Cold Tolerance

Abstract

Considerations of preparations for a changing climate will generate thoughts of mitigating a rise in temperature and greenhouse gas emission and a change in water availability. Accordingly, reduced prioritization on future research objectives aimed at crop adaptations sufficient to instigate and sustain cold tolerance or winter hardiness expression at any specific location might be deemed by some as the logical outcome. However, such a conclusion would be a grave mistake. With increasing frequency, crops of high agricultural value are being grown at locations beyond their natural ranges of adaptation, a consequence in part of farmers attempting to seize new opportunities to exploit some positive scenarios of climate change that might provide more profitable agricultural output. A second and even greater driver is man’s response to the ever-increasing requirement to feed a growing global population, and with only limited and finite land available that is deemed suitable for agricultural use. For the latter, there is increased use of marginal locations for agricultural production, which will include those locations at high altitude where temperatures are frequently suboptimal for crop production and, in many cases, likely to challenge crop persistency over winter months. In certain temperate locations, where winter temperatures are considered generally moderate, crop growing seasons are becoming extended, encouraged frequently by national policy makers seeing economic advantages in management practices that can achieve an all-year-round cropping potential, but with a great risk. The maintenance of crop growth is the consequence of failure, at least in part, of the initiation and subsequent expression of the appropriate adaptive responses necessary to assure a high probability of winter survival which include growth cessation. Such scenarios place crops at risk of total collapse following any sudden temperature drop and especially onsets of frost conditions. In situations of fluctuating winter temperatures, assured crop survival requires the maintenance of the required adaptive response in place until such time as there is little likelihood of any further incidence of frosts. For optimal crop production, the subsequent appropriate timing of the cessation of the adaptive responses is also essential to enable crop growth to proceed fully as soon as possible, once growth advantageous spring conditions arise.

Cold tolerance and winter survival are complex traits, each having distinct genetic controls and involving responses to the many interacting stresses, their relative importance dependent on crop location. Frost tolerance is considered the trait of main priority with the understanding and manipulation of the factors necessary to optimize initiation of the appropriate cold acclimation responses sufficient to retain cell membrane integrity and prevent desiccation, the most appropriate objectives in crop improvement. Gene expression sufficient to initiate frost tolerance has many equivalent requirements and responses to those required to combat other abiotic stresses that can induce cell desiccation such as prolonged exposures to conditions of drought or salinity. Some of the major aspects and their relative importance are reviewed herein.