几种非豆科植物根瘤内生菌侵染特征的研究

自不同科、属、种的非豆科植物根瘤分离内生菌,对其寄主植物进行了交叉侵染,结果表明,这些Frankia菌对不同寄主的侵染没有明显的专一性,供试菌可以进行跨越科、属、种的侵染,但有的菌株对于某些植物的侵染,可能存在一些特殊情况,相同菌株对不同植物的侵染能力,以及不同菌株对同一寄主的侵染能力是有差异的。从同一种植物根瘤中分离的不同菌株,侵染能力也有高低之分,供试菌随寄主植物的改变,侵染能力及所建立的共生系统固氮活性有所降低,侵染原寄主植物所形成的根瘤固氮活性较高的菌株,在改变寄主后所形成的根瘤固氮活性也比较高,在一定条件下,寄主植物的结瘤量与根瘤固氮活性呈正相关,而侵染不同寄主后,根瘤中菌体孢子的表面结构也发生了一定变化。     

几种非豆科植物根瘤内生菌侵染特征的研究

自不同科、属、种的非豆科植物根瘤分离内生菌,对其寄主植物进行了交叉侵染,结果表明,这些Frankia菌对不同寄主的侵染没有明显的专一性,供试菌可以进行跨越科、属、种的侵染,但有的菌株对于某些植物的侵染,可能存在一些特殊情况,相同菌株对不同植物的侵染能力,以及不同菌株对同一寄主的侵染能力是有差异的。从同一种植物根瘤中分离的不同菌株,侵染能力也有高低之分,供试菌随寄主植物的改变,侵染能力及所建立的共生系统固氮活性有所降低,侵染原寄主植物所形成的根瘤固氮活性较高的菌株,在改变寄主后所形成的根瘤固氮活性也比较高,在一定条件下,寄主植物的结瘤量与根瘤固氮活性呈正相关,而侵染不同寄主后,根瘤中菌体孢子的表面结构也发生了一定变化。     

核盘菌致病机理研究进展

菌核病(Sclerotinia stem rot,SSR)是我国油料作物生产中主要病害之一,严重制约长江中下游地区油菜主产区的产业发展。菌核病的病原是子囊菌门的核盘菌,是一种世界性分布的重要植物病原真菌。其寄主范围广泛,引起的菌核病对多种作物的产量和品质造成重要影响。核盘菌作为典型的死体营养型病原真菌,侵染寄主植物时通过直接杀死细胞和破坏组织攫取生长所需的营养物质。核盘菌的致病机理相对复杂,前期研究主要集中在其分泌的水解酶类(角质酶、细胞壁降解酶和蛋白酶等)和草酸在核盘菌侵染寄主植物中的作用。近些年来,越来越多的研究证实了分泌蛋白在核盘菌的致病过程中同样发挥着重要作用。分泌蛋白(效应蛋白)主要通过诱导植物细胞死亡或抑制寄主细胞的免疫反应,促进核盘菌的侵染和定殖。综述了水解酶类、草酸和分泌蛋白等在核盘菌致病机制中的作用,并对核盘菌致病机理研究进行了展望,以期为菌核病的安全防控提供理论参考。     

棉花黄萎病菌的侵染过程

深入揭示黄萎病菌的致病机理,为培育高抗新品种提供理论依据和技术途径,是有效控制黄萎病的根本.本文系统探讨了土壤中微菌核或孢子受寄主根系分泌物的刺激,开始萌发、产生的菌丝在寄主根表面定殖、穿过表皮、在皮层中发生及在寄主体内扩展和症状形成等黄萎病菌侵染棉花的过程,阐述了寄主植物形成多级防御反应阻击病原菌的入侵.对黄萎病菌侵染寄主植物过程及其机理下一步研究的问题和内容进行了讨论.     

小麦纹枯病菌侵染过程的组织学研究

本文报道了小麦纹枯病菌(Rhizoctonia cerealis)侵染小麦的过程。病菌在穿透寄主之前产生侵染垫、菌丝圈以及形态简单的单附着胞等侵染结构。由侵染垫基部菌丝或附着胞产生的侵染菌丝直接或通过气孔侵入寄主,也可见菌丝直接侵入寄主;菌丝侵入寄主表皮后,迅速在受侵细胞内呈网状扩展,并直接穿透毗邻细胞壁,向其它细胞纵横扩展。受病组织出现细胞变形、变空;接近菌丝的质膜发生质壁分离,质膜断裂：叶绿体变形、变小或接近消失,类囊体被破坏,叶绿体内嗜饿颗料减少或无;线粒体解体等系列组织病变。     

晶杯菌科3个新种（英文）

对来自四川、甘肃和青海的晶杯菌科盘菌采集物进行分类研究,发现了3个新种,它们隶属于黄杯菌属和绒被盘菌属。竹黄杯菌的子囊盘直径0.2-0.5mm,子实层表面米色至米灰色;子囊具8个子囊孢子,孔口在Melzer’s试剂中呈蓝色,58-68×4.5-5.5μm;子囊孢子梭形,具一个分隔,8-12×2.3-3μm。单胞黄杯菌的子囊盘盘状,直径1mm,子实层表面污黄色;子囊具8个子囊孢子,孔口在Melzer’s试剂中呈蓝色,82-92×6-8μm;子囊孢子梭形,14-21×2-3.5μm。隔孢绒被盘菌的子囊盘盘状,直径0.5-1mm,子实层表面白色至淡灰色,子层托表面具短棒状细胞延伸物;子囊棒状至近圆柱形,具8个子囊孢子,孔口在Melzer’s试剂中呈蓝色,73-84×6.8-7.5μm;子囊孢子柱梭形,具3个分隔,18-20.5×2.5-3.3μm。     

Lanzia berggrenii及其相关种的系统发育地位(英文)

系统发育分析结果表明,尽管Lanzia berggrenii能在寄主中形成基物子座,但与膜盘菌属的核心种关系较近,而与蜡盘菌科成员关系较远,应该归属于膜盘菌属。在广义的膜盘菌属的系统树中该种及在新西兰发现的4个新种构成一个单系群,分别命名为Hymenoscyphus haasticus,H. kiko,H.ohakune和H.waikaia。它们的共同特征:基物均为南青冈叶片,侧丝顶端分枝形成类似囊层被的结构,覆盖于子实层上部。Lanzia berggrenii var.metrosideri应为膜盘菌属中一个独立的种,即Hymenoscyphus metrosideri。     

烟粉虱(Bemisia tabaci)的寄主选择性

通过田间系统调查、实验室嗅觉测定、笼内和培养皿内自由扩散观察,对烟粉虱的寄主选择性进行了研究.结果表明,在田间,烟粉虱对不同的寄主植物存在明显的寄主选择性,其中对茄子、花椰菜、黄瓜等植物具有较强的嗜性,而对蕹菜、芹菜、苋菜等植物的嗜性较差;烟粉虱对同一植物的不同品种也有明显的选择性.烟粉虱对寄主植物颜色有明显的选择性,选择结果与烟粉虱对这些寄主的嗜性趋势基本一致.烟粉虱对单株寄主植物的嗅觉反应不敏感,但对植物叶片的乙醇抽提物有明显的嗅觉反应,并表现出较强的寄主选择性.在养虫笼内,烟粉虱从虫源皿向寄主植物自由扩散的过程中,在不同寄主植物和同一植物的不同品种上着落的成虫数量不同,并且在一定的时间范围内,着落在寄主叶片上的虫量还会不断的发生变化.     

茶树上斑痣盘菌科一新种

茶树（Ｃａｍｅｌｌｉａｓｉｎｅｎｓｉｓ（Ｌｉｎｎ．）Ｋｕｎｔｚｅ）枝上小双梭孢盘菌属一新种,即茶小双梭孢盘菌（Ｂｉｆｕｓｅｌｌａ　ｃａｍｅｌｌｉａｅ）．该属在阔叶树寄主上为首次报道。模式标本保藏在安徽农业大学森林保护教研室。     

不同培养基质和寄主植物对AMF扩繁的影响

研究了在室内盆栽条件下,不同培养基质和不同寄主植物对丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)扩繁的影响。在纯土、纯沙和沙土混合不同基质中,接种3种AMF于玉米武科2号、玉米陕单335、高粱和三叶草4种不同寄主植物,测量每种AMF的侵染率、孢子密度和寄主植物地下干重,筛选适宜的培养基质和寄主植物。结果表明,不同培养基质、不同种类和不同品种的寄主植物对AMF的侵染率、孢子密度和寄主植物地下干重均有显著影响。地表球囊霉(Geosiphon versiforme)的最适基质是纯土,最适寄主是高粱;根内球囊霉(Rhizophagus irregularis)和摩西球囊霉(Funneliformis mosseae)的最适基质是沙土混合,最适寄主是玉米武科2号。     

Modelling Fungal (Neozygites cf. Floridana) Epizootics in Local Populations of Cassava Green Mites (Mononychellus Tanajoa)

The fungus, Neozygitis cf. floridana is parasitic on the cassava green mite, Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) in South America and may be considered for classical biological control of cassava green mites in Africa, where cassava is an important subsistence crop, cassava green mites are an imported pest and specific natural enemies are lacking. Spider mites generally have a viscous structure of local populations, a trait that would normally hamper the spread of a fungus that is transmitted by the contact of susceptible hosts with the halo of capilliconidia surrounding an infectious host. However, if infected mites search and settle to produce capilliconidia on sites where they are surrounded by susceptible mites before becoming infectious, then the conditions for maximal transmission in a viscous host population are met. Because the ratio between spider mites and the leaf area they occupy is constant, parasite-induced host searching behaviour leads to a constant per capita transmission rate. Hence, the transmission rate only depends on the number of infectious hosts. These assumptions on parasite-induced host search and constant host density lead to a simple, analytically tractable model that can be used to estimate the maximal capacity of the fungus to decimate local populations of the cassava green mite. By estimating the parameters of this model (host density, per capita transmission rate and duration of infected and infectious state) it was shown that the fungal pathogen can reduce the population growth of M. tanajoa, but cannot drive local mite populations to extinction. Only when the initial ratio of infectious to susceptible mites exceeds unity or the effective growth rate of the mite population is sufficiently reduced by other factors than the fungus (e.g. lower food quality of the host plant, dislodgement and death by rain and wind and predation), will the fungal pathogen be capable of decimating the cassava green mite population. Under realistic field conditions, where all of these growth-reducing factors are likely to operate, there may well be room for effective control by the parasitic fungus. This revised version was published online in November 2006 with corrections to the Cover Date.     

Biotic Interaction between a Rust Fungus, Uromyces erythronii Pass., and its Host Plant, Erythronium japonicum Decne. (Liliaceae)

Abstract A characteristic pattern of infection by a rust fungus, Uromyces erythronii Pass, on its host plant, Erythronium japonicum Decne. (Liliaceae) was observed in a field population for three years from 1981 to 1983. Due to the primary infection by teliospores of U. erythronii in the soil layer, spermogonia and aecia were formed on the abaxial leaf surface along the midrib of E. japonicum. In the case of flowering individuals, however, spermogonia and aecia were only formed on the larger of the two leaves. An increase of individuals bearing telia was restricted by rapid decaying of leaf tissue of the host plant. A high percentage of rusted individuals was observed in the Erythronium populations, and U. erythronii obviously has some effects on the growth of its host plant. However, its infection does not appear to be a direct cause of the death of Erythronium individuals in the field populations.     

Infection by powdery mildew Erysiphe cruciferarum (Erysiphaceae) strongly affects growth and fitness of Alliaria petiolata (Brassicaceae)

Garlic mustard (Alliaria petiolata) is an invasive biennial that negatively impacts plant and animal communities throughout North America and lacks significant herbivory in its invasive range. Throughout Ohio, many garlic mustard populations support the powdery mildew fungus Erysiphe cruciferarum, although disease incidence varies among populations and environments. Effects of infection on plant growth, as well as both plant and fungal responses to drought and light conditions, were examined on greenhouse-grown, first-year garlic mustard plants. Also, the effects of the fungus on plant growth and fitness were studied in a naturally growing population of second-year plants in the field. Powdery mildew significantly reduced growth of first-year plants in the greenhouse, eventually causing complete mortality. Simulated drought slowed both plant growth and disease development, independent of light conditions. In the field, plants with little incidence of disease after their first year grew taller during their second year, producing significantly more siliques and twice as many seeds as heavily diseased plants did. Seed germination rates did not differ between plants with different levels of disease severity. Consistent reductions in survival, growth, and fitness caused by fungal infection may reduce populations of garlic mustard. These effects may be more evident in moist sites that favor fungal development.     

Variation in host susceptibility among and within populations ofPlantago lanceolata L. infected by the fungusPhomopsis subordinaria (Desm.) Trav.

Summary Susceptibility toPhomopsis stalk disease ofPlantago lanceolata genotypes, sampled in three different populations with a variable degree of infection by the fungusPhomopsis subordinaria, was determined under greenhouse conditions. Susceptibility of the host varied within, but not among populations. No relationship between the intensity of the disease in the field and the mean susceptibility of the host genotypes sampled at those locations could be established. Host susceptibility appeared to be composed of the host genotypes sampled at those locations could be established. Host susceptibility appeared to be composed of different (uncorrelated) plant characteristics. Determining whether host genotypes are highly or slightly susceptible can only be achieved by field trials, where the plants are exposed to the whole set of disease inducing factors. The relevance of host susceptibility to the intensity of disease in the field is discussed in relation to the variation in pathogenicity of the fungus and the variation in environmental factors prevailing inP. lanceolata populations underP. subordinaria pathogen pressure. Grassland Species Research Group Number 123     

The Differentiation of Infection Structures as a Result of Recognition Events between some Biotrophic Parasites and their Hosts

Most uredospores of rust fungi develop infection structures in a typical pattern so that they can infect the host plant. The function of these infection structures is divided into the following three phases:

• 1 In the recognition phase, the germ tube recognizes the cuticle and the stoma. This process may occur independently from the host plant since copies of the cuticle induce similar reactions of the fungus. During fungal growth on the epidermis, unspecific stress responses of the plant are triggered.
• 2 In the signal phase, the fungal substomatal vesicle and infection hypha(e) contact the host cells within the leaf parenchyma. A signal from the host induces further development of the fungus. Haustorium mother cell differentiation is effected and haustorium formation is initiated. At the same time, the fungus suppresses the synthesis of stress metabolites by the plant.
• 3 In the parasitic phase, the fungus penetrates the host cell and complex interactions between host and parasite begin. A highly specialized interface around the haustorium develops presumably in order to allow a more efficient nutrient transfer from host to parasite. Eventual defence reactions of the plant, generally on the race-cultivar level, fail to be evoked or are suppressed in compatible combinations.

     

SEX-SPECIFIC COSTS OF RESISTANCE TO THE FUNGAL PATHOGEN USTILAGO VIOLACEA (MICROBOTRYUM VIOLACEUM) IN SILENE ALBA

Costs of resistance are often invoked to explain the maintenance of polymorphisms for resistance to fungal pathogens in natural plant populations. To investigate such costs, 27 half-sib families of Silene alba, collected from a single host population, were grown in experimental populations in the presence and absence of the anther-smut fungus Ustilago violacea, a host-sterilizing pathogen transmitted by insects that are both pollinators and vectors of the disease. Host families differed significantly in resistance to inoculation, indicating the presence of genetic variation for mechanisms that impede fungal growth once the disease is encountered (“biochemical” resistance) within the host population. In addition, host families differed significantly in onset of flowering and in flower production in the absence of the disease. Path analysis revealed that late onset of flowering in male host families made a direct contribution to high field resistance (P < 0.01), probably due to a reduced rate of contact between hosts and vectors carrying high spore loads (avoidance, or “phenological” resistance). The contribution of low flower production to field resistance only approached significance (P < 0.10). There was a significantly positive genetic association between biochemical and phenological resistance, suggesting that delayed flowering is either a pleiotropic effect of biochemical resistance, or that genes governing these traits are in linkage disequilibrium. Path analysis revealed that biochemical resistance made both a direct contribution to field resistance (P < 0.01) and a positive indirect contribution via its association with phenology and flower production (P < 0.05) in male hosts. Costs of resistance were sex specific. Male host families with high field resistance had significantly lower reproductive success in healthy populations, indicating a fitness cost of field resistance (P < 0.01), whereas no costs were detected for female hosts. Path analysis revealed that the biochemical component of field resistance made no direct contribution to the observed fitness cost in male hosts, whereas its indirect effect through phenology was only marginally significant (P < 0.10). This finding indicates that fitness costs were mainly due to the phenological component of field resistance. Because the host population had no known history of disease, it is not clear whether the fitness costs are responsible for maintenance of the resistance polymorphism or whether the polymorphism is present for reasons unrelated to pathogen infection. Interactions between host families and pathogen strains with respect to inoculation success were not significant. Hence, there was no evidence for indirect costs of biochemical resistance, that is, reduced resistance to alternative strains. Infection rates in experimental populations with an initially patchy distribution of the pathogen were lower than in populations with a uniform pathogen distribution, suggesting that the effective pathogen pressure and hence the relative success of susceptible and resistant individuals may, in addition to fitness costs of resistance, depend on the spatial population structure of the pathogen.     

EXPERIMENTAL EVIDENCE FOR GENETIC VARIATION IN COMPATIBILITY BETWEEN THE FUNGUS ATKINSONELLA HYPOXYLON AND ITS THREE HOST GRASSES

Variation in compatibility has been documented within and among several natural plant populations infected by fungal pathogens. In this study, seeds and isolates of the fungus Atkinsonella hypoxylon (Ascomycetes, Clavicipitaceae) were collected from three populations of the grass Danthonia spicata, two populations of D. compressa, and four populations of Stipa leucotricha. Each fungal strain was reciprocally inoculated into seedlings grown in aseptic culture from its original host population, into seedlings from other conspecific host populations, and into seedlings from the other two host species. There were three distinct patterns of compatibility, as evidenced by the ability of the fungus to grow on the seedling and to colonize new tillers. Fungal strains from one host genus were incompatible with seedlings from the other host genus. Strains from the two Danthonia species were broadly compatible among Danthonia populations and had very high rates of infection, while strains from Stipa also were broadly compatible among Stipa populations but had relatively low rates of infection. Literature surveys indicate that, in contrast to pathogenic microorganisms, mutualistic microorganisms typically exhibit broad patterns of compatibility among hosts, which lack resistance to infection. The effect of A. hypoxylon on host fitness is most detrimental in Stipa, where the fewest seedlings became infected, and most beneficial in Danthonia, where most seedlings became infected.     

Preliminary host specificity testing of Endophyllum osteospermi (Uredinales, Pucciniaceae), a biological control agent against Chrysanthemoides monilifera ssp. monilifera

Chrysanthemoides monilifera ssp. monilifera, indigenous to the Western Cape Province of South Africa, is a serious invader of native vegetation in south-eastern Australia. The rust fungus Endophyllum osteospermi causes witches' brooms on C. monilifera ssp. monilifera in South Africa, and is associated with a reduction in growth and seed production of its host under natural conditions, as well as mortality of severely infected bushes. This rust fungus is considered to be a potential biological control agent for use against C. monilifera ssp. monilifera in Australia. Endophyllum osteospermi has a long latent period, typically between 6 and 24 months between infection and the initiation of witches' brooms. This long latent period makes the logistics of doing traditional host specificity testing, in which all test plant species are inoculated and observed for symptom development, unfeasible for this rust fungus. Germination of aecidioid teliospores and penetration by basidiospores were observed on the surface of excised leaves of 32 test plant species at 4 days after inoculation, and compared to that on C. monilifera ssp. monilifera. Germinating aecidioid teliospores aborted on 14 test plant species, whilst no penetration was attempted on a further 12 test plant species. Penetration only occurred on nine of the 32 test plant species, in addition to C. monilifera ssp. monilifera. Inoculating whole plants of nine selected test plant species confirmed the above results. Therefore, only the test plant species in which penetration occurred, or at least was attempted, need to undergo comprehensive host specificity testing. Pending these results, E. osteospermi may be suitable for release in Australia for the biological control of C. monilifera ssp. monilifera.     

Inbreeding alters resistance to insect herbivory and host plant quality in Mimulus guttatus (Scrophulariaceae)

Previous studies have demonstrated genetic variation for resistance to insect herbivores and host plant quality. The effect of plant mating system, an important determinant of the distribution of genetic variation, on host plant characteristics has received almost no attention. This study used a controlled greenhouse experiment to examine the effect of self- and cross-pollination in Mimulus guttatus (Scrophulariaceae) on resistance to and host plant quality for the xylem-feeding spittlebug Philaenus spumarius (Homoptera: Cercopidae). Spittlebugs were found to have a negative effect on two important fitness components in M. guttatus, flower production and above ground biomass. One of two M. guttatus populations examined showed a significant interaction between the pollination and herbivore treatments. In this case, the detrimental effects of herbivores on biomass and flower production were much more pronounced in inbred (self) plants. The presence of spittlebug nymphs increased inbreeding depression by as much as three times. Pollination treatments also had significant effects on important components of herbivore fitness, but these effects were in opposite directions in our two host plant populations. Spittlebug nymphs maturing on self plants emerged as significantly larger adults in one of our host plant populations, indicating that inbreeding increased host plant quality. In our second host plant population, spittlebug nymphs took significantly longer to develop to adulthood on self plants, indicating that inbreeding decreased host plant quality. Taken together these results suggest that the degree of inbreeding in host plant populations can have important and perhaps complex effects on the dynamics of plant-herbivore interactions and on mating-system evolution in the host.