Heritable improvement of frost tolerance in winter wheat by in vitro selection of hydroxyproline-resistant proline overproducing mutants

In a previous study (Dorffling et al., J. Plant Physiol. 142, 222-225, 1993) in vitro-selection and regeneration of hydroxyproline (Hyp)-resistant lines of winter wheat (Triticum aestivum cv. Jo 3063) with increased frost tolerance and increased proline contents was reported. In this study the heritability of these traits was investigated. The F-1 progenies derived from the pollination of regenerated plants with pollen from wild type plants developed higher mean frost tolerance (lower LT(50) values) and higher proline levels compared with in vitro-controls and wild type plants. In the F-2 generation, which was obtained by self-pollination, segregation of the Hyp-lines in a 3:1 phenotypic ratio with regard to the traits frost tolerance and proline content was observed. Subsequent selection of extremes in the F-2 yielded homozygous plants in the F-3 generation. Lower LT(50) values and increased proline contents in those F-3 plants were significantly correlated. Furthermore, improved frost tolerance of one of the selected mutants was also observed in studies with whole plants in the F-4 generation. These results, which are similar to results of parallel studies on winter barley, provide strong evidence for the heritability of the traits 'increased frost tolerance' and 'increased proline content' obtained by this in vitro-selection procedure. The mutation seems to be due to a single incompletely dominant gene. A comparison of frost tolerance values from F-3 Hyp-progenies with those of seven standard varieties differing in frost tolerance indicates a considerable improvement of frost tolerance by the described in vitro-selection method.