Response of an International Triticale Collection to Puccinia triticina and Puccinia recondita sensu stricto and Assessment of Temperature Sensitivity in Leaf Rust Isolates

Triticale is derived from a cross between wheat and rye and the leaf rust pathogen of wheat, Puccinia triticina (Pt), and that of rye, P. recondita sensu stricto (Pr), can potentially cause disease in this crop. Recent studies showed that wheat rust fungi could adapt to warmer temperatures. In this paper, we report on the comparative virulence of three Pt races and one Pr isolate (all were collected in South Africa) on triticale as well as their in vitro response to temperature. Seedling infection types (SITs) of 169 triticale entries to Pt races 3SA144 (North American code SDDN), 3SA145 (CCPS) and 3SA248 (CFPS) and Pr isolate UVPr2 revealed that 3SA144 is the most virulent with 106 triticale entries found susceptible to this race. The three Pt races were avirulent to the four rye cultivars included as controls. UVPr2 was avirulent on all the triticale entries and 49 entries were considered resistant to the Pt races tested. Freshly harvested urediniospores of the above isolates were tested at constant temperature regimes of 10 °C, 22.5 °C and 35 °C to study germination characteristics. Mean urediniospore germination percentages as determined for 3SA144 (61.3%) and UVPr2 (62.6%) were significantly lower when compared to 3SA145 (83.7%) and 3SA248 (84.9%). Race 3SA144 was most sensitive to the higher temperature regime of 35 °C (5.2% germination). Among the investigated races, 3SA144 showed significantly lower mean germ tube elongation rates at all three incubation temperatures. This is the first report of differences in temperature adaptation between Pt races from SA

Origin and evolution of the bread wheat D genome

Bread wheat (Triticum aestivum) is a globally dominant crop and major source of calories and proteins for the human diet. Compared with its wild ancestors, modern bread wheat shows lower genetic diversity, caused by polyploidisation, domestication and breeding bottlenecks1,2. Wild wheat relatives represent genetic reservoirs, and harbour diversity and beneficial alleles that have not been incorporated into bread wheat. Here we establish and analyse extensive genome resources for Tausch’s goatgrass (Aegilops tauschii), the donor of the bread wheat D genome. Our analysis of 46 Ae. tauschii genomes enabled us to clone a disease resistance gene and perform haplotype analysis across a complex disease resistance locus, allowing us to discern alleles from paralogous gene copies. We also reveal the complex genetic composition and history of the bread wheat D genome, which involves contributions from genetically and geographically discrete Ae. tauschii subpopulations. Together, our results reveal the complex history of the bread wheat D genome and demonstrate the potential of wild relatives in crop improvement

Isozyme characterisation of Fusarium graminearum isolates associated with head blight of irrigated wheat in South Africa

Head blight, caused by certain species in the genus Fusarium, has become an economically important disease of wheat under centre pivot-irrigation along the Orange River region in South Africa. Isozyme analysis, by means of starch gel electrophoresis, was employed to compare 73 Fusarium isolates, obtained from three farms in this region, with isolates of Fusanum acuminatum, F. chlamydosporum, F. compactum, F. crookwellense, F. culmorum, F. equiseti, F. graminearum Group I and Group II. F. moniliforme, F. oxysporum, F. solani, and F. subglutinans. For all 11 Fusarium species, nine loci were identified in eight enzyme systems and 19 electrophoretic phenotypes (EPs) were detected, each composed of isolates from one species only. The extent of isozyme polymorphisms found among these Fusarium spp. provides a potential method for delineating isolates at species level. Six EPs, of which the most common one comprised 36 isolates, were identified within isolates obtained from the three farms. These isolates clustered together with the F. graminearum Group II reference isolates. Based on perithecial production, their identity was confirmed as F. graminearum Group II

Development of a doubled haploid mapping population and linkage map for the bread wheat cross Kariega x Avocet S

A doubled haploid wheat population of 150 lines was constructed from the F1 of a cross between cultivars Kariega and Avocet S using the wheat-maize technique. Segregation and linkage analysis of 203 DNA markers, two storage protein markers and the stem rust resistance gene Sr26 yielded 31 linkage groups of which 28 were chromosome-anchored. These linkage groups covered the entire genome of 21 chromosomes. SSR markers were advantageous for chromosome anchoring and AFLP markers for consolidation of the various linkage groups. A significant feature of the linkage map is a relatively low level of polymorphism for markers on the D genome, viz, 18.5% of all markers mapped. The Kariega X Avocet S doubled haploid population and linkage maps have emerged as valuable resources for further genetic studies of qualitative and quantitative traits of economic importance in bread wheat.Articl