Population dynamics of fusarium head blight causing species in South Africa

English: Wheat, after maize, is globally the most widely cultivated cereal crop and the staple diet of most people around the world. In South Africa, wheat, as the second most important grain crop, is produced in all nine provinces under either irrigation or dryland conditions. Diseases, however, restrain wheat production due to yield and grain quality reduction. Fusarium head blight (FHB) is a globally devastating fungal disease of wheat, primarily caused by F. graminearum. This disease is not only responsible for economic losses due to yield and quality reduction, but also contaminates the grain with trichothecene mycotoxins. This study concentrated on the genetic structure of the FHB causing populations present in seven South African wheat-growing areas under centre-pivot irrigation (Prieska, Barkly West, Orania, Douglas, Greytown, Cradock and Potchefstroom). Fusarium graminearum was identified as the dominating causal agent of FHB in South Africa and the tricothecene genotype of these isolates indicated a higher frequency of DON rather than NIV producers. DON producers have been described as more pathogenic to plants than NIV producers. This might explain the high DON frequency as well as the displacement of other Fusarium species in the less temperate regions of the South African wheat-growing areas with F. graminearum. AFLP analysis was used to place 793 South African F. graminearum isolates into the phylogenetic groups as described by O’Donnell and associates. South African F. graminearum isolates clustered with the lineage 7 reference isolates, although previous reports indicated the presence of lineages 3 and 5 in South Africa. Even though the currently studied population was dominated by lineage 7 isolates, significant genetic variation was detected. The observed genetic variation within individual populations was higher than the genetic variation between populations. The genotypic variation was consistent with outbreeding occurring under field conditions in South Africa. Although the Prieska population tended to be isolated, with a relatively high frequency of clones, the low genetic variation between all seven field populations suggested a larger randomly mating FHB population for South Africa due to similar allele frequencies. These results are consistent with previous reports on the genetic structure of FHB populations in other parts of the world. Knowledge gained from analyses of the genetic structure of this population might assist with the development of effective control strategies, i.e. resistance breeding against FHB, using resistance sources from other lineage 7 regions. This will provide an incentive to farmers to plant wheat, thus improving wheat production in South Africa.