Despite being 10,000 km apart, the current study emphasizes the potential vulnerability of Australia to wind-borne Puccinia graminis f. sp. tritici (Pgt) spore introductions from southern Africa. Of four Pgt introductions into Australia since 1925, at least two (races 326-1,2,3,5,6 and 194-1,2,3,5,6) are thought to have originated from southern Africa. Microsatellite analysis of 29 Australian and South African Pgt races confirmed close genetic relationships between the majority of races in these two geographically separated populations, thus supporting previously reported phenotypic similarities. Using Lagrangian Particle Dispersion Model simulations with finely-resolved global meteorological data over a 14-year period and a three-day urediniospore survival time, the study showed that long distance dispersal of Pgt from southern Africa to Australia is possible, albeit rare. Transmission events occurred most frequently from central South Africa, but were also possible from southern South Africa and Zimbabwe; while none occurred from a representative source-location in Tanzania. Direct dispersal incursions into both the western and eastern Australian wheat belts were feasible. Together, the genetic and simulation data strongly support the hypothesis that earlier introductions of Pgt into Australia occurred through long-distance wind-dispersal across the Indian Ocean. The study thus acts as a warning of possible future Pgt dispersal events to Australia which could include members of the Ug99 race group. This emphasizes the continued need for Pgt surveillance on both continents.
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Leaf rust is a common wheat disease in South Africa. Annual surveys conducted by the Agricultural Research Council - Small Grain Institute (ARC-SGI) during the last 35 years used infection type (IT) data on a defined differential set to identify individual field isolates. Results from these surveys confirmed that the South African Pt population is affected by both local evolution and foreign introductions. A good correlation was found between avirulence/virulence phenotypes and simple sequence repeat (SSR) genotypes in the South African Pt population. We therefore evaluated whether identification of field isolates by SSR analysis would complement the traditional IT analysis using 47 field isolates collected during the 2013 growing season. Of the 39 phenotyped isolates, 35 were correctly genotyped while three were incorrectly genotyped only because the corresponding race was not included as a control. Five isolates that could not be phenotyped due to non-viable spores were successfully genotyped. The dominant race 3SA145 (North American race annotation CCPS) was represented by nine different genotypes sharing 82% genetic similarity. The SSR data further showed that the field isolates formed part of two distinct lineages with little admixture between them. This study confirmed the supporting value of SSR genotyping to traditional race analysis in monitoring the South African Pt population.
Wheat is an economically important food crop in South Africa and production is influenced by a number of diseases caused by fungal pathogens, especially leaf rust, stem rust, stripe rust and Fusarium head blight. The aim of the study is to combine durable rust and FHB resistances into a single wheat line with a high percentage of cv. Krokodil genetic background. Two sets of wheat lines respectively resistant to the three rusts or FHB were developed from different breeding programs at the University of the Free State. These lines were used as parents to combine durable rust and FHB resistance genes/QTL into a single line. Three of the best rust resistant lines were selected as female parents containing rust resistance genes/QTL Lr19, Lr34/Yr18/Sr57, Sr2, Sr26, Sr39 and QYr.sgi-2B.1. FHB resistant BC2F2 and BC2F6 lines were selected as male parents; these lines contained different combinations of Fhb1, Qfhs.ifa-5A-1 and Qfhs.ifa-5A-2. All parental lines were evaluated using molecular markers to confirm the presence of the expected genes/QTL. More than 100 crosses were made between the rust and FHB resistant parents. Since the parents were not homozygous for all markers, leaf material from six-week-old F1 seedlings was collected for marker-assisted selection and to identify the best plants with combined rust and FHB resistances. The best selected lines will be use to develop a backcross population using cv. Krokodil as the recurrent parent. Lines with different combinations of resistance genes/QTL are currently being evaluated in the field to confirm the presence of these genes/QTL.
While Africa is home to three Berberis species (B. holstii, B. hispanica and B. vulgaris), genera of the family Berberidaceae do not occur naturally in South Africa. However, due to the trade in ornamental plants, a total of 11 Berberis species, 11 cultivars and 8 hybrids were historically and/or are currently cultivated in the country. The current invasive status of most of these species is unknown, but two naturalized Berberis populations were recently discovered. B. julianae was found in the Golden Gate Highlands National Park in eastern Free State province, and B. aristata was found in the Woodbush Forest Reserve in Limpopo province. Since several Berberis species could act as alternate hosts for Puccinia graminis and P. striiformis, a phylogenetic study was conducted to identify both naturalized species, as well as several cultivated specimens. One of the cultivated specimens was identified as B. vulgaris, a species well known for its susceptibility to P. graminis. Knowledge gained from this study will be used to intensify the search for more naturalized Berberis populations, as well as to assess the potential threat to wheat cultivation in the country.