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

Evaluation of the Ability of Seven Active Ingredients of Fungicides to Suppress <i>Phytophthora cactorum</i> at Diverse Life Stages, and Variability in Resistance Found among Isolates

Phytophthora cactorum is considered an important plant pathogen which is causing major damage to strawberry plants worldwide. In the current study, the ability of the active ingredients of seven different fungicides, azoxystrobin, cymoxanil, dimethomorph, fenamidone, fluopicolide, metalaxyl and propamocarb, to suppress the mycelial growth, sporangial formation and zoospore release of P. cactorum isolates, was tested. The variation in resistance against various fungicides was found among the isolates. The active ingredients are also unequally efficient against different life stages of P. cactorum, which is probably associated with their different modes of action. A significant level of resistance was recorded against metalaxyl and dimethomorph; however, these were totally inefficient against the zoospore release, while azoxystrobin did not inhibit mycelial growth. The only fungicide efficient against all three P. cactorum life stages tested was fluopicolide, although the calculated resistance factor gives evidence of the rise of resistance in the majority of isolates even against this fungicide. Significant differences were found between responses to fungicides of isolates from strawberry and from other host species. Based on the Mahalanobis distances calculated in the discriminant analysis comprising all of the assays performed, the similarities among isolates were estimated

Insecticidal activity of two formulations of essential oils against the cereal leaf beetle

Purpose: Plant-derived essential oils and their encapsulations have recently received increasing interest as an alternative to synthetic biopesticides suitable for integrated pest management and organic farming. In this study, combinations of essential oils (EO) from Rosmarinus officinalis with Cymbopogon citratus and Pelargonium graveolens with Thymus vulgaris in two formulations including encapsulate were tested for their potential for wheat protection against adults and larvae of Oulema melanopus (L.). Materials and methods: The chemical composition of the essential oils was analyzed by gas chromatography-mass spectrometry (GC-MS). Testing of insecticidal activity of the evaluated substances was conducted with 2.5 ml of tested combinations of EOs sprayed on the paper. Ten adults or larvae of O. melanopus were placed into a vessel. Control of mortality of O. melanopus specimens was assessed after 24 h after establishment of the experiment. Results and conclusions: Tarsal contact toxicity assay showed the effectiveness of EO in concentration against O. melanopus larvae and adults in both formulations (essential oil and encapsulation) causing 100% mortality within 24 h. These results indicate the great potential of these essential oils and their encapsulations for future use in crop protection against insect pests