Modern agriculture and conventional breeding and the liberal use of high inputs has resulted in the loss of genetic diversity and the stagnation of yields in cereals in less favourable areas. Increasingly landraces are being replaced by modern cultivars which are less resilient to pests, diseases and abiotic stresses and thereby losing a valuable source of germplasm for meeting the future needs of sustainable agriculture in the context of climate change. Where landraces persist there is concern that their potential is not fully realised. Much effort has gone into collecting, organising, studying and analysing landraces recently and we review the current status and potential for their improved deployment and exploitation, and incorporation of their positive qualities into new cultivars or populations for more sustainable agricultural production. In particular their potential as sources of novel disease and abiotic stress resistance genes or combination of genes if deployed appropriately, of phytonutrients accompanied with optimal micronutrient concentrations which can help alleviate aging-related and chronic diseases, and of nutrient use efficiency traits. We discuss the place of landraces in the origin of modern cereal crops and breeding of elite cereal cultivars, the importance of on-farm and ex situ diversity conservation; how modern genotyping approaches can help both conservation and exploitation; the importance of different phenotyping approaches; and whether legal issues associated with landrace marketing and utilisation need addressing. In this review of the current status and prospects for landraces of cereals in the context of sustainable agriculture, the major points are the following: (1) Landraces have very rich and complex ancestry representing variation in response to many diverse stresses and are vast resources for the development of future crops deriving many sustainable traits from their heritage. (2) There are many germplasm collections of landraces of the major cereals worldwide exhibiting much variation in valuable morphological, agronomic and biochemical traits. The germplasm has been characterised to variable degrees and in many different ways including molecular markers which can assist selection. (3) Much of this germplasm is being maintained both in long-term storage and on farm where it continues to evolve, both of which have their merits and problems. There is much concern about loss of variation, identification, description and accessibility of accessions despite international strategies for addressing these issues. (4) Developments in genotyping technologies are making the variation available in landraces ever more accessible. However, high quality, extensive and detailed, relevant and appropriate phenotyping needs to be associated with the genotyping to enable it to be exploited successfully. We also need to understand the complexity of the genetics of these desirable traits in
BackgroundRecessively inherited natural and induced mutations in the barley Mlo gene confer durable broad-spectrum resistance against the powdery mildew pathogen, Blumeria graminis f.sp. hordei. Mlo codes for a member of a plant-specific family of polytopic integral membrane proteins with unknown biochemical activity. Resistant barley mlo mutant alleles identify amino acid residues that are critical for Mlo function in the context of powdery mildew susceptibility.ResultsWe molecularly analyzed a novel set of induced barley mlo mutants and used site-directed mutagenesis in combination with transient gene expression to unravel novel amino acid residues of functional significance. We integrate these results with previous findings to map functionally important regions of the heptahelical Mlo protein. Our data reveal the second and third cytoplasmic loop as being particularly sensitive to functional impediment by mutational perturbation, suggesting that these regions are critical for the susceptibility-conferring activity of the Mlo protein. In contrast, only mutations in the second but not the third cytoplasmic loop appear to trigger the Endoplasmic Reticulum-localized quality control machinery that ensures the biogenesis of properly folded membrane proteins.ConclusionOur findings identify functionally important regions of the polytopic barley Mlo protein and reveal the differential sensitivity of individual protein domains to cellular quality control.
Two!hundred and thirty!two accessions of barley landraces collected from Tunisia were screened for resistance to powdery mildew[ A number of race!speci_c genes were detected using the detached leaf technique[ Among the 121 accessions tested\ 058 were susceptible to powdery mildew\ 19 were resistant and 32 showed di}erential reactions to the three isolates of powdery mildew used[ An attempt was made to deter! mine the number of genes\ the types of gene\ the types of gene action and the gene loci in 19 resistant accessions[ Three types of cross were made] "0# the accessions were crossed to the susceptible variety {Pallas|\ "1# the accessions were crossed with {Pallas| isolines\ and "2# accessions with identical powdery mildew reaction patterns were intercrossed[ Three isolates of Erysiphe`raminis f[ sp[ hordei were used] Bzm!0\ KM 07Ð64\ R02C[ A number of di}erent resistance genes were detected among the 19 resistant accessions[ Surprisingly\ segregation indicating single genes only were detected with the isolates used[ Some of these genes could be associated with loci already known[ In 08 cases a domi! nant and in one a recessive mode of inheritance was detected[ The recessive gene was not located at the mlo locus[ This investigation represents the _rst systematic study of race!speci_c genes for powdery mildew resistance in Tunisian landraces[ The newly identi_ed sources of resistance may be used in many strategies of breeding for disease resistance[
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