Yahyaoui, A. | bioRxiv Science

bioRxiv2020

Influence of historical and human factors on genetic structure and diversity patterns in peripheral populations: implications for the conservation of Moroccan trout

O_LIThe brown trout s.l. has been the focus of numerous phylogeographic and conservation studies due to its socioeconomic importance, its marked genetic and phenotypic differentiation and its broad distribution range. Especially interesting evolutionary patterns are observed for populations occupying peripheral areas of a distribution range, such as in the case of the highly isolated trout populations in Morocco. C_LIO_LIContinuous stocking programs may conceal natural genetic patterns, making it challenging to discern evolutionary patterns. In Morocco, trout stocking programs have been implemented to increase the genetic diversity of native populations by pooling fish of different origins in the Ras el Ma hatchery (Azrou region) and then stocking them in the different basins. In this study, phylogenetic and phylogeographic patterns, as well as genetic structure and diversity, of Moroccan trout populations were analyzed to evaluate the impact of continuous fish stocking on evolutionary processes in order to better distinguish between natural and human-mediated patterns. C_LIO_LITwo mitochondrial and nine microsatellite markers were analyzed for all populations along the entire distribution range of brown trout in Morocco. Phylogenetic and phylogeographic analyses rendered two highly divergent evolutionary lineages, one comprising populations in the Draa Basin and a second grouping the remaining Moroccan populations. Divergence of the Draa lineage occurred during the Upper Pliocene, whilst differentiation within the second lineage coincided with the onset of the Pleistocene. C_LIO_LIGenetic structuring among populations was evident. Nevertheless, populations exhibiting higher levels of genetic diversity were those affected by human-mediated processes, making it difficult to associate this diversity with natural processes. In fact, highly geographically isolated, not stocked populations showed the lowest values of genetic diversity. Although stocking management may increase the genetic diversity of these populations, it could also lead to the loss of local adaptive genotypes. Hence, current trout conservation programs should be revised. C_LI

evolutionary biology↗

bioRxiv2019

Improved control of Septoria tritici blotch in durum wheat using cultivar mixtures

Mixtures of cultivars with contrasting levels of resistance can suppress infectious diseases in wheat, as demonstrated in numerous field experiments. Most studies focused on airborne pathogens in bread wheat, while splash-dispersed pathogens have received less attention, and no studies have been conducted in durum wheat. We conducted a two-year field experiment in Tunisia, to evaluate the performance of cultivar mixtures with varying proportions of resistance (0-100%) in controlling the polycyclic, splash-dispersed disease Septoria tritici blotch (STB) in durum wheat. To measure STB severity, we used a high-throughput method based on digital image analysis of 3074 infected leaves collected from 42 and 40 experimental plots during the first and second years, respectively. This allowed us to quantify pathogen reproduction on wheat leaves and to acquire a large dataset that exceeds previous studies with respect to accuracy and precision. Our analyses show that introducing only 25% of a disease-resistant cultivar into a pure stand of a susceptible cultivar provides a substantial reduction of almost 50% in disease severity compared to the susceptible pure stand. However, comprising the resistant component of two cultivars instead of one did not further improve disease control, contrary to predictions of epidemiological theory. Susceptible cultivars can be agronomically superior to resistant cultivars or be better accepted by growers for other reasons. Hence, if mixtures with only a moderate proportion of the resistant cultivar provide a similar degree of disease control as resistant pure stands, as our analysis indicates, such mixtures are more likely to be accepted by growers. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=126 SRC="FIGDIR/small/664078v3_ufig1.gif" ALT="Figure 1"> View larger version (100K): org.highwire.dtl.DTLVardef@1d153c3org.highwire.dtl.DTLVardef@1d23ca7org.highwire.dtl.DTLVardef@18c3045org.highwire.dtl.DTLVardef@b504db_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗