The study is aimed at establishing an efficient protocol for ”in vitro” medium term conservation of sweet potato. Three medium variants and three different temperatures were used for this purpose. In this experiment 6 varieties of sweet potato were tested (Juhwangmi, KSC1, Yulmi, KSP1, Hayanmi and VSP1). Uninodal segments of fully developed sweet potato plants already established ”in vitro” were cultured on MS basal medium with and without osmotic regulators (mannitol and sorbitol). The cultures were incubated at three different temperatures: 24±2ºC, 20±2ºC and 16±2ºC. After 140 days of ”in vitro” conservation shoots height, number of leaves, number of roots and survival rate (%) were measured. Culture condition variants V1 (MS, 24±2ºC) and V2 (MS + 10g/l mannitol + 10 g/l sorbitol, 20±2ºC) ensured the best results regarding shoots height, number of leaves and number of roots. The highest survival rate (87.78% and 84.44%, respectively) were observed in the V2 and V3 (MS + 15g/l mannitol + 15 g/l sorbitol, 16±2ºC) culture condition variants. The slow growth technique allowed the successful ”in vitro” medium term conservation of sweet potato genotypes.

At present, the base for seed potato production is the potato minitubers produced in protected” insect-proof” spaces. For seed potato production it is essential to use a healthy and high-quality biological material, which contributes to obtaining superior production, both quantitatively and qualitatively. In potatoes, to eradicate viruses and obtain a healthy initial material, we have at our disposal the technique of sampling and “in vitro” cultivation of meristems. In 2024, 11 potato cultivars grown in greenhouses were evaluated. The mini-tubers are derived from "in vitro" cultivated plants. Before micropropagation, the plantlets have been subjected to viral testing using the ELISA technique. Potato microplants used for "in vitro" multiplication were obtained from meristem cultures. Regarding the average number of minitubers/pot, the best results were obtained in 'Castrum' (11.50), 'Ervant' (10.80) and 'Sevastia' (10.10) cultivars. The best results in terms of the average weight of minitubers/plant were obtained in 'Brașovia' (271.62 g), 'Darilena' (270.13 g) and 'Ervant' (258.87 g) cultivars. The 'Brașovia' and 'Darilena' cultivars also recorded the highest values of the average weight of minitubers (53.2 g and 50.92 g, respectively). The highest percentage of minitubers >30 mm (60%) was found for 'Brașovia' and 'Darilena' cultivars. Also, for 'Asinaria', 'Cosiana', 'Ervant', 'Foresta', 'Marvis' and 'Sarmis' cultivars, the highest rate was recorded for minitubers in the size fraction 25-30 mm and >30 mm. By selecting appropriate cultivars and managing them according to their specific needs, potato growers can enhance the efficiency of seed production systems and achieve higher yields in field multiplication stages.

The potato varieties studied in this paper were created at the National Institute of Research and Development for Potato and Sugar Beet Braşov. They have a high biological production capacity and are attractive and very appreciated by farmers, potato producers, consumers and processors, but manifest recalcitrance to the in vitro culture techniques. Thus we tried to find an optimal culture medium variant for these varieties, in order to obtain healty potato seed material in a short time. The study compared the effects of five different culture media using MS medium containing various concentrations of gibberelic acid (GA3) in combination with α-naphthalene acetic acid (NAA) in micropropagation of two recalcitrant potato varieties, Marvis and Brasovia. The longest shoots, maximum number of nodes and leaves, the longest roots and the best rooting efficiency were recorded on MS medium containing 2 mgL-1 GA3 and 1 mgL-1 NAA, for both varieties. The use of a larger quantity of GA3 negatively influenced the potato shoots and roots growth. The culture media using MS medium containing 4 mgL-1 GA3 and 1 mgL-1 NAA had an inhibitory effect on all the studied plantlet characteristics. The results showed that a certain combination of growth regulators (NAA and GA3) improved the micropropagation capacity of the two recalcitrant potato cultivars studied and resulted in the maximum improvement in the parameters.

The production of minitubers using the hydroponic method has become an important component in the production of seed potatoes in developed countries. The objective of the study is obtaining minitubers (Prebase), free from diseases, from the transplantation of vitroplants on industrial substrate and different hydroponic systems. The hydroponic culture involves growing plants on artificial substrates, or in a sterile, porous substrate with a high-water permeability. The parameters analyzed in this study were: average number of minitubers / plant and average weight of minitubers/plant. By using hydroponic system, a high minitubes production was obtained. The trifactor experience of the type 4 x 2 x 2 with 16 variants used the following graduations of the studied factors: experimental factor a, variety, with four graduations: a1 - Braşovia; a2 - Castrum; a3 - Marvis; a4 - Sarmis; experimental factor b, culture substrate, with two graduations: b1 - expanded clay; b2 - perlite; experimental factor c, the hydroponic system: c1 - Wilma; c2 - Nutrient Film Technique. These variants were experimented in 3 repetitions. Castrum variety was remarked by obtaining a high number of minitubers and also by weight of minitubers. Nutrient Film Technique hydroponic system had a positive influence on minituberization, for minitubers number, but also for weight of minitubers. Perlite substrate has determined obtaining high values for both studied parameters.

Hydroponics growing method has proven to be a very successful strategy for the production of pre-base seed potatoes. NIRDPSB Brasov applied this method in 2016, by using two types of culture: with circulating nutrient solution and with static layer of nutrient solution and for both cases the substrate used was perlite. As biological material plantlets of four cultivars (Braşovia, Castrum, Marvis and Sarmis) were used and grown hydroponically in a space “insect-proof” under controlled conditions. The number of minitubers/plant and weight of minitubers/plant were compared for the used cultivars. By using circulating nutrient solution in hydroponic system, Marvis variety (13.80 minitubers/plant) and Castrum variety (11 minitubers/plant) were the best performing of the four cultivars. The hydroponic system with circulating nutrient solution had a positive impact on the mean weight of minitubers/plant, with Marvis variety, recording the highest value (121.6 g).

Currently there are several culture systems that can provide disease-free mini tubers, and provide multiple yield of seed potato as compared to the conventional methods. The minituberization process was evaluated on different culture systems, in a bifactorial experience, type 4*4, where factor a was culture system, with four gradations: a1 - system without automation on industrial substrate; a2 - nutrient system film technique NFT; a3 - Wilma system; a4 - conventional system, without automation on peat-perlite substrate, and factor b: variety, with four graduations: Azaria, Brașovia, Cosiana and Cezarina. Culture system, variety and their interaction significantly influenced number and weight of potato mini tubers. The values of number and weight of mini tubers obtained in the system without automation on perlite substrate differ significantly, in a positive sense, from the other systems. The variety Azaria recorded the highest average number of mini tubers in the 4 culture systems, followed by the variety Cezarina. The NFT culture system contributed significantly to increasing minituberization capacity for Azaria variety, which led to the highest number of mini tubers recorded.