Freezing Tolerance in the Triticeae - Translational Genomics for Crop Breeding: Abiotic Stress, Yield and Quality - page 99

Chapter 7

Freezing Tolerance in the Triticeae

GalibaGabor,EricJ.Stockinger,EnricoFrancia,JustynaMilc,GaborKocsy,and
NicolaPecchioni

Abstract

In the face of growing food demand, major variation in cereal yield from year to year resulting from
drought and low temperatures poses a serious problem for agricultural production and for the stability
of agricultural trade. Furthermore, in the coming decades climate change is predicted to cause dramatic
shifts in temperature and rainfall, posing further challenges to agriculture. Accordingly, maintaining
high and stable yields in the driest and coldest cereal-growing areas is becoming one of the most
urgent aims for plant breeding. From a biological point of view, the strategy of escape relies on
developmental plasticity (Levitt 1980), that is, successful completion of reproduction before the onset
of severe stress such as drought and frost. However, escape is probably not the best strategy for
maximizing agricultural productivity, or at least, it should not be the only route pursued. In fact, given
the limited area of cultivatable land, a tendency to perennialism coupled with an increasing tolerance
to abiotic stresses over the growth cycle could be for herbaceous crops a significant genetic alternative
to the agronomic one of double-cropping. As an example, because of their longer growing period,
winter cereals usually have higher yield potential than spring varieties, which are planted later in the
spring. In order to withstand stresses, a plant tolerant to freezing −

has to cope with dehydration. Ice formation in the intercellular space subtracts water from the cell;
at -10 ◦ C more than 90% of the osmotically active water typically moves out of the cells. At the
same time, plasma membranes, as well as the organellar ones, are damaged and can lose integrity.
Survival at freezing temperatures is a phenomenon dependent on a number of factors, including frost
duration and severity, alternation of frost and thaw periods, and synthesis of toxic substances affecting
recovery capacity. However, the ability to survive freezing is based on the effectiveness of the cold
acclimation process (Thomashow 1999). Cold acclimation is a relatively slow, adaptive response that
takes place during the fall, when the temperature, length of the day, and light intensity decrease
gradually. All these factors are important for attaining a genetically determined freezing tolerance.
The physiological process comprises biochemical changes that enable tissues to enhance their frost
resistance. Plant species that do not acclimate, generally those of tropical origin, are severely damaged
even at temperatures just below 0 ◦ C. For this reason, studies aimed at understanding the molecular

− just as one tolerant to drought