Aegilops Species with S, C, and U Genomes As Sources of Novel Genes for Abiotic Stress Tolerance.

Screening of wild Triticum and Aegilops species at the Punjab Agricultural University, India showed that Aegilops species with S, C and U genomes exhibit greater tolerance to high temperature during grain filling period, drought tolerance and cold tolerance. All the accessions of  Aegilops speltoides (SS) and Ae. triuncialis (CCUU) had viable pollen (> 90 percent viability) at temperatures as high as greater than 40⁰ C. The seed set and seed size was normal under the high temperature in these accessions. Field screening for drought tolerance by withholding irrigation at flowering and grain filling periods showed that all accessions of Aegilops speltoides (SS) were tolerant whereas all Triticum dicoccoides (AABB) accessions were highly susceptible with no accessions possessing tolerance to drought. In another experiment, majority of accessions which recovered from freezing stress at seedling stage belonged to Aegilops speltoides and Aegilops species with C and U genomes. None of the accessions of Aegilops squarrosa (DD) survived. Aegilops species with S, C, and U genomes have vernalization requirement for induction of flower development and it is plausible that these species have novel allelic variance at Vrn loci governing this trait in cultivated and related wheat species. In these species, Vrn loci have been mapped on homoeologous group 5 chromosomes. Studies have shown that Quantitative trait loci/genes for various types of abiotic stress tolerance are located in the same position as Vrn loci. It has been shown that variation in Vrn1 is sufficient to determine differences in freezing tolerance. The studies on abiotic stress tolerance have suggested general role of some regulatory factors in environmental adaptation mechanisms and there is possibility to find some common Quantitative trait loci/genes influencing more than one adaptation processes. In this context, this paper explains that how the relationship of Vrn loci with abiotic stress tolerance can be exploited to utilize Aegilops species with S, C and U genomes as sources for cloning of novel genes for abiotic stress tolerance.