SUITABILITY OF POTATO VARIETIES AND BREEDING MATERIAL FOR GROWING UNDER STRESSFUL CONDITIONS IN NORTH KURZEME REGION OF LATVIA

Potato (Solanum tuberosum L.) is mostly suitable for growing in moderate climate conditions at temperature 20 ° C. Yields are influenced by many factors: soil characterization, available nutrients, distribution of pests and weeds, agrotechnology, genotype or variety and climatic conditions during the vegetation period. In recent years summary of meteorological conditions (precipitation and air temperature), showed that stressful conditions during the vegetation period had a diverse influence on the growth and development of plants.  Excess or lack of humidity in soil or drought and heat affected the size and shape of the potato tubers. The heat stress is the problem of agriculture in many regions of the world in the last years. The aim of the study was to evaluate cultivars and clones from the breeding material under the stress conditions at the Stende Research Centre. The field trials were set up due to project of the Latvian Ministry of Agriculture: "Evaluation of breeding material to implement integrated and organic agriculture crop production technologies"(2015-2018). The article summarizes results of nine potato clones and nine varieties in both integrated and organic systems during 2017-2018, when 2018 was one of the driest and hottest in the last 100 years. The evaluation of the varieties and breeding material phenological phases in two years showed that germination and flowering differed from year to year.  Due to hot and dry weather conditions flowering was weak for several varieties and the bud flowering was observed. In 2018 germination for some varieties was slower compared to the previous year, but for many varieties (‘Lenora’, ‘Prelma’, ‘Imanta’) and breeding material germination was not delayed (Table 1). The earlyest germination and flowering were observed for variety 'Monta'. Earlier germination compared to other varieties and clones was recorded to S01085-21 and S03067-33 and the variety ‘Rigonda’.  In the organic field earlier germination was observed for the varieties 'Rigonda', 'Monta', 'Prelma' and clones S01085-21, S07169 -35. The yield of varieties and breeding material lines in both years was good but still lower tuber yields were obtained in the integrated growing system and only one line (S01085-21) and variete ‘Gundega’ had significantly higher yield in comparison 2017. In the organic growing system tuber yields of all varieties and breeding material lines were significantly lower than the 2017 year. Yield reduction is not significant for 3 breeding material lines: S10063-128, 19922.29 and S2008-6.5.