Genetic variation in morpho-physiological traits associated with frost tolerance in faba bean (Vicia faba L.)

Frost stress is one of the most significant abiotic stresses affecting crops in Europe and limits e.g. winter faba bean growth. Faba bean is therefore mainly sown as a spring crop in cool-temperate regions. The objective of this study is to study the genetic variation in frost tolerance between elite winter faba beans. To address this challenge, 200 highly homozygous lines were tested in a frost growth chamber. Two different experiments, with frost stress and with hardening conditions were conducted. A number of morphological traits of shoots (loss of leaf turgidity, loss of leaf color, regrowth after frost and disposition to survive) and of roots (root frost susceptibility and root length) were visually scored in the frost experiments. Moreover, total leaf fatty acid (after hardening) and water content (after hardening and after frost stress) in shoots as physiological parameters were analyzed. The frost tolerance index was calculated to improve two traits: disposition to survive and regrowth after frost. High significant genetic variation was found between genotypes in all traits scored and analyzed. Disposition to survive showed high significant phenotypic (r = 0.77**) and genotypic (r = 0.85) correlations with regrowth after frost test. Moreover, roots traits showed higher significant phenotypic and genotypic correlations with frost tolerance than traits scored on shoots (loss of leaf turgidity and loss of leaf color). For physiological traits, water content before and after frost showed stronger significant correlation with frost tolerance than leaf fatty acid composition. Repeatability estimates (h(2)) ranged from 0.58 to 0.95 for morphological traits and from 0.63 to 0.89 for physiological traits. The best 20 genotypes for each morphological trait were determined. As a result, 12 genotypes were identified with superior frost tolerance. The results indicate the possibility of genetically improving the frost tolerance in winter faba bean through selection programs.