## 2 Results and Discussion
Figure 6: Kinetics of root growth and time of its growth up to 30 cm in length, as affected by the seed potatoes storage at 4 \({}^{\circ}\)C from harvest until inoculation with phytopathogens on 10 February and then at 15 \({}^{\circ}\)C and 80% RH before planting in the soil on 10 March, 10 April, and 10 May. C—Control, Fo—_F. oxysporum_, Pc—_P. corotovorum_, Rs—_R. solani_. Means marked with the same letters do not differ statistically at the significance level \(p=0.05\). LSD was calculated at the significance level of \(p=0.05\). A quick examination of the effect of phytopathogens was possible thanks to the use of elaborated plant microcosms, which, in a short time, enabled to trace the entire development cycle of individual plant organs before planting the seed potatoes in the field [17; 18]. The markers used for the evaluation of the potato development in plant microcosms demonstrated, in a short time period, the high sowing value of seed potatoes, which were planted on 10 March, 10 April, and 10 May. They exhibited that the stems and roots obtained from the more sprouted seed potatoes and those planted later developed faster and produced a higher yield of fresh and dry biomass of tubers. As a result, the plants obtained from the sprouted seed potatoes planted in the substrate in May, with sprouts approximately 5 cm long, developed the fastest and gave the highest yield. The analyzed data are consistent with the research of [PERSON] [68], in which the storage of seed potatoes in similar conditions until April had a positive effect on the growth of stems. They are also consistent with the findings of [PERSON] et al. [69] who studied only the stem growth from seed potatoes stored by various methods. According to the Research Centre for Cultivar Testing in Poland [70], the yield of potato tubers of the Impresja cv. 40 days after emergence was 0.44 kg per plant with a spacing of 50,000 plants per ha and 0.49 kg with 45,000 plants per ha, hence, similar to the crop used here in plant microcosms. The conducted research demonstrated that the most useful and quick marker of seed potato infection by phytopathogens was the kinetics of root growth and development, enabled to perform in plant microcosms. The intensity of growth kinetics of both individual roots and the entire root system, evaluated on the basis of their filling of the soil profile, was strictly dependent on the degree of seed potato infestation by phytopathogens, which was increased when the period from inoculation to tuber planting was longer. The usefulness of this marker was high because the development and physiological activity of roots, closest to sprout eyes, were earlier than of stems, and it was dependent on the health and yielding potential of seed potatoes. Moreover, roots determine to a large extent the stems' growth, nutrients, and water uptake, as well as vigor, quality, and yielding of plants. The dynamics of root growth can also be a valuable and quick-to-perform marker of plant development in the case of contamination by phytopathogens deriving from the soil. Root growth kinetics also showed, to a greater extent than other markers, the degree of pathogenicity of phytopathogens inoculated to sprouted seed potatoes. By using this marker, it was also demonstrated that all the tested phytopathogens, i.e., _Fusarium oxysporum_, _R Rhizectonia solani_, and _Pectobacterium corotovorum_, had a negative effect on the growth, development, and yielding of plants, while _Fusarium oxysporum_ exhibited a greater infection potential. This was most evident in the case of sprouted seed potatoes