Ecology. Michael Begon

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Ecology - Michael  Begon

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2.14a shows that for both cultivars, several cycles of selection for freezing tolerance led to a significant decline in LT50 between the first cycle and later cycles of selection: in other words, individuals in the populations subject to selection were able to tolerate lower winter temperatures. Associated biochemical (Figure 2.14b, c) and genetic patterns (Figure 2.14d) provide good evidence that recurrent selection for superior freezing tolerance in alfalfa induces marked changes in influential traits. And if deliberate selection can change the tolerance of a domesticated plant we can certainly expect that natural selection has done the same thing for plants, animals and microorganisms in nature.

Graphs depict alfalfa that can be selected for improved freezing tolerance. (a) Tolerance to freezing of populations of two cultivars of alfalfa used for animal forage in eastern Canada, before selection or after several cycles of recurrent selection for freezing tolerance. (b, c) Starch and sucrose concentrations in crowns of alfalfa plants during autumn and winter before (0) and after five or six cycles of selection. (d) Relative expression of the cold-induced gene cas15 before (0) and after five or six cycles of selection.

      Source: From Castonguay et al. (2011).

      APPLICATION 2.4 Selection for cold tolerance in crops to increase their productivity and geographic range

      There have been many striking cases where the geographic range of a crop species has been extended into colder regions of the world by plant breeders. Traditional crop breeding practices have generally used crossing of closely related varieties to produce new crops with desired cold‐tolerance traits.

Bar chart depicts the chilling tolerance of Miscanthus can be transferred to Saccharum.

      Source: From Głowacka et al. (2016).

      potential of genomics, transcriptomics and proteomics in crop breeding

      Future crop improvements to increase production and range in colder environments are certain to involve identification of the genes responsible for cold tolerance (both chilling and sub‐zero tolerance) and acclimatisation. Erath et al. (2017) have, for example, identified genomic regions involved in frost tolerance of winter rye (Secale cereale) by mapping of quantitative trait loci (QTLs). A QTL is a section of DNA that correlates with variation in the quantitative trait of the phenotype (cold tolerance in this case); the QTL can be expected to contain the genes that control the trait. In winter rye, a QTL on chromosome 5R harbours the Frost resistance locus 2 (Fr‐R2) and the ‘Puma’ allele at this locus was found to significantly increase frost tolerance. Discoveries of this kind can be expected to increase selection intensity for frost tolerance by preselecting plant breeding lines based on markers from the Fr‐R2 locus.

      2.3.6 Life at high temperatures

      Perhaps the most important thing about dangerously high temperatures is that, for a given organism, they usually lie only a few degrees above the metabolic optimum. This is largely an unavoidable consequence of the physicochemical properties of most enzymes (Wharton, 2002). High temperatures may be dangerous because they lead to the inactivation or even the denaturation of enzymes, but they may also have damaging indirect effects by leading to dehydration.

      high temperature and water loss in terrestrial environments

      Most of the plant species that live in very hot environments suffer severe shortage of water and are therefore unable to use the latent heat of evaporation of water to keep leaf temperatures down. This is especially the case in desert succulents in which water loss is minimised by a low surface to volume ratio and a low frequency of stomata. In such plants the risk of overheating or of damage to photosynthetic machinery may be reduced by spines (which shade the surface of a cactus) (Loik, 2008) or hairs

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