Thirty-eight isolates of Rhizoctonia spp. were isolated from Scots pine (Pinus sylvestris) seedlings with damping-off symptoms, originating from two forest nurseries in central-west Poland (Wronczyn and Jarocin) and from diseased seedlings grown in soil from Wronczyn nursery. Majority of these isolates (79%) had multinucleate cells and were identified as Rhizoctonia solani. The remaining isolates were recognized as binucleate Rhizoctonia spp. R. solani isolates were characterized using hyphal anastomosis and were divided into five anastomosis groups (AG). The most prevalent was AG5 (37% of isolates), followed by AG2-1 (30%) and 27% of the isolates were identified as AG4. Groups AG1-IB and AG2-2 were only represented by single isolates. The virulence recorded as mortality (in percentage) was comparatively high for binucleate and multinucleate isolates of Rhizoctonia spp. Sequence analysis of the polymerase chain reaction (PCR)-amplified internal transcribed spacer (ITS) rDNA region was used for phylogenetic analysis. The dendrogram showed that isolates were distinctly separated based on their AG types and there was no relationship between pathogenicity on Scots pine seedlings and the AG to which the isolates belong to. The results are discussed with respect to pathogenic potential of the various AG groups.

The ability of plant resistance inducers to provide protection against viral diseases is one of their main advantages over conventional pesticides. In the case of viral diseases that cannot be controlled directly with pesticides, insecticides are used to control the vectors of viruses. However, the effectiveness of such treatments is strictly dependent on the time of application. The plant response to the application of systemic acquired resistance (SAR) inducers, as a result of the stimulating action of these substances, does not depend on the time of application as it triggers the plant’s natural defence mechanism. The best-recognised substance showing SAR inducer activity is acibenzolar-S-methyl ester (ASM, BTH). As its activity against different plant pathogens of crops has been well documented, the current research is concentrated on the search for novel substances of the type. The tested substance, N-methoxy-N-methylbenzo(1,2,3)thiadiazole-7-carboxamide (BTHWA), is an amide derivative of benzothiadiazole, showing plant resistance-inducing activity. This article presents the activity of BTHWA that has led to increased resistance of zucchini (Cucurbita pepo convar. giromontiina) towards viral infections. In addition, since the occurrence of the fungal pathogen, powdery mildew, was also observed during the two-year field experiments, the activity of BTHWA related to the reduction of infection with this fungus was also investigated. The substance was applied in two different variants either four or eight times, over the whole vegetation season. Surprisingly, the variant of four applications performed at the beginning of the vegetation season proved more effective in protection against viruses and fungus. A possible explanation may be the occurrence of the growth–immunity trade-off phenomenon that is known in the literature. Disturbance in plant metabolism resulting from eight applications may lead to lower yields of plants treated with SAR inducers. Perhaps such overstimulation of the plants we treated eight times may not have brought the optimum increase in plant resistance.

The effect of selected essential oils on rape pathogens such as Sclerotinia sclerotiorum, Phoma lingam, Rhizoctonia solani and Fusarium oxysporum was estimated in vitro studies. S. sclerotiorum showed the lowest susceptibility to the examined essential oil treatments. The thyme oil displayed the highest fungistatic effect and suppressed the culture growth of all tested fungal species when applied at the concentration of 0.2 and 0.02%. The lemongrass oil applied at the concentration of 0.2 and 0.02% inhibited the culture growth of the examined species from 90 to 100%. The tea tree and grapefruit essential oils applied and the concentration less than 0.2% showed poor effectiveness or no fungistatic effect on F. oxysporum and S. sclerotiorum.

Tansy phacelia (Phacelia tanacetifolia Benth.) is considered a disease-resistant plant. The aim of the study was to determine which fungi (pathogens and saprofites) colonize phacelia plants. The greenhouse and field experiments were conducted in 2016. Phacelia plants were treated with fungicides from different chemical groups. Three combinations of products in the greenhouse experiment and 4 combinations in the field experiment were used. Plants without any protective treatments were used as a control. Parts of plants showing some disease symptoms were selected for isolation of saprotrophic and pathogenic fungi. The isolated and identified fungus species obtained from individual samples differed qualitatively and quantitatively. Among the pathogenic fungi the most important were Fusarium spp. [mainly Fusarium solani (Mart.) Sacc., Fusarium avenaceum (Fr.) Sacc., Fusarium equiseti (Corda) Sacc. and Fusarium oxysporum Schltdl.], Botrytis cinerea Pers., Sclerotinia sclerotiorum (Lib.) de Bary, Alternaria alternata (Fr.) Keissl. and Pythium irregulare Buisman. In some cases large differences in the occurrence of pathogens have been observed, depending on the site of the experiment (field and greenhouse) and on the type of fungicides.

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