白粉病菌侵染诱导的大麦叶肉细胞变化的超微结构与细胞化学

 从超微结构和细胞化学角度对大麦白粉病菌侵染诱导的寄主叶肉细胞变化进行了研究。结果发现,病原菌接种后12 h,叶肉细胞光合作用的标志性酶RCA和Rubisco含量发生迅速的变化,感病大麦(Ingrid)中RCA和Rubisco含量急剧减少,而抗病大麦(mlo-3)中则趋势相反。随后,不论在感病或抗病大麦中这2种蛋白的含量一直下降,但感病品种中一直维持相对较高水平。超微结构观察表明,病原菌侵染能够诱导侵染点附近叶肉细胞中叶绿体的增殖,新叶绿体的不断产生,从而延缓了叶肉细胞的衰老和死亡,增加了光合产物的形成。以上结果说明,叶肉细胞可能从养分供给上影响到了表皮细胞中病原菌吸器的发育。     

湖北麦区小麦白粉病菌毒性结构分析

对湖北省不同年度（2001、2003年和 2007年）、同一年度（2007年）不同生态区间的小麦白粉病菌毒性基因频率进行了比较。结果表明,毒性基因 V2、V4b、V13、V20、V21、V2+MLD、V2+6、V4+8和V4b+Mli在测定的 3个年度中毒性频率均低于25%,而V1、V3b、V3c、V3d、V3e、V5、V8、V17和V193个年度的毒性频率均高于50%;白粉病菌毒性结构年度之间和生态区之间均基本相似,但个别毒性基因年度及生态区间存在一定的差异; V2、V3a、V3b、V3c、V3e、V5、V6、V7、V8和V20在十堰以及武昌 2 个生态区毒性频率年度间均有明显的上升趋势,而V4b、V5（MLi）、V13、V21、V5+6则表现为下降的趋势;2007年仅在十堰生态区检测到V2+Mld和V2+6菌株。     

Virulence patterns in populations of Erysiphe graminis f.sp. hordei in Europe in 1986

A total of 3166 single colony progeny of Erysiphe graminis f.sp. hordei , constituting random samples of the aerial inoculum from 68 regions of Western Europe, were analysed in the laboratory for virulence to barley resistance genes Mlra, Mlg, Mla6+Mlg. MILa, Mla7+Mlk, Mlall, Mla9, MlaI3 + MlRu3. Mlal, Mla3 and mlo. No isolate virulent to mlo was detected. Distinct regional patterns were observed for the frequencies of most of the other virulence genes. They stressed the role of selection exerted by the cultivars grown, as well as the effect of wind dissemination of mildew populations. These two phenomena are particularly well exemplified by the data on early stages in the evolution of the newly emerging Val3 virulence in Denmark. In contrast with the preceding evolution, there was a considerable decrease of the frequency of a broadly distributed virulence ( Va6); the most probable reasons for this are outlined.     

Development of genetic SSR markers in Blumeria graminis f. sp. hordei and application to isolates from Australia

The barley powdery mildew pathogen, Blumeria graminis f. sp. hordei (Bgh), exists in numerous haplotypes and displays significant differences in fungicide sensitivity. It causes considerable yield losses throughout the world. Microsatellite SSRs are useful tools to study the population level and biogeographic aspects of intraspecific diversity, but so far none have been defined for Bgh. Here, eight polymorphic microsatellite loci were identified and characterized. Primer pairs amplifying the loci were then applied to 111 isolates of Bgh from Australia. The number of alleles per locus ranged from 4 to 13, and Nei's genetic diversity ranged from 0·25 to 0·76. The microsatellite primers detected several clones among the isolates and defined 97 unique haplotypes. There was little evidence for regional genotypic subdivision, suggesting that gene flow may not be restricted among geographic regions. All data was consistent with high levels of genetic diversity, potentially resulting from random mating and spread within each region.     

Impact of proquinazid on appressorial development of the barley powdery mildew fungus Blumeria graminis f.sp hordei

The effect of a novel mildew-specific quinazolinone fungicide, proquinazid, on the barley powdery mildew fungus, Blumeria graminis f.sp. hordei, has been studied using scanning electron microscopy and quantitative RT-PCR. Proquinazid has previously been shown to perturb conidial morphogenesis, similar to quinoxyfen, a currently widely used mildewicide. In this study, we confirm an effect of proquinazid on appressorial differentiation. By comparison to quinoxyfen, however, proquinazid affects this highly coordinated process differently, with more deformed appressorial germ tubes observed, often growing away from the leaf surface. Comparison of the expression of genes involved in the transduction of signals directing conidial development has also suggested differences in the affects of proquinazid and quinoxyfen. In particular, the expression of the Ras-type GTPase activating gene, previously implicated in quinoxyfen resistance, is distinctly affected by proquinazid treatment at time points critical to normal conidial morphogenesis. Together, these data indicate differences in the mechanisms by which proquinazid perturbs appressorial differentiation in comparison with quinoxyfen.     

Genetics of avirulences in Erysiphe graminis f.sp. hordei

The genetics of avirulences towards barley mildew resistances were analysed in crosses of the Ervsiphe graminis f.sp. hordei isolate DH14 with CC107 and with CC138. Nine avirulences, Av r_a9, Avr _a10, Avr _a11, Avr _a12, Avr _Ab, Avr _CP, Avr _h, Avr _k and Avr _La, segregated as single genes in one or other cross. However. F₁ segregation data were consistent with avirulence matching the Mla7 resistance gene being controlled by two genes, designated Avr _a7 1 and Avr _a7 2. Infection types of avirulent isolates differed on varieties in which Mla7 had been derived from each of the four known sources of that resistance. Linkage was detected between Avr _a7 1 and Avr _h in the cross CC107 × DH14, and between Avr _a10 and Avr _k, Avr _a11 and Avr _La, and Avr _h and the triadimenol response gene Tdl2 in CC138 × DH14.     

Relative tolerances of wild and cultivated barleys to infection by Blumeria graminis f.sp. hordei (Syn. Erysiphe graminis f.sp. hordei). I. The effects of infection on growth and development

The two lines of wild barley, B19909 and I-17-40 and the cultivated barley, cv. Prisma used in this investigation were found to be the most susceptible to infection of 25 wild and four cultivated barley lines when exposed to the local population of Blumeria graminis f.sp. hordei. All three lines were susceptible during the early stages of growth but expressed some level of adult plant resistance although this level of resistance was significantly higher in line I-17-40 than in either of the other two.The relative tolerances of the lines to the mildew were determined by comparing the effects of infection on their growth and development in growth cabinet experiments. Mildew developed more slowly on line I-17-40 than on the other two lines and by the third week after inoculation, when mildew cover on B19909 and cv. Prisma had reached about 27%, only about 15% of the green leaf area of line I-17-40 was covered. Mildew continued to increase on line B19909 and cv. Prisma so that 6 weeks after inoculation it covered 40% of their leaf-blades. On line I-17-40 30% of the green leaf area was colonised by 4 weeks after inoculation but because of adult plant resistance coupled with the loss of the earlier infected leaves through senescence mildew cover then reduced falling to 15% by 6 weeks. Although total mildew biomass, measured as conidial production was higher on line B19909 than on cv. Prisma all its growth parameters were reduced less indicating that it was the more tolerant line. Conidial production on the lower susceptible leaves of line I-17-40 was slightly lower than on cv. Prisma yet the reaction of these leaves to infection was the same on both lines indicating that tissues of I-17-40 were slightly less tolerant than those of the cultivated barley. However, during the later stages of growth when its upper leaves expressed high levels of ‘adult plant resistance’ dry matter production in this line increased to levels higher even than in the controls. This capacity for compensatory photosynthesis ensured that by the end of growth few differences in any of the measured growth parameters between infected and uninfected plants of line I-17-40 were significant.The greater tolerance of line B19909 over the other two lines and of cv. Prisma over line I-17-40 during the early stages of growth appears to be due to a lower sensitivity to infection of those processes which regulate dry matter accumulation and its distribution around the plant.     

An apparatus for collecting total conidia of Blumeria graminis f.sp. hordei from leaf colonies using electrostatic attraction

Conidia from living conidiophores of barley powdery mildew ( Blumeria graminis f.sp. hordei ) on host leaves were collected consecutively using an electrostatic spore collector. The collector consisted of an electrical conductor plate linked to an electrostatic voltage generator and insulator plates placed abreast on a timed conveyer. The conductor plate was negatively charged by the potential supplied from the voltage generator. The negatively charged conductor plate caused dielectric polarization of the insulator plate, and the surface charge on the insulator plate attracted mature conidia abstricted from conidiophores on colonies growing on leaves placed 2 cm from the insulator plate. The surface charge on the insulator plate was proportional to the voltage applied to the conductor plate. Under optimized conditions, abstricted conidia were attracted to the electrostatically activated insulator plates without any detriment to their survival. During a colony's life span of c . 460 h, conidia were released throughout the day and c . 12 × 10⁴ conidia were collected during the lifetime of the colony. This is the first report on the direct quantification of progeny conidia produced by powdery mildew infecting host leaves.     

High diversity, low spatial structure and rapid pathotype evolution in Moroccan populations of Blumeria graminis f.sp. hordei

Limited information is available about the spatial distribution and evolution of Blumeria graminis f.sp. hordei populations in North African countries, such as Morocco. Frequencies of virulence alleles in B. graminis populations are mainly driven by selection exerted by host resistance genes in addition to neutral processes such as migration and genetic drift. In Morocco, in contrast to Europe, there has been no systematic deployment of resistant cultivars, although some R genes are present in the traditional varieties. This is expected to result in the evolution of pathotypes with virulence to different R genes, and higher diversity in Morocco compared to Europe. To test this, we used 24 differential cultivars to characterise 72 isolates from Morocco in 2009. We assessed diversity and spatial structure of pathotypes and compared them to past isolates from the same area (collected in 1992). There was a high diversity of pathotypes. Isolates from 2009 were distinct from isolates from 1992, due to loss of virulence to Mla12, increased virulence to Mla8, Mla3 and Mlk1, and decreased virulence to Mla6, Ml(Ru2), Mlg and MlLa. Many virulences were different from those observed in European and Asian populations of B. graminis. At the spatial scale investigated, airborne dispersal and a lack of strong selection in the host population likely prevented the formation of population structure and allowed the accumulation of high isolate diversity. The evolution of novel and distinct pathotypes since 1992 is likely attributable to gene flow from Europe and selection by the host population in Morocco.     

Effect of Film-forming Polymers on Infection of Barley with the Powdery Mildew Fungus, Blumeria graminis f. sp. hordei

The effects of three film-forming compounds, Ethokem, Bond and Vapor Gard, on infection of barley by the powdery mildew fungus Blumeria graminis f. sp. hordei were examined in glasshouse and field experiments. The three compounds provided significant control of powdery mildew infection when applied as pre- or post-inoculation treatments in the glasshouse. Such treatment had no effect on plant growth. Bond and Vapor Gard reduced the germination of conidia of B. graminis by 78% and 85% respectively, and reduced the subsequent formation of appressoria (73% and 85% respectively) and haustoria (75% and 79% respectively). The three compounds were less effective in field experiments, although they provided significant control of mildew infection and had no impact on plant growth and grain yield.     

甘肃省小麦白粉菌群体毒性及小麦品种苗期抗白粉病性分析

由Blumeria graminis f.sp.tritici引起的小麦白粉病是危害甘肃省小麦安全生产的重要病害之一,分析病原菌毒性结构和抗病基因有效性对于指导白粉病的有效控制具有重要意义。2013年对甘肃省小麦白粉菌群体进行毒性分析结果表明,91个供试菌系中,对Pm1、Pm2、Pm3a、Pm3b、Pm3c、Pm3d、Pm3e、Pm3f、Pm4a、Pm4b、Pm5a、Pm6、Pm7、Pm8、Pm19、Pm33、Pm5+Pm6、Pm4+Pm8、Pm4b+Pm5b和PmEra的毒力频率达到70%以上,已无利用价值;对Pm13、Pm16、Pm21和Pm24的毒性频率在15%以下,尚可利用。选用甘肃省不同毒性谱的单孢堆菌系,对35个甘肃省及国内生产品种(系)进行苗期致病性测定,发现仅有‘绵麦37’具有优异抗病性。供试白粉菌系对‘定西40号’等22个品种(系)的毒性频率达到60%以上,甘肃省及中国生产品种中,苗期抗病品种(系)匮乏。     

小麦白粉病菌对氟唑菌酰羟胺的敏感基线建立

氟唑菌酰羟胺是一种新型琥珀酸脱氢酶抑制剂(succinate dehydrogenase inhibitor, SDHI)类杀菌剂,2019年在我国登记在小麦上防治赤霉病,为明确其对小麦白粉病的潜在防治效果,以及为监测小麦白粉病菌群体对其是否产生抗药性,本文采用离体叶段法测定了2000年前和2019年采自我国河南、山东等9省市的110株小麦白粉病菌菌株对氟唑菌酰羟胺的敏感性。结果表明,采自2019年的88株菌株,其EC50范围为0.010 2~0.766 8 μg/mL,平均EC50为(0.224 3±0.179 6)μg/mL;采自2000年前的22株菌株,其EC50范围为0.052 1~0.882 4 μg/mL,平均EC50为(0.356 3±0.279 6)μg/mL;两组菌株群体间的敏感性无显著差异。氟唑菌酰羟胺对110株菌株的EC50范围为0.010 2~0.882 4 μg/mL,平均EC50为(0.250 7±0.210 3)μg/mL,敏感性频率分布呈单峰曲线,可作为小麦白粉病菌对氟唑菌酰羟胺的敏感基线。本研究结果可为氟唑菌酰羟胺防治小麦白粉病以及未来监测该病原菌对药剂的抗性提供参考依据。     

Effect of early infection on pathotype frequencies in barley powdery mildew (Blumeria graminis f.sp. hordei) populations in field plots

A field experiment with barley powdery mildew ( Blumeria graminis f.sp. hordei ) was designed in order to study how the time of arrival of inoculum in the field influenced pathotype frequencies in the resulting populations. Three isolates belonging to pathotypes that were absent or rare in the local aerial inoculum were used to inoculate field plots of winter barley cv. Plaisant. Two successive inoculations with different combinations of the three isolates were performed with an approximately two-generation delay, and frequencies of inoculated pathotypes were assessed four and nine generations after the first inoculation. Pathotypes of the first inoculated isolates generally persisted throughout the period of sampling; this is described as an 'early arrival' effect. During the epidemics the inoculated isolates were not replaced by isolates from the natural airborne inoculum. Pathotype frequencies depended mainly on the time of arrival of inoculum in the plot, but frequencies also depended on the isolate that had been inoculated. The most frequent isolate, GL1, belonged to the clonal lineage dominant in powdery mildew populations on winter barley in the north of France. These results confirmed that the composition of a powdery mildew population in a field is largely determined by the composition of the initial inoculum.     

Infection-inhibition activity of avenacin saponins against the fungal pathogens Blumeria graminis f. sp. hordei, Bipolaris oryzae, and Magnaporthe oryzae

Triterpenoid saponins are sugar-modified triterpene derivatives. Cereals and other grasses are generally deficient in these secondary metabolites with the exception of oat. Oat accumulates antimicrobial triterpenoid saponins in its roots. These oat-root-derived compounds, called avenacins, confer broad-spectrum resistance to soil-borne pathogens. Here, we tested the effect of avenacins on the development of infection structures of fungal pathogens Blumeria graminis f. sp. hordei and Bipolaris oryzae and Magnaporthe oryzae. We show that avenacins are able to inhibit the infection process of these phytopathogens on plant hosts.     

Susceptibility-inducing factor (suppressor) from Blumeria graminis f. sp. hordei has no effect on the primary infection of the fungus

When fungal germlings, after forming haustoria of Blumeria graminis f. sp. hordei (B. graminis), were removed from the surfaces of barley coleoptiles by cellulose acetate, followed by challenge inoculation with the non-pathogen Erysiphe pisi, they infected the nonhost barley coleoptile cells. This phenomenon was not observed on the coleoptile surface when the fungal germlings of B. graminis were removed before the formation of haustoria. Also, when the surface was inoculated with the pathogen of barley B. graminis as a challenger, after removing the fungal germlings of inducer post haustorial formation, the penetration efficiency of the fungi increased significantly compared with that of the control. Furthermore, when we extracted the crude-susceptibility inducing factor (suppressor) from coleoptiles before and after the formation of haustoria of B. graminis, suppressor activity against infection with E. pisi was observed only in the extract of barley coleoptiles that included haustoria of B. graminis about 18 h or later after inoculation. Surprisingly, however, the extract did not increase the penetration efficiency of B. graminis significantly. Thus, we hypothesize that the suppressor extracted from barley coleoptiles in which B. graminis had formed haustoria has no effect on increasing the penetration efficiency of the primary infection from the appressorium of B. graminis but has an effect on the infection with non-pathogen E. pisi.     

Structure and evolution of a population of Erysiphe graminis f.sp. hordei

Samples of single colony isolates of Erysiphe graminis f.sp. hordei were collected in Cambridge on three dates in 1985, and tested for the presence of 12 virulence alleles and resistance to two fungicides, triadimenol and ethirimol. The frequency of the virulence V-(La) fell during 1985, while the frequency of V-h. virulence on cv. Triumph and higher levels of resistance to each fungicide and combined resistance to both fungicides rose. Two phenotypes, both of which possessed virulence on cv. Triumph and three unnecessary virulence alleles and had similar sensitivities to ethirimol, but differed in their level of resistance to triadimenol, accounted for 35.9% of all isolates. The high frequency of these phenotypes accounted for most of the observed gametic phase disequilibria between pathogenicity characters. Most individuals with these two phenotypes may be members of the same clone. It was estimated that 25% of the spore population which initiated the autumn epidemic of E.g. f.sp. hordei originated from ascospores formed by sexual reproduction in the summer. It is proposed that genetic drift followed by hitch-hiking selection, due to intense selection for a clone virulent on a newly-introduced cultivar, is a major factor influencing the frequency of unnecessary virulence alleles.     

The spread oi Erysiphe graminis f. sp. hordei in mixtures of barley varieties

A model is proposed of mechanisms which might affect the progress of Erysiphe graminis f. sp. hordei in mixtures of barley varieties. Results obtained from two field trials indicate that the efffect of mixtures may be panitioned into three categoriesof the influence of the reduced density of the susceptible plants, the barrier effect of the resistant plants, and the induced resistance due to the non-virulent pathogen biotypes. In the early stages of plant growth the lower density of susceptible plants accounted for most of the reduction in pathogen development in mixtures. As the epidemic progressed, the barrier and induced resistance effects increased in importance and the total mixture effect was at a maximum mid-way through epidemic development. Towards the end of the trials the overall mixture effect declined though the influence of induced resistance was at its maximum. The reasons for these changes and their implications for the use of host varietal mixtures in disease control are discussed.
Mixtures also protected the crop against a pathogen other than the target organism.