Apoplastic Sugar Concentration and pH in Barley Leaves Infected with Brown Rust

Soluble sugars were extracted by low speed centrifugation fromthe apoplast of leaves of barley (Hordeum distichum L.) infiltratedwith water. Infection of the leaf with the brown rust fungus(Puccinia hordeii) resulted in a reduction in the concentrationof sucrose, glucose and fructose in the apoplast. Sugars werepresent in an apoplastic space occupying 12 and 17 cm³ m^–2of leaf area in healthy and infected tissue, respectively. Uptakeof hexoses by intercellular hyphae is suggested as a cause ofthis reduction. The pH of apoplastic sap extracted from rust-infectedleaves was increased to pH 7·3 from pH 6·6 incontrols. The effect of a reduced apoplastic sugar pool andincreased pH on export from infected leaves is discussed. Key words: Apoplast, barley (Hordeum distichum L.), brown rust (Puccinia hordeii Otth.), pH, sucrose, hexose     

The Effects of Brown Rust and Phosphate on Cold Acclimation in Winter Barley

The green leaf area of winter barley, cv. Sonja, sampled fromthe field at different times during winter was always greatestin plants grown at high soil phosphate and smallest in plantsgrown at low soil phosphate, and at each fertilizer level wasgreater in healthy plants than in plants infected by rust (Pucciniahordei). In leaves that survived the coldest period of winter,the percentage area that was damaged was increased by rust infectionwhich prevented the ameliorating effects of high soil P. Rustand low P interacted to reduce the increases in leaf area andshoot d. wt that occurred when higher temperatures prevailedin spring. Under controlled conditions in the laboratory, phosphate reducedthe injury suffered when plants not acclimated to low temperatureswere exposed to freezing conditions, but this effect was removedby rust infection. After rust infection, freezing temperatureswere damaging even to acclimated plants, particularly if grownwith low soil P. Evidence of visible symptoms, and quantitativemeasurements of electrolyte efflux from intact leaves, chlorophyllfluorescence in vivo, and ethane and ethylene evolution fromcold-acclimated plants, showed that infection raised the minimumtemperature at which tissues could survive without injury. Infectedleaves were more sensitive to low temperature post-sporulationthan presporulation. Measurements of electrolyte efflux andchlorophyll fluorescence on plants growing under cold conditionsshowed that infection inhibited the processes of acclimationto low temperatures. Winter barley, Puccinia hordei, injury, low temperature, acclimation     

大麦抗叶锈病慢锈性鉴定技术及抗性评价方法

成功的病原菌接种和准确的病情调查是大麦(Hordeum vulgare)抗病研究的基础。该文总结了大麦抗叶锈病慢锈性鉴定实验中几种常用的喷雾和涂抹接种方法, 以及主要的抗性评价指标, 并对操作过程中的一些注意事项进行了说明。     

Quantitative Differences in Powdery Mildew Resistance Among Spring Barley Cultivars

Quantitative powdery mildew resistance in compatible host-pathogen-combinations was measured by the number of pastules/cm² leaf area. Spring barley cultivar ‘Proctor’ was significantly less infected than ‘Golden Promise”. Using these two cultivars (having no effective major resistance gene) as controls, MO- and AR-resistant cultivars were inoculated with virulent mildew isolates. ‘Mona”, ‘Grit’ and ‘Nudinka’ had a higher or, at least, the same level of quantitative resistance as ‘Proctor”. None of the remaining cultivars showed the high susceptibility expressed by ‘Golden Promise”. Ranking of host genotypes was nearly constant while that of mildew isolates varied considerably. Only a small portion of the observed variance was due to interaction between host cultivars and pathogen isolates. ‘Triesdorfer Diva’ gave a resistant infection type after inoculation with different AR-virulent isolates, indicating that this cultivar has major resistance other than that conditioned by gene Ml-a12.     

Quantitative Studies of Resistance Induced By Avirulent Cultures of Erysiphe graminis f. sp. hordei in Barley

Quantification of resistance induced by avirulent cultures of Erysiphe graminis f. sp. hordei against virulent cultures in barley was attempted. Four mildew cultures and 4 barley varieties with known genes of virulence and resistance respectively were used. Pre, post and simultaneous inoculation of leaves was done with avirulent and virulent cultures. Pre-inoculation with avirulent cultures induced resistance in the host such that the pustule number and spore production by later inoculation of virulent cultures was reduced significantly. Once induced, such resistance was active up to 8 days. There was some indication of induced susceptibility if the inducing culture was characterized by medium virulence. Increase of inceulum density of the avirulent (inducer) culture increased the amount of induced resistance Further studies of the phenomenon of induced resistance are needed in relation to possible applications for disease control through inoculations. varietal mixtures and multilines.     

Inoculation Technique for Fungus Cultures

A plastic straw and wood applicator stick serve as a simple, inexpensive, and disposable inoculation unit for fungal studies. The method gives a uniform and intact inoculum. The technique is especially useful because a large number of agar plates can be inoculated rapidly.     

Superoxide Generation in Chemically Activated Resistance of Barley in Response to Inoculation with the Powdery Mildew Fungus

In a previous work, a phenotype-specific accumulation of superoxide radical anions (O^??₂) after attack of the powdery mildew fungus (Blumeria [syn. Erysiphe] graminis f.sp. hordei) in near-isogenic barley (Hordeum vulgare L.) lines bearing different Mlx genes for resistance was described (Hückelhoven and Kogel, 1998). We have now a histochemical study of the pathogenesis-related O^??₂ generation in the systemic activated resistance (SAR) response induced in barley cv Pallas by the plant activator 2,6-dichloroisonicotinic acid (DCINA). SAR-specific defence was conducted prevalently characterized by penetration resistance. Fungal arrest was observed before haustorium formation by a highly localized cell wall reinforcement (effective papillae) and, in most cases, by a subsequent hypersensitive cell death (HR). No O^??₂ generation was found in association with these plant defence responses. However, a strong O^??₂ burst in the attacked epidermal cells was detected in the control plants which were not activated by DCINA. This burst coincided with cell wall penetration and subsequent contact of the pathogen with the host plasma membrane. A strong SAR-related O^??₂ burst was induced in the mesophyll tissue beneath the attacked and hypersensitively reacting epidermal cells in plants treated with DCINA. The accumulation of O^??₂ was confined to chloroplasts. The remarkable burst in mesophyll tissue was not followed by mesophyll-HR indicating that chloroplastic O^??₂ generation is not sufficient for the hypersensitive cell death. Since the same pattern of pathogenesis-related O^??₂ accumulation was identified for race-specific response mediated by the Mlg gene for powdery mildew resistance, the present data are consistent with the hypothesis that the SAR phenotype is a phenocopy of the Mlg-type resistance (Kogel et al., 1994).     

Application of Genomic and Quantitative Genetic Tools to Identify Candidate Resistance Genes for Brown Rot Resistance in Peach

The availability of a complete peach genome assembly and three different peach genome sequences created by our group provide new opportunities for application of genomic data and can improve the power of the classical Quantitative Trait Loci (QTL) approaches to identify candidate genes for peach disease resistance. Brown rot caused by Monilinia spp., is the most important fungal disease of stone fruits worldwide. Improved levels of peach fruit rot resistance have been identified in some cultivars and advanced selections developed in the UC Davis and USDA breeding programs. Whole genome sequencing of the Pop-DF parents lead to discovery of high-quality SNP markers for QTL genome scanning in this experimental population. Pop-DF created by crossing a brown rot moderately resistant cultivar ‘Dr. Davis’ and a brown rot resistant introgression line, ‘F8,1–42’, derived from an initial almond × peach interspecific hybrid, was evaluated for brown rot resistance in fruit of harvest maturity over three seasons. Using the SNP linkage map of Pop-DF and phenotypic data collected with inoculated fruit, a genome scan for QTL identified several SNP markers associated with brown rot resistance. Two of these QTLs were placed on linkage group 1, covering a large (physical) region on chromosome 1. The genome scan for QTL and SNP effects predicted several candidate genes associated with disease resistance responses in other host-pathogen systems. Two potential candidate genes, ppa011763m and ppa026453m, may be the genes primarily responsible for M. fructicola recognition in peach, activating both PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI) responses. Our results provide a foundation for further genetic dissection, marker assisted breeding for brown rot resistance, and development of peach cultivars resistant to brown rot.     

玉米抗镰刀菌穗腐病接种方法及抗病资源筛选研究

对玉米抗穗腐病性鉴定中采用的牙签法与花丝通道注射法进行比较研究表明,牙签法接种果穗的发病程度重于花丝通道注射法接种。牙签法接种病菌于果穗子粒与穗轴之间,有利于病原菌的发育扩展,是一种比较理想的、容易操作的接种方法。采用牙签法接种串珠镰刀菌,对178份玉米自交系和15份杂交种进行抗穗腐病鉴定,筛选出高抗(HR)自交系1份、抗病(R)玉米自交系34份、抗病(R)玉米杂交种12份。     

Identification and Validation of a Major Quantitative Trait Locus for Slow-rusting Resistance to Stripe Rust in Wheat

Stripe (yellow) rust,caused by Puccinia striiformis Westend.f.sp.tritici Eriks (Pst),is one of the most important wheat (Triticum aestivum L.) diseases and causes significant yield losses.A recombinant inbred (RI) population derived from a cross between Yanzhan 1 and Xichang 76-9 cultivars was evaluated for resistance to wheat stripe rust strain CYR32 at both the seedling and adult plant stages.Four resistance quantitative trait loci (QTLs) were detected in this population,in which the major one,designated as Yrq1,was mapped on chromosome 2DS.The strategy of using the Brachypodium distachyon genome,wheat expressed sequence tags and a draft DNA sequences (scaffolds) of the D-genome (Aegilops tauschii Coss.) for the development of simple sequence repeat (SSR) markers was successfully used to identify 147 SSRs in hexaploid wheat.Of the 19 polymorphic SSRs in the RI population,17 SSRs were mapped in the homeologous group 2 chromosomes near Yrq1 region and eight SSRs were genetically mapped in the 2.7 cM region of Yrq1,providing abundant DNA markers for fine-mapping of Yrq1 and marker-assisted selection in wheat breeding program.The effectiveness of Yrq1 was validated in an independent population,indicating that this resistance QTL can be successfully transferred into a susceptible cultivar for improvement of stripe rust resistance.     

An Early Indicator of Resistance in Barley to Russian Wheat Aphid

During early stages of infestation by Russian wheat aphids (Diuraphis noxia [Mordvilko]; RWAs), barley (Hordeum vulgare L.) leaf cells collapsed and showed autofluorescence in the mesophyll and bundle sheath adjacent to the RWA stylet sheath. The response was visually similar to the hypersensitive cell death response, typical of resistance to microbial pathogens. Resistant barley produced significantly more collapsed, autofluorescent cells (CAC) than did susceptible barley. RWA stylet entry sites and sheath paths also fluoresced, making them easy to observe in whole leaf sections. The number of CAC increased with the number of RWAs and with the number of days of feeding in resistant plants. The CAC could be observed 1 d following infestation, making this the most rapid plant response toward the RWAs known to date. The response may be useful in screening for resistant plants and may provide insight into resistance mechanisms in barley.     

Physiologic Races of the Brown Rust of Brome Grasses

A number of cultures of the brown rust of Brome grasses havebeen isolated and maintained as single-spore strains. By theirinfection reactions on a representative selection of Brormusspp. at least five physiologic races have been characterized.Two of these have host-ranges confined to a single section ofthe genus, but others have a much wider host-range within thegenus. The uredospore stage of all was identical. Studies ofthe teleutospores have been limited and knowledge of the speciesof rust involved is incomplete. All belong to the group-speciesPuccinia dispersa Erikss. & Henn.; the species P. brominaErikss. and P. symphyti-bromorum Müller were included amongthe cultures studied, possibly also P. bromi-maximi Guyot. Ina large series of inoculations, over a period of in all 14 years,all physiologic races have been remarkably stable in their infectiontypes and host-range, and no confirmation of Marshall Ward's‘bridging-host’ theory has been obtained. Cultivationof two physiologic races for 164 generations on Bromus arduennensis,a species considered by Ward to have special significance asa bridging-host, induced no changes in their host-range.     

玉米抗南方锈病基因的QTL定位

为发掘新的抗南方锈病基因资源,本研究以感病自交系黄早四为母本、抗病自交系W456为父本,构建F2群体并开展抗病基因定位研究。采用人工接种鉴定的方法对两个亲本、F1、F2群体及对照材料进行表型鉴定和遗传分析。利用均匀覆盖10条染色体的200个SSR标记,分析240个F2单株的基因型并构建含有200个SSR位点的遗传连锁图,连锁图总长度3331 cM,标记间平均距离16.6 cM。使用QTL IciMapping V4.1软件中的完备区间作图法对抗病QTL进行分析,共检测到6个控制南方锈病的QTL:qSCR3、qSCR7、qSCR8-1、qSCR8-2、qSCR9和qSCR10,邻近标记分别为umc2105和umc1729、umc1066和bnlg2271、umc1904和umc1984、umc1984和bnlg1651、umc1957和bnlg1401、umc2034和umc1291,分别位于3、7、8、9和10号染色体上,其中8号染色体上有两个位点,标记区间长度在5～19 cM之间。单个QTL的表型贡献率在2.61%～24.19%之间,可以解释表型总变异的62.3%,其中3个QTL贡献率大于10%,位于10号染色体上的qSCR10贡献率最大,可解释表型变异的24.19%。通过对目标区间标记加密,将该位点的定位区间进一步缩小到2.51 cM内,与两侧标记的距离分别是2.15 cM和0.36 cM。初步定位得到10号染色体上存在抗南方锈病的主效QTL,可为抗病品种的培育提供参考。     

小麦秆锈抗性遗传及抗性基因研究进展

目前国际上已发现近80个小麦抗秆锈基因,其中45个抗秆锈基因已被正式定名,58个抗秆锈基因已定位在小麦特定染色体上,其中12个基因被标记。本文对小麦抗秆锈病基因抗源、抗秆锈性遗传、分子标记研究现状及存在问题加以综述,并对抗秆锈分子遗传前景进行展望。     

Inoculation of Barley with efficient mycorrhizal fungi stimulates seed yield

Summary This short communication proposes the use of soils whose organic N has been lightly enriched in¹⁵N to screen plants for N₂-fixing activity. The major advantage of this approach is that it provides a reliable, integrated estimate of N₂-fixation up to any point in the life cycle of the plant, while using very few plants. The feasibility of the method, from the points of view of cost and availability of suitable soils, is discussed.     

Changes in the Ribonuclease Activity of Flax Cotyledons following Inoculation with Flax Rust

There was a significant increase in the ribonuclease activity of both resistant (Bombay) and susceptible (Bison) varieties of flax (Linum usitatissimum L.) 3 to 4 days after inoculation with flax rust (Melampsora lini [Pers.] Lev., race No. 3). A second and much greater increase in the activity of this enzyme occurred only in the susceptible host at later stages of disease development. While a similar increase in ribonuclease level was also caused by mechanical injury, evidence is presented showing qualitative differences between the enzyme from parasitized tissue and that from the mechanically injured cotyledons. Comparison of the enzyme from healthy and inoculated cotyledons and from flax rust revealed the presence of a relatively unstable component and some unique catalytic properties in the enzyme from inoculated cotyledons.