Identification of a major gene (Mex-1) from Coffea canephora conferring resistance to Meloidogyne exigua in Coffea arabica

Among the most damaging root-knot nematode species, Meloidogyne exigua is especially common in Latin America and constitutes a major agronomic constraint in all major coffee-growing ( Coffea arabica ) areas. Growing nematode-resistant coffee represents the most promising option for control of the pest. The present study aimed to determine the mode of inheritance of the M. exigua resistance transferred into C. arabica from a related species, Coffea canephora , and to identify associated molecular markers. Segregation data analysis of F ₂ progeny derived from a cross between the resistant introgression line T5296 and the susceptible accession Et6 showed that the resistance to M. exigua is controlled by a simply inherited major gene (designated the Mex -1 locus). The gall index distribution exhibited by the F ₂ individuals suggested incomplete dominant expression. Fourteen AFLP markers were found associated with the resistance to M. exigua and a localized genetic map of the chromosome segment carrying Mex -1 was constructed. Furthermore, the association of the identified AFLP markers with Mex -1 was confirmed by analysis of a set of genotypes involving 28 introgression Arabica lines either resistant or susceptible to M. exigua in field conditions. These results represent an important starting point to enhance backcross breeding programmes and to perform an early selection of resistant seedlings.     

Aggressiveness profiling of the coffee pathogen Colletotrichum kahawae

Colletotrichum kahawae is a specialized plant pathogen of arabica coffee in Africa, able to infect green berries. The economic impact of this pathogen means there is an urgent need to better understand its pathogenic lifestyle, in particular its aggressiveness. In this study, several quantitative traits including disease severity, latent period and incubation period were measured to concomitantly assess the aggressiveness of 26 C. kahawae isolates. The results show that the area under disease progression curve is the most informative variable, particularly when joined together with the index disease intensity 10 days after inoculation and latency period, while the incubation period is not a reliable trait to distinguish aggressiveness levels in C. kahawae. This study also confirms the suitability of hypocotyls and detached green berries to perform C. kahawae aggressiveness assays, revealing that hypocotyls are a more reproducible testing material. Based on isolate profiles, three aggressiveness classes were established (high, moderate and low). A cytological analysis of representative isolates from each class showed that aggressiveness can be related to the development of post-penetration stages, rather than conidia germination and appressoria differentiation. This study provides, for the first time, the best metrics to evaluate C. kahawae aggressiveness, characterizing the profile of a broad range of isolates, and defining a set of parameters that can be used to classify new isolates. Furthermore, the collected information will contribute to the improvement of coffee breeding programmes, through the selection of tester isolates for prescreening of resistant coffee materials, and offers the opportunity to engage on future genotype–phenotype studies.     

Inheritance of resistance to angular leaf spot (Pseudomonas syringae pv. lachrymans) in cucumber and identification of molecular markers linked to resistance

Angular leaf spot is a common disease of cucumber ( Cucumis sativus ) caused by Pseudomonas syringae pv. lachrymans . Genetics of resistance to this disease was investigated using two sets of parameters: (i) disease severity, i.e. the number and size of necrotic and chlorotic lesions on the infected leaves, and (ii) presence or absence of a chlorotic halo around the necrotic spots on the infected leaves. Disease severity appears to be controlled by multiple genes and the heritability of the resistance was estimated to be 53%. The presence or absence of the chlorotic halo was determined to be governed by a single gene, with the presence of the halo (the susceptible phenotype) being a dominant character. A RAPD marker linked to the gene conferring the chlorotic halo was identified. Genetic distance between this marker, OP-AO07, a polymorphic 420 bp amplicon in the DNA of the susceptible plants, and the locus encoding the chlorotic halo was estimated to be 13 cM.     

Cytogenomic characterization of Colletotrichum kahawae,the causal agent of coffee berry disease,reveals diversity in minichromosome profiles and genome size expansion

Colletotrichum kahawae is an emerging fungal pathogen, which has recently undergone a speciation process from a generalistic ‘C. gloeosporioides species complex' background by acquiring the unique capacity to infect green coffee berries, thus causing coffee berry disease. This is a severe and widespread disease in Africa and an imminent threat to Arabica coffee cultivation in Asia and America, if the pathogen enters those continents. Genetic diversity within C. kahawae is low but notorious differences in pathogen aggressiveness have been described. This work characterized two cytogenomic traits (genome size and minichromosome profiles) of a collection of C. kahawae isolates, representing the breadth of its genetic diversity and distinct aggressiveness classes, along with closely related taxa. The results obtained constitute the first flow cytometry‐based genome size estimation in the genus Colletotrichum and show a c. 8 Mb genome size expansion between C. kahawae (79·5 Mb on average) and its closest relatives (71·3 Mb), corroborating evidence indicating that C. kahawae (i.e. the coffee berry disease pathogens) should remain as a distinct species. Results have also shown the presence of two to five minichromosomes in C. kahawae, suggesting a positive relationship between the number of minichromosomes and the level of aggressiveness of the different isolates analysed, while no correlation could be established between aggressiveness and whole genome size. Overall, these results may be the basis for the identification of pathogenicity/aggressiveness‐related factors in such minichromosomes, and may provide clues to the characterization of specific markers for aggressiveness classes.     

Role of rainfall in the development of coffee berry disease in Coffea arabica caused by Colletotrichum kahawae,in Cameroon

The development of coffee berry disease (CBD) epidemics (caused by Colletotrichum kahawae) in Cameroon was monitored over two successive years (2004 and 2005) on coffee trees protected from rainfall by transparent plastic sheets and on unprotected control trees. This work was done to assess how rain affected disease development when it did not fall directly onto the coffee trees and to determine the influence of primary inoculum on the severity of CBD. Weekly observations over the 2 years showed that there were 1·1% diseased berries on coffee trees completely protected from rainfall, compared with 45% diseased berries on unprotected coffee trees. Disease severity on unprotected trees during the 2 years of the experiment was estimated at 53% diseased berries, compared with 27% on trees only protected in the first year. These results confirmed rainfall as one of the key physical factors in the development of Arabica CBD. They also provided evidence of a subsequent effect of protecting coffee trees from rainfall in 2004 on the severity of CBD in 2005. This suggested some practices that might lead to very effective cultural control of CBD in regions where severe epidemics of the disease occur.     

Evidence of cork barrier formation as a resistance mechanism to berry disease (Colletotrichum coffeanum) in arabica coffee

The histology of resistance to coffee berry disease (CBD) was studied in artificially inoculated berries and hypocotyls of 6-week old seedlings of a number of varieties ofCoffea arabica L. In resistant varieties a phellogen was quickly formed some cell layers below the site of infection and progress of the fungal invasion was effectively blocked by a complete barrier of suberized cells. Such barriers were absent or incompletely developed in CBD susceptible varieties. A highly significant correlation (r=0.87) was found between the frequencies of complete barrier formation in berries and in hypocotyls of young seedlings, while both were also highly correlated to observed mature plant resistance (r>-0.93). Resistance to CBD in arabica coffee may to an important extent be based on the formation of cork barriers. These cork barriers confine the pathogen to the small volume of tissue external to the barrier so that its growth is severely restricted. Such a resistance mechanism is likely to be stable (race-nonspecific). The almost identical response to infection observed in berries and hypocotyls provides further evidence that plants with resistance to CBD can be reliably preselected by the hypocotyl inoculation test.     

梨抗黑星病AFLP标记筛选

 Pear scab caused by Venturia nashicola is one of the most destructive diseases of pears. Molecular markers linked to scab resistance gene is expected to be useful for improving pear. In this study, the F₁ population derived from the cross of ‘Huangguan’ and ‘Yali’ was analyzed genetically. The resistance of pear to scab was proved to be controlled by a single gene in a dominant manner. Bulked segregant analysis (BSA) was conducted to screen 64 fluorescent AFLP primer pairs. A marker designated as D3-365 was found to be linked to the resistant locus. Selective genotype linkage analysis showed that the genetic distance between the marker and the resistant locus was 14.9 cM.     

与番茄枯萎病抗病基因I-1连锁的AFLP和SSR分子标记

本研究以番茄枯萎病抗病品种‘05045’与感病品种‘051451’为亲本配制杂交组合。用870对AFLP引物及319对SSR引物对348个F2代分离群体进行连锁分析,得到4个与番茄枯萎病抗病基因I-1连锁的AFLP标记和2个SSR标记,分别是E41M60-D、E41M62-C、E86M36-B、E32M44-E和SSR108、SSR276,与抗病基因I-1的连锁遗传距离分别为4.7、5.3、8.9、11.5cM和6.1、9.3cM。     

Introgression of crown rust (Puccinia coronata) resistance from meadow fescue (Festuca pratensis) into Italian ryegrass (Lolium multiflorum): genetic mapping and identification of associated molecular markers

Crown rust ( Puccinia coronata ) resistance (CRres), which had been introgressed from meadow fescue ( Festuca pratensis ) into the Italian ryegrass ( Lolium multiflorum ) background, was genetically mapped with amplified fragment length polymorphism (AFLP) and sequence tagged site (STS) markers to a terminal segment of chromosome 5. Comparative mapping had previously shown that this region of the Lolium / Festuca genome has a degree of conserved genetic synteny with chromosomes 11 and 12 of rice. Sequences from rice chromosome 12 were used as templates for identifying further STS markers that cosegregated with CRres. The relative genomic positions of molecular markers associated with CRres in L. multiflorum , L. perenne , F. pratensis and oats is discussed, along with their relationships to physical positions on rice chromosomes C11 and C12.     

小麦材料PI31抗条锈性鉴定及其抗性基因SSR标记

 小麦材料PI31对我国当前流行的条锈菌小种条中30、31和32免疫;遗传分析表明,PI31携带一个显性抗条锈病基因。等位性测定显示,PI31所携带的抗条锈病基因与已知抗锈基因Yr5、Yr10和Yr15不等位。抗源系谱分析表明,该基因来源于叙利亚普通小麦品系叙18;故将此材料携带的抗条锈病基因暂定名为Yr-XU。利用分组分析(BSA)法,筛选到1个位于1 BS的SSR标记WM S11-193 bp片段与Yr-XU紧密连锁,将Yr-XU定位于小麦1BS上;对F₂分离群体142个单株分析结果表明,Yr-XU与WM S11-193 bp的遗传距离为2.1 cM,可将此标记用于小麦抗条锈病分子标记辅助育种。     

抗黄矮病小麦新品系的分子标记检测研究

本研究对以小麦-中间偃麦草异附加系L1和小麦-中间偃麦草部分双二倍体‘无芒中4’为抗源选育出的抗黄矮病小麦新品系进行分子检测和抗病性鉴定.通过应用RAPD、SSR、SCAR 3种分子标记OPF15、Xgwm37、SC-W37进行分子检测,并采用人工接种和大田自然感病的方式进行抗黄矮病鉴定,筛选到了‘93646’、‘2003-2’等高抗黄矮病的小麦新品系.分子检测抗黄矮病基因与田间抗病鉴定结果基本一致,应用的3种PCR标记都可以检测出抗病材料,但SCAR标记SC-W37特异性强、稳定性好,可在小麦抗黄矮病育种早代选择过程中发挥重要作用.     

西瓜抗小西葫芦黄花叶病毒基因的连锁分子标记研究

 小西葫芦黄花叶病毒中国株系(Zucchini yellow mosaic virus Chinese strain,ZYMV-CH)是危害我国西瓜的主要病毒。本实验以抗病毒病西瓜野生种质P.I.595203与感病的普通西瓜自交系98R为亲本,采用单粒传方式得到109个E代株系,分别对亲本、F₁及109个F₃代株系群体进行了苗期抗ZYMV-CH接种鉴定,通过F₃代群体的抗感分离情况,推测得到F₂代各单株的基因型,采用集团分离分析法(bulked segregant analysis,BSA)在F₂代建立抗感基因池,以亲本、F₁和抗感基因池为模板,对640条RAPD引物进行PCR扩增筛选,其中引物AK13在亲本、F₁和抗感基因池之间扩增出一条多态性片段(644bp),在F₂代群体上验证该多态性条带与ZYMV-CH的抗性基因呈现连锁关系,遗传连锁距离为8cM,定名为AK13_-644,该连锁标记在ZYMV-CH抗性转育后代自交系上得到了验证。最终将此RAPD标记成功转化成SCAR标记SCAK13_-644,该标记可以作为西瓜抗病毒病辅助选择的分子标记。     

小麦抗白粉病基因Pm6的微卫星标记鉴定

 Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is a prevalent disease worldwide. Breeding and planting resistance cultivars have been proved effective and environmental friendly for control of the disease. To develop easily used PCR-based markers in marker assisted selection (MAS) for Pm6, a dominant powdery mildew resistance gene in wheat, 25 microsatellite markers on chromosome 2BL in wheat were screened between susceptible parent Yumai13 and resistance parent Timgalen carrying Pm6. F₂ population derived from Yumai13 and Timgalen was further analyzed by the marker Xgwm501. The results indicated that Xgwm501 was a co-dominant marker linked to Pm6 gene at a distance of 14.8 cM. 29 Pm-carrying varieties were tested by the marker Xgwm501 and only those carrying Pm6 showed 117 bp resistance specific band. This marker is proved to have high practicability and can be used in MAS of Pm6 gene in wheat breeding programs.     

Identification and development of molecular markers linked to Phytophthora root rot resistance in pepper (Capsicum annuum L.)

Phytopthora root rot in pepper (C. annuum) is caused by Phytophthora capsici L., which exhibits a high level of pathogenic diversity. Resistance to this disease is conditioned by a number of quantitative trait loci. Pyramiding resistance alleles is desirable and could be simplified by the use of molecular markers tightly linked to the resistance genes. The purpose of this study was development of molecular markers linked to Phytophthora root rot resistance. An F₈ recombinant inbred line (RIL) population derived from a cross between YCM334 and a susceptible cultivar ‘Tean’ was used in combination with bulk segregant analysis utilizing RAPD and conversion of AFLP markers linked to Phytophtora root rot resistance into sequence-characterized amplified region (SCAR) markers. In conversion: one marker was successfully converted into a co-dominant SCAR marker SA133_4 linked to the trait. In bulked segregant analysis (BSA): three RAPD primers (UBC484, 504, and 553) produced polymorphisms between DNA pools among 400 primers screened. Genetic linkage analysis showed that the SCAR and RAPD markers were located on chromosome 5 of pepper. Quantitative trait locus (QTL) analysis showed that the SA133_4 and UBC553 were linked to Phytophtora root rot resistance. These markers were correctly identified as resistant or susceptible in nine promising commercial pepper varieties. These markers will be beneficial for marker-assisted selection in pepper breeding.     

100个小麦品种资源抗条锈性鉴定及重要抗条锈病基因的SSR检测

了解小麦品种资源对中国条锈菌生理小种的抗病性水平及其所含重要抗条锈病基因,可为合理种植和利用小麦品种提供理论依据。选用中国小麦条锈菌不同生理小种CYR17、CYR32、CYR33和V26及条锈菌混合小种分别对100个小麦品种资源进行苗期和成株期抗条锈性鉴定,并采用SSR分子标记技术检测重要抗条锈病基因Yr5、Yr10、Yr15、Yr18、Yr24和Yr26。结果表明,在苗期对4个生理小种均表现抗病性的有‘Mos311’、‘兰天15号’等30个品种;在成株期表现抗病性的有‘Yeoman’、‘兰天1号’、‘小红麦’等88个品种;苗期和成株期均抗病的有‘Mos311’、‘兰天15号’等30个品种。SSR检测发现,‘贵农22’可能含有Yr5,‘兰天23号’、‘兰天24’号、‘中梁04260’和‘中梁04335’可能含有Yr10,‘Little Joss’和‘中梁5号’可能含有Yr15,‘清农3号’、‘兰天2号’、‘中梁04335’等19个品种可能含有Yr18,检测品种可能均不含Yr24和Yr26。在鉴定中保持稳定抗病性的‘Mos311’、‘兰天15号’等8个品种在抗病品种选育中有重要应用价值。     

番茄抗黄化曲叶病基因Ty-2的分子标记及种质资源初步鉴定

以抗番茄黄化曲叶病毒病材料‘CLN2498D’为父本,感病材料‘早粉2号’为母本,以其F2代为研究对象,采用AFLP及SSR两种标记方法,筛选与Ty-2基因连锁的标记。通过对256对AFLP引物及30对SSR引物的筛选,共获得5个AFLP标记和2个SSR标记与Ty-2基因连锁,其中标记E02M11距离目标基因5.8cM,另有3个标记距离均在10cM以内。将标记E02M11用于30份番茄材料的种质资源筛选,获得12个含有该标记的番茄材料,为番茄抗黄化曲叶病毒育种工作提供基础。     

Evolution of resistance to diclofop-methyl in ryegrass (Lolium multiflorum): investigation of the role of introgression with related species

Populations of Lolium multiflorum (ryegrass) exposed to increasing levels of herbicide selection have variability in the rate of evolution of herbicide resistance. We tested the hypothesis that herbicide dose and gene flow with related species are important factors regulating the rate of evolution of herbicide resistance in L. multiflorum. Seeds of the latter were planted in pure stands and in mixture with Festuca rubra and subjected to four herbicide rates. The level of herbicide resistance attained by the offspring after two years of selection was evaluated. Evolution of resistance observed in the field was compared to that calculated by Gressel and Segel's rotational model. ©1997 SCI     

小麦品种(系)抗白粉病基因推导及分子标记鉴定

利用基因推导法和分子标记对我国主要麦区的小麦品种(系)进行了抗白粉病基因的鉴定。结果表明,南30-10等15个品种(系)含有Pm8,新麦2号等9个品种(系)含有Pm4,中植4号等9个品种(系)含有Pm21,郑麦113含有Pm4b+5b,杨09-111和新紫1号含有Pm2+mld。研究发现,基因推导和分子标记相结合,可大大提高小麦品种(系)抗白粉病基因鉴定结果的准确性,鉴定结果可为抗病育种和品种布局及白粉病的防治提供依据。     

青海青稞主栽品种(系)对条纹病和云纹病的抗性鉴定

本研究旨在明确青海青稞主栽品种和后备品种对条纹病和云纹病的抗性,以期为抗病育种及田间病害防治提供理论依据。试验采用田间自然病圃法,对青海主栽的30个青稞品种(系)进行了条纹病和云纹病田间抗性鉴定。结果表明,供试青稞品种(系)对2种病害的抗性存在显著差异,但缺乏免疫品种。对条纹病表现高抗的有13个品种(系),占鉴定总数的43.3%,其中主栽品种有3个,即‘门农1号’、‘昆仑13号’、‘巴青1号’。品系17发病率最低。对云纹病表现高抗的有品系1、品系2、品系6、品系17、品系28、RQKQ-3、RQKQ-5、RQKQ-6、RQKQ-7、RQKQ-8、‘门农1号’、‘互青2号’、‘北青6号’和‘昆仑10号’,共14个,其病情指数均在10以下;表现中抗的共有8个,分别为品系5、品系11、RQKQ-1、RQKQ-9、‘巴青1号’、‘北青3号’、‘北青7号’和‘昆仑13号’。     

小麦品种贵农22 抗条锈基因的遗传分析及分子标记

 贵农22 是由簇毛麦、硬粒小麦以及普通小麦杂交选育而成的普通小麦品种,其对我国目前所有已知条锈菌生理小种均表现高度抗病。为了明确其抗条锈性遗传基础,并对抗条锈基因进行分子作图,本研究选用条锈菌重要小种CYR29、CYR30、CYR32、CYR33 和Su11鄄11,对贵农22 与条锈病感病品种辉县红或铭贤169 杂交F2 代、BC1 F1 代、BC1 F2 代进行抗锈性遗传分析,并对贵农22 控制Su11鄄11 抗病性的1 对隐性基因进行SSR 标记。结果表明,贵农22 至少含有3 对抗条锈病基因。利用272 株贵农22 / 铭贤169 BC1 F2 群体筛选到2 个与贵农22 控制Su11鄄11 抗性的隐性基因连锁的SSR 标记Xwmc44 和Xcfa2147,遗传距离分别为5. 1 和7. 3 cM,并将抗病基因定位于小麦1BL 上,暂命名为YrGn22。基因来源、抗病性分析以及分子检测结果表明,YrGn22 不同于1BL 上的已知小麦抗条锈病基因Yr3、Yr9、Yr21 和Yr29,可能是1 个新基因。