Quantitative trait loci of stripe rust resistance in wheat

KEY MESSAGE: Over 140 QTLs for resistance to stripe rust in wheat have been published and through mapping flanking markers on consensus maps, 49 chromosomal regions are identified. ABSTRACT: Over thirty publications during the last 10 years have identified more than 140 QTLs for stripe rust resistance in wheat. It is likely that many of these QTLs are identical genes that have been spread through plant breeding into diverse backgrounds through phenotypic selection under stripe rust epidemics. Allelism testing can be used to differentiate genes in similar locations but in different genetic backgrounds; however, this is problematic for QTL studies where multiple loci segregate from any one parent. This review utilizes consensus maps to illustrate important genomic regions that have had effects against stripe rust in wheat, and although this methodology cannot distinguish alleles from closely linked genes, it does highlight the extent of genetic diversity for this trait and identifies the most valuable loci and the parents possessing them for utilization in breeding programs. With the advent of cheaper, high throughput genotyping technologies, it is envisioned that there will be many more publications in the near future describing ever more QTLs. This review sets the scene for the coming influx of data and will quickly enable researchers to identify new loci in their given populations

Gene-specific markers for the wheat gene Lr34/Yr18/Pm38 which confers resistance to multiple fungal pathogens

The locus Lr34/Yr18/Pm38 confers partial and durable resistance against the devastating fungal pathogens leaf rust, stripe rust, and powdery mildew. In previous studies, this broad-spectrum resistance was shown to be controlled by a single gene which encodes a putative ATP-binding cassette transporter. Alleles of resistant and susceptible cultivars differed by only three sequence polymorphisms and the same resistance haplotype was found in the three independent breeding lineages of Lr34/Yr18/Pm38. Hence, we used these conserved sequence polymorphisms as templates to develop diagnostic molecular markers that will assist selection for durable multi-pathogen resistance in breeding programs. Five allele-specific markers (cssfr1-cssfr5) were developed based on a 3bp deletion in exon 11 of the Lr34-gene, and one marker (cssfr6) was derived from a single nucleotide polymorphism in exon 12. Validation of reference genotypes, well characterized for the presence or absence of the Lr34/Yr18/Pm38 resistance locus, demonstrated perfect diagnostic values for the newly developed markers. By testing the new markers on a larger set of wheat cultivars, a third Lr34 haplotype, not described so far, was discovered in some European winter wheat and spelt material. Some cultivars with uncertain Lr34 status were re-assessed using the newly derived markers. Unambiguous identification of the Lr34 gene aided by the new markers has revealed that some wheat cultivars incorrectly postulated as having Lr34 may possess as yet uncharacterised loci for adult plant leaf and stripe rust resistanc

Agronomic characteristics of the spring forms of the wheat landraces (einkorn, emmer, spelt, intermediate bread wheat) grown in organic farming

Organic farmers look to the possibilities of growing neglected crops, such as the spring forms of hulled wheat – einkorn, emmer and spelt – for support in developing the organic farming system. In 2008, 169 landraces from the gene bank at the Crop Research Institute in Prague were tested on certifi ed organic plots. The experiment was aimed at fi nding suitable varieties for the organic farming system. In summary, our fi ndings show that einkorn (Triticum monococcum L.) and emmer wheat [Triticum dicoccum Schrank (Schuebl)] are resistant to powdery mildew and brown rust, spelt wheat (Triticum spelta L.) is less resistant to these two diseases, and the intermediate forms of bread wheat are very sensitive to such infestation. The varieties evaluated incline to lodging, as they have long and weak stems. Einkorn and emmer wheat have short and dense spikes and a low thousand grains weight, whereas spelt wheat has long and lax spikes. The level of the harvest index is low. Potentially useful varieties were found during the fi eld experiment and evaluation, and our future efforts will therefore focus on improving resistance to lodging and increasing the productivity of the spike

Enhancing the genetic diversity and durability of leaf rust resistance in durum wheat

The importance of leaf rust, caused by Puccinia triticina, has increased dramatically in recent years in durum wheat (Triticum turgidum ssp. durum) worldwide. Little is known on the occurrence and nature of resistance in this crop. Thirty durum wheat lines derived from the International Maize and Wheat Improvement Center (CIMMYT) were characterized for their resistance to the Mexican P. triticina race BBG/BN which was identified in 2001 and caused susceptibility of a large number of the world's durum wheat cultivars. Ten genotypes with race-specific resistance displayed low to intermediate seedling reactions to leaf rust. In the field, eight genotypes were immune and two displayed moderate levels of resistance. The slow rusting resistant lines displayed a range of disease severity responses indicating genetic diversity. The yield protection conferred by race-specific and slow rusting resistance was investigated in yield loss trials under high leaf rust pressure in the field. Race-specific resistance provided effective protection against yield losses caused by leaf rust. Yield losses for slow rusting resistant lines were higher than for immune race-specific resistant ones, but significantly lower than for the susceptible checks. Slow rusting lines with high resistance levels and reduced yield losses were identified. The slow rusting components; latent period, uredinium size and receptivity, were determined in greenhouse experiments, and associations of these components with leaf rust progress in the field were calculated. The results indicated that predominantly uredinium size contributed to slow leaf rust progress in durum wheat. The genetic basis and diversity of race-specific resistance was also determined in progenies from crosses of nine durum wheat lines with a leaf rust susceptible parent, and from intercrosses among the resistant parents. Five distinct sources of resistance were identified, four of which involved single partially, or completely, dominant genes, of which two were closely linked, and a pair of partially dominant complementary genes. Using molecular tools, the two linked genes were located on the long arm of chromosome 6B. The best slow rusting resistant lines and the five distinct race-specific resistance sources can be used for enhancing the diversity and durability of leaf rust resistance in durum wheat