This study provides the first long-term, cross-border evaluation of Lithuanian potato (Solanum tuberosum L.) cultivars, integrating agronomic performance, tuber quality, and resistance to major pathogens across diverse environments. Field and controlled trials conducted in Lithuania and Ukraine from 2014 to 2024 revealed substantial genetic variability among 14 national cultivars, enabling their classification into five distinct maturity groups. Maincrop cultivars outperformed others in yield and starch accumulation, with ‘VB Meda’, ‘Goda’, and ‘VB Aista’ exhibiting a superior balance of productivity (up to 49 t ha⁻¹), starch content (>19%), and moderate-to-high resistance to Phytophthora infestans. A broader genetic screening of 287 accessions—including varieties, breeding lines, and hybrids—demonstrated wide diversity in phenological development, disease resistance, and reproductive traits. Notably, Ro₁ pathotype resistance was identified in 85 genotypes, predominantly with yellow-skinned tubers, while genotypic sterility in flowering and berry set was associated with both parental lineage and elevated temperatures. Although no complete immunity to P. infestans was detected, several genotypes displayed stable polygenic field resistance, suggesting the presence of horizontally inherited defense mechanisms effective under variable agroclimatic conditions. These results underscore the strategic breeding potential of Lithuanian potato germplasm for developing high-performing cultivars with enhanced resilience to late blight and nematodes and offer valuable insights for climate-adapted potato breeding in Northern and Eastern Europe.

The research was conducted between 2014 and 2024 at the Vokė Branch of the Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry. Experimental plots were established on sandy loam soil with carbonaceous fluvio-glacial gravel eluviated substrate (IDp), classified as Haplic Luvisols (LVh) according to the FAO-UNESCO system. The study involved a comprehensive evaluation of a potato (Solanum tuberosum L.) collection consisting of 287 varieties and hybrids originating from major potato-producing regions, as well as breeding material developed in Lithuania. The analysis revealed a high level of genetic diversity within the collection. Varieties exhibited significant variation in morphological, physiological, immunological, and agronomic traits, both within and across maturity groups. This genetic diversity has been directly applied in Lithuanian potato breeding programmes. Hybridisation methods were employed using the genetic resources preserved in the national collection, with the primary aim of developing disease-resistant varieties possessing superior agronomic performance and culinary quality. In addition, the study assessed the resistance of Lithuanian potato varieties to Phytophthora infestans (late blight) under diverse pathogen populations and climatic conditions in both Lithuania and Ukraine. The findings contribute valuable insights for the selection of resistant genotypes in the context of climate change and evolving pathogen pressures.