Understanding Genetic Control of Freezing Resistance Using Potato Species as a Model System

Abstract

Freezing stress resistance is generally regarded as a complex trait with multigenic inheritance (Marshall, 1982; Stushnoff et al., 1984; Blum, 1988). However, there is no consensus on the mode of gene action. For example the gene action for freezing tolerance has been reported to vary from recessive (Puchkov and Zhirov, 1978) to partially dominant (Parodi et al., 1983; Gullord et al., 1975) to both additive and non-additive (Sutka, 1994) in winter wheat, largely additive (Daday and Greenham, 1960) to dominant (Perry et al., 1987) in Alfalfa. The lack of consensus is, in part, due to heavy reliance on field test for assessing winter survival. Each winter is different in terms of the early fall frost episodes, lowest temperature, snow cover, mid-winter thaw periods followed by cold temperatures. Thus field selection has many inherent problems. Ideally one hopes for a “test frost episode” or a “test winter” that is severe enough to kill the most sensitive genotypes, cause various degrees of injury to intermediate genotypes, and cause no injury to most resistant genotypes. However such test frost episodes or test winters are rare. Thus when evaluating under field conditions one may not get the same results every winter or every frost episode. For example it has been shown that severity of winter or the stress level can determine whether the control of freezing tolerance was recessive or dominant (Muehlbauer et al., 1970). Furthermore, rank order of wheat cultivars for hardiness has been found to depend on the hardening technique used (Roberts, 1986).