Inheritance of Powdery Mildew Resistance in Cucumber （Cucumis sativus L.） and Development of an AFLP Marker for Resistance Detection

Cucumber powdery mildew is one of the most destructive diseases of cucumber throughout the world. In the present study, inheritance of powdery mildew resistance in three crosses, and linkage of resistance with amplified fragment length polymorphism （AFLP） markers are studied to formulate efficient strategies for breeding cultivars resistant to powdery mildew. The joint analysis of multiple generations and AFLP technique has been applied in this study. The best model is the one with two major genes, additive, dominant, and epistatic effects, plus polygenes with additive, dominant, and epistatic effects （E-l-0 model）. The heritabilities of the major genes varied from 64.26% to 97.82%, and susceptibility was incompletely dominant for the two major genes in the three crosses studied. The additive effects of the two major genes and the dominant effect of the second major gene were high, and the epistatic effect of the additive-dominant between the two major genes was the highest in cross I . In cross II, the absolute value of the additive effect, dominant effect, and potential ratio of the first major gene were far higher than those of the second major gene, and the epistatic effect of the additive-additive was the highest. The genetic parameters of the two major genes in cross III were similar to those in cross II. Correlation and regression analyses showed that marker E25/M63-103 was linked to a susceptible gene controlling powdery mildew resistance. The marker could account for 19.98% of the phenotypic variation. When the marker was tested on a diverse set of 29 cucumber lines, the correlation between phenotype and genotype was not significant, which suggested cultivar specialty of gene expression or different methods of resistance to powdery mildew. The target DNA fragment was 103 bp in length, and only a small part was found to be homologous to DNA in the other species evaluated, which indicated that it was unique to the cucumber genome.     

Genetic Analysis of the Resistance to Aspergillus flavus Infection in Maize （Zea mays L.）

Maize （Zea mays L.）, one of main crops in the world, is easily susceptible to Aspergillusflavus （Link： fr） infection, resulting huge loses worldwide. Breeding for A. flavus resistance has been proved an efficient way to solve the problem of aflatoxin contamination. Genetic analysis of the sources of resistance to A.flavus in maize is necessary for this purpose. The complete diallel crosses of 6 inbred lines with different resistance to A.flavus infection were implemented. Inoculation categorical data of each cross were analyzed with the additive-dominant and additive-dominant-epitasis genetic models. Results indicated some crosses fitted the 2 major genes with additive-dominant-epitasis genetic model. Others fitted the major gene and polygene mixed model. Moreover, the additive, dominant, and epitasis effects varied in crosses. The A.flavus resistance was controlled by both major gene and polygene.     

Genetic Analysis of Embryo, Cytoplasm and Maternal Effects and Their Environment Interactions for Isoflavone Content in Soybean [Glycine max （L.） Merr.]

Soybean seed products contain isoflavones （genistein, daidzein, and glycitein） that display biological effects when ingested by humans and animals. These effects are species, dose and age dependent. Therefore, the content and quality of isoflavones in soybeans is a key factor to the biological effect. Our objective was to identify the genetic effects that underlie the isoflavone content in soybean seeds. A genetic model for quantitative traits of seeds in diploid plants was applied to estimate the genetic main effects and genotype x environment （GE） interaction effects for the isoflavone content （IC） of soybean seeds by using two years experimental data with an incomplete diallel mating design of six parents. Results showed that the IC of soybean seeds was simultaneously controlled by the genetic effects of maternal, embryo, and cytoplasm, of which maternal genetic effects were most important, followed by embryo and cytoplasmic genetic effects. The main effects of different genetic systems on IC trait were more important than environment interaction effects. The strong dominance effects on isoflavone from residual was made easily by environment conditions. Therefore, the improvement of the IC of soybean seeds would be more efficient when selection is based on maternal plants than that on the single seed. Maternal heritability （65.73%） was most important for IC, followed by embryo heritability （25.87%） and cytoplasmic heritability （8.39%）. Based on predicated genetic effects, Yudou 29 and Zheng 90007 were better than other parents for increasing IC in the progeny and improving the quality of soybean, The significant effects of maternal and embryo dominance effects in variance show that the embryo heterosis and maternal heterosis are existent and uninfluenced by environment interaction effects.     

Genetic analysis of the maximum germination distance of Striga under Fusarium oxysporum f. sp. strigae biocontrol in sorghum

Maximum germination distance(MGD) is an important component of Striga resistance in sorghum. The objective of this study was to determine gene action influencing MGD of Striga hermonthica and Striga asiatica among selected sorghum lines treated with a biocontrol agent, Fusarium oxysporum f. sp. strigae(FOS) for effective breeding with Striga resistance, and FOS compatibility. Twelve sorghum genotypes were selected based on their Striga resistance, FOS compatibility, and superior agronomic performance. Selected genotypes were crossed using a bi-parental mating design to generate six families for genetic analysis. Agar-gel assays were used to determine low haustorium initiation factor(LHF) using the 12 parental lines, their F_1 progenies, backcross derivatives, and F_2 segregants in two sets. One set had S. hermonthica seed and the other one had S. asiatica seed. Both were treated with and without FOS. Genotypes were evaluated using a split-plot design with three replications and MGD data were recorded followed by generation mean analysis. FOS reduced MGD by 1cm under both S. hermonthica and S. asiatica infestations. Additive, dominance, and epistatic gene actions were involved in the control of MGD of the two Striga species in the evaluated populations. On average, the relative contribution of additive, additive×additive and dominance×dominance genetic effects on the MGD of S. hermonthica and S. asiatica, with FOS, were 20, 33, and 36%; and 21, 32, and 35%, respectively. Breeding methods exploiting these genetic effects may provide enhanced response to selection for Striga resistance and FOS compatibility in integrated Striga management(ISM) programmes.     

Diallel Crossing Analyses of Resistance to Main Diseases in Pepper （Capsicum annuum L.）

Fifteen capsicum combinations were made with 6 parents by （1/2）n（n-1） diallel crossing. Genetic parameters in the resistance to TMV, CMV, phytophthora blight, bacterial spot of these combinations were studied by Hayman. The results indicated that the resistance to TMV, CMV and bacterial spot conformed genetically to the “additive-dominant” model but the resistance to phytophthora blight did not and significant epistatic dominance effect existed in it. F1 hybrid＇s resistance to CMV was controlled by homozygous dominant gene （s）, but resistance to bacterial spot by heterozygous one （s）. There were little, or no sum of dominant effect and genomes controlling the dominant expression of F1 hybrids in its phytophthora blight resistance.     

Postulation of Seedling Resistance Genes in 20 Wheat Cultivars to Yellow Rust （ Puccinia striiformis f. sp. triticl）

The gene postulation, cluster analysis and pedigree analysis of 20 wheat cultivars to 28 physiological races of yellow rust （Puccinia striiformis） were conducted under greenhouse conditions, The spectrum of their resistance were compared each other. None of the 20 cultivars were resistant to all the test pathogens. The cultivars containing resistance genes Yr5 and Yr24 were not find and genes Yr8, Yrl9 and Yr27 could not be postulated from cultivars tested due to the susceptibility to all isolates used. A total of 6 probale seedling yellow rust resistance genes or gene combinations （Yrl, Yr2, Yr2 ＋ YrHVII, Yr3 ＋ unknown, Yr3 ＋ Yr4, YrAlba） were postulated in the wheat cultivars （Atou, Flanders, Maris Huntsman, Bouquet, Holdfast, Elite Lepeuple, and Vilmorin 27）. The gene combination Yr2＋YrHVII with the highest frequency （35%） was present in 7 cultivars. The Yr genes present in some wheat cultivars could not be postulated because of non-matching virulence combinations with any of known genes. Cluster result showed that Yr2 and Yr3 are the most important genes in the cultivars. The 13 cultivars are believed to have the pedigree of Noe, which was selected from South Russian wheat. These results will be useful for wheat breeding and provide information about genetic control of wheat yellow rust.     

Genetic and Genotype x Environment Interaction Effects for Appearance Quality of Rice

This study was conducted to generate genetic information in rice varieties based on a complete diallel crosses over two years. The results indicated that genotype effect was significant for all traits. Genotype × environment interaction effects were significant only for cooked grain length （CGL） and cooked grain shape （CGSH）. General combining ability （GCA） and specific combining ability （SCA） effects were significant for entire traits, which indicated the important roles of both additive and non-additive gene actions. GCA x environment interaction effects were significant for CGL, CGSH and grain elongation index （GEI）. In the controlling of the inheritance of milled grain shape （GSH）, milled grain width （MGW）, GEI, milled grain length （MGL）, CGSH and cooked grain width （CGW）, the additive gene effects were more important than non-additive one. The average degree of dominance was within the range of partial dominance for all of the traits. The narrow-sense heritability was ranged from 0.65 （GSH） to 0.36 （CGL）. GCA effects were significant for all of the parents in milled grain length and it was significant for some of the parents in other traits. The crosses of Deilmani × IRFAON-215 exhibited significant SCA for GEI. The positive mean of heterosis was observed for CGW. The highest maximum values of heterosis were revealed in GEI, flowed by GSH, MGW and CGW. GCA and MPV were significantly and positively correlated together for all traits.     

Application of Synthetic Hexaploid Wheat Derived from T.Durum,Ae,Taushii in Common Wheat Breeding for FHB Resistance

The F1 and F4 plants of ‘synthetic hexaploid wheat/common wheat’ crosses and part of their parents were inoculated with Fusarium graminearum to evaluate FHB resistance.The results showed tht the scab resistance in the F1 varied with the synthetic wheat accessions used as crossing parents.In the F4,some resistant head lines were generated from the crosses,although their parents had different scab resistance levels.It indicated that synthetic hexaploid wheat are useful in wheat breeding for scab resistance.     

Studies on the Developmental Genetics of Tiller Number in Three-line Indica Hybrid Rice

Following NC Ⅱ design, the developmental genetic behavior of tiller number (TN) in three-line indica hybrid rice was studied using additive-dominance developmental genetic models and the corresponding statistical methods. The results showed that dominance effects were predominant for TN. The expression of those additive effects were affected by environment and genotype interaction, but the expression of dominance effects were not affected. Heterosis was the strongest in the middle developmental periods of TN. Additive effects and dominance effects were selectively expressed throughout in the entire tillering developmental stage.Analysis of genetic correlation between TN at different stages and the productive panicles indicated that a close correlation appeared earlier in the populations with higher heterosis than in those with less heterosis. Utilization of heterosis at the middle tillering stage might enhance the final biomass but reduce the percentage of productive panicles.     

Progress Towards Genetics and Breeding for Minor Genes Based Resistance to Ug99 and Other Rusts in CIMMYT High-Yielding Spring Wheat

Wheat rusts continue to cause significant losses worldwide despite major efforts given to their genetic control. This is due to frequent evolution and selection of virulence in pathogen overcoming the deployed race-specific resistance genes. Although the life of effective race-specific resistance genes can be prolonged by using gene combinations, an alternative approach being implemented at CIMMYT is to deploy varieties that posses adult plant resistance （APR） based on combinations of minor, slow rusting genes. When present alone, the APR genes do not confer adequate resistance especially under high disease pressure; however, combinations of 4 or 5 minor genes usually result in ＂near-immunity＂ or a high level of resistance. Although only a few APR genes are catalogued, various APR QTLs are now known and could lead to further characterization of additional genes. Four characterized genes have pleiotropic effects in conferring partial APR to all 3 rusts and powdery mildew, thus simplifying the task of breeding wheat varieties that are resistant to multiple diseases. Significant progress was made recently in developing high-yielding wheat germplasm that possesses high levels of APR to all three rusts by implementing a Mexico- Kenya shuttle breeding scheme. Parents with APR to Ug99 were hybridized with high-yielding parents that had adequate to high levels of APR to leaf rust and yellow rust. Segregating populations and advanced lines from these crosses were selected under high rust pressures in Mexico （leaf rust and yellow rust） and Kenya （Ug99 stem rust and yellow rust） to identify high- yielding progenies that possess high to adequate APR to all three rusts. International distribution of these high-yielding wheats is underway through CIMMYT intemational yield trials and screening nurseries. It is expected that several wheat varieties with APR to three rusts will be released and grown in various countries in the near-future that will allow determining the durability of resistance.     

Epistasis and Maternal Effect in Resistance to Puccinia coronata Cda.f.sp. avenae Eriks in Oats(Avena sp.)

The objective of this paper was to investigate the mode of heredity for resistance in oats(Avena sp.)to crown rust caused by Puccinia coronata Cda.f.sp.avenae Eriks.Eight generations of 2 crosses were used to estimate genetic effects and narrow-sense heritability(NSH).Separate generation means analysis(GMA)indicated a complex gene action controlling this trait with additive,dominance,epistatic and maternal effects(ME).The genetic model which assumed no epistasis and no ME did not accurately describe the resistance to P.coronata.In both crosses,the digenic epistatic model with ME was sufficient to explain variation in generation means for isolate CRPc58 and isolate CRPc46.Additive dominance and epistatic components were negative in most cases,suggesting that gene effects contributed more to the resistance than to the susceptibility.The estimated values of NSH were 15-99% depending upon the cross and isolates.The results indicated that appropriate choice of maternal parent and recurrent selection would increase resistance to crown rust in oats.     

甘蔗对锈病的抗性遗传与育种策略Ⅱ．亲本组合抗锈病的配合力分析

对甘蔗９个亲本品种及其选配的２０个杂交组合抗锈病的配合力分析表明,甘蔗对锈病的抗性遗传主要是由基因的加性效应所控制,母本对后代抗性的影响较大．发现抗锈ｇｃａ效应高的亲本为ＣＰ７２－１２１０、新台糖１号、川５７－４１６、崖８４－１５３和ＣＰ５７－６１４,可作为抗源亲本利用．根据配合力总效应评价组合,认为ＣＰ７２－１２１０×川５７－４１６、新台糖１号×崖８４－１５３、ＣＰ７２－１２１０×崖７３－５１２、Ｃ５７－６１４×川５７－４１６和ＣＰ７２－１２１０×崖７１－３７４是抗锈病强的亲本组合,可以用于甘蔗的抗锈育种．     

三种麦类作物对叶(冠)锈菌非寄主抗病性与品种抗病性的组织病理学研究

比较研究了小麦、黑麦和燕麦对小麦叶锈菌、黑麦叶锈菌和燕麦冠锈菌的非寄主抗病性与品种抗病性的组织病理学特点。接种幼苗的荧光显微检查表明,非寄主抗病性除不同程度地中断侵入外,主要抑制侵染菌丝生长和吸器母细胞的形成,引起菌落早期败育和叶肉细胞坏死。这些特点与品种抗病性的过敏性坏死反应相同。这种类型的抗病性具有小种专化性,因而即使用遗传操作技术将这种非寄主抗病性转移到寄主品种中,也可能因病菌小种的变异而不会持久。     

玉米主要性状的基因效应其与杂种优势关系的研究

利用7个性状差異较大的玉米自交系组成4个杂交第1代(F_1)以及B_1B_2和F_2,采用世代均数分析法,以最适模型或六参数模型的效应值为数量指标,对玉米主要性状的基因效应进行了分析,探讨了基因效应与优势表现和衰退的关系,结果表明:1.穗长、穗直径、穗行数、行粒数、穗粒数、单穗粒重和百粒重等,显性作用明显,加性效应和上位性效应作用程度的大小因组合而異;2.根的抗拉力、叶而积、叶向值,株高和吐丝期的叶绿素含量等,显性作用明显,上位性效应因组合不同而大小各異,加性效应作用最小;3.叶片数和果位高的加性效应在所有组合中均达到显著水平,其效应值的高低因组合而異,上位性效应和显性效应在多数组合中作用明显;4.根的抗拉力和百粒重的遗传,参试的所有组合均符合加性,显他和上位性双基因互作模型,其中根的抗拉力符合重复互作类型,5.基因效应的分析结果与杂种优势的表现和衰退基本一致。杂种优势的表现和衰退是显性效应或显性与上位性效应共同作用的结果。     

普通小麦-柔软滨麦草易位系M8657-4抗条锈病基因的遗传分析

[目的]对普通小麦-柔软滨麦草易位系M8657-4的抗条锈病基因进行遗传分析,明确其抗条锈病基因及遗传特点。[方法]用中国小麦条锈菌CYR29、CYR30、CYR31、CYR32、Su11-4及Su11-11共6个生理小种对易位系M8657-4的苗期抗条锈性进行评价;采用常规杂交法对M8657-4的抗条锈病基因进行遗传分析。[结果]易位系M8657-4对中国小麦条锈菌具有良好的抗性;M8657-4对菌系CYR29和Su11-4的抗锈性由2对核基因（互补作用）控制,对CYR31的抗锈性由1对隐性核基因控制,对Su11-11的抗病性,M8657-4做母本时由2对基因（互补作用）控制,M8657-4做父本时由1对隐性基因控制。[结论]易位系M8657-4的抗条锈性由主效基因控制,可将其作为优良种质加以开发利用。     

Genetics and Molecular Mapping of Stripe Rust Resistance Gene YrShan515in Chinese Wheat Cultivar Shan 515

Stripe rust is one of the most important wheat diseases worldwide. To identify new resistance genes is significant in wheat breeding. In this study, stripe rust resistance of a Chinese cultivar Shah 515 was tested with Chinese predominant races of P. striiformis f. sp. tritici in the seedling stage, and genetic analysis and simple sequence repeats (SSR) technique were used to identify the inheritance model of seedling stripe rust resistance in cultivar Shan 515 and to mark the sites of resistance gene(s) on chromosome. The genetic analysis indicated that the resistance of Shan 515 against Su 11-4 was conferred by a single dominant gene, which was temporarily designated as YrShan515. Using bulked segregant analysis (BSA) and SSR markers, 12 SSR markers (Xwmc335, Xwmc696, Xwmc476, Xbarc267, Xgwm333, Xwmc653, Xwmc396,Xgwm213, Xgwm112, Xgwm274, Xcfd22, Xgwm131, and Xwmc517) located on wheat chromosome 7BL were linked to YrShan515 with genetic distance ranging from 3 to 24 eM. Based on the previously published genetic map and Chinese Spring nulli-tetrasomic analysis, YrShan515 was located on wheat chromosome 7BL. Polymorphism of wheat cuitivars collected from Huanghuai wheat grown regions were screened with two markers, Xwmc653 and Xbarc267, and all of these wheat cultivars tested did not present the polymorphic bands as Shan 515 did. Therefore, it suggested that YrShan515 might be a allele of the available yellow rust resistance gene. The mapping of the new resistance gene in Shan 515 is useful for wheat breeding and diversification of resistance genes against stripe rust in commercial wheat cultivars in China.     

玉米株型性状的基因效应研究

采用世代分析方法对玉米株型性状的遗传模型、基因效应及其与亲本的关系进行了研究。结果表明，６个月组合的６０个性状中分别为１０个和２２个性状的遗传符合加性－－显性，加性－－显性－－上位性遗伟模型。     

中国小麦叶锈菌群体的毒性基因分析

 1986-1991年间，利用已知抗叶锈病基因的小麦近等基因系（或单基因系）作鉴别寄主，首次采用毒性基因频率、毒性因子（FV）、毒性值（VV）和Shannon-Wiener多样性指数等反映群体水平的参数，对我国小麦叶锈菌的毒性基因结构、频率、时间动态、空间格局及不同生理小种毒性基因的异质性等进行了比较分析。结果表明，毒性基因 V2a、V9、V15、V19、V24、V28、V29的出现频率较低（小于30%），其对应的抗性基因为目前我国小麦叶锈菌的有效抗病基因；V1、V3ka、V10、V26的频率处于升高的趋势，V2a、V15的频率有下降的趋势；不同地区叶锈菌群体的毒性因子、毒性值和毒性基因组合的多样性明显不同，我国和北美的叶锈菌至少存在4-5个毒性基因的差异；不同生理小种的毒性基因结构差异显著，叶中3号不具备V26基因，叶中34号不具有V1、V14a、V17和V27基因，而叶中4号携带有这些毒性基因。文中还对利用近等基因系作鉴别寄主的优点进行了讨论。