Characterisation of the low temperature tolerant locus (Ltp1) on wheat chromosome 5D

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Wheat production will need to increase by 60% in the next 50 years. However, this increase will need to happen against a background of climatic change. Temperatures are predicted to fluctuate globally by several degrees by the end of this century. The wheat growing area of nearly one billion people will be affected by major temperature fluctuations and an associated reduction in yield. Higher temperatures during wheat's flowering can have a major effect on subsequent grain yield. The climate is also going to become increasingly unpredictable with more extremes of weather in other regions, including the UK. Cold weather during floral development is also associated with sudden reductions in wheat yields. Cold wet weather occurring during floral development during mid-1980s resulted in significant sterility, leading to a 70% reduction in yields in the UK. Wheat yields need to increase against this background of climate change. Clearly it is possible to screen wild relatives of wheat for those exhibiting greater temperature tolerance than wheat. Such characters can then be transferred from the wild relative to wheat through prebreeding. However, there are problems with this approach. Firstly, studies have shown that the relatives are more tolerant of temperature simply because their genome structure is simpler than wheat, not because they necessarily carry genes which provide them with a higher level of temperature tolerance. Secondly, there are particular stages in wheat's floral development that are more sensitive to temperature effects than others. Wheat varieties and wild relatives may also seem apparently more temperature tolerant simply because they have altered the timing of their pre-meiotic and meiotic stages, to avoid the extremes of temperature. Of course, such a strategy does not alleviate the problem of dealing with marked changes in temperatures during day and night. Thus, developing wheat whose floral development stages are truly more tolerant of temperatures is an important priority. Selection of plants truly tolerant of temperatures would require the identification of large numbers of plants at the temperature sensitive stage of floral development, then subjecting them to a range of temperatures, before scoring the subsequent effect on the level of seed set. This approach would be hugely time consuming and laborious. Realistically, it needs to be performed on a limited number of plants. Our project addresses this problem. It will provide tools for selecting wheat that is more tolerant of temperatures during floral development. Our strategy is based around the fact that our recent research has narrowed down a temperature sensitivity stage of floral development covering pre-meiosis when replication occurs. Previous research showed that the long arm of 5DL also carries a locus which provides cells at this pre-meiotic stage with a tolerance to low temperatures. Our recent studies confirmed and extended these observations, namely that the long arm of wheat chromosome 5D (5DL) carries a locus, Ltp1 which provides cells at this stage with a tolerance to low (and high) temperatures, subsequently affecting whether chromosomes pair homologously or homoeologously. We have undertaken preliminary mapping and have defined the locus to the proximal region of 5DL, which includes the location of the Ph1 homoeoallele. We will refine the mapping to identify Ltp1 controlling low temperature tolerance during pre-meiosis, and generate resources to characterise the 5DL Ph1 homoeoallele. The resources generated will be used to assess whether these loci are also controlling tolerance to high temperature. The characterisation of Ltp1 will provide us with tools for screening a large number of wheat varieties to identify those with different variants of the locus. Such plants can be assessed for level of their temperature tolerance, to identify the variant providing the plant with the highest level of temperature tolerance.