小麦的种和品种对白粉病抗性的初步研究

 在对白粉病具不同抗性的11个小麦的种和品种上进行的按种试验表明,在接种后8小时内,分生孢子达到最高萌发率(约为60%),并形成附着孢。在抗病的和感病的小麦叶片上,分生孢子的萌发率和萌发速度没有差异。接种后12小时,在感病的材料上,发现真菌侵入寄主,但在抗病的材料上,发现最早侵入时间,至少要比在感病材料上约晚4小时。接种后36小时,在高感的材料上,萌发的分生孢子有83%已侵入寄主,其中约有70~80%已形成吸胞。在感病、抗病和高抗材料上的侵入率,分别为70,45,27%。形成或开始形成吸胞的分别为55~61,14~27,4~8%。在抗病材料的表皮细胞内,真菌形成的吸胞较小,并有点畸形。在抗病材料的叶面上,真菌的菌丛稀薄,产孢也很少。     

Interaction between powdery mildew and barley with mlo5 mildew resistance

Powdery mildew infection of barley with the mlo5 barley powdery mildew resistance gene was examined, using near-isogenic barley lines, with and without mlo5 resistance, and two near-isogenic powdery mildew isolates, HL3/5 and GE3 with high (virulent) or low (avirulent) penetration efficiency on the resistant barley line. In all isolate–host combinations (except GE3 on the resistant barley line), frequency of haustorium formation increased significantly from zero at 11 h after inoculation to a maximum by 13 h, and there was no subsequent increase up to 24 h. In the susceptible barley line, 27% of appressoria from both isolates formed haustoria. Although this was significantly higher than the frequency of haustorium formation (18%) of HL3/5 on the resistant barley line, HL3/5 was much more successful than GE3 (frequency of haustorium formation less than 1%). The fact that HL3/5 did not possess a generally higher ability to penetrate successfully to form haustoria on the susceptible barley line, indicates that HL3/5 did not overcome the mlo5 resistance by being generally more vigorous. In the resistant barley line, papillae were larger than in the susceptible line; however, both isolates were associated with papillae of the same diameter at the time of penetration. We suggest that the mlo5 resistant barley line confers two different forms of resistance: isolate-specific and isolate-nonspecific.     

Cytological events in tomato leaves inoculated with conidia of <Emphasis Type="Italic">Blumeria graminis</Emphasis> f. sp. <Emphasis Type="Italic">hordei</Emphasis> and <Emphasis Type="Italic">Oidium neolycopersici</Emphasis> KTP-01

Leaves of tomato and barley were inoculated with conidia of Blumeria graminis f. sp. hordei race 1 (R1) or Oidium neolycopersici (KTP-01) to observe cytological responses in search of resistance to powdery mildew. Both conidia formed appressoria at similar rates on tomato or barley leaves, indicating that no resistance was expressed during the prepenetration stage of these fungi. On R1-inoculated tomato leaves, appressoria penetrated the papillae, but subsequent haustorium formation was inhibited by hypersensitive necrosis in the invaded epidermal cells. On the other hand, KTP-01 (pathogenic to tomato leaves) successfully developed functional haustoria in epidermal cells to elongate secondary hyphae, although the hyphal elongation from some conidia was later suppressed by delayed hypersensitive necrosis in some haustorium-harboring epidermal cells. Thus, the present study indicated that the resistance of tomato to powdery mildew fungi was associated with a hypersensitive response in invaded epidermal cells but not the prevention of fungal penetration through host papilla.     

Defining the resistance risk of the new powdery mildew fungicide quinoxyfen

The new powdery mildew fungicide quinoxyfen belongs to the novel quinoline class of chemistry. Although its biochemical mode of action is unknown, quinoxyfen does not act in the same way as other cereal fungicides. It is a systemic protectant which inhibits the early stages of mildew infection on a wide range of crops, and provides season-long protection from a single early-season spray applied around GS 31. The base-line sensitivity profile of quinoxyfen was defined for barley powdery mildew (Erysiphe graminis f.sp. hordei) from over 340 field isolates collected from different parts of the UK from 1991 onwards. Sensitivities ranged from <0·0001→0·16 mg litre^-1 with a mean of 0·003 mg litre^-1. Current work is extending the base-line sensitivity studies to wheat powdery mildew (E. graminis f.sp. tritici), and includes isolates from European trials, but so far this new data set has shown no differences from barley powdery mildew. Quinoxyfen-resistant mutants were generated in the laboratory, and some similar resistant strains were obtained from treated field crops. These laboratory and field strains were always defective, in some way, for sporulation and, curiously, all required the presence of quinoxyfen for survival in culture. Attempts to generate resistant mutants that sporulated normally were unsuccessful. These studies suggested that the resistance risk for quinoxyfen is low. The recommended anti-resistance strategy accompanying introduction of quinoxyfen avoids seed treatments and late-season applications. Instead, a single early (GS 31) treatment using either pre-formulated mixtures or alternating with a fungicide with different mode of action is recommended. This strategy will be supported by continued monitoring of wheat and barley powdery mildew. ©1997 SCI     

Characterization of Resistance Mechanisms to Erysiphe pisi in Medicago truncatula

ABSTRACT In this work, we studied the resistance of 277 Medicago truncatula accessions against powdery mildew and further characterized the defense mechanisms of resistant plants. Ten resistant accessions were selected according to macroscopic assessment. Histological studies showed a range of defense mechanisms, acting alone or combined, that impeded fungal development at different stages. Some accessions allowed a reduced spore germination frequency compared with that of the susceptible control. In others, the fungus was arrested at penetration stage due to papilla formation. Epidermal cells of several accessions were penetrated by the fungus but then hypersensitive response (HR) leading to cell death hampered fungal development. In some cases, cell death was very fast and no haustorium could be observed in epidermal cells, whereas in others, haustoria and secondary hyphae indicated a slow HR. Finally, in some accessions in which no HR was observed, colony growth was restricted through posthaustorial defense mechanisms. Characterization of defense mechanisms will be useful for further cellular and molecular studies to unravel the bases of resistance in this species in particular and in legume-powdery mildew interaction in general.     

细胞乳突的形成和小麦白粉菌成功侵染的关系

 用一套己知抗白粉病单基因的小麦材料,研究了小麦白粉菌诱发寄主表皮细胞产生的乳突与成功侵染的关系。抗病小麦叶片上,诱发产生乳突的分生孢子占测定分生孢子数的58.8%,感病品种为63.8%。这表明抗性不同的小麦材料接种白粉菌之后,叶表皮细胞内形成乳突的百分率相近,然从在抗病材料和感病材料中形成的乳突阻止病原物发育和成功侵染的作用不相同,在抗病叶片上,诱发产生乳突的分生孢于中有88%停留在压力孢阶段,不继续发育,仅有12%能突破乳突形成吸器,使得侵染成功。与此对照,在感病叶片上只有32%诱发乳突的分生孢子不能穿透乳突,而68%则能突破乳突。成功地与寄主建立寄生关系。我们的研究表明,乳突能否成功地阻止白粉菌侵入可能与乳突形成的迟早有关。     

New tools for studying epidemiology and resistance of grape powdery mildew to DMI fungicides

Using a Random Amplified Polymorphic DNA (RAPD) assay, we investigated the genetic polymorphism existing among 62 European isolates of the grape powdery mildew fungus (Uncinula necator [Schw.] Burr.). Isolates overwintering as mycelium in buds were genetically distinct from isolates overwintering as ascospores, suggesting the existence of two genetically isolated powdery mildew populations, and consequently of two independent sources of inoculum in the vineyard. Isolates resistant to fungicides inhibiting sterol 14α-demethylation (DMIs) were found in both populations, suggesting that resistance to DMIs may arise independently in the two powdery mildew populations. A PCR assay targeting the gene encoding U. necator 14α-demethylase has been developed which will permit an early, specific detection of U. necator infections, and may be useful for spraying programmes. ©1997 SCI     

A standardised method for the quantitative analysis of resistance to grapevine powdery mildew

Powdery mildew caused by Erysiphe necator is one of the most important diseases affecting grapevine (Vitis vinifera, L.). Control of this pathogen is based on the use of fungicides, which cause environmental damage and increase production costs. A cost-effective and environmentally friendly alternative to control the disease relies on using resistant varieties. While most V. vinifera cultivars are susceptible to powdery mildew, several species belonging to the Vitaceae have been described as resistant. Several loci for resistance to grapevine powdery mildew have been identified through genetic analysis of segregating populations derived from different resistance sources. Identifying quantitative trait loci (QTL) with minor effects on the resistance may prove valuable in a strategy of pyramiding, which aims at increasing the durability of the resistance. However, current methods for evaluation of resistance either do not take into account quantitative variations, or, if they do, are not adapted to large sample sets. Here we develop a method for the analysis of quantitative resistance to grapevine powdery mildew in large populations. We devised a semi-quantitative resistance scale and confirmed the usefulness of a cell counter to quantify sporulation. We compared three inoculation methods and identified dry inoculation using a settling tower as the one giving the best infection. Finally, we confirmed the value of the method by applying it to a set of plants segregating for resistance to E. necator. Using the method described here for the quantitative analysis of the resistance to powdery mildew will prove valuable for breeding for durable resistance.     

小麦与白粉病菌互作中β-1,3-葡聚糖的细胞定位

 利用免疫胶体金方法对小麦与白粉病菌互作过程中β-1,3-葡聚糖酶底物,即β-1,3-葡聚糖的合成与分布情况进行了研究。结果发现,白粉病菌的所有器官包括分生孢子、附着胞、入侵栓、吸器和菌丝中均未发现β-1,3-葡聚糖存在;相反,β-1,3-葡聚糖是小麦各种细胞壁的正常组分,在气孔保卫细胞、纤维细胞、导管分子等的细胞壁中含量非常丰富。病原菌的侵染导致植物细胞中β-1,3-葡聚糖的合成增加,但在乳突结构中不含β-1,3-葡聚糖。以上结果说明,往小麦中导入外源β-1,3-葡聚糖酶基因并高效表达,不会对病原菌结构产生直接的破坏和抑制作用;相反,有时可能会影响到某些植物细胞的正常发育。     

Cellular characteristics of temporary partial breakdown of mlo- resistance in barley to powdery mildew

When water-stress is relieved, powdery mildew (Erysiphe graminis f.sp. hordei) infection increases on both Mlo -susceptible and mlo -resistant spring barley cultivars. The breakdown is temporary and is determined by the genetic background rather than the specific resistance allele. The relief of water-stress time-point for maximum mildew infection frequency on mlo -resistant barley is approximately 7 h post-inoculation. The degree of breakdown varies with epidermal cell type; increased infection frequency is greatest on short followed by long and adjacent epidermal cell types, rather than on the stomatal subsidiary cells with which occasional colonies are typically associated. Infection frequency on the short cells of mlo -resistant cv. Atem increases from less than 1% under a non-stressed watering regime to more than 10% after a relief of water-stress at 7 h post-inoculation. Following haustorium formation, colonies develop and reach sporulation within 7 days post-inoculation. In host epidermal cells, the extent of cross-linked protein at interaction sites is reduced under conditions of water-stress or stress-relief. Cross-linked protein is reduced in terms of the frequency of occurrence at primary germ tube interaction sites 7 h post-inoculation and the deposition size at appressorial germ tube interaction sites 24 h post-inoculation. This indicates a delayed or reduced defence response during the recovery period. These data demonstrate a differential cellular response to powdery mildew in barley genotypes prone to resistance expression breakdown following relief of water-stress.     

The resistance to powdery mildew (Oidium lycopersicum) in Lycopersicon species is mainly associated with hypersensitive response

The cultivated tomato ( Lycopersicon esculentum) is susceptible to powdery mildew ( Oidium lycopersicum). Six accessions of three related Lycopersicon species show high levels of resistance (Lindhout et al., 1994b). The present research aimed at describing the development of O. lycopersicum on susceptible cv Moneymaker and characterizing the defence response to O. lycopersicum in Lycopersicon accessions by histological analysis. Spore germination and (primary) haustorium formation in resistant accessions were as frequent as in the susceptible L. esculentum cv Moneymaker. A high frequency of necrosis of epidermal cells in which a haustorium was formed appeared to be the major defence response, indicating that resistance to O. lycopersicum in the Lycopersicon genus was predominantly based on the hypersensitive reaction. However, the resistance in L. parviflorum was less associated with hypersensitivity than in other resistant accessions, suggesting the existence of a different but still unknown resistance mechanism. In addition, evidence is provided that the level of resistance could depend on the genetic background and the plant age.     

The Course of Colonization of Two Different Vitis Genotypes by Plasmopara viticola Indicates Compatible and Incompatible Host-Pathogen Interactions

ABSTRACT The course of colonization of leaf mesophyll by the causal agent of grapevine downy mildew, Plasmopara viticola, in a susceptible and a resistant grapevine genotype was examined in order to characterize the development of the pathogen in compatible and incompatible host-pathogen interactions. Within a few hours after inoculation, the pathogen was established in the susceptible Vitis vinifera cv. Müller-Thurgau and formed primary hyphae with a first haustorium. No further development occurred in the following 10 to 18 h. The next step, in which the hyphae grew and branched to colonize the intercellular space of the host tissue, was observed 1.5 days after inoculation. After 3 days, the intercostal fields were entirely filled with mycelium and sporulation was abundant under favorable environmental conditions. The first infection steps were essentially the same in the resistant V. rupestris. However, the invasive growth of P. viticola was delayed, and further development ceased before the intercostal fields were filled with mycelium.     

Concepts and methods in biological control of diseases in apple orchards1

The project ‘Promotion of Biological Methods in Apple Growing’ which started in Switzerland in 1985 concentrates on the control of Venturia inaequalis (scab) and Podosphaera leucotricha (powdery mildew). The project considers the selection of suitable cultivars resistant or only slightly susceptible to fungal diseases and the assessment of tolerable economic loss. It also includes curative treatments with sterol-synthesis-inhibiting fungicides, according to scab infection periods, as well as applications of plant extracts (proposed by the Institute of Biological Husbandry) and suspensions of antagonists or their culture filtrates as plant-protecting agents. Screening experiments on apple seedlings showed that root extracts of Rumex obtusifolium significantly reduced powdery mildew infections under greenhouse conditions. In field experiments treatments with R. obtusifolium extracts at intervals of 7–10 days were less effective. Saponin-containing extracts of different plants gave satisfying control of scab on seedlings in the growth chamber but were not very effective in the field. Applications of spore suspensions and culture filtrates of the phyllosphere fungi Chaetomium spp. reduced scab and mildew infections on apple seedlings to some extent. It was found that in the last 2 years even primary infections of P. leucotricha were severely parasitized by Ampelomyces quisqualis. Preliminary studies showed that the lack of efficacy of this biocontrol system is due to the delayed spread of the hyperparasite.     

Mechanisms of powdery mildew resistance of wheat – a review of molecular breeding

Powdery mildew (Blumeria graminis f. sp. tritici) results in serious economic loss in wheat production. Exploration of plant resistance to wheat powdery mildew over several decades has led to the discovery of a wealth of resistance genes and quantitative trait loci (QTLs). We have provided a comprehensive summary of over 200 powdery mildew genes (permanently and temporarily designated genes) and QTLs reported in common bread wheat. This highlights the diverse and rich resistance sources that exist across all 21 chromosomes. To manage different data for breeders, here we also present a bridged mapping result from previously reported powdery mildew resistance genes and QTLs with the application of a published integrated wheat map. This will provide important insights to empower further breeding of powdery mildew resistant wheat via marker-assisted selection (MAS).     

分子标记辅助选择小麦抗白粉病兼抗赤霉病聚合体

 Sumai 3, a wheat variety resistant to Fusarium head blight(FHB), was crossed with Neimai 9, a commercial wheat cultivar with the resistance to powdery mildew.The SCAR(sequence characterized amplified region) markers of powdery mildew resistance gene Pm21 and four SSR(simple sequence repeats)markers flanking the major FHB resistance QTL(Qfhs.ndsu-3BS) in Sumai 3 were used to detect the resistance loci by marker assisted selection(MAS) in the plants of the F₂ population.Identification of resistance to both powdery mildew and FHB in field showed that 12 plants resistant to both diseases were obtained.In addition, the agronomic traits of these plants were better than those of Sumai 3, and are perhaps the excellent parental materials for wheat breeding.     

Characteristics and host range of tomato powdery mildew

The anamorphic state of a powdery mildew, which first appeared on tomato in the UK in 1987, currently listed as Erysiphe orontii (anamorph Oidium violae ), was examined microscopically on both tomato and alternative hosts. Host range studies were also carried out. In 1993–95, species and cultivars of plants from 26 of the 30 families listed as hosts of E. orontii were inoculated with tomato powdery mildew in the glasshouse and assessed for susceptibility on a 0–3 scale based on degree of sporulation and growth. Thirteen families contained species or varieties that were susceptible and a total of 80 varieties, including many economically important Cucurbitaceae and Solanaceae, supported sporulation to some extent (susceptibility score 1–3). Necrosis was not a constant feature of plants exhibiting resistance, as it could accompany sporulation on some susceptible varieties. Microscopic measurements showed that conidial size, conidiophore length, conidiophore foot-cell length and width, and the number of cells distal to the foot-cell were remarkably constant between samples of powdery mildew taken from tomato each year and from the various alternative hosts. Based on the production of conidia singly, the presence of nipple-shaped to moderately lobed appressoria, and occurrence of straight conidiophores, it is concluded that this fungus on tomato should more correctly be named Oidium lycopersicum until the sexual stage is discovered. The highly polyphagous nature of this powdery mildew would suggest that it represents a potential risk to UK agriculture and horticulture, but the failure to recover any powdery mildew from 120 samples of potato, including varieties Cara and Maris Piper, on which the tomato powdery mildew could sporulate in the glasshouse, suggests that environmental factors may play a key role in preventing establishment of this powdery mildew on alternative hosts on a commercial scale in the field.     

小麦抗白粉病基因Pm21 的抑制基因

 小麦-簇毛麦6VS. 6AL 易位染色体含有抗白粉病基因Pm21,在我国的小麦育种中被广泛应用。近年来,一些含有Pm21 基因的小麦品种(系)开始感染白粉病。为探索含Pm21 的品种(系)感染白粉病的原因,本研究在6VS. 6AL 易位系与小麦品系(种)R14 和川农12 的杂交后代中利用分子标记CINAU17-1086 和CINAU18-723 辅助选择的遗传背景相对简单的F7 和F8 近等基因系为材料,研究了小麦抗白粉病基因Pm21 的抗病性表达。结果发现,在3 个含有6VS. 6AL 易位染色体的感病F6 植株繁殖的F7 近等基因系中发生了白粉病抗性的分离,分离比率符合13 感病︰ 3 抗病的理论值。在随机选取的F7 感病小麦单株所繁殖的F8 近等基因系中,有7 / 13 的株系一致地重感白粉病,有6 / 13 的株系发生了抗白粉病的分离,其中2 / 13 的株系分离比符合3 感病︰ 1 抗病、4 / 13 的株系分离比符合13 感病︰ 3 抗病的分离模式。这一结果指出,小麦株系中的抗白粉病基因Pm21 的抗性表达受小麦基因组中的一对显性抑制基因所控制,该基因来源于小麦品种(系)川农12或R14,建议命名为SuPm21。本研究指出,在把外源基因引入小麦的研究中,有利的外源基因与不含抑制基因的受体遗传资源同等重要。     

What types of powdery mildew can infect wheat-barley introgression lines?

This work is a detailed study of the infection of fungal biotrophic pathogens causing powdery mildew diseases on introgression lines originating from the intergeneric hybridisation between wheat and barley (Triticum aestivum L. × Hordeum vulgare L.). Powdery mildew fungi are among the most widespread biotrophic pathogens of plants also and infect dicot and monocot species. Most powdery mildew species are strictly host specific. They colonize only a narrow range of species or one particular host species. The intergeneric hybridisation between wheat and barley could result in expansions of host ranges of the barley powdery mildew. Our experiments covered natural infections in the field and artificial infections under greenhouse conditions. Formae speciales of powdery mildew were identified on the basis of the sequencing results of ribosomal internal transcribed spacer sequences (rDNA-ITS). We identified Blumeria graminis f.sp. tritici isolate 14 (HM484334) on the wheat parent and all wheat-barley introgression lines and B. g. f. sp. hordei isolate MUMH1723 (AB 273556) on the barley parent, respectively. The wheat-barley introgression lines were inoculated with barley powdery mildew under greenhouse conditions. According to our results the added barley chromosomes (or segments) do not cause host range expansion of barley powdery mildew.