Comparative ultrastructure of aecial and telial infections of the autoecious rust fungus Puccinia tuyutensis

This study demonstrates morphological differences between aecial and telial stages of the autoecious rust Puccinia tuyutensis. The aeciospores possess verrucose ornamentation while the teliospores have smooth surfaces. The aecial and telial haustoria of this rust produced in the mesophyll of Cressa cretica differ morphologically in the following respects:(1) the haustorial mother cell of telial haustorium is more differentiated than that of aecial haustorium and its wall at the penetration site is composed of 4 layers; (2) the aecial haustorium is filamentous in appearance and slightly constricted at the point of entry into the host cell, while the telial haustorium is clavate and possesses a narrow neck with a densely staining neckband and swollen body; (3) the neck of the telial haustorium is always associated with numerous vesicles while that of the aecial haustorium is not. Vascular tissue of host leaves is heavily invaded by aecial haustoria but not by telial haustoria.     

Cronartium orientale, sp. nov., segregation of the pine gall rust in eastern Asia fromCronartium quercuum

The Asian pine gall rust, which has hitherto been assigned toCronartium quercuum distributed in North America, is described asC. orientale, sp. nov. The spermogonial and aecial states occur on hard pines, and the uredinial and telial states occur on various oaks.Cronartium orientale has globose, almost hyaline basidiospores in contrast to the ellipsoid, yellow-orange ones of North AmericanC. quercuum s.l. Characteristics of the new rust species in morphology, DNA analysis, and host alternation are discussed.     

A new rust species ofRoestelia onSorbus collected in China

A rust species ofRoestelia onSorbus collected in China is newly described asR. echinulata. This species is morphologically different from the otherRoestelia spp. and aecial stages ofGymnosporangium species in surface structures of aeciospores and peridial cells. Contribution No. 141, Laboratory of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

Phylogenetic relationships among Puccinia hemerocallidis, P. funkiae, and P. patriniae (Uredinales) inferred from ITS sequence data

Puccinia hemerocallidis and P. funkiae resemble each other morphologically; however, they are biologically and taxonomically distinct, with telia of the former being restricted to species of Hemerocallis and the latter to Hosta species. However, both fungi share a macrocyclic and heteroecious life cycle with Patrinia villosa as the spermogonial and aecial host. An additional microcyclic rust fungus, P. patriniae, is also known on P. villosa. This microcyclic fungus is similar to the two macrocyclic fungi in its telial structure and teliospore morphology. These similarities in morphology and host relationships suggest the three fungi may also share a close evolutionary relationship. To determine the phylogenetic relationships of the three species, a portion of the nuclear ribosomal DNA repeat encoding the ITS and 5.8S subunit regions was amplified by PCR, sequenced, and analyzed. The resulting phylogenetic trees showed that P. hemerocallidis and P. funkiae share a recent common ancestor and that P. patriniae is closely allied with P. hemerocallidis. The results suggest a possible evolutionary derivation of microcyclic P. patriniae from macrocyclic heteroecious P. hemerocallidis, which fits the evolutionary interpretation of correlated species known as Tranzschel's law.     

Aeciospore surface structures ofGymnosporangium andRoestelia (Uredinales)

Aeciospore surface structures of 40Gymnosporangium species and 7Roestelia species were investigated with a scanning electron microscope. The surface structures of aeciospores were classified into 12 types on the basis of shape and size of processes. Surface structures of the aeciospores were stable within each species. Therefore, it is suggested that surface structures of aeciospores could be used as an important diagnostic criteria in identifyingGymnosporangium andRoestelia species. Contribution No 139, Laboratory of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

Phylogenetic studies in <Emphasis Type="Italic">Ravenelia esculenta</Emphasis> and related rust fungi

Ravenelia esculenta Naras. and Thium. is a rust fungus, which infects mostly thorns, inflorescences, flowers and fruits of Acacia eburnea Willd. Aecial stages of the rust produce hypertrophy in infected parts. DNA of the rust fungus was isolated from aeciospores by ‘freeze thaw’ method. 18S rDNA was amplified and sequenced by automated DNA sequencer. BLAST of the sequence at NCBI retrieved 96 sequences producing significant alignments. Multiple sequence alignment of these sequences was done by ClustalW. Phylogenetic analysis was done by using MEGA 3.1. UPGMA Minimum Evolution tree with bootstrap value of 1000 replicates was constructed using these sequences. From phylogenetic tree it is observed that Ravenelia esculenta and the genus Gymnosporangium share a common ancestry, though Ravenelia esculenta is autoecious on angiosperm and the genus Gymnosporangium is heteroecious with pycnia, aecia on angiosperm and uredia, telia on gymnosperm. Two major clades are recognized which are based on the nature of aecial host (gymnosperm or angiosperm). These clades were also showing shift from pteridophytes to angiosperms as telial hosts. The tree can be interpreted in the other way also where there is separation of 14 families of Uredinales depending upon nature of teliospores, nature of aeciospores and structure of pycnia. These studies determine the phylogenetic position of Ravenelia esculenta among other rust fungi besides broad separation of Uredinales into two clades. These studies also show that there is phylogenetic correlation between molecular and morphological data. This is first report of DNA sequencing and phylogenetic positioning in genus Ravenelia from India.     

Observations on the ultrastructure of the uredinial stage ofPuccinia polypogonis onPolypogon monspeliensis

The ultrastructure of the uredinial stage of the rust fungus,Puccinia polypogonis onPolypogon monspeliensis is described, using scanning and transmission electron microscopy. This study examined the urediniospores, intercellular hyphae, and haustoria of the fungus. The formation and structure of urediniospores is similar to those of otherPuccinia species. The ultrastructure of intercellular hyphae and haustoria is similar to those of other rust fungi, but with some differences. No modifications are observed in the wall of the haustorial mother cells during penetration. A collar is found only around old haustoria. In most cases, one nucleus is detected inside the haustorial body and no nucleoli are seen in the nuclei of intercellular hyphae and haustoria. The host-parasite interface, including extrahaustorial matrix and extrahaustorial membrane, is also discussed and compared with those of other rust fungi.     

Studies on the rust,Maravalia cryptostegiae,a potential biological control agent of rubber-vine weed,Cryptostegia grandiflora (Asclepiadaceae: Periplocoideae), in Australia,III: Host range

Seventy-one plant species, which were selected using a centrifugal phylogenetic method, were screened againstMaravalia cryptostegiae, an endemic rust of rubber-vine (Cryptostegia grandiflora) in Madagascar. All species and variants of the genusCryptostegia proved to be highly susceptible to the rust under optimum greenhouse conditions. Two other species belonging to the same subfamily Periplocoideae,Gonocrypta grevei from Madagascar andCryptolepis grayi from Australia, developed fertile sori but could still be classified as partially resistant, based on the results of a leaf clearing and staining technique. Fifteen assessment categories and 10 susceptibility ratings were designated by analysing both macro- and microsymptoms. Five resistance mechanisms were identified in the non-hosts and these are described and illustrated. Resistance reactions ranged from complete suppression of spore germination on the plant cuticle to restriction of sorus development due to the collapse of rust haustoria. The significance of host range studies are discussed in relation to the use of rust fungi as classical biological control agents of weeds, and specifically the release ofM. cryptostegiae in Australia.     

Natural variation of ascospore and conidial germination by Fusarium verticillioides and other Fusarium species

Fusarium verticillioides and other Fusarium species were examined for their spore germination phenotypes. In general, germinating spores of F. verticillioides formed germ tubes that immediately penetrated into agar. Such invasive germination was the predominant growth phenotype among 22 examined field isolates of F. verticillioides from a broad range hosts and locations. However, two of the field isolates were unique in that they formed conidial germ tubes and hyphae that grew along the surface of agar before penetration eventually occurred. Conidia of 22 other Fusarium species were assessed for their germination phenotypes, and only some strains of F. annulatum, F. fujikuroi, F. globosum, F. nygamai, and F. pseudoanthophilum had the surface germination phenotype (21 % of the strains assessed). Sexual crosses and segregation analyses involving one of the F. verticillioides surface germination strains, NRRL 25059, indicated a single locus, designated SIG1 (surface vs. invasive germination), controlled the germ tube growth phenotypes exhibited by both conidia and ascospores. Perfect correlation was observed between an ascospore germination phenotype and the germination phenotype of the conidia produced from the resulting ascospore-derived colony. Recombination data suggested SIG1 was linked (7 % recombination frequency) to FPH1, a recently described locus necessary for enteroblastic conidiogenesis. Corn seedling blight assays indicated surface germinating strains of F. verticillioides were less virulent than invasively germinating strains. Assays also indicated pathogenicity segregated independently of the FPH1 locus. Invasive germination is proposed as the dominant form of spore germination among Fusarium species. Furthermore, conidia were not necessary for corn seedling disease development, but invasive germination may have enhanced the virulence of conidiating strains.     

Comparative studies on the teliospore morphology and ontogeny ofSpumula serispora,spec. nova,andRavenelia texensis (Uredinales,Raveneliaceae)

A new rust fungus,Spumula serispora, is described. The morphology of the teliospores and the telia was studied. In the teliospores ofS. serispora andS. quadrifida, the type species of the genus, sterile cells could be found, which are comparable to apical cells of otherRaveneliaceae. Similar sterile cells were also present in the telial heads ofRavenelia texensis. The ontogeny of the teliospores ofS. serispora and the teliospore heads ofRavenelia texensis was studied and compared. In both species the ontogeny of the spores heads was similar. InR. texensis hygroscopic cysts sustaining the spore heads were produced by division and not by conversion of basal sterile cells of the teliospore heads.Part 114 of the series Studies inHeterobasidiomycetes.     

中国蓼科植物柄锈菌的分类研究

蓼科植物((Polygonaceae)具有重要的经济意义.其中有粮食作物,著名中药,蜜源植物,观赏植物以及其它经济植物.柄锈菌(Puccinia)是蓼科植物的重要的病原真菌.本文对我国寄生于蓼科植物的柄锈菌进行了分类研究. 在中国首先报告蓼科植物柄锈的是日本人三宅市郎(1914).我国真菌学家从30年代起分别描述或记载过各种蓼科植物的柄锈,并发表过一些中国特有的新种. 本文作者重新研究了中国科学院微生物研究所真菌标本室收藏的全部蓼科植物柄锈的标本以及近年来采集的未定名标本.共鉴定标本262号,得柄锈30种,包括5个新种:汶川柄锈(Pucinia wencuanensis),雾灵柄锈(P. wulingensis),南迩巴瓦柄锈(P.namjagbarwana),太白柄锈(P. taibaiana),掌叶大黄柄锈(P. rhei palmati),和五个国内新记录种:装饰柄锈(P, ornata),岩手山柄锈(P. iwateyamensis),山蓼柄锈(P. oxyriae),赫尔顿柄锈(P.hultenii),箭叶蓼柄锈(P.polygoni-sieboldii).寄主植物包括蓼科8属47种.     

Morphological Alterations of Metarhizium anisopliae During Penetration of Boophilus microplus Ticks

Chronological histological alterations of Metarhizium anisopliae during interaction with the cattle tick Boophilus microplus were investigated by light and scanning electron microscopy. M. anisopliae invades B. microplus by a process which involves adhesion of conidia to the cuticle, conidia germination, formation of appressoria and penetration through the cuticle. Twenty-four hours post-infection conidia are adhered and germination starts on the surface of the tick. At this time, the conidia differentiate to form appressoria exerting mechanical pressure and trigger hydrolytic enzyme secretion leading to penetration. Massive penetration is observed 72 h post-inoculation, and after 96 h, the hyphae start to emerge from the cuticle surface to form conidia. The intense invasion of adjacent tissues by hyphae was observed by light microscopy, confirming the ability of M. anisopliae to produce significant morphological alterations in the cuticle, and its infective effectiveness in B. microplus.     

Accumulation of genes for susceptibility to rust fungi for which barley is nearly a nonhost results in two barley lines with extreme multiple susceptibility

Nonhost resistance is the most common type of resistance in plants. Understanding the factors that make plants susceptible or resistant may help to achieve durably effective resistance in crop plants. Screening of 109 barley (Hordeum vulgare L.) accessions in the seedling stage indicated that barley is a complete nonhost to most of the heterologous rust fungi studied, while it showed an intermediate status with respect to Puccinia triticina, P. hordei-murini, P. hordei-secalini, P. graminis f. sp. lolii and P. coronata ff. spp. avenae and holci. Accessions that were susceptible to a heterologous rust in the seedling stage were much more or completely resistant at adult plant stage. Differential interaction between barley accessions and heterologous rust fungi was found, suggesting the existence of rust-species-specific resistance. In particular, many landrace accessions from Ethiopia and Asia, and naked-seeded accessions, tended to be susceptible to several heterologous rusts, suggesting that some resistance genes in barley are effective against more than one heterologous rust fungal species. Some barley accessions had race-specific resistance against P. hordei-murini. We accumulated genes for susceptibility to P. triticina and P. hordei-murini in two genotypes called SusPtrit and SusPmur, respectively. In the seedling stage, these accessions were as susceptible as the host species to the target rusts. They also showed unusual susceptibility to other heterologous rusts. These two lines are a valuable asset to further experimental work on the genetics of resistance to heterologous rust fungi.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00425-004-1319-1Abbreviations ff. spp Formae speciales - RIL Recombinant inbred line - DC Double cross - DC-S Progeny produced by selfing of double-cross plants     

A new species of Melampsora on Populus yunnanensis from China

Melampsora nujiangensis, a rust fungus found on Populus yunnanensis in China, is described as a new species. Light and scanning electron microscopy with herbarium specimens of the rust fungus show that the shape of its urediniospores differs from that of other known species of Melampsora, and its urediniospore walls are thinner than the other species. Furthermore, in phylogenetic trees based on the DNA sequences (28S and ITS) the rust fungus is phylogenetically separated by high bootstrap values. These results indicate that the fungus is an isolated species among the genus Melampsora. Contribution no. 202 from the Laboratory of Plant Parasitic Mycology, Graduate School of Life and Environmental Sciences, University of Tsukuba, Japan     

On some rust fungi (Uredinales) collected in an Acacia koa–Metrosideros polymorpha woodland, Mauna Loa Road, Big Island, Hawaii

Nine species of rust fungi (Uredinales) were found during a 1-day field study in an Acacia koa–Metrosideros polymorpha woodland in Volcanoes National Park on Big Island, Hawaii. Two species, both found on Acacia koa, are native (endemic) rusts whereas 7 species are nonnative on nonnative hosts, highlighting the high proportion of introduced species in the Hawaiian flora even in more or less natural habitats. One species, Uromyces linearis on Panicum repens, constitutes the first record of this rust for the Hawaiian archipelago, bringing the total to 93 species on the islands, 70 (75.3%) of which are introduced. The species records are annotated with emphasis on the geographic origin of each taxon. In addition, the study has led to the molecular reevaluation of the genus Racospermyces, indicating that it is synonymous with Endoraecium, and six new combinations are proposed for the species previously placed in Racospermyces. The high number of introduced species in Hawaii coupled with the paucity of native species when compared to other global regions is discussed.     

Effect of Temperatures on Dormancy and Germination in Three Species in the Lamiaceae Occurring in Northern Wetlands

In the temperate region temperature is the main factor influencing the germination period of plant species. The purpose of this study was to examine effects of constant and fluctuating temperatures on dormancy and germination under laboratory and field conditions in the three wetland species Lycopus europaeus, Mentha aquatica and Stachys palustris. The results should give indications if the temperature-dependent regulation of dormancy and germination is phylogenetically constrained. Tests for germination requirements showed a minimum temperature for germination of 9 °C in Mentha and 12 °C in Lycopus and Stachys, and a maximum temperature of 33 °C for Lycopus and 36 °C for Mentha and Stachys. Fluctuating temperatures promoted germination in all three species but the amplitude required for high germination (>50%) differed: it was 8 °C in Mentha, 10 °C in Stachys and 14 °C in Lycopus (mean temperature 22 °C). The effect of temperatures on the level of dormancy was examined in the laboratory by imbibing seeds at temperatures between 3 °C and 18 °C for periods between 2 and 28 weeks, as well as by a 30-month burial period, followed by germination tests at various temperatures, in light and darkness. In the laboratory only low temperatures (≤12 °C) relieved primary dormancy in seeds of Lycopus, while in Mentha and Stachys also higher temperatures lead to an increase of germination. Dormancy was only induced in Lycopus seeds after prolonged imbibition at 12 °C in the laboratory. Buried seeds of all species exhibited annual dormancy cycles with lower germination in summer and higher germination from autumn to spring. Exhumed seeds, however, showed considerable differences in periods of germination success. Dormancy was relieved when ambient temperatures were below 12 °C. Ambient temperatures that caused an induction of dormancy varied depending on species and test condition, but even low temperatures (8 °C) were effective. At high test temperatures (25 °C) in light, exhumed seeds of all three species showed high germination throughout the year. The three species showed various differences in the effects of temperatures on dormancy and germination. Similarities in dormancy and germination found among the species are in common with other spring-germinating species occurring in wetlands, so it seems that the temperature dependent regulation of dormancy and germination are related to habitat and not to phylogenetic relatedness.     

Seed dispersal by the Florida box turtle (<Emphasis Type="Italic">Terrapene carolina bauri</Emphasis>) in pine rockland forests of the lower Florida Keys,United States

Seed dispersal by animals is one of the most important plant-animal mutualisms, but saurochory, the dispersal of seeds by reptiles, has received little attention. We investigated the role of the Florida box turtle (Terrapene carolina bauri) as a seed dispersal agent in pine rockland forests of the lower Florida Keys and examined the effect of turtle digestion on seed germination. We obtained seeds of 11 species with fleshy fruits and 2 species with non-fleshy fruits (a grass and legume) from the feces of 145 box turtles collected on Key Deer National Wildlife Refuge from 1999 to 2000. We planted the seeds of nine species and germination percentage (percentage of seeds that germinated during the experiment) varied from 10% to 80%. Comparative germination experiments were conducted with Thrinax morrissii, Serenoa repens, and Byrsonima lucida. We compared the germination percentage and germination rate (number of days from planting to seedling emergence) of seeds from three treatments (seeds recovered from feces, control seeds with pulp, and control seeds without pulp) and continued these experiments for up to 2 years. Passage through the box turtle digestive tract greatly enhanced the germination percentage and germination rate of S. repens, but decreased the germination percentage of B. lucida and T. morrissii, and decreased germination rate for T. morrissii. Subsequent destructive seed viability tests revealed that many ungerminated T. morrissii seeds remained viable, suggesting long-term seed dormancy may occur, even after passage through the turtle digestive system. In addition, the proportion of ungerminated seeds which remained viable was greater for seeds recovered from turtle feces than from control seeds with pulp. Furthermore, removal of fleshy pulp either manually or by the turtle digestive system may allow T. morrissii to escape insect predation.     

Deciphering species complexes: Puccinia andropogonis and Puccinia coronata, examples of differing modes of speciation

Species of macrocyclic, heteroecious grass rusts often have been defined with wide host ranges and variation in spore morphology. Consequently, some are species complexes and contain genetically distinct forms. Molecular analyses, together with morphological and biological methods, provide powerful means to dissect these complexes. Puccinia coronata is a complex species that has a broad telial host range including more than 45 genera of grasses and a narrow aecial host range. Phylogenetic analysis of nuclear ribosomal internal transcribed spacer (ITS) DNA sequences from 15 aecial and telial collections grouped P. coronata into six distinct clades supporting separation of this complex into four distinct species. Puccinia andropogonis, a common rust of tall prairie grasses in North America, is also a complex species. However, in contrast to P. coronata, P. andropogonis has a narrow telial host range and a broad aecial host range. DNA sequence analysis grouped 15 collections of P. andropogonis into six distinct clades representing at least four distinct species. Speciation of P. coronata appears to have occurred primarily by radiation onto new telial hosts, whereas in P. andropogonis speciation appears to have occurred primarily by radiation onto new aecial hosts.     

Life cycle and morphology ofMelampsora yezoensis onSalix serissaefolia

Uredinial and telial states of aMelampsora species occurring on the leaves ofSalix serissaefolia were for the first time recorded. Field observations and inoculation experiments showed that the spermogonial and aecial states of the fungus were formed onChelidonium majus var.asiaticum andCorydalis incisa. The fungus was identified asMelampsora yezoensis based on the morphological observation of all the spore states. Urediniospores were able to infectS. erocarpa andS. pierotii as well asS. serissaefolia andS. jessoensis. Salix serissaefolia, S. eriocarpa, andS. pierotii are new uredinial and telial hosts ofM. yezoensis, andC. majus var.asiaticum andC. incisa are new spermogonial and aecial hosts of the fungus. Contribution No. 124, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry University of Tsukuba.     

黄土丘陵区退耕还草植被恢复阶段优势种铁杆蒿的化感效应

为揭示黄土丘陵区退耕还草植被恢复阶段植被群落结构的形成与植物化感作用之间的关系,阐明退耕还草植被恢复阶段铁杆蒿群落形成的原因,采用种子萌发实验,对黄土丘陵区退耕还草中后期群落优势种铁杆蒿(恢复10 a、15 a、20 a、30 a)浸提液(水浸提液和甲醇浸提液)对其伴生种达乌里胡枝子(Lespedeza davurica,LD)、狗尾草(Setaria viridis,SV)、茵陈蒿(Artemisia capillaries,AC)以及铁杆蒿(Artemisia sacrorum,AS)自身化感作用进行研究。结果表明:铁杆蒿浸提液对3种伴生种以及自身种子萌发的化感作用差异显著(P0.05),总体表现出低促高抑"浓度效应",且根受到的抑制作用要强于芽。茎叶浸提液的浓度为0.1 g/mL时,对茵陈蒿种子萌发和幼苗生长的化感指数RI为-1.00,达到完全抑制。铁杆蒿不同器官的化感作用差异显著(P0.05),茎叶及根系浸提液不同程度的抑制LD、AC种子的萌发和幼苗生长,且在同一浓度下抑制作用随着恢复时间的增长逐渐增强。根际土浸提液促进了伴生植物及铁杆蒿自身种子的萌发,抑制了LD和AC幼苗的生长。铁杆蒿种群的化感作用可能是导致铁杆蒿在退耕还草中后期成为优势种的原因之一。