QTL-qSB-9^(Tq) utilized in molecular breeding program of japonica rice against sheath blight

The major QTL-qSB-9^Tq conferring partial resistance to rice （Oryza sativa L.） sheath blight （Rhizoctonia solani Kvhn） has been verified on chromosome 9 of the indica rice cultivar, Teqing. In this study, the prospect of this QTL utilized in molecular breeding program of japonica rice for sheath blight resistance was investigated. Most of the japonica rice cultivars showed lower level of sheath blight resistance than the indica rice cultivars. At the corresponding site of qSB-9^Tq, nine typical japonica rice cultivars from different ecological regions or countries proved to possess the susceptible allele（s）. Introgression of qSB-9^Tq into these cultivars enhanced their resistance level by decreasing sheath blight score of 1.0 （0.5-1.3）, which indicated that qSB-9^Tq had a large potential in strengthening the resistance of japonica rice to sheath blight. The use of the three molecular markers, which were polymorphic between Teqing and many japonica rice cultivars, promotes the application of qSB-9^Tq in a concrete molecular breeding program.

Comprehensive Characteristics of MicroRNA Expression Profile Conferring to Rhizoctonia solani in Rice

MicroRNAs(miRNAs)are about 22 nucleotides regulatory non-coding RNAs that play versatile roles in reprogramming plant responses to biotic and abiotic stresses.However,it remains unknown whether miRNAs confer the resistance to necrotrophic fungus Rhizoctonia solani in rice.To investigate whether miRNAs regulate the resistance to R.solani,we constructed 12 small RNA libraries from susceptible and resistant rice cultivars treated with water/pathogen at 5 h post inoculation(hpi),10 hpi and 20 hpi,respectively.By taking the advantage of next-generation sequencing,we totally collected 400–450 known miRNAs and 450–620 novel miRNAs from the libraries.Expression analysis of miRNAs demonstrated different patterns for known and novel miRNAs upon R.solani challenge.Thirty-four miRNA families were identified to be expressed specifically in rice,and most of them were involved in plant disease resistance.A particular Kyoto Encyclopedia of Genes and Genomes(KEGG)pathway analysis result revealed that a great majority of target genes of regulated miRNAs belonged to the pathway of plant-pathogen interaction.Moreover,miR444b.2,miR531a,mir1861i,novel_miR1956 and novel_miR135 conferred response to R.solani infection confirmed by Northern blot.Our global understanding of miRNA profiling revealed that the regulation of miRNAs may be implicated in the control of rice immunity to R.solani.Analysis of the expression of miRNAs will offer the community with a direction to generate appropriate strategies for controlling rice sheath blight disease.

Characterization of a Novel Weak Allele of RGA1/D1 and Its Potential Application in Rice Breeding

Semi-dwarfing improves the lodging resistance and yield of rice,and the vast majority of modern rice varieties harbor the sd1 allele to decrease plant height,resulting in reduced genetic diversity and negative agronomic traits.Thus,exploring alternative sources of dwarfism is imperative for rice breeding.Here,we identified a novel RGA1 allele,d1-w,from a local indica variety Xiaolixiang(XLX)using a map-based cloning approach.Compared with other rice varieties,RGA1 in XLX contained a unique single nucleotide polymorphism that resulted in an additional transcript and reduced functional RGA1 transcript level.The RGA1 from Nipponbare was introduced into XLX to estimate the value of d1-w in rice breeding.Compared with transgenic XLX plants(XLX^(D1)),XLX exhibited reduced plant height,increased stem strength,lower reactive oxygen species accumulation,delayed senescence,stronger photosynthesis,higher grain yield and quality(including external,milling and nutritional qualities),and enhanced resistance to drought and Rhizoctonia solani.Therefore,we proposed that the d1-w allele has potential as an excellent dwarfism resource for rice breeding.

不同品种及有关外因对水稻纹枯病抗性的影响

选择 9个具不同纹枯病抗性的水稻品种 ,采用 3个纹枯病菌株和 2种接种方法 ,在 2个生长季进行水稻品种纹枯病抗性的综合评价。结果表明 ,生长季、接种方法和菌株极显著地影响水稻品种对纹枯病的抗性反应 ,其中 ,以生长季因子的效应最大。不同接种方法对水稻纹枯病发病程度的影响因生长季的不同有所变化。不同品种在同一生长季、接种方法和菌株条件下 ,抗性反应存在极显著差异。在本试验中 ,籼稻品种“白叶秋”在 2个生长季、2种接种方法和 3个菌株接种条件下表现了较稳定的纹枯病抗性 ,可作为纹枯病抗性种质用于水稻抗病育种。

田间水稻纹枯病抗性鉴定体系的确立与完善

建立科学的田间水稻纹枯病抗性鉴定体系,是开展水稻抗纹枯病遗传研究的关键环节之一。描述了田间水稻纹枯病发生、发展的特点,强调只有在充分认识并依据这些特点所建立的抗性鉴定体系才具科学性。分析认为Rush的总体抗性鉴定体系最为合理。为适应抗性QTL精细定位的精度要求,在Rush的总体思想体系基础上,提出并试行了以“最高病斑达到的叶鞘位”为基础的新的病情评定标准,以进一步完善水稻纹枯病抗性鉴定体系。

对水稻纹枯病抗源的初步研究

:对引自美国的水稻纹枯病抗源进行了 2年的田间接种试验和 1年的田间性状考察。结果显示 ,抗源与感病对照以及抗源间 ,在抗性水平上存在极显著的差异 ,且品种与年份间的互作不显著 ,抗性与株型性状及生育期的相关也不显著 ,表明抗性是一个真实存在的遗传性状。多数抗源在中美两地的抗性表现大体一致 ,且多数引进抗源为半矮秆品种 (系 )或推广品种 ,具有较好的农艺性状和经济性状 。

水稻纹枯病改良新抗源YSBR1的抗性评价

从籼粳交后代群体中筛选到一份抗纹枯病水稻新种质YSBR1。多年的大田和温室接种鉴定以及立枯丝核菌毒素对水稻胚根伸长抑制率试验结果均表明,YSBR1的抗性水平极显著高于其他参试品种(系),且稳定、可靠,在大田接种试验中的纹枯病平均病级为2.39±0.23级(按0～9级评价标准),达"抗病"水平。YSBR1的株高为(102±4.32)cm,叶片稍内卷而挺拔,株形优良,生育期适中,在水稻抗纹枯病遗传育种中可有较大研究价值和利用前景。

水稻纹枯病抗性QTL分析

对籼稻窄叶青 8号 (ZYQ8)和粳稻京系 17(JX17)以及由它们构建的加倍单倍体 (DH)群体 ,分别在杭州和海南岛 ,采用注射器接种法进行纹枯病抗性鉴定 ,并使用该群体的分子连锁图谱进行数量性状座位 (QTL)分析。共检测到 4个抗纹枯病的QTL(qSBR 2、qSBR 3、qSBR 7和qSBR 11) ,分别位于第 2、第 3、第 7和第 11染色体。其中qSBR 2、qSBR 3、qSBR 7的抗性基因由抗病亲本ZYQ8贡献 ,而qSBR 11的抗性基因来自感病亲本JX17。qSBR 2、qSBR 3和qSBR 7在杭州和海南岛都能检测到 ,而qSBR 11只在杭州检测到。在杭州的实验中 ,纹枯病病级与秆长和抽穗期呈显著负相关 ;在控制秆长和抽穗期的QTL中 ,控制秆长的qCL 3与qSBR 3位于同一染色体区域 ,其余QTL与抗纹枯病的QTL之间无连锁关系。

水稻抗纹枯病育种成效的初步评价

以广东省和江苏省里下河农科所新近育成的部分籼稻品种 (系 )、扬州大学农学院的研究组以不同抗源杂交后代向抗感两个极端选育的 9份籼稻品系以及另一组合向抗病方向选育的 5份籼稻品系为材料 ,设置抗感病对照 ,进行田间纹枯病菌接种试验。结果表明品种间对纹枯病的抗性存在极显著差异 ;聚类分析将参试材料按抗性水平高低聚为 6类 :高度感病、感病、中等感病、中等抗病、抗病和更高水平抗病。广东品种在 6种类型中均有分布 ,但属于抗和更抗类型的品种只有 3个。扬州大学农学院对抗×抗杂交向抗感两个极端选育的品系在病级的中间类型中几乎没有分布 ;而向抗病方向选育的品系则仅分布于中抗至抗病的范围内 ,且属于抗的品种数占此类品种的 6 0 %。江苏省里下河农科所近些年育成的几个品种则只分布于后 4类之中 ,且最高水平抗性的 3个品种中 ,其品种占 2 / 3。表明水稻对纹枯病的抗性是可遗传的性状 。

抗水稻纹枯病遗传研究的改良方法及其验证

报道了抗水稻纹枯病遗传研究的一种新方法体系 ,包括采用新的接种方法、评定病级指标和适宜调查时间 ,采用永久性遗传分析群体设置有重复的田间试验 ,田间保持中肥水平 ,以及浅水灌溉不脱水等内容。用 F2 无性系群体和重组自交系群体 ,对新方法进行了 4年的验证试验 ,证明新方法有相当好的重演性。