Phylogeography and virulence structure of the powdery mildew population on its 'new' host triticale

Background: Powdery mildew, caused by the obligate biotrophic fungus Blumeria graminis, is a major problem in cereal production as it can reduce quality and yield. B. graminis has evolved eight distinct formae speciales (f.sp.) which display strict host specialization. In the last decade, powdery mildew has emerged on triticale, the artificial intergeneric hybrid between wheat and rye. This emergence is probably triggered by a host range expansion of the wheat powdery mildew B. graminis f.sp. tritici. To gain more precise information about the evolutionary processes that led to this host range expansion, we pursued a combined pathological and genetic approach. Results: B. graminis isolates were sampled from triticale, wheat and rye from different breeding regions in Europe. Pathogenicity tests showed that isolates collected from triticale are highly pathogenic on most of the tested triticale cultivars. Moreover, these isolates were also able to infect several wheat cultivars (their previous hosts), although a lower aggressiveness was observed compared to isolates collected from wheat. Phylogenetic analysis of nuclear gene regions identified two statistically significant clades, which to a certain extent correlated with pathogenicity. No differences in virulence profiles were found among the sampled regions, but the distribution of genetic variation demonstrated to be geography dependent. A multilocus haplotype network showed that haplotypes pathogenic on triticale are distributed at different sites in the network, but always clustered at or near the tips of the network. Conclusions: This study reveals a genetic structure in B. graminis with population differentiation according to geography and host specificity. In addition, evidence is brought forward demonstrating that the host range expansion of wheat isolates to the new host triticale occurred recently and multiple times at different locations in Europe

The quest for the ideal dew retting promoting micro-organism

Dew retting of hemp stems lying on the field is a spontaneous microbiological process in which pectin and hemicellulose are degraded in order to release the cellulose bast fibers from its stem. The process is weather dependent and strongly affects the desired fiber quality needed for textile applications. Adding specific bacteria or consortia on the stems during retting might achieve a more controlled process. We set out to isolate, characterize and identify the ideal retting micro-organism, which will degrade hemicellulose and pectin without degrading cellulose, of which the hemp fiber is made. In 2021 samples of both hemp stems and underlying soil were taken from field trials in Bottelare, Belgium. Bacteria were isolated using the dilution to extinction method and identified through 16s rRNA gene sequencing. After identification, the bacteria were screened for their ability to degrade pectin, hemicellulose and cellulose. In total 57 bacteria were successfully isolated and identified. These bacteria belonged to 4 main phyla; 29% Actinobacteria, 27% Bacteroidota, 12% Firmicutes and 32% Proteobacteria. After screening for degradation of the plant biopolymers, six isolates with the right characteristics were found, namely the potential of degrading hemicellulose and pectin without degrading cellulose, belonging to the genera Clavibacter, Microbacterium, Rhodococcus, Flavobacterium, Pedobacter and Luteimonas sp. These isolates are being screened further through in-vitro mini-rettingexperiments to assess the extent to which they are able to release the fibres without damaging them

Biotic stresses in the anthropogenic hybrid triticale (xTriticosecale Wittmack): current knowledge and breeding challenges

Triticale (xTriticosecale Wittmack) is the intergeneric hybrid derived by crossing wheat (Triticum spp.) and rye (Secale spp.). Consequently, the same spectrum of fungal diseases occurring on the parent crops can impede optimal triticale production. With the expansion of the triticale growing area, the scientific interest into these fungal pathogens has gained momentum. This review considers the major fungal diseases occurring on triticale: powdery mildew, rust diseases, and Fusarium head blight and highlights breeding strategies or opportunities to control these pathogens. Although there are several models to explain the emergence of pathogens in newly introduced crops, for powdery mildew on triticale, it is accepted that it emerged through a host range expansion of wheat powdery mildew. Moreover, this host range expansion of wheat powdery mildew occurred recently, multiple times and at different locations in Europe. For rust diseases and Fusarium, evidence for such an abrupt host shift is rather thin and suggests an evolution in disease incidence and virulence confluent with evolving management practices, variable seasons, mutations, recombination and variety selection. In order to overcome these fungal pathogens in triticale, plant breeding is a powerful tool. Despite the multiple parallelisms between fungal diseases in triticale and wheat, the narrow genetic background, partially due to the narrow genetic background of the parental crops, is a serious issue in triticale breeding. It remains a challenge for future breeding strategies to broaden the genetic background of new varieties that are being developed, through introgression and deployment of new sources of disease resistance. Especially, quantitative and multi-pathogen sources of resistance have to be considered. In this way, triticale can retain its position as important low input farming cereal crop

Development, maturation and germination of chorse chestnut somatic embryos

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Phylogeography and virulence structure of the powdery mildew population on its 'new' host triticale

Abstract Background Powdery mildew, caused by the obligate biotrophic fungus Blumeria graminis, is a major problem in cereal production as it can reduce quality and yield. B. graminis has evolved eight distinct formae speciales (f.sp.) which display strict host specialization. In the last decade, powdery mildew has emerged on triticale, the artificial intergeneric hybrid between wheat and rye. This emergence is probably triggered by a host range expansion of the wheat powdery mildew B. graminis f.sp. tritici. To gain more precise information about the evolutionary processes that led to this host range expansion, we pursued a combined pathological and genetic approach. Results B. graminis isolates were sampled from triticale, wheat and rye from different breeding regions in Europe. Pathogenicity tests showed that isolates collected from triticale are highly pathogenic on most of the tested triticale cultivars. Moreover, these isolates were also able to infect several wheat cultivars (their previous hosts), although a lower aggressiveness was observed compared to isolates collected from wheat. Phylogenetic analysis of nuclear gene regions identified two statistically significant clades, which to a certain extent correlated with pathogenicity. No differences in virulence profiles were found among the sampled regions, but the distribution of genetic variation demonstrated to be geography dependent. A multilocus haplotype network showed that haplotypes pathogenic on triticale are distributed at different sites in the network, but always clustered at or near the tips of the network. Conclusions This study reveals a genetic structure in B. graminis with population differentiation according to geography and host specificity. In addition, evidence is brought forward demonstrating that the host range expansion of wheat isolates to the new host triticale occurred recently and multiple times at different locations in Europe.</p

Development, maturation and germination of horse chestnut somatic embryos

Somatic embryogenesis could represent a way to clonally propagate mature elite trees of horse chestnut. However, while a number of protocols describe successfully the induction and proliferation of somatic embryos a low frequency of embryos converted successfully into plants. The objective of this research was to identify a maturation medium that could contribute to the outcome of more efficient germination results. Therefore, in a first approach the effects of sucrose 3 and 6%, and maltose 3%, were evaluated on somatic embryo maturation, in terms of subsequent somatic embryo germination. Carbon source and concentration had a marked influence on maturation, and subsequent germination of horse chestnut somatic embryos, with sucrose 6% promoting the highest frequency of germinated embryos larger than 1 cm