The improvement of leaf rust resistance in selected bread wheat lines

[摘要] English: The objective of this study was not only to improve leaf rust (caused byPuccinia triticina) resistance in selected wheats (Triticum aestivum L.), but tofocus on durability as well as agronomic acceptability of resistant lines. Thiswas achieved by traditional breeding techniques as well as with the use ofAFLP analysis. Seven bread wheat lines were obtained from ARC-Small Grain Institute (SGI)where they were developed. Six leaf rust resistance sources were obtainedfrom the University of the Free State. The breeding strategy focused oncreating lines that contained both seedling and adult plant resistance genes.Lr34 was chosen as the adult plant resistance source as it is an importantgene due to its durability and interaction with other leaf rust resistance genes.It is also an easy gene to follow as it is associated with leaf tip necrosis. In anattempt to create genotypes that will remain durable, four seedling leaf rustresistance genes (Lr21, Lr32, Lr36 and Lr41) were each combined with Lr34in the seven SGI backgrounds. By combining seedling and adult plant genes,and selecting only the lowest infection types throughout all phases of testing,a significant shift in the leaf rust resistance of the population occurred. Greenhouse evaluations of plant architecture and agronomic performance oflines containing both a seedling gene and Lr34, indicated that individualplants, similar or better than the original SGI parent, had been selected.Several of these selections can therefore be incorporated in larger,mainstream breeding programmes. It is, however, imperative that theagronomic and quality value of selections be determined under fieldconditions. More efficient manipulation of an undesignated Lr gene was also attempted.This gene, which originates from T. monococcum, was incorporated in certainbread wheat lines and cultivars. Since the gene is characterized by an immune response to South African pathotypes of leaf rust, it is consideredvaluable in terms of rust resistance. However, its single gene nature implies itwill not remain durable and that it has to be protected in complex resistancegene combinations. To achieve this, linked molecular markers are needed. Inthis study a putative AFLP marker for leaf rust resistance was generated byS12/M14 and S12/M44 using pooled DNA. Analysis of individual plants fromwhich the DNA bulks were constructed indicated that the marker might not beclosely linked to the Lr gene of interest. Validation in three additionalbackgrounds revealed several instances of recombination between the markerand the gene, emphasising the need to do a proper linkage study. Should thelinkage distance be acceptable, the marker might still be useful as it proved tobe polymorphic in five different wheat backgrounds. The linkage distance isalso needed before the intensive effort to clone and convert the AFLP band toa more user-friendly STS marker will be considered.

[发布机构] University of the Free State