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.

Resistance to Multiple Tuber Diseases Expressed in Somaclonal Variants of the Potato Cultivar Russet Burbank

Multiple disease resistance is an aim of many plant breeding programs. Previously, novel somatic cell selection was used to generate potato variants of “Russet Burbank” with resistance to common scab caused by infection with an actinomycete pathogen. Coexpression of resistance to powdery scab caused by a protozoan pathogen was subsequently shown. This study sought to define whether this resistance was effective against additional potato tuber diseases, black scurf, and tuber soft rot induced by fungal and bacterial pathogens. Pot trials andin vitroassays with multiple pathogenic strains identified significant resistance to both tuber diseases across the potato variants examined; the best clone A380 showed 51% and 65% reductions in disease severity to tuber soft rot and black scurf, respectively, when compared with the parent line. The resistance appeared to be tuber specific as no enhanced resistance was recorded in stolons or stem material when challengedRhizoctonia solanithat induces stolon pruning and stem canker. The work presented here suggests that morphological characteristics associated with tuber resistance may be the predominant change that has resulted from the somaclonal cell selection process, potentially underpinning the demonstrated broad spectrum of resistance to tuber invading pathogens.

Pathogens of potato (Solanum tuberosum L.) tuber (Phytophtora infestans) occurring in treatments with foliar fertilization

The paper presents the results of a three-year exact plot experiment (2008-2010) established in Bałcyny (NE Poland). Three potato cultivars were grown: medium-early &lsquo;Adam&rsquo;, medium-late &lsquo;Pasja Pomorska&rsquo;, and late &lsquo;Ślęza&rsquo;. The experimental factors were foliar fertilizers applied alone or in combination (Basfoliar 12-4-6, ADOB Mn, Solubor DF) and two levels of soil mineral fertilization (N₁P₁K₁-80 kg N × ha^-1, 80 kg P × ha^-1, 120 K × ha^-1; N₂P₂K₂-120 kg N × ha^-1, 144 kg P × ha^-1, 156 K × ha^-1). The experimental materials comprised potato tubers. The symptoms of soft rot (<em>Pectobacterium carotovorum </em>subsp. <em>carotovorum</em>), late blight (<em>Phytophthora infestans</em>) and dry rot (<em>Fusarium </em>spp.) were evaluated in 5 kg potato samples, and were expressed as the percentage mass of infected tubers. The rates of common scab (<em>Streptomyces scabies</em>) and black scurf (<em>Rhizoctonia solani</em>) infection were estimated on 100 tubers collected randomly after harvest, according to a nine-point scale, and were presented as a percentage infection index. In the laboratory, fungi were isolated on PDA medium from potato tubers immediately after harvest and after five-month storage. The incidence of tuber diseases depended on potato cultivars affected. The severity of tuber diseases varied between treatments with two levels of NPK fertilization and foliar fertilization. The lowest number of <em>Fusarium-</em>infected tubers was obtained from treatments where three foliar fertilizers were applied in combination, which was confirmed by the lowest abundance of fungal isolates. More fungi were isolated from potato tubers after harvest than after storage, but pathogens were more frequently isolated from stored tubers. After harvest, the lowest number of pathogenic fungi was isolated from the tubers of cv. &lsquo;Adam&rsquo; in the non-fertilized treatment, and after storage – from the tubers of the late cultivars in the treatment with three foliar fertilizers applied in combination.