Early determination of genotypes for apple scab resistance by forced flowering of test cross progenies

Summary Apple selections with different major genes for resistance to apple scab (Venturia inaequalis) derived from Malus floribunda and M. pumila were crossed with each other. The progenies were screened as young seedlings for their reaction to V. inaequalis race 1. A gene for resistance from M. pumila, causing stellate necrotic (SN) lesions, was epistatic to a second gene for resistance from M. floribunda, causing irregular chlorotic (Chl) lesions. Although in most cases SN, Chl and susceptible phenotypes were clearly distinct, occasionally reactions were difficult to characterize or varied from one inoculation to another. Selected seedlings showing resistant or susceptible reactions were forced to flower in 16–20 months in the greenhouse and test crossed with susceptible cultivars. Test cross seedlings were screened for scab reaction. The presence of both genes for resistance in a resistant plant was indicated by presence of both Chl and SN resistant phenotypes in the test cross progeny. Chi-square analysis of four large progenies produced a good fit to the expected ratio. The use of the forced flowering technique to determine scab resistance genotypes in 28 months demonstrated its value in breeding apples with multiple disease resistance.     

Identification of an RAPD Marker Linked to the Vf Gene for Scab Resistance in Apples

Resistance to V. inaequalis, derived from the small-fruited species Malus floribunda 821, is determined by a major dominant gene, assigned as Vf. The material used in this paper is based on the introgression of the Vf gene from M. floribunda into commercial apple varieties. Comparing RAPD patterns of a genomic DNA sample of M. floribunda with a pooled DNA sample of resistant individuals and that of 10 susceptible commercial apple varieties, fragments were identified which are derived from M. floribunda. One of them, the fragment OPD20/600, proved to be linked to the Vf gene with a recombination value of about 0.20—0.25. It is the first DNA marker so far for scab resistance.     

Mapping QTL involved in powdery mildew resistance of the apple clone U 211

Scab and powdery mildew, caused by Venturia inaequalis (Cke.) Wint. and Podosphaera leucotricha (Ellis et Ev.) Salm. are the most important apple diseases. The apple clone U 211 is resistant to scab and is also highly resistant to powdery mildew under field conditions. The interval mapping method was applied for the identification of genomic regions conferring U 211 resistance to powdery mildew. The genetic maps of the ‘Idared’ and U 211 genome sectors were constructed using amplified fragment lenght polymorphism and simple sequence repeat markers and 98 individuals from the progeny of the cross ‘Idared’× U 211. On the basis of the phenotypic and molecular marker data 10 powdery mildew resistance quantitative trait loci (QTL) were identified in U 211 and ‘Idared’. One of the QTL in the clone U 211 explained 48‐72% of the phenotypic variation and its effect was stable over years.     

Identification of marker alleles linked to fire blight resistance QTLs in apple genotypes

Molecular marker analysis can be an effective tool when searching for new fire blight resistance donors. It can speed up the breeding process as well, even though many of the available markers linked to fire blight resistance QTLs have not yet been tested by screening a large number of cultivars. The aim of this study was to search for alternate sources of the three major QTLs of fire blight resistance; FBF7, FB_MR5 and FB_E, as well as to test the efficiency of some markers linked to minor QTLs. Altogether, nine primer pairs were used on 77 genotypes including new Hungarian cultivars and old apple cultivars from the Carpathian basin. Several marker alleles of FB resistance QTLs have been detected in the screened genotypes, most importantly the alleles coupling with FB_MR5 in the old cultivars ‘Kéresi muskotály’, ‘Szabadkai szercsika’ and ‘Batul’. We propose these cultivars as the first available resistance donors of FB_MR5 instead of the crabapple Malus × robusta 5. The results also bring new information regarding the resistance alleles of new Hungarian cultivars and selections.     

Isolation of two microsatellite markers from BAC clones of the Vf scab resistance region and molecular characterization of scab‐resistant accessions in Malus germplasm*

A polymerase chain reaction (PCR)‐based method was developed to isolate microsatellite markers from large‐insert genomic DNA clones of bacterial artificial chromosome (BAC) libraries. The method is fast and economic since it does not require subcloning. It was applied to isolate a microsatellite marker from a BAC clone of the chromosomal region containing the apple scab resistance gene Vf. The Vf gene of Malus floribunda 821 is the most widely used source of scab resistance in apple breeding. A second microsatellite was found on the extremity of a BAC clone flanking the Vf locus. The two microsatellites allowed the identification of the presence of the Vf gene in the scab‐resistant accessions M. micromalus SA573‐3, ‘Golden Gem’, M. prunifolia 19651 and MA 16 not previously known to carry this gene. They were also used to verify the correctness of the published genealogical tree of the Vf cultivar ‘Florina’, in which a probable mistake was identified. This analysis shows the importance of genotyping the Vf locus when choosing scab‐resistant germplasm as parents in breeding programmes.     

Screening fruit tree genetic resources in Belgium for disease resistance and other desirable characters

Summary The wide diversity of old fruit-tree cultivars originating or introduced into Belgium during the 18 ^th and 19 ^th centuries was collected as far as feasible over the last fifteen years at the State Plant Pathology Station in Gembloux. Out of the 2400 accessions now collected, one quarter was recovered from old public collections, and three quarters came from farms or gardens. The initial intention was to screen the material for disease resistance and other characters of agronomic interest with a view to using the best cultivars as breeding parents. However, as the collection developed, genetic resources conservation also became an objectiveper se. The collection presently contains 1150 apple, 850 pear and 300 plum accessions, and smaller numbers of other fruit species. Each accession is evaluated in an experimental orchard for at least ten years. In view of the growing public interest in old fruit-tree cultivars, the Plant Pathology Station has for several years been releasing to the nursery trade the better cultivars emerging from the evaluation, namely nine apple and four plum cultivars, and one peach cultivar. The principal features of the apple cultivars are presented in this paper. Since 1988, old apple and plum cultivars have been being used at the Station as parents in a breeding programme, with both controlled and open pollination. In some instances, old apple cultivars have also been crossed with a modern parent carrying the Vf gene for scab resistance. The preliminary observations on some of these seedlings are presented.     

澳洲青苹与红富士苹果冷破碎混合果浆发酵酒品质研究

以澳洲青苹(Granny Smith apple)与红富士苹果(Fuji apple)为原料,采用SY酵母不同比例(GSA与FA果浆体积比1∶1,1∶2,1∶3,1∶4,0∶1)的冷破碎混合果浆,制备低度苹果酒,分析果酒各项品质指标。结果表明,不同比例混合果浆发酵,其残糖与酒精度与单种果浆发酵均无显著性变化;混合果浆发酵酒的酸度(100%)随GSA果浆添加比例减小而降低(66±0.31>58±0.23>44±0.11>39±0.18>33±0.33),总酚含量(53.3±0.11<57.7±0.30<59.7±0.24<65.7±0.61<68.5±0.43 mg/100 mL)随GSA果浆占比的减小而增大,但抗氧化活性随GS添加比例提高而增大,其色值减小不易发生褐变;有机酸随着GSA比例的增大而增加(8.28±0.03>6.99±0.10>6.23±0.06>5.62±0.03>5.33±0.01 mg/mL);混合发酵酒香气中共检测出42种呈香物质(19种酯类物质、11种醇类物质、9种低级脂肪酸及3种醛酮类),不同比例GSA与FA混合发酵酒的呈香物质主要区别在酯类,而醛酮类、低级脂肪酸及醇类基本无显著差异。加入澳洲青苹原料可使发酵果酒不易褐变,颜色明亮,GSA与FA混合果浆最佳体积比为1∶1。     

梨黑星病抗性机理的研究进展

综述了梨黑星菌的分化类型、侵入机制、抗性遗传及抗性机理的研究进展。梨黑星菌在叶片中寄生的具体位置是果胶层。V．nashicola对抗性、易感和非寄主材料的初期侵染相似，当真菌侵入角质层之后，亚角质层菌丝在易感材料中的增长速率远远高于抗性和非寄主材料，并且在抗性和非寄主材料上出现死亡菌丝，这些都表明抗性是在真菌侵入角质层之后表达的。梨黑星病抗性等位基因和敏感性等位基因定位于不同的连锁基因组上，梨黑星病抗性基因与苹果黑星病抗性基因具有同源性。     

Combining ability of resistance to head blight caused by Fusarium culmorum (W.G. Smith) in the F1 of a seven parent diallel of winter wheat (Triticum aestivum L.)

Fusarium head blight (FHB, scab) caused by Fusarium spp. is a widespread disease of cereals causing relevant yield and quality losses and contaminating cereal products with mycotoxins. Breeding resistant cultivars is the method of choice for controlling the disease. Resistance to FHB is a quantitative trait and is most likely governed by several genes. We present the results of an F₁ diallel analysis of FHB resistance involving six resistant and one susceptible European winter wheat genotypes of diverse origin in order to identify promising combinations for the selection of improved cultivars. Parents and F₁s including reciprocals were evaluated for FHB resistance in an artificially inoculated field trial. Two traits were assessed: visual disease symptoms on the heads and the percentage of Fusarium damaged kernels in a harvested sample. General combining ability (GCA) and specific combining ability (SCA) effects were statistically significant for visual symptoms and kernel damage, whereas reciprocal effects were small or not significant. Heterosis for resistance was common, indicating that the parental genotypes possess different resistance genes. Selection of transgressive segregates should be feasible from such heterotic combinations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of resistance to pea blight (Ascochyta pinodella) and induction of resistance in pea (Pisum sativum L.)

Summary Pea blight caused by Assochyta pinodella does considerable damage to the pea crop every year. To ascertain the inheritance of resistance to pea blight and incorporate resistance in the commercial cultivars, crosses were made between Kinnauri resistant to pea blight and four highly susceptible commercial pea cultivars — Bonneville, Lincoln, GC 141 and Sel. 18. Studies of the F₁'s, F₂'s, back crosses and F₃'s indicated that Kinnauri carries a dominant gene imparting resistance to pea blight.     

Breeding for resistance to lentil Ascochyta blight

Ascochyta blight, caused by Ascochyta lentis, is one of the most globally important diseases of lentil. Breeding for host resistance has been suggested as an efficient means to control this disease. This paper summarizes existing studies of the characteristics and control of Ascochyta blight in lentil, genetics of resistance to Ascochyta blight and genetic variations among pathogen populations (isolates). Breeding methods for control of the disease are discussed. Six pathotypes of A. lentis have been reported. Many resistant cultivars/lines have been identified in both cultivated and wild lentil. Resistance to Ascochyta blight in lentil is mainly under the control of major genes, but minor genes also play a role. Current breeding programmes are based on crossing resistant and high‐yielding cultivars and multilocation testing. Gene pyramiding, exploring slow blighting and partial resistance, and using genes present in wild relatives will be the methods used in the future. Identification of more sources of resistance genes, good characterization of the host‐pathogen system, and identification of molecular markers tightly linked to resistance genes are suggested as the key areas for future study.     

小麦品种赤霉病抗性的遗传研究

利用8个不同抗性小麦品种双列杂交的F1及其亲本,以赤霉病病粒率为抗性指标,研究了小麦赤霉病抗性的遗传。结果表明,参试品种间存在3～4对赤霉病抗性基因的差异,苏麦3号、宁麦9号和扬麦158具有较多控制赤霉病抗性遗传的显性基因,对于减少它们杂交后代的病粒率有较高的一般配合力。小麦赤霉病抗性符合加性-显性模型。赤霉     

玉米抗纹枯病QTL定位

以玉米自交系R15（抗）×掖478（感）的229个F₂单株为作图群体,构建了包含146个SSR标记位点的遗传连锁图谱,全长1 666 cM,平均图距11.4 cM。通过麦粒嵌入法对F2:4群体进行人工接种纹枯病菌,并以相对病斑高为病级划分标准鉴定了玉米纹枯病的抗性。用复合区间作图法分析抗病QTL及遗传效应,共检测到9个抗性QTL,分布于第1、2、3、4、5、6和10条染色体上,单个QTL可解释表型方差的3.72%~7.19%,其中有2个QTL位于染色体6.01抗病基因簇附近。     

Inheritance of resistance to Fusarium head blight in the wheat lines 'CJ 9306' and 'CJ 9403'

Fusarium head blight (FHB or scab) caused by Fusarium graminearum is a worldwide serious disease in wheat. Exploitation and genetic studies of elite resistance sources can speed up the development of resistant cultivars. To characterize the inheritance of host plant resistance in two new lines, ‘CJ 9306’ and ‘CJ 9403’, developed from a recurrent selection programme in China, six generations P₁, P₂, F₁, F₂, B₁ and B₂ of four crosses and 137 F_{6 : 7} recombinant inbred lines (RILs) from one cross were evaluated in the greenhouse for scab resistance using single‐floret inoculation. The data of area under disease progress curve (AUDPC) in F₂, backcross (BC) and RIL populations exhibited mono‐modal distributions without clear‐cut demarcations and skewing towards resistance. An additive–dominance model was well‐fitted, additive effects played a predominating role, and dominance effects were also significant. Continuous distributions with two major peaks and one minor peak for the number or percentage of scabby spikelets (NSS or PSS) in segregating populations implied the existence of major genes or quantitative trait loci (QTL) for resistance. The estimates of broad‐sense and narrow‐sense heritabilities based on the six‐generation experiment were 56–76% and 26–67% respectively. The estimates of broad‐sense heritabilities based on anova with RILs were 89–90%. These two improved lines with excellent scab resistance and good agronomic traits are of interest for wheat breeding and production.     

Identification of QTLs associated with resistance to Phomopsis pod blight (Diaporthe toxica) in Lupinus albus

Phomopsis blight in Lupinus albus is caused by a fungal pathogen, Diaporthe toxica. It can invade all plant parts, leading to plant material becoming toxic to grazing animals, and potentially resulting in lupinosis. Identifying sources of resistance and breeding for resistance remains the best strategy for controlling Phomopsis and reducing lupinosis risks. However, loci associated with resistance to Phomopsis blight have not yet been identified. In this study, quantitative trait locus (QTL) analysis identified genomic regions associated with resistance to Phomopsis pod blight (PPB) using a linkage map of L. albus constructed previously from an F₈ recombinant inbred line population derived from a cross between Kiev-Mutant (susceptible to PPB) and {"type":"entrez-protein","attrs":{"text":"P27174","term_id":"14195583","term_text":"P27174"}}P27174 (resistant to PPB). Phenotyping was undertaken using a detached pod assay. In total, we identified eight QTLs for resistance to PPB on linkage group (LG) 3, LG6, LG10, LG12, LG17 and LG27 from different phenotyping environments. However, at least one QTL, QTL-5 on LG10 was consistently detected in both phenotyping environments and accounted for up to 28.2% of the total phenotypic variance. The results of this study showed that the QTL-2 on LG3 interacts epistatically with QTL-5 and QTL-6, which map on LG10 and LG12, respectively.     

Mapping association of molecular markers and sheath blight (<Emphasis Type="Italic">Rhizoctonia solani</Emphasis>) disease resistance and identification of novel resistance sources and loci in rice

Sheath blight (ShB) disease caused by Rhizoctonia solani is one of the major threats to rice crop world-wide. Progress in breeding for resistant rice varieties is limited due to lack of highly resistant germplasm against sheath blight. In present study, diverse rice landrace were phenotyped against R. solani and resistant and moderately resistant sources were identified from the panel of 134 germplasm pool. Landrace Nizam shait showed resistance, where as Bidar local-2, Jigguvaratiga, NavaliSali, Jaddu and Tetep exhibited moderate resistance. Population structure was analysed by genotyping the accessions using 63 genome wide Rice Microsatellite markers which divided the mapping panel into two groups. Association mapping using GLM?+?Q model of TASSEL indicated significant association between twenty-one marker loci on nine chromosomes with ShB resistance with phenotypic variation (R²) ranging 3.02–22.71 per cent. We identified 13 new markers to be associated with ShB resistance. The present work validates previously identified eight markers flanking different shB QTLs. None of the allele from the tested markers was unique and common among resistant and moderately resistant landraces identified in this work except allele 420 bp of RM337 and allele 310 bp of RM5556 noticed only in Tetep. Our findings predict the possible presence of unreported QTL region in marker interval of RM337 and RM5556 on chromosome 8 for ShB resistance in Tetep which invites further investigation.     

Genetics of resistance in lettuce to races 1 and 2 of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> from different host species

Race 1 resistance against Verticillium dahliae in lettuce was originally shown in the cultivar La Brillante to be conditioned by a single dominant gene (Verticillium resistance 1, Vr1). Multiple, morphologically diverse sources of germplasm have been identified as resistant to race 1. In this study, allelism tests indicated that resistance in these different lettuce cultivars is closely linked or allelic to the Vr1 gene. The Vr1 gene is defeated by race 2 isolates of V. dahliae. Only partial resistance to race 2 isolates is available in a few plant introductions (PIs). Greenhouse and field experiments conducted with these PIs demonstrated partial resistance to V. dahliae race 1 as well as race 2 isolates from lettuce. Cultivars resistant to race 1 and PIs with partial resistance to race 2 were challenged with several race 1 and 2 isolates originating from hosts other than lettuce. This indicated that cultivars resistant to race 1 and the breeding lines derived from them would also be resistant to race 1 isolates from other hosts; similarly, the partial resistance would be effective against race 1 and 2 isolates from hosts other than lettuce. Nevertheless, there were specific interactions that warrant further study. Although race 1 currently predominates in the major lettuce production area of the Salinas Valley, CA, breeding lettuce for resistance to V. dahliae should take both races into account.     

Genetic mapping of gummy stem blight (Didymella bryoniae) resistance genes in Cucumis sativus-hystrix introgression lines

Gummy stem blight (GSB, Didymella bryoniae (Auersw.) Rehm) is a devastating disease occurring worldwide in cucumber (Cucumis sativus L.) production and causing considerable yield loss. No commercially available cultivars are resistant to GSB. By screening 52 introgression lines (ILs) derived from the cross of C. hystrix × C. sativus and eight cucumber cultivar/lines through a whole plant assay, three ILs (HH1-8-1-2, HH1-8-5, HH1-8-1-16) were identified as GSB resistant lines. Six common introgression regions in these three ILs were on Chromosomes 1, 4, and 6. To further map the resistance in the ILs, three mapping populations (2009F₂, 2009F₂′ and 2010F₂) from a cross between resistant IL HH1-8-1-2 and susceptible 8419 were constructed and used for QTL mapping with SSR markers. Two quantitative trait loci (QTLs) were identified; one on Chromosome 4 and the other on Chromosome 6. The interval for Chromosome 4 QTL is 12 cM spanning 3.569 Mbp, and the interval for Chromosome 6 QTL is 11 cM covering 1.299 Mbp. The mapped QTLs provide a foundation for map-based cloning of the genes and establishing an understanding of the associated mechanisms underlying GSB resistance in cucumber.     

Identification of markers associated with bacterial blight resistance loci in cowpea [Vigna unguiculata (L.) Walp.]

Cowpea bacterial blight (CoBB), caused by Xanthomonas axonopodis pv. vignicola (Xav), is a worldwide major disease of cowpea [Vigna unguiculata (L.) Walp.]. Among different strategies to control the disease including cultural practices, intercropping, application of chemicals, and sowing pathogen-free seeds, planting of cowpea genotypes with resistance to the pathogen would be the most attractive option to the resource poor cowpea farmers in sub-Saharan Africa. Breeding resistance cultivars would be facilitated by marker-assisted selection (MAS). In order to identify loci with effects on resistance to this pathogen and map QTLs controlling resistance to CoBB, eleven cowpea genotypes were screened for resistance to bacterial blight using 2 virulent Xav18 and Xav19 strains isolated from Kano (Nigeria). Two cowpea genotypes Danila and Tvu7778 were identified to contrast in their responses to foliar disease expression following leaf infection with pathogen. A set of recombinant inbred lines (RILs) comprising 113 individuals derived from Danila (resistant parent) and Tvu7778 (susceptible parent) were infected with CoBB using leaf inoculation method. The experiments were conducted under greenhouse conditions (2007 and 2008) and disease severity was visually assessed using a scale where 0 = no disease and 4 = maximum susceptibility with leaf drop. A single nucleotide polymorphism (SNP) genetic map with 282 SNP markers constructed from the same RIL population was used to perform QTL analysis. Using Kruskall-Wallis and Multiple-QTL model of MapQTL 5, three QTLs, CoBB-1, CoBB-2 and CoBB-3 were identified on linkage group LG3, LG5 and LG9 respectively showing that potential resistance candidate genes cosegregated with CoBB resistance phenotypes. Two of the QTLs CoBB-1, CoBB-2 were consistently confirmed in the two experiments accounting for up to 22.1 and to 17.4% respectively for the first and second experiments. Whereas CoBB-3 was only discovered for the first experiment (2007) with less phenotypic variation explained of about 10%. Our results represent a resource for molecular marker development that can be used for marker assisted selection of bacterial blight resistance in cowpea.