INHERITANCE OF FREEZING RESISTANCE IN TUBER-BEARING SOLANUM SPECIES -EVIDENCE FOR INDEPENDENT GENETIC-CONTROL OF NONACCLIMATED FREEZING TOLERANCE AND COLD-ACCLIMATION CAPACITY

Frost or winter survival is regarded as a complex trait with polygenic inheritance. Two major components of this survival in crop plants are freezing tolerance in the nonacclimated state and cold acclimation ca pacity. To date researchers have not distinguished the two components as separate heritable traits. The mode of inheritance of these two tra its was investigated in F1 and backcross populations of two wild diplo id potato species (Solanum commersonii and Solanum cardiophyllum) exhi biting extremes of freezing tolerance and acclimation capacity. Precis e assessment of these two traits allowed distinction of small but sign ificant differences among genotypes. The two traits were not correlate d in segregating populations, suggesting independent genetic control. Analyses of generation means indicate that all of the variance for acc limation capacity and a major proportion of the variance for the nonac climated freezing tolerance can be best explained by an additive-domin ance model with both traits being partially recessive. Recovery of par ental phenotypes in limited populations suggests that both traits are controlled by relatively few genes. To our knowledge this is the first study demonstrating independent genetic control of the two main trait s associated with frost or winter survival. Our results show that it s hould be possible to incorporate these traits from wild germ plasm int o cultivated crop plants by independent selection. These results help explain the lack of progress in improving winter survival through fiel d selection. Furthermore, our study demonstrates relative simplicity o f the inheritance of cold acclimation, thus providing avenues for unde rstanding the link between biochemical and genetic aspects of low-temp erature stress in crop plants.