The Growth Kinetics of RhizoctoniasolaniAfter 1 MeV Electron Irradiation

Crops, especially potatoes, are prone to a wide range of fungal, viral and bacterial diseases, including black scurf caused by Rhizoctoniasolani. This study focused on the radiation treatment of the phytopathogenic fungus RhizoctoniasolaniKuhn, grown from sclerotium irradiated with 1 MeV electrons in the dose range from 20 to 4500 Gy. The doses absorbed by the sclerotia were determined using computer simulation. The growth of the fungus samples was monitored after 24, 48, 72, and 96 hours from the time of seeding. It was found that the dependence of the radial growth velocity of R. solani on the time after irradiation with doses ranging from 20to 1800 Gywas nonlinear. Irradiation at a dose over 4500 Gyled to complete suppression of the germination of R. solani sclerotia. Keywords: radiation treatment, electron radiation, radiation dose, sclerotia of Rhizoctoniasolani, Kuhn, radial velocity of growth

Foliar Application of Fungicides Registered Against Late Blight Influences Main Potato Tuber Diseases and Key Quantitative Characteristics of Tubers

Adequate integrated management of potato leaf diseases can have an influence on pathogens which are challenging to control and cause main potato tuber diseases. Deriving from this hypothesis, an experiment was designed to evaluate the efficacy of foliar application of twelve fungicides on late blight in tubers, common scab, black scurf and silver scurf. In the period of 2013 to 2017, the fungicides were equally applied six times in registered doses during the growing seasons. Eight tuber disease indicators and eight yield characteristics were then evaluated in harvested tuber samples. Significant differences were found among the fungicides used. In comparison to the negative control (n. c.), the application of Infinito, Ranman Top and Revus Top reduced the quantity of tubers infected by late blight by 72% on average. The incidence of common scab increased by 65% of n. c. under the effect of copper oxychloride, while an average reduction by 19% of n. c. was observed with the use of Acrobat MZ WG, Curzate Gold and Consento. The occurrence of silver scurf was significantly enhanced by Curzate Gold and Consento (105% of n. c.), while it was suppressed by Revus Top and Revus (85% of n. c.). All fungicides were ineffective on black scurf yet had a positive influence on the potato yield and quality, with the choice of fungicide having a great impact on the quality of tubers. The application of any safe fungicide is important, especially in years similar to 2015, which was the most devastating recent year for potato production in terms of structural changes in yield of tubers.

In Vitro Evaluation of Bacterial Bioagents and Fungicides Efficiency against Rhizoctonia solani Isolates the Causal agent of Black Scurf Disease of Potato

The efficacy of two isolates of bacterial bioagents and two fungicides via, Rhizoctonia solani isolates were evaluated in vitro. In the dual culture assays, significance inhibition ratio of R. solani hyphal growth was obtained in all treatments of Pesudomonas fluoresnces and Bacillis subtilis compared to control. Also, Bacillus subtilis exhibit the highest significant suppression for the mycelial growth of R. solani isolates more than Pseudemonas fluorescens, and the ratios of inhibition differed according to the bioagents and R. solani isolates similar to those results in antifungal activity technique. The volatile metabolite studies revealed that in the first period (three days) inhibition percentage significantly differed according to the tested isolates of R. solani and the applied bioagents, B. subtilis gave the highest inhibition (57.41%) in R. solani isolate 3. Similarly in P. fluoresnces treatments, the highest inhibition was (57.41%) was detected in isolate 3 of R. solani considering that the second tested time period (five day inoculation). B. subtilis showed highest inhibition value on isolate 1, on the other hand P. flouresnce showed high value of inhibition on isolate 2, whereas the lowest inhibition values were produced on isolate 1.Non volatile activity both bacterial bioagents isolates showed different values of inhibition on R. solani isolates. On the other hand Rezolex was most effective against R. solani at two concentrations (0.2 and 0.3), however Topsin-M showed fluctuate inhibition values at two concentration used (0.04% and 0.075%). Further incubation of plates showed suppressed the formation of sclerotia by all the antagonists tested. The results implied that the extent of inhibition by B. subtilis and P. fluoresnces rovides the use of excellent potential antagonists capable of controlling the R. solani in vitro.

Occurrence and Anastomosis Grouping of Rhizoctonia spp. Inducing Black Scurf and Greyish-White Felt-Like Mycelium on Carrot in Sweden

Carrots with different Rhizoctonia-like symptoms were found in the main Swedish carrot production areas from 2001–2020. The most commonly observed symptoms were a greyish-white felt-like mycelium and black scurf, the latter often associated with Rhizoctonia solani anastomosis group (AG) 3-PT on potato. An overall increase in disease incidence in all studied fields over time was observed for both symptoms. The majority of Rhizoctonia isolates sampled from carrot in the period 2015–2020 were identified as AG 3 (45%) and AG 5 (24%), followed by AG 1-IB (13%), AG 11 (5%), AG-E (5%), AG BI (3%), AG-K (3%) and AG 4-HGII (2%). To our knowledge, this is the first report describing AG 5 in Sweden as well as AG 3, AG 11 and AG-E inducing Rhizoctonia-like symptoms on carrot. Secondly, we report for the first time that R. solani AG 3, and the less observed AGs: AG 1-IB and AG 5 can induce black scurf symptoms on the taproot of carrots. Due to a widely used carrot-potato crop rotation in Swedish areas, a possible cross-over from potato to carrot is suggested. This information is of high importance to reduce Rhizoctonia inoculum in soils, since avoiding carrot-potato crop rotations needs to be considered.