Pythium montanum sp. nov., a new species from a spruce stand in the Bavarian Alps

Peronosporales Species Associated with Strawberry Crown Rot in the Czech Republic

The symptoms of crown rot on strawberry plants are considered typical for the pathogen Phytophthora cactorum, which causes high losses of this crop. However, an unknown number of related species of pathogens of Peronosporales cause symptoms quite similar to those caused by P. cactorum. To determine their spectrum and importance, strawberry plants were sampled from 41 farms in the Czech Republic. The cultures were isolated from the symptomatic plants using the baiting method, with subsequent cultivation on a semiselective medium. Isolates were identified to the species level using nuclear ribosomal internal transcribed spacer (ITS) barcoding after preliminary morphological determination. In total, 175 isolates of 24 species of Phytophthora, Phytopythium, Pythium, and Globisporangium were detected. The most represented was Phytophthora cactorum, with 113 (65%) isolates, which was recorded in 61% of farms, and the Pythium dissotocum complex with 20 (11%) isolates, which was recorded in 27% of farms. Other species were represented in units of percent. Large differences between farms in the species spectra were ascertained. The differences between species in cardinal growth temperatures and different management of the farms are discussed as a main reason for such a diversification. Regarding the dissimilar sensitivity of various species of Peronosporales against fungicides, the proper determination of the cause of disease is of crucial significance in plant protection.

Taxonomic and pathogenic characterization of Phytopythium species from West Azarbaijan, Iran, and description of two new species

Phytopythium is a globally distributed genus, species of which occur in various ecological niches. Despite their importance as plant pathogens, information on species diversity and their distribution in West Azarbaijan Province of Iran is limited. This study aimed to investigate the taxonomy and plant pathogenicity of Phytopythium isolates recovered from soils in the province. A polyphasic taxonomy based on morphological, cultural, and multilocus sequence data revealed two new species, described here as P. babaiaharii and P. longitubum. In addition, a putatively new species and five known species, P. boreale, P. carbonicum, P. mercuriale, P. ostracodes, and P. vexans, were found in the studied region. Phytopythium ostracodes, P. mercuriale, and P. boreale were the three most frequent species isolated from soil, although P. mercuriale was only found in one field. Among the studied species, P. mercuriale, P. ostracodes, and P. vexans exhibited various levels of pathogenicity on sugar beet, sunflower, and tomato, and P. boreale was documented for first time as a plant pathogen. Phytopythium ostracodes was highly aggressive on sugar beet and sunflower but lowly aggressive on tomato, whereas P. vexans exhibited high aggressiveness toward the three crop plants. Both P. boreale and P. mercuriale were found to be lowly aggressive on the host plants. The results indicated that members of Phytopythium, particularly plant-pathogenic species, are common in arable soils of West Azarbaijan Province and can pose a threat to agricultural crops in the region.

Diversity, host, and habitat specificity of oomycete communities in declining reed stands (Phragmites australis) of a large freshwater lake

We studied the diversity of oomycetes in a declining reed belt (Phragmites australis) of Lake Constance, Germany, using conventional baiting with specific reed and standard oak baits, accompanied by molecular techniques. Apart from an Aphanomyces sp. and a Phytophthora sp., baiting from reed rhizosphere samples from flooded, as well as drier, littoral sites revealed only Pythium spp. A total of 67 oomycete isolates was classified according to PCR-RFLP banding patterns and ITS sequencing, and 18 different sequence types could be separated. The majority of these seemed previously unknown species, as indicated by the degree of similarity to those deposited in nucleotide databases. Species communities in both flooded and drier habitats or both reed and oak baits clearly differed from one another, and only few species occurred in both dry and flooded sites, or in both oak and reed baits. A frequently occurring group of related Pythium species appeared to be specifically associated with reed, and these were the only species that proved pathogenic towards this host in vitro. Our study proved that unexplored natural ecosystems harbour diverse communities of oomycete species with specific habitat and host preferences within close-by, but ecologically contrasting, sites. Among the species isolated, those associated with the predominating plant might accumulate and thus may be reed pathogens of considerable importance.

Morphological and molecular taxonomy ofPythium longisporangiumsp. nov. isolated from the Burgundian region of France

During the course of an investigation on the Pythiaceous oomycetes occurring in the Burgundian vineyards, some species of Pythium possessing mainly hypogynous antheridia were found. These had been classified as oomycetes belonging to the "Pythium rostratum" group for a long time. Three of these isolates, having similar structures and growth, are very closely related to a recently described species, Pythium bifurcatum Paul. A close look at these, however, underlines some fundamental differences with the latter. Not all of them produce zoospores but have very large sporangia. The type specimen is F-1200 (B 76a) which is a medium-slow growing saprophyte. The sequence of the ITS region of the rDNA also shows a very close relationship with P. bifurcatum. On the basis of morphological and molecular analysis, we now describe this species as Pythium longisporangium sp. nov. Morphological features of this new species, the sequences of the ITS region of its nuclear ribosomal DNA, and its comparison with related species are discussed.

Molecular phylogeny and taxonomy of the genus Pythium

The phylogeny of 116 species and varieties of Pythium was studied using parsimony and phenetic analysis of the ITS region of the nuclear ribosomal DNA. The D1, D2 and D3 regions of the adjacent large subunit nuclear ribosomal DNA of half the Pythium strains were also sequenced and gave a phylogeny congruent with the ITS data. All the 40 presently available ex-type strains were included in this study, as well as 20 sequences of recently described species from GenBank. Species for which no ex-type strains were available were represented by either authentic strains (6), strains used in the 1981 monograph of the genus by van der Plaats-Niterink (33), or strains selected on morphological criteria (17). Parsimony analysis generated two major clades representing the Pythium species with filamentous or globose sporangia. A small clade of species with contiguous sporangia was found in between the two main clades. A total number of 11 smaller clades was recognized, which often correlated with host-type or substrate and in several cases with a subset of morphological characters. Many characters used in species descriptions, such as antheridium position, did not correlate with phylogeny. A comparison of the ex-type and representative strains with all ITS sequences of Pythium in GenBank revealed limited infraspecific variation with the exception of P. rostratum, P. irregulare, P. heterothallicum, and P. ultimum. The total number of species examined was 116 (including 60 ex-type strains). Twenty-six species had ITS sequences identical or nearly identical to formerly described species, suggesting possible conspecificity. The importance of comparing ITS sequences of putative new species to the now available ITS database in order to avoid unwarranted new species names being introduced.