Influence of abiotic factors, inoculum source, and cultivar susceptibility on the potato tuber blemish diseases black dot (Colletotrichum coccodes) and silver scurf (Helminthosporium solani)

Abstract

Black dot and silver scurf are potato blemish diseases whose economic impact has increased in recent years. Because their symptomatology on tubers is visually similar, disease assessment does not usually differentiate between the two pathogens, which share the same ecological niche. The epidemiology of black dot has been extensively studied, especially in the UK, but the factors that influence silver scurf have been less investigated. In this study, the influence of cultivar, source of inoculum, and environmental conditions on both diseases was studied in field trials over a three-year period (2016-2018) in Switzerland. Planting minitubers did not prevent either disease in daughter tubers, indicating the contribution of soil as an inoculum reservoir. An arbitrary threshold of Colletotrichum coccodes soil inoculum could be set to discriminate between low and high disease risk. For the first time, Helminthosporium solani DNA was detected in stolons, and infections appeared earlier in stolons than in tubers. H. solani stolon and tuber infections usually appeared later in the season than those of C. coccodes. Black dot severity correlated positively with precipitation, while silver scurf severity correlated positively with temperature. Table potato cultivars commonly grown in Switzerland exhibited significant differences in susceptibility to both diseases, and cultivars with low susceptibility to both silver scurf and black dot were identified. These results gave new insights into understanding the factors driving the epidemiology of potato blemish diseases and may contribute to building a risk assessment scheme to manage both diseases simultaneously.

Health Parameters of Potato Tubers under the Influence of Soil Applied Bio-Preparations and Bio-Stimulants

“…Potato peel diseases are a problem for potato growers and producers worldwide. This is due to, among other things, the lack of genetic resistance of potato varieties and the low efficiency of chemicals [13,16,82,83]. R. solani shows a unique resistance to synthetic fungicides [84,85].…”

“…Direct consumption dominates in European countries, but consumption of French fries and chips is clearly increasing [5,13]. The trend toward the consumption of processed potatoes, as well as consumer purchases of potatoes washed and packed in small, transparent consumer packs, makes the processing and marketing of potatoes subject to increased health standards for tubers [13][14][15][16]. In such a situation, potato skin diseases such as black scurf (Rhizoctonia solani), silver scurf (Helminthosporium solani Durieu and Mont), and common scab (Streptomyces scabies Thaxter) are also of economic importance.…”

“…The result of the infection includes extensive stains with silver gloss. Water is lost through the damaged skin during storage, the tubers shrink, and the loss of mass may reach 17% [16,38,39]. An important factor in reducing the disease severity is to ensure adequate sanitary conditions and to reduce inoculum near the tubers by removing crop and soil residues [13].…”

A Complex Approach to Control Black Dot Disease in Potato

“…The development of skin blemish diseases can be controlled via a complex approach, which includes the use of healthy seed material, correct land treatment, and modern chemical fungicides [12,15,16]. However, black-dot-resistant potato cultivars for largescale production are almost absent, while most of those used in potato production are susceptible to this disease [17].…”

“…The development and severity of black dot disease also depends on crop cultivation conditions (temperature, irrigation, length of the cultivation period, cultivar susceptibility, fungicide application, crop rotation, etc. ), the virulence of the pathogen population, and the predominant inoculum potential [16]. At the same time, like many diseases, which are not accompanied by a significant plant infection or even death, the severity of black dot may depend on the immune status of a plant, i.e., weak immunity or stress conditions may provide more severe affections.…”