Freezing tolerance, cold acclimation and oxidative stress in potato. Paraquat tolerance is related to acclimation but is a poor indicator of freezing tolerance

Abstract

Potato is a species commonly cultivated in temperate areas where the growing season may be interrupted by frosts, resulting in loss of yield. Cultivated potato, Solanum tuberosum, is freezing sensitive, but it has several freezing‐tolerant wild potato relatives, one of which is S. commersonii. Our study was aimed to resolve the relationship between enhanced freezing tolerance, acclimation capacity and capacity to tolerate active oxygen species. To be able to characterize freezing tolerant ideotypes, a potato population (S1), which segregates in freezing tolerance, acclimation capacity and capacity to tolerate superoxide radicals, was produced by selfing a somatic hybrid between a freezing‐tolerant Solanum commersonii (LT50=‐4.6°C) and ‐sensitive S. tuberosum (LT50=‐3.0°C). The distribution of non‐acclimated freezing tolerance (NA‐freezing tolerance) of the S1 population varied between the parental lines and we were able to identify genotypes, having significantly high or low NA‐freezing tolerance. When a population of 25 genotypes was tested both for NA‐freezing and paraquat (PQ) tolerance, no correlation was found between these two traits (R = 0.02). However, the most NA‐freezing tolerant genotypes were also among the most PQ tolerant plants. Simultaneously, one of the NA‐freezing sensitive genotypes (2022) (LT50=‐3.0°C) was observed to be PQ tolerant. These conflicting results may reflect a significant, but not obligatory, role of superoxide scavenging mechanisms in the NA‐freezing tolerance of S. commersonii. The freezing tolerance after cold acclimation (CA‐freezing tolerance) and the acclimation capacity (AC) was measured after acclimation for 7 days at 4/2°C. Lack of correlation between NA‐freezing tolerance and AC (R =‐0.05) in the S1 population points to independent genetic control of NA‐freezing tolerance and AC in Solanum sp. Increased freezing tolerance after cold acclimation was clearly related to PQ tolerance of all S1 genotypes, especially those having good acclimation capacity. The rapid loss of improved PQ tolerance under deacclimation conditions confirmed the close relationship between the process of cold acclimation and enhanced PQ tolerance. Here, we report an increased PQ tolerance in cold‐acclimated plants compared to non‐acclimated controls. However, we concluded that high PQ tolerance is not a good indicator of actual freezing tolerance and should not be used as a selectable marker for the identification of a freezing‐tolerant genotype.