## 4 Discussion  
Plant diseases are an integral part of the cultivation systems and, at the same time, a very important factor in reducing the quality and size of yields [76,77]. The pathogen species, the development phase of the plant in which the first infections appeared, the manner of parasitism, the rate of infesting the plant organs, and the spread under certain environmental conditions determine the level of losses incurred. Knowledge of etiological factors and the functioning of the pathosystem is necessary when deciding on the control method and the preparations. Currently, an extremely important criterion for plant protection and plant production, in general, is to minimize and even withdraw the use of chemicals. In our study, symptoms of common scab, black scurf, and silver scurf were diagnosed on the surface of the tubers of Typhoon potatoes. The mean severity (DSI) of these disease units in the control treatments was high, i.e., 62.0%, 57.9%, and 54.2%, respectively. The extent of the problem is even better reflected by other morbidity parameters, such as the proportion of tubers infected in the crop and the average degree of tubers infected (ADIIT). Taking these into account, on average, 91.7% of the tubers were infected with symptoms of cork-like scabs induced by _S. scabies_, taking about 42.9% of the surface (Figure 3). On average, black, contaminating sclerootia of _R. solani_ covered 10% to as much as 81.7% of the  
Figure 6: Regression model of the total yield of the tubers and the total severity of the potato skin diseases. surface of potato tubers. In contrast, extensive silver stains caused by _H. solani_ covered as much as 47.68% (ADIIT = 3.74) and were identified on 74% of potato tubers. Since disease resistance is a genetic feature of potato varieties and environmental conditions are a factor determining health, it is difficult to find adequate tests in the literature. Taking these issues into account in the comparative assessment, we conclude that the phytosanitary status of potato tubers in Poland has deteriorated significantly over the last decade. In 2003-2005, the average DSI value for common scab was 8.2%, for black scurf 12.8%, and 20.1% for silver scurf [30]. The study by [PERSON] and [PERSON] [78] indicates that between 2005 and 2007, common scab symptoms were shown in about 24.4% of tubers, and in our study, this indicator was as high as 91.7%. The assessment carried out in 1998-2000 shows that DSI for silver scurf was 19.3-37.6% [79]. In our study, the DSI of this disease varied from 30.5% to 50.0%, regardless of the factors studied (Figure 4). From an epidemiological point of view, such intensive infection disqualifies potato tubers as a seeding material [13; 36; 80]. However, in this study, we highlight the significance of the tuber skin pathogens as an important factor in assessing the quality of potato tubers in terms of their suitability for processing and direct consumption. Black scurf alone, accompanied by deformations and cracks in tubers, can cause a 30% loss in commercial yield [81]. Surface, oblique and deep necroses of tubers caused by _S. scabies_ make them inadequate on the market [82]. These diseases are associated with losses during peeling and overall efficiency losses in the production of French fries and chips. The intensive growth of _H. solani_ causes the thickening of the skin, which is worn down unevenly during the mechanical peeling of French fries and chips [36]. As a result, in the areas of the infected skin, during frying, these products burn and are ugly and untasty. 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]. In our study, an ecological strategy for combating soil pathogens threatening potato tubers was adopted.