The presence of Fusarium spp. causing Fusarium head blight (FHB) of wheat was studied in Flanders (Belgium) in 2007 and 2008. Symptoms, deoxynivalenol content (DON), Fusarium spp. and trichothecene chemotypes were determined at seven locations on different commercial wheat varieties. Overall, significant differences in disease pressure between locations and varieties were observed within 1 year. In addition, we were able to detect consistent and significant resistance differences among the common varieties both under high disease pressure (2007) and low disease pressure (2008). The accumulation of DON was not related to the presence of F. graminearum but showed a clear correlation with rainfall during and after the period of anthesis. During the two-year survey, characterisation of 756 Fusarium samples by species-specific PCR designated F. poae and F. graminearum as the predominant species in Flanders. Furthermore, most of the ears were colonised by multiple FHB pathogens in 2007 whereas the Fusarium population was less complex in 2008. Loglinear analysis of these multiple (two-and three-way) species interactions revealed a clear correlation between F. poae and several pathogens of the FHB disease complex. Finally, chemotype analysis showed that F. culmorum and F. graminearum were respectively of the NIV chemotype and DON chemotype. 3-ADON and 15-ADON chemotypes occurred in more or less equal amounts within the F. graminearum population both in 2007 and 2008. The congruence of these results with observations throughout Europe are discussed.

BackgroundPowdery 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.ResultsB. 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.ConclusionsThis 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.

Fusarium head blight (FHB) is a devastating disease of wheat, which is influenced by weather conditions and agronomic factors. Since FHB is a mostly monocyclic disease, the quantity of primary inoculum is a key factor influencing the FHB incidence. To investigate the connection between the primary Fusarium inoculum and the final population on wheat ears, naturally occurring populations of Fusarium avenaceum, Fusarium culmorum, Fusarium graminearum, Fusarium poae and Microdochium nivale were studied at eight locations in Flanders, Belgium. To determine the composition of the primary inoculum in November 2008, gramineous weeds, wheat residues, maize residues and soil samples were examined. In July 2009, wheat ears were examined to gain insight into the composition of the population at the end of the growing season. Comparing both populations can give an indication to what extent the primary inoculum in November 2008 contributes to the final FHB population in July 2009. Fusarium species residing saprophytically on gramineous weeds and crop residues or species persisting in soil as chlamydospores certainly contribute to the primary inoculum that will lead to infection of cereal crops grown on that field. Knowledge of the correlation between the primary inoculum and the composition of the FHB population at the end of the growing season can be important to predict the occurrence of FHB contamination and to implement control strategies for Fusarium Head Blight.

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Fusarium head blight is a disease caused by a complex of Fusarium species. F. poae is omnipresent throughout Europe in spite of its low virulence. In this study, we assessed a geographically diverse collection of F. poae isolates for its genetic diversity using AFLP (Amplified Fragment Length Polymorphism). Furthermore, studying the mating type locus and chromosomal insertions, we identified hallmarks of both sexual recombination and clonal spread of successful genotypes in the population. Despite the large genetic variation found, all F. poae isolates possess the nivalenol chemotype based on Tri7 sequence analysis. Nevertheless, Tri gene clusters showed two layers of genetic variability. Firstly, the Tri1 locus was highly variable with mostly synonymous mutations and mutations in introns pointing to a strong purifying selection pressure. Secondly, in a subset of isolates, the main trichothecene gene cluster was invaded by a transposable element between Tri5 and Tri6. To investigate the impact of these variations on the phenotypic chemotype, mycotoxin production was assessed on artificial medium. Complex blends of type A and type B trichothecenes were produced but neither genetic variability in the Tri genes nor variability in the genome or geography accounted for the divergence in trichothecene production. In view of its complex chemotype, it will be of utmost interest to uncover the role of trichothecenes in virulence, spread and survival of F. poae.

As the awareness on the ecological impact of chemical phosphate fertilizers grows, research turns to sustainable alternatives such as the implementation of phosphate solubilizing bacteria (PSB), which make largely immobile phosphorous reserves in soils available for uptake by plants. In this review, we introduce the mechanisms by which plants facilitate P-uptake and illustrate how PSB improve the bioavailability of this nutrient. Next, the effectiveness of PSB on increasing plant biomass and P-uptake is assessed using a meta-analysis approach. Our review demonstrates that improved P-uptake does not always translate in improved plant height and biomass. We show that the effect of PSB on plants does not provide an added benefit when using bacterial consortia compared to single strains. Moreover, the commonly reported species for P-solubilization, Bacillus spp. and Pseudomonas spp., are outperformed by the scarcely implemented Burkholderia spp. Despite the similar responses to PSB in monocots and eudicots, species responsiveness to PSB varies within both clades. Remarkably, the meta-analysis challenges the common belief that PSB are less effective under field conditions compared to greenhouse conditions. This review provides innovative insights and identifies key questions for future research on PSB to promote their implementation in agriculture.

Triticale (×Triticosecale) is the intergeneric hybrid between the female parent wheat and the male parent rye. With the expansion of the triticale growing area, powdery mildew emerged on this new host and has become a significant disease on triticale. Recent research demonstrated that this “new” powdery mildew on triticale has emerged through a host range expansion of powdery mildew of wheat. Moreover, this expansion occurred recently and multiple times at different locations in Europe. An effective and environmentally sensitive approach to controlling powdery mildew involves breeding crop plants for resistance. The main goal of this study was to identify the presence of powdery mildew resistance in commercial triticale cultivars. First, the avirulence (AVR) genes and gene complexity carried by this new powdery mildew population on triticale were characterized. Virulence was identified for all the resistance genes evaluated in the present study, and virulence frequencies higher than 50% were recorded on the genes Pm3f, Pm5b, Pm6, Pm7, Pm8, and Pm17. Using molecular markers, the presence of resistance genes Pm3f and Pm17 was identified in certain triticale cultivars. The triticale cultivars were also evaluated for the presence of quantitative resistance at adult plant growth stages in a 2-year field experiment. Despite the high disease pressure, cultivars highly resistant at the adult-plant growth stages were identified. Because ‘Grenado’ also showed effective race-specific resistance, this cultivar could be of high value for breeding for durable resistance to powdery mildew. Altogether, this study reveals valuable information on the presence of powdery mildew resistance in commercial triticale cultivars, which can be used in breeding programs in triticale. Additionally, this study underscores the need to broaden the base of powdery mildew resistance in triticale through introgression and deployment of new sources of mildew resistance, including quantitative resistance.

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