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.

A Three-Way Transcriptomic Interaction Study of a Biocontrol Agent (Clonostachys rosea), a Fungal Pathogen (Helminthosporium solani), and a Potato Host (Solanum tuberosum)

Helminthosporium solani causes silver scurf, which affects the quality of potato. The biocontrol agent Clonostachys rosea greatly limited the severity of silver scurf symptoms and amount of H. solani genomic DNA in laboratory experiments. Transcriptomic analysis during interaction showed that H. solani gene expression was highly reduced when coinoculated with the biocontrol agent C. rosea, whereas gene expression of C. rosea was clearly boosted as a response to the pathogen. The most notable upregulated C. rosea genes were those encoding proteins involved in cellular response to oxidative stress, proteases, G-protein signaling, and the methyltransferase LaeA. The most notable potato response to both fungi was downregulation of defense-related genes and mitogen-activated protein kinase kinase kinases. At a later stage, this shifted, and most potato defense genes were turned on, especially those involved in terpenoid biosynthesis when H. solani was present. Some biocontrol-activated defense-related genes in potato were upregulated during early interaction with C. rosea alone that were not triggered by H. solani alone. Our results indicate that the reductions of silver scurf using C. rosea are probably due to a combination of mechanisms, including mycoparasitism, biocontrol-activated stimulation of plant defense mechanisms, microbial competition for nutrients, space, and antibiosis.

Analysing quality deficiencies of three potato cultivars during the storage period

The aim of this work was to assess quality deficiencies in three potato cultivars (Christian, Roclas, and Cumidava) during the storage period. According to the results, the Roclas presented the highest level of susceptibility to pathogens; this, however, can be attributed to the dry rot that causes greater damage in this cultivar. No significant positive correlations between the plant’s vegetative parameters and the most dangerous diseases and pests in Christian were detected. There was a significant positive correlation between the biomass of the tubers and the silver scurf blemish disease, respectively between tuber numbers and dry rot in Cumidava and significant positive correlations between tuber numbers and the silver scurf blemish disease, between biomass of the tubers and dry rot, respectively between tuber numbers and wireworm larvae at Roclas. Altogether, we can conclude that the most susceptible cultivar was Roclas followed by Cumidava, while the least susceptible was the Christian cultivar.

Evaluation of Fungicides Applied Via Drip Irrigation for Control of Silver Scurf on Potato in Western Washington

Silver scurf is an economically important disease on potato tubers caused by Helminthosporium solani. Two studies were established near Mount Vernon, WA at Washington State University NWREC on 20 May 2011 and 21 May 2012 in Skagit silt loam soil. Five treatments included: penthiopyrad applied at 45 days after planting (dap), penthiopyrad applied at 60 dap, azoxystrobin (Quadris; 9 oz/acre) applied at 45 dap, and azoxystrobin applied at 60 dap, and a non-treated non-irrigated control. This study did not control for the effect of irrigation, as azoxystrobin- and penthiopyrad-treated plots were drip-irrigated while non-treated plots were not irrigated. The results of this study are therefore limited but do suggest a reduction in silver scurf incidence and severity with no significant impact on yield of potatoes when treated fungicide applied through drip irrigation systems.

Effect of Extended Crop Rotations on Incidence of Black Dot, Silver Scurf, and Verticillium Wilt of Potato

Potato tubers were collected and evaluated for symptoms and signs of black dot, silver scurf, and Verticillium wilt to determine the effect of extended crop rotations on disease incidences in the Columbia Basin. Incidence of tubers with black dot collected from storage significantly decreased as the number of years between potato crops increased from 3 to 5 years and beyond and significantly increased as the number of previous potato crops increased to 16. The highest incidence of black dot (range of 73 to 98%) was from fields rotated out of potatoes for 1 to 3 years. The mean incidence of black dot was 56% for fields out of potatoes for 0 to 4 years and 12% for fields out of potatoes 5 and more years. A low incidence (0 to 9%) of black dot was detected at 15 years out of potatoes. Years out of potato and number of prior potato crops accounted for 71% of the variability associated with the incidence of black dot. Severity of black dot on tuber periderm peels significantly increased as incidence of tuber periderm peels with Colletotrichum coccodes increased. Coefficient of determination was 0.87 for log severity on regressed on black dot incidence. Incidence of silver scurf was highest from fields out of potatoes for 1 year. Incidence of silver scurf infected tubers significantly increased as the number of previous potato crops increased due to short rotations between potato crops. Incidence of tubers with Verticillium dahliae was not related to years between potato crops or number of previous potato crops. The present study confirmed that black dot can be reduced with rotations out of potatoes greater than 5 years.