Insights into the structure and phylogeny of the 28S rRNA expansion segments D2 and D3 of the plant-infecting nematodes from the genus Ditylenchus (Nematoda: Anguinidae)

Recently, it has been shown that the stem nematode, Ditylenchus dipsaci (Nematoda: Anguinidae), is genetically more related to the gall-forming nematodes from genera Anguina, Heteroanguina, and Mesoanguina than to other members of the genus Ditylenchus. This finding was provided by molecular data written in the evolutionary variable, non-coding internal transcribed spacers (ITS1 and ITS2) of the ribosomal DNA (rDNA). In the current paper, we analyze the nucleotide sequences and predict the secondary structures of two expansion segments (D2, D3) of the 28S ribosomal RNA (rRNA)-coding gene for the plant-parasitic nematodes from the genus Ditylenchus and their related anguinids. In general, the expansion segment D2 appeared to be more variable than the segment D3 illustrating their different evolutionary constraints. Comparative analysis of the aligned sequences and predicted secondary structures revealed similar trend showing the tight relationships between the stem nematodes (D. dipsaci, D. gigas, D. weischeri) and gall-forming nematodes from the subfamily Anguininae. Phylogeny reconstructions disjoined the family Anguinidae into two monophyletic clusters (Clade 1 and 2). Clade 1 constitutes the stem nematodes (D. dipsaci, D. gigas, etc) and gall-forming nematodes from the genera Anguina, Heteroanguina, Subanguina and Mesoanguina, while clade 2 includes other Ditylenchus species like D. destructor and D. halictus. Collectively, deciphering the exact phylogenetic relationships within the family Anguinidae (Nematoda: Tylenchida) with respect to our results should provide a framework for a taxonomic revision in order to reflect biological history of these nematodes. In addition, we provide novel molecular data, which may be exploited in diagnostic tools for phytosanitary control of these economically important plant parasites

Study of sugar beet viruses transmitted by Polymyxa betae in the Czech Republic

Sugar beet viruses transmitted by Polymyxa betae are very widespread in the Czech Republic. Beet soil-borne virus (BSBV) is present in almost all fields used for sugar beet growing, beet virus Q (BVQ) is present in about 50% of fields but beet necrotic yellow vein virus (BNYVV) is present in some limited regions only. It means that mixed infections of sugar beet by at least two viruses are quite common in the field. P. betae also occurs in almost all fields where sugar beet is now grown. Only two populations of P. betae not transmitting any virus were found. Cystosori of P. betae can harbour viruses without loosing infectivity for a very long time. We were able to detect these viruses in plants grown in soil stored dry for 12 years. BNYVV can cause serious yield losses under mideuropean conditions reaching up to 50% of sugar yield, whereas harmfulness BSBV and BVQ is questionable, because they also occur in fields with no problems concerning sugar beet growing. The host range of these viruses was studied. Both infect all types of beet (sugar fodder, red beet, mangold) and spinach and usually are detectable in root system only. Other chenopodiaceous plants are infected only by some virus strains. These strains are also able to spread into above-ground parts of plants

Significance of Sexual Reproduction of Phytophthora infestans in the Czech Republic

A total of 187 naturally late blight‑diseased potato leaves were sampled from 31 sites and five regions of the Czech Republic during the growing season in 2012–2014 and 2016 and examined microscopically for the ability of Phytophthora infestans to produce oospores in infected leaves under field conditions. Although the occurrence of the A1 and A2 mating types required for sexual reproduction of P. infestans was previously confirmed in the Czech Republic, no oospores were detected in this study. To study the effect of temperature on the survival of oospores produced from crosses of three pairs of P. infestans isolates, oospores in leaf discs and agar were exposed to temperatures ranging from –24 to 10 °C and then evaluated for viability with the plasmolysis test. Oospore viability ranged from 13.02 to 63.90 % and from 7.77 to 63.37 % for oospores produced in agar and leaf discs, respectively, with the highest frequencies of viable oospores occurring at 4 and 10 °C. To determine whether oospores may survive under field conditions, agar plates with oospores were buried in soil in Prague‑Suchdol and Svitavy for seven months during the overwintering period (October–May) in 2011–2015. There were statistically significant differences in oospore viability examined by the plasmolysis test between the localities, and oospore viability ranged from 29 to 43 % and from 15 to 44 % in Prague‑Suchdol and Svitavy, respectively

Field Validation of the Effect of Soil Fumigation of Ethanedinitrile (EDN) on the Mortality of <i>Meloidogyne</i> <i>hapla</i> and Carrot Yield Parameters

With the increasing importance of soilborne plant pest nematodes and the relatively recent phase-out of methyl bromide as a key soil fumigant, there is an urgent need for new fumigants with good nematicidal properties. Ethanedinitrile (EDN) is a promising fumigant and preparation because of its physical, agrochemical, and nematicidal properties. However, its efficacy against nematode pests of different crops under field conditions has not been fully validated and understood. Therefore, the aim of our study was to evaluate the effect of two concentrations of EDN on the survival of northern root-knot nematodes (Meloidogynehapla) and on carrot yield and quality under field conditions. The evaluation was performed using naturally infested carrot plots, and EDN application to the soil was followed by covering the treated area with film. A high biological effect was observed for both EDN concentrations tested, with even the lower dose (30 g·m−2) being sufficient for M. hapla suppression. Positive effects of EDN application—likely due to EDN partial conversion into biologically available nitrogen in soil—on carrot root weight, in comparison with the untreated control, were also observed

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

A Comparison of the Ability of Some Commercially Produced Biological Control Agents to Protect Strawberry Plants against the Plant Pathogen Phytophthora cactorum

A comparison of the ability of commercially produced biological control agents—Contans, Gliorex, Hirundo, Polyversum, Prometheus, Clonoplus, Integral Pro and Xilon GR, completed with an isolate of Clonostachys rosea and of Pseudomonas sp.—to protect strawberry plants against Phytophthora cactorum was performed. The experiment was performed on strawberry cultivars Sonata, Karmen, and Wendy—cultivated in a cultivating room and greenhouse. The health of plants was affected negatively by the pathogen in all variants of biological agents used, but differences were seen in the rates of this decrease. The results revealed the ability of some tested agents to improve the growth of plants in the absence of the pathogen; the preparation Polyversum (Pythium oligandrum) was the most beneficial, in both the presence and absence of the pathogen. Contrarily, some agents alone decreased the health of plants; Integral Pro (Bacillus subtillis) and a strain of Pseudomonas sp. caused a deterioration in the health of the plants, even in the absence of a pathogen. The results of our analysis demonstrate the varied usefulness of all agents under unified environmental conditions; their effect seems to be dependent on the conditions and on the combination of the genotypes of all three participants in the interaction: plant–pathogen–antagonist

Mixed-Mating Model of Reproduction Revealed in European <i>Phytophthora cactorum</i> by ddRADseq and Effector Gene Sequence Data

A population study of Phytophthora cactorum was performed using ddRADseq sequence variation analysis completed by the analysis of effector genes—RXLR6, RXLR7 and SCR113. The population structure was described by F-statistics, heterozygosity, nucleotide diversity, number of private alleles, number of polymorphic sites, kinship coefficient and structure analysis. The population of P. cactorum in Europe seems to be structured into host-associated groups. The isolates from woody hosts are structured into four groups described previously, while isolates from strawberry form another group. The groups are diverse in effector gene composition and the frequency of outbreeding. When populations from strawberry were analysed, both asexual reproduction and occasional outbreeding confirmed by gene flow among distinct populations were detected. Therefore, distinct P. cactorum populations differ in the level of heterozygosity. The data support the theory of the mixed-mating model for P. cactorum, comprising frequent asexual behaviour and inbreeding alternating with occasional outbreeding. Because P. cactorum is not indigenous to Europe, such variability is probably caused by multiple introductions of different lineages from the area of its original distribution, and the different histories of sexual recombination and host adaptation of particular populations

Evaluation of Ethanedinitrile as a Potential Fumigant against <i>Plasmodiophora brassicae</i>, the Clubroot Pathogen

Clubroot, caused by Plasmodiophora brassicae Woronin, is one of the most challenging diseases to control in oilseed rape (Brassica napus L.) and other crucifers globally. Ethanedinitrile (EDN) is a promising fumigant shown to be effective against various pests and soil-borne pathogens. However, its efficacy against P. brassicae is yet to be tested. Therefore, the current study is focused on evaluating the effectiveness of EDN against P. brassicae at different rates, applied for different durations of exposure. Clubroot-susceptible oilseed rape plants, grown in fumigated soil, were evaluated for disease severity and growth parameters in greenhouse conditions. EDN exhibited good efficacy against the pathogen, with 81.39% disease suppression compared to the control. Complete control of the disease was achieved at the rates of 42 g/m3 and 50 g/m3 as well as in the treatment variant of 35 g/m3-48 h. In addition, EDN improved plant health by increasing shoot weight by 58.24%. However, the combination of a prolonged fumigation period and higher rates resulted in a decline in the seedling emergence rate and plant shoot weight, indicating a potential adverse residual effect of higher rates and longer durations of exposure in plants