Resistance to <Emphasis Type="Italic">Rice yellow mottle virus</Emphasis> in rice germplasm in Madagascar

Rice yellow mottle virus (RYMV) is a recent and major threat to rice production in Madagascar. A large scale screening of resistance to RYMV in rice germplasm in Madagascar was conducted by visual symptom scoring and virus-assessment through ELISA tests. The response to virus inoculation of 503 local or introduced rice accessions was assessed. Most of them were susceptible to RYMV. A few cultivars expressed partial resistance at a level similar to the partially resistant Oryza sativa japonica cv. Azucena. Only one O. sativa cultivar expressed high resistance characterised by a lack of symptoms and an undetectable level of virus. It was a Malagasy traditional indica cultivar, named Bekarosaka, which originated from the northwest of the country. It was selected by farmers for its field resistance to RYMV. The response of cv. Bekarosaka to four pathotypes of RYMV was similar to that of cv. Gigante, the only other highly resistant indica cultivar. The sequence of the middle domain of the eIF(iso)4G, the genetic determinant of Rymv1 resistance on chromosome 4, of cv. Bekarosaka was similar to that of cv. Gigante. Subsequently, cvs Bekarosaka and Gigante probably carried the same resistance allele Rymv1-2. Rymv1-2 resistance was efficient against isolates of the major strains of RYMV, but was readily overcome by a pathotype from the northwest of Madagascar.     

Quantitative trait Loci mapping of resistance to sugarcane mosaic virus in maize

ABSTRACT Sugarcane mosaic virus (SCMV) is an important virus disease of maize (Zea mays) in Europe. In this study, we mapped and characterized quantitative trait loci (QTL) affecting resistance to SCMV in a maize population consisting of 219 F(3) or immortalized F(2) families from the cross of two European maize inbreds, D32 (resistant) x D145 (susceptible). Resistance was evaluated in replicated field trials across two environments under artificial inoculation. The method of composite interval mapping was employed for QTL detection with a linkage map based on 87 restriction fragment length polymorphism and 7 mapped microsatellite markers. Genotypic and genotype x environment interaction variances for SCMV resistance were highly significant in the population. Heritabilities ranged from 0.77 to 0.94 for disease scores recorded on seven consecutive dates. Five QTL for SCMV resistance were identified on chromosomes 1, 3, 5, 6, and 10 in the joint analyses. Two major QTL on chromosomes 3 and 6 were detected consistently in both environments. Significant epistatic effects were found among some of these QTL. A simultaneous fit with all QTL in the joint analyses explained between 70 and 77% of the phenotypic variance observed at various stages of plant development. Resistance to SCMV was correlated with plant height and days to anthesis.     

High resistance to rice yellow mottle virus in two cultivated rice cultivars is correlated with failure of cell to cell movement

Rice yellow mottle virus (RYMV) accumulation in protoplasts and whole plants was investigated in two highly resistant cultivars, Tog5681 (Oryza glaberrima) and Gigante (Oryza sativa). Three susceptible cultivars, i.e. one O. glaberrima Tog5673 and two O. sativa (IR64, Ac. 2428), and a partially resistant cultivar (Azucena) were used as control. After inoculation, accumulation of coat protein (CP) and viral RNA were monitored on protoplasts, inoculated leaves, sheaths of inoculated leaves and newly infected leaves by serological and Northern blot analysis. Viral RNA accumulated to a similar extent in protoplasts from all cultivars studied. In contrast, three distinct in planta behaviors were noted. In susceptible plants (IR64, Tog5673 and Ac. 2428), there was high CP and RNA accumulation at 5 d.p.i. in whole plants, suggesting that cell to cell and vascular movements occurred before 5 d.p.i. in inoculated leaves. The second behavior concerned Azucena, which showed a delay (around 7 d.p.i.) of viral accumulation in inoculated leaves. The third behavior involved the highly resistant cultivars Tog5681 and Gigante. CP and viral RNA were not detected in these cultivars. The comparison of viral accumulation in protoplasts and plants suggested that resistance of the highly resistant cultivars Tog5681 (O. glaberrima) and Gigante (O. sativa) was not due to the inhibition of virus replication but rather to the failure of cell to cell movement.     

抗稻瘿蚊品种多抗1的抗性遗传分析及抗性基因定位

稻瘿蚊是亚洲稻区主要害虫,采用抗虫品种进行防治是最理想的方法。1993～1995年,广东省农科院与国际水稻研究所有关专家紧密合作,对能抗华南4个稻瘿蚊生物型的品种多抗1作进一步抗性遗传分析,确认多抗1对中国稻瘿蚊生物型1和4的抗性受显性单基因控制,这个基因暂定名为GM—6(t)。以多抗1×丰银占1组合的F3代160个家系作基因标记,据DNA库分离个体分析(BSA)原理,用随机扩增多态性DNA(RAPD)标记物OPM6(1.4kb),首次成功地标记了这个抗性基因。随后多态性扩增产物经~(32)p标记,用作探针,检测另一个参考作图群体IR64×Azucena,将这个抗性基因定位在水稻第4条染色体上,位于RG214和RG163两个DNA限制性片段长度多态性(RFLP)标记之间。应用这些分子标记辅助选择有可能不必通过稻瘿蚊的直接筛选,快速准确地选育抗稻瘿蚊品种或进行抗性基因累加。     

Molecular mapping of Loci conferring resistance to different pathotypes of the spot blotch pathogen in barley

ABSTRACT Spot blotch, caused by Cochliobolus sativus, is an important disease of barley in many production areas and is best controlled through the deployment of resistant cultivars. Information on the genetics of resistance in various sources can be useful in developing effective breeding strategies. Parents of the doubled haploid mapping population Calicuchima-sib/ Bowman-BC (C/B) exhibit a differential reaction to pathotypes 1 and 2 of C. sativus. To elucidate the genetics of spot blotch resistance in this population, C/B progeny were evaluated with both pathotypes at the seedling stage in the greenhouse and at the adult plant stage in the field. At the seedling stage, progeny segregated 84 resistant to 26 susceptible based on the qualitative analysis of infection response (IR) data to pathotype 1. This fit best to a 3:1 ratio, indicating that two genes were involved in conferring resistance. Quantitative analysis of the raw IR data to pathotype 1 revealed a single quantitative trait locus (QTL) on chromosome 4(4H) explaining 14% of the phenotypic variance. Adult plant resistance to pathotype 1 was conferred by QTL on chromosome 2(2H) and chromosome 3(3H), explaining 21 and 32% of the phenotypic variation, respectively. Bowman contributed the resistance alleles on chromosome 3(3H) and chromosome 4(4H), whereas Calicuchima-sib contributed the resistance allele on chromosome 2(2H). Resistance to pathotype 2 was conferred by a single gene (designated Rcs6) on chromosome 5(1H) based on qualitative analysis of data. Rcs6 was effective at both the seedling and adult plant stages and was contributed by Calicuchima-sib. This result was corroborated in the quantitative analysis of raw IR (seedling stage) and disease severity (adult plant stage) data as a single major effect (r(2) = 0.93 and 0.88, respectively) QTL was identified on chromosome 5(1H). Progeny with resistance to both pathotypes were identified in the C/B population and may be useful in programs breeding for spot blotch resistance.     

Genetic and physical mapping of the partial resistance gene, pi34, to blast in rice

ABSTRACT Partial resistance to rice blast in the Oryza sativa japonica group cv. Chubu 32 is controlled by Pi34, a major quantitative trait locus (QTL) on chromosome 11, and several uncharacterized QTLs. The objectives of the study were (i) high-resolution genetic and physical mapping of Pi34 and (ii) identification of new QTL imparting resistance to rice blast. Chubu 32 was crossed with a susceptible chromosomal segment substitution line (CSSL) of cv. Koshihikari. From 4,012 of segregating individuals, 213 recombinants in the Pi34 region were screened by using polymerase chain reaction-based markers and tested resistance in the field and greenhouse. The Pi34 locus is located in the 54.1-kb region on the genomic sequence of cv. Nipponbare. We constructed a bacterial artificial chromosome (BAC) library of Chubu 32, selected the clone containing Pi34, and sequenced it. The Pi34 locus consequently was located on an interval of 65.3 kb containing 10 predicted open reading frames (ORFs). Two of these ORFs were predicted only in Chubu 32 and encoded transposable elements. The other eight ORFs were found in both Chubu 32 and Nipponbare and one of them, which encoded an unknown protein, showed significantly different amino acid sequences between two cultivars. The new QTL, Piq6(t), was detected on the short arm of chromosome 6 and the genetic distance of flanking markers was 16.9 centimorgans in Nipponbare. Pi34 and Piq6(t) acted additively on resistance to rice blast but the effect of Piq6(t) was relatively small compared with Pi34.     

Screening rice varieties for resistance to rice yellow mottle virus disease

Abstract

Rice yellow mottle virus (RYMV) is one of the major constraints to rice production in Kenya. The reactions of 30 varieties of rice to an isolate of RYMV were studied. The appearance and development of symptoms in the various varieties were scored on a 0–5 scale. The observed reactions ranged from highly susceptible to highly resistant. Thirty‐six per cent of the varieties showed a high level of resistance while 23.3% were highly susceptible. The intermediate reactions were 16.7% resistant, 6.6% susceptible and 16.7% moderately susceptible.     

Tagging and validation of a major quantitative trait locus for leaf rust resistance and leaf tip necrosis in winter wheat cultivar forno

ABSTRACT A major leaf rust (Puccinia triticina) resistance quantitative trait locus (QTL) (QLrP.sfr-7DS) previously has been described on chromosome 7DS in the winter wheat (Triticum aestivum) cv. Forno. It was detected in a population of single-seed descent (SSD) lines derived from the cross Arina x Forno. QLrP.sfr-7DS conferred a durable and slow-rusting resistance phenotype, co-segregated with a QTL for leaf tip necrosis (LTN) and was mapped close to Xgwm295 at a very similar location as the adult plant leaf rust resistance gene Lr34 found in some spring wheat lines. Here, we describe the validation of this QTL by mapping it to the same chromosomal region close to Xgwm295 on chromosome 7DS in a population of SSD lines from the winter wheat x spelt (T. spelta) cross Forno x Oberkulmer. In both populations, the log of the likelihood ratio curves for leaf rust resistance and LTN peaked at identical or very similar locations, indicating that both traits are due to the same gene. We have improved the genetic map in the target region of QLrP.sfr-7DS using microsatellite and expressed sequence tag (EST) markers. Two EST loci (Xsfr.BF473324 and Xsfr.BE493812) define a genetic interval of 7.6 centimorgans containing QLrP.sfr-7DS, a considerably more precise genetic location for this QTL than previously described both in spring and winter wheat. The identified genetic interval is physically located in the distal 39% of chromosome 7DS. Single-marker analysis identified Xsfr.BF473324 and Xgwm1220 as the most informative loci for QLrP.sfr-7DS and QLtn.sfr-7DS. In the rice genome, the two ESTs flanking the QLrP.sfr-7DS/QLtn.sfr-7DS chromosomal segment in wheat are conserved on chromosome 6S in a region colinear with wheat chromosome 7DS. There, they define a physical region of three rice bacterial artificial chromosomes spanning approximately 300 kb.     

Selection for quantitative trait loci associated with resistance to Stewart's wilt in sweet corn

The objectives of this research were to identify quantitative trait loci (QTL) for Stewart's wilt resistance from a mapping population derived from a sweet corn hybrid that is highly resistant to Pantoea stewartii and to determine if marker-based selection for those QTL could substantially improve Stewart's wilt resistance in a population derived from a cross of resistant lines and a highly susceptible sweet corn inbred. Three significant QTL for Stewart's wilt resistance on chromosomes 2 (bin 2.03), 5 (bin 5.03), and 6 (bin 6.06/6.07) explained 31% of the genetic variance in a population of 110 F(3:4) families derived from the sweet corn hybrid Bonus. The three QTL appeared to be additive in their effects on Stewart's wilt ratings. Based on means of families that were either homozygous or heterozygous for marker alleles associated with the resistance QTL, the QTL on chromosomes 2 and 6 appeared to have dominant or partially dominant gene action, while the QTL on chromosome 5 appeared to be recessive. A population of 422 BC(2)S(2) families was derived from crosses of a sweet corn inbred highly susceptible to Stewart's wilt, Green Giant Code 88 (GG88), and plants from two F(3:4) families (12465 and 12467) from the Bonus mapping population that were homozygous for marker alleles associated with Stewart's wilt resistance at the three QTL. Mean Stewart's wilt ratings for BC(2)S(2) families were significantly (P < 0.05) lower for families that were homozygous for the bnlg1902 marker allele (bin 5.03) from resistant lines 12465 or 12467 than for families that were heterozygous at this marker locus or homozygous for the bnlg1902 marker allele from GG88. Resistance associated with this QTL was expressed only if F(3:5) or BC(2)S(2) families were homozygous for marker alleles associated with the resistant inbred parent (P(1)). Marker alleles identified in the F(3:5) mapping population that were in proximity to the resistance QTL on chromosomes 2 and 6 were not polymorphic in crosses of GG88 with 12465 and 12467. Selection for other polymorphic marker loci adjacent to these two regions did not improve Stewart's wilt resistance of BC(2)S(2) families.     

沿黄稻区水稻品种对水稻条纹叶枯病抗性评价

2007年和2008年在田间自然发病条件下, 鉴定了河南省沿黄稻区25个主要推广品种、育种高代品系对水稻条纹叶枯病的抗性。结果表明,在两个年份均表现为抗病的有5个粳稻（5/17）、3个籼稻（3/3）和2个旱稻（2/5）品种;但有4个品种（4/25）表现不一致。2007年17个粳稻品种中的11个表现为感病或中感（64.70%）,5个旱稻品种中2个表现感病或中感（40％）。2008年17个品种中有10个表现为感病或中感（58.80%）,5个旱稻品种中3个表现为感病或中感（60％）。 2008年对25个品种的病情变化和田间灰飞虱种群动态的调查结果表明,抗、感品种间的病情变化具有明显的差异,不同水稻品种间灰飞虱的虫口数量也具有显著的差异,但品种对水稻条纹叶枯病的抗性程度和灰飞虱的虫口数量并不完全一致。     

Evaluation of bacterial wilt resistance in tomato lines nearly isogenic for the Mi gene for resistance to root-knot

Resistance to bacterial wilt, caused by Ralstonia solanacearum , in tomato lines CRA 66 and Caraïbo is reported to be decreased by root-knot nematode galling and by introduction of the Mi gene for nematode resistance. The Mi gene is located on tomato chromosome 6, which also carries a major quantitative trait locus (QTL) for resistance to bacterial wilt. Bacterial wilt resistance was evaluated in F3-progenies derived from two crosses between near-isogenic lines, Caraïbo × Carmido and CRA 66 × Cranita, differing for small and large introgressions from Lycopersicon peruvianum that carry the Mi gene, respectively. These introgressed regions were mapped using RFLP markers. Plants homozygous Mi⁺/Mi⁺ (susceptible to the nematode) and homozygous Mi/Mi (resistant) for the Mi gene were selected in F2 and used to produce F3 progenies. Parents and F3-lines with Mi/Mi had resistance to bacterial wilt reduced by 30% in Caraïbo × Carmido and by 15% in CRA 66 × Cranita. Caraïbo and Carmido were demonstrated to be isolines and the small introgression from L. peruvianum resulted in loss of the QTL for bacterial wilt resistance, which is probably allelic or linked in repulsion to the Mi gene. In contrast, resistance to bacterial wilt segregated in the F3 lines from the cross CRA 66 × Cranita, giving families varying in resistance between the levels shown by the parents. Consequently, two hypotheses were considered: (i) after only four backcrosses, the parents were not isolines and the genes for resistance to bacterial wilt from CRA 66 were still segregating, and (ii) the parents were isolines and variation in resistance to bacterial wilt in F3 was due to recombination events among the large L. peruvianum introgressed chromosome region from Cranita.     

Characterization and mapping of oat crown rust resistance genes using three assessment methods

ABSTRACT Resistance is the primary means of control for crown rust of oat (Avena sativa L.), caused by Puccinia coronata f. sp. avenae, and better knowledge of the genetics of resistance will enhance resistance breeding. Disease data were generated in the field and greenhouse for parents and recombinant inbred lines of the Ogle/TAM O-301 (OT) oat mapping population using (i) a new quantitative assay that employs quantitative real-time polymerase chain reaction (q-PCR) to estimate fungal growth in the host, (ii) digital image analysis, and (iii) visual ratings. The objectives of this study were to evaluate each assessment method's ability to map a major gene from cv. Ogle and potential quantitative trait loci (QTL) contributed by Ogle and TAM O-301. All three assessment methods identified the major gene in Ogle, which was mapped to linkage group OT6. The resolution produced by q-PCR, however, enabled more precise mapping of the major gene. Quantitative analysis indicated that 64% of the phenotypic variation was accounted for using q-PCR, whereas 41 and 52% were accounted for using visual and digital assessments, respectively. Data generated by q-PCR permitted identification of QTL on linkage groups OT32, accounting for 6% of the phenotypic variation, and OT2, accounting for 4% of the variation. QTL on both OT32 and OT2 were conferred by TAM O-301, one of which (OT2) was indiscernible using data from the visual and digital assessments. The new method of precisely phenotyping crown rust resistance provided a more accurate and thorough means of dissecting resistance in the OT mapping population. Similar methods could be developed and applied to other important cereal rust diseases.     

Effects of initial nematode population density and water regime on resistance and tolerance to the rice root-knot nematode Meloidogyne graminicola in African and Asian rice genotypes

The rice root-knot nematode (RKN), Meloidogyne graminicola, is an important pathogen affecting rice production in South and Southeast Asia. Efficacy of resistance and tolerance in selected M. graminicola-resistant African rice genotypes TOG5674, TOG5675 and CG14 and -susceptible Asian rice genotypes IR64 and UPLRi-5 were examined under a range of initial population densities (Pi) and water regimes. Resistance to M. graminicola in resistant rice genotypes was not broken with increasing pathogen pressure (Pi = 15,000 to 60,000 J2/plant). Resistant rice genotypes were even tolerant to the damage and yield loss caused by high pathogen pressure. On the other hand, increasing Pi levels caused more damage on susceptible rice genotypes. Final nematode population densities in the root systems of resistant and susceptible rice genotypes were significantly lower under flooded conditions than under upland and drought conditions. TOG5674, TOG5675 and CG14 were more tolerant to M. graminicola infection even when grown under upland and drought conditions while IR64 and UPLRi-5 were highly sensitive.     

Mapping of quantitative trait Loci for fusarium head blight resistance in barley

ABSTRACT Fusarium head blight (FHB) is a devastating disease that causes significant reductions in yield and quality in wheat and barley. Barley grains infected with deoxynivalenol (DON), a vomitoxin produced by Fusarium graminearum, are rejected for malting and brewing. Among six-rowed barley cultivars tested thus far, only cv. Chevron exhibited resistance. This study was conducted to map genes and to identify DNA markers for marker-assisted breeding for FHB resistance in cv. Chevron with restriction fragment length polymorphism (RFLP) markers. A doubled haploid (DH) population was created from a cross between cv. Chevron and susceptible cv. Stander. Seven field experiments were conducted in four different locations in 2 years. A RFLP map containing 211 loci and covering over 1,000 centimorgans (cM) of the genome was used to map quantitative trait loci (QTL) associated with relatively low FHB severity and DON concentration. Morphological traits differing between the parents were also measured: heading date, plant height, spike angle, number of nodes per cm of rachis in the spike, and kernel plumpness. Many of the QTL for FHB and DON coincided with QTLs for these morphological traits. The "fix-QTL" algorithm in Mapmaker QTL was used to remove the part of the variance for FHB resistance that may be explained by heading date or plant height. Results from this study suggest that QTLs with major effects for FHB resistance probably do not exist in cv. Chevron. Three QTL intervals, Xcmwg706-Xbcd441 on chromosome 1H, Xbcd307b-Xcdo684b on chromosome 2H, and Xcdo959b-Xabg472 on chromosome 4H, that are not associated with late heading or height may be useful for marker-assisted selection.     

Near immunity to rice tungro spherical virus achieved in rice by a replicase-mediated resistance strategy

ABSTRACT Rice tungro disease is caused by rice tungro bacilliform virus (RTBV), which is responsible for the symptoms, and rice tungro spherical virus (RTSV), which assists transmission of both viruses by leafhoppers. Transgenic japonica rice plants (Oryza sativa) were produced containing the RTSV replicase (Rep) gene in the sense or antisense orientation. Over 70% of the plants contained one to five copies of the Rep gene, with integration occurring at a single locus in most cases. Plants producing antisense sequences exhibited significant but moderate resistance to RTSV (60%); accumulation of antisense RNA was substantial, indicating that the protection was not of the homology-dependent type. Plants expressing the full-length Rep gene, as well as a truncated Rep gene, in the (+)-sense orientation were 100% resistant to RTSV even when challenged with a high level of inoculum. Accumulation of viral RNA was low, leading us to conclude that RTSV Rep-mediated resistance is not protein-mediated but is of the cosuppression type. Resistance was effective against geographically distinct RTSV isolates. In addition, RTSV-resistant transgenic rice plants were unable to assist transmission of RTBV. Such transgenic plants could be used in an epidemiological approach to combat the spread of the tungro disease.     

甜玉米小斑病抗性的遗传分析与主效QTL定位

为培育抗病品种,利用抗小斑病甜玉米自交系T14和感小斑病自交系T18为亲本配制杂交组合,对玉米抗小斑病性状进行遗传分析和抗病基因分子标记定位,用主基因＋多基因混合遗传模型和P₁、P₂、F₁、B₁、B₂、F₂ 6世代联合分析的方法对单位叶面积病斑数量进行遗传分析,并应用复合区间作图法检测抗小斑病QTL。结果表明,单位叶面积病斑数量受2对加性-显性-上位性主基因控制,自交系T14的抗病性在各个分离世代都以主基因遗传为主。在第4染色体上检测到4个相互连锁的小斑病抗性QTL,解释表型变异的7.7%、30.9%、14.8%和11.5%;在第6染色体上定位了1个抗病QTL,可解释表型变异的37.7%。检测到的小斑病抗性主效QTL位于第4和第6染色体的特征与2对主基因的遗传模型相吻合。     

Molecular mapping of the blast resistance genes Pi2-1 and Pi51(t) in the durably resistant rice 'Tianjingyeshengdao'

Tianjingyeshengdao' (TY) is a rice cultivar with durable resistance to populations of Magnaporthe oryzae (the causal agent of blast) in China. To understand the genetic basis of its resistance to blast, we developed a population of recombinant inbred lines from a cross between TY and the highly susceptible 'CO39' for gene mapping analysis. In total, 22 quantitative trait loci (QTLs) controlling rice blast resistance were identified on chromosomes 1, 3, 4, 5, 6, 9, 11, and 12 from the evaluation of four disease parameters in both greenhouse and blast nursery conditions. Among these QTLs, 19 were contributed by TY and three by CO39. Two QTL clusters on chromosome 6 and 12 were named Pi2-1 and Pi51(t), respectively. Pi2-1 was detected under both growth chamber and natural blast nursery conditions, and explained 31.24 to 59.73% of the phenotypic variation. Pi51(t) was only detected in the natural blast nursery and explained 3.67 to 10.37% of the phenotypic variation. Our results demonstrate that the durable resistance in TY is controlled by two major and seven minor genes. Identification of the markers linked to both Pi2-1 and Pi51(t) in this study should be useful for marker-aided selection in rice breeding programs as well as for molecular cloning of the identified resistance genes.     

Identification and fine mapping of the new bacterial blight resistance gene, <Emphasis Type="Italic">Xa31(t)</Emphasis>, in rice

Zhachanglong (ZCL), a regional rice variety from Yunnan province in southwest China, has a high level of resistance to a broad spectrum of Xanthomones oryzae pv. oryzae (Xoo) isolates. In a previous study, a bacterial blight (BB) resistance (R) gene, Xa22(t), with resistance against Xoo strain Px061 on chromosome 11 was identified in ZCL. Here, we report another BB R-gene, tentatively named Xa31(t), with resistance against Xoo strain OS105 and susceptible to Px061 identified in ZCL. To determine the location of Xa31(t), 102 polymorphic RFLP markers on 12 rice chromosomes were selected for bulked segregation analysis (BSA). Twelve RFLP markers on chromosome 4 detected DNA polymorphisms between ZCL and Zhengzhu Ai (ZZA), as well as in the OS105-resistant and -susceptible bulks from F₂ populations derived from ZCL × ZZA. Genetic linkage analysis and fine mapping localised Xa31(t) within a genetic distance of 0.2 cM between two RFLP markers, G235 and C600, on the end of the long arm of chromosome 4, using two F₂ populations from the cross ZCL × ZZA and two F₃ populations, consisting of 3,311 plants with 301 F₃ random families and 3,333 plants with 303 F₃ Pxo61-susceptible families, derived from the same F₂ populations from the cross ZCL × ZZA. Using two flanking markers, G235 and C600, to screen the MH63 BAC library, the Xa31(t) locus was limited to one BAC clone with a length of about 100 kb.     

苯并噻二唑诱发水稻对纹枯病的抗性

研究了苯并噻二唑(B1H)诱发水稻产生对纹枯病的抗性。离体条件下，1．0mmol／L BTH对纹枯病菌菌丝生长无明显抑制作用。BTH叶面或灌根处理四叶一心期水稻幼苗，并将植株第2、3和4叶离体接种纹枯病菌，水稻叶片纹枯病病斑长度明显下降，BTH诱发苗期水稻产生抗性的最佳诱导期在处理后的3—5天，最佳浓度为0．1mmol／L，BTH灌根处理诱发抗性的效果较好。用BTH溶液叶面喷雾处理成株期水稻倒二叶后离体接种纹枯病菌，倒二叶、倒一叶和剑叶上病斑长度显著低于对照，最佳诱导期在处理后3—5天。用BTH处理苗期水稻第2叶或成株期倒二叶，可使未经处理的苗期水稻第3和4叶以及成株期水稻倒一叶和剑叶上纹枯病病斑长度显著下降。     

Quantitative trait loci for Fusarium head blight resistance in a recombinant inbred population of Wangshuibai/Wheaton

Use of diverse sources of Fusarium head blight (FHB)-resistant germplasm in breeding may significantly improve wheat resistance to FHB. Wangshuibai is an FHB-resistant Chinese landrace unrelated to cv. Sumai 3, the most commonly used FHB-resistant source. In all, 139 F(6) recombinant inbred lines were developed from a cross between Wangshuibai and an FHB-susceptible cultivar, Wheaton, to map quantitative trait loci (QTL) for wheat resistance to initial infection (type I resistance), spread of FHB symptoms within a spike (type II resistance), and deoxynivalenol (DON) accumulation (type III resistance) in infected grain. The experiments were conducted in a greenhouse at Manhattan, KS from 2003 to 2005. More than 1,300 simple-sequence repeat and amplified fragment length polymorphism markers were analyzed in this population. Five QTL for type I resistance were detected on chromosomes 3AS, 3BS, 4B, 5AS, and 5DL after spray inoculation; seven QTL for type II resistance were identified on chromosomes 1A, 3BS, 3DL, 5AS, 5DL, and 7AL after point inoculation; and seven QTL for type III resistance were detected on chromosomes 1A, 1BL, 3BS, 5AS, 5DL, and 7AL with the data from both inoculation methods. These QTL jointly explained up to 31.7, 64, and 52.8% of the phenotypic variation for the three types of FHB resistance, respectively. The narrow-sense heritabilities were low for type I resistance (0.37 to 0.41) but moderately high for type II resistance (0.45 to 0.61) and type III resistance (0.44 to 0.67). The QTL on the distal end of 3BS, 5AS, and 5DL contributed to all three types of resistance. Two QTL, on 7AL and 1A, as well as one QTL near the centromere of 3BS (3BSc), showed effects on both type II and type III resistance. Selection for type II resistance may simultaneously improve type I and type III resistance as well. The QTL for FHB resistance identified in Wangshuibai have potential to be used to pyramid FHB-resistance QTL from different sources.