Living yeast-based biostimulants: different genes for the same results?

Nowadays, many products are available in the plant biostimulants market. Among them, living yeast-based biostimulants are also commercialized. Given the living aspect of these last products, the reproducibility of their effects should be investigated to ensure end-users' confidence. Therefore, this study aimed to compare the effects of a living yeast-based biostimulant between two different soybean cultures. These two cultures named C1 and C2 were conducted on the same variety and soil but in different locations and dates until the VC developmental stage (unifoliate leaves unrolled), with Bradyrhizobium japonicum (control and Bs condition) and with and without biostimulant coating seed treatment. The foliar transcriptomic analysis done first showed a high gene expression difference between the two cultures. Despite this first result, a secondary analysis seemed to show that this biostimulant led to a similar pathway enhancement in plants and with common genes even if the expressed genes were different between the two cultures. The pathways which seem to be reproducibly impacted by this living yeast-based biostimulant are abiotic stress tolerance and cell wall/carbohydrate synthesis. Impacting these pathways may protect the plant from abiotic stresses and maintain a higher level of sugars in plant.

Screening of wheat endophytes as biological control agents against Fusarium head blight using two different in vitro tests.

In order to find biological control agents (BCAs) for the management of Fusarium head blight (FHB), a major disease on wheat crops worldwide, 86 microorganisms isolated from inner tissues of wheat plants were discriminated for their ability to inhibit the growth of Fusarium graminearum and Fusarium culmorum by in vitro dual culture assays. A group of 22 strains appeared very effective to inhibit F. graminearum (inhibition of 30-51%) and they were also globally effective in controlling F. culmorum (inhibition of 15-53%). Further evaluation of a subselection of strains by screening on detached spikelets in vitro confirmed three species, namely Phoma glomerata, Aureobasidium proteae and Sarocladium kiliense, that have not yet been reported for their efficacy against Fusarium spp., indicating that looking for BCAs toward FHB among wheat endophytes proved to be promising. The efficacy of some strains turned out different between both in vitro screening approaches, raising the importance of finding the most appropriate screening approach for the search of BCAs. This study pointed out the interest of the test on detached wheat spikelets that provided information about a potential pathogenicity, the growth capacity and efficacy of the endophyte strains on the targeted plant, before testing them on whole plants.

Spatial and Temporal Variation of Cultivable Communities of Co-occurring Endophytes and Pathogens in Wheat.

The aim of this work was to investigate the diversity of endogenous microbes from wheat (Triticum aestivum) and to study the structure of its microbial communities, with the ultimate goal to provide candidate strains for future evaluation as potential biological control agents against wheat diseases. We sampled plants from two wheat cultivars, Apache and Caphorn, showing different levels of susceptibility to Fusarium head blight, a major disease of wheat, and tested for variation in microbial diversity and assemblages depending on the host cultivar, host organ (aerial organs vs. roots) or host maturity. Fungi and bacteria were isolated using a culture dependent method. Isolates were identified using ribosomal DNA sequencing and we used diversity analysis to study the community composition of microorganisms over space and time. Results indicate great species diversity in wheat, with endophytes and pathogens co-occurring inside plant tissues. Significant differences in microbial communities were observed according to host maturity and host organs but we did not find clear differences between host cultivars. Some species isolated have not yet been reported as wheat endophytes and among all species recovered some might be good candidates as biological control agents, given their known effects toward plant pathogens.

Grapevine NAC1 transcription factor as a convergent node in developmental processes, abiotic stresses, and necrotrophic/biotrophic pathogen tolerance.

Transcription factors of the NAC family are known to be involved in various developmental processes and in response to environmental stresses. Whereas NAC genes have been widely studied in response to abiotic stresses, little is known about their role in response to biotic stresses, especially in crops. Here, the first characterization of a Vitis vinifera L. NAC member, named VvNAC1, and involved in organ development and defence towards pathogens is reported. Expression profile analysis of VvNAC1 showed that its expression is closely associated with later stages of leaf, flower, and berry development, suggesting a role in plant senescence. Moreover, VvNAC1 expression is stimulated in Botrytis cinerea- or microbe-associated molecular pattern (MAMP)-infected berries or leaves. Furthermore, cold, wounding, and defence-related hormones such as salicylic acid, methyl jasmonate, ethylene, and abscisic acid are all able to induce VvNAC1 expression in grapevine leaves. VvNAC1-overexpressing Arabidopsis plants exhibit enhanced tolerance to osmotic, salt, and cold stresses and to B. cinerea and Hyaloperonospora arabidopsidis pathogens. These plants present a modified pattern of defence gene markers (AtPR-1, AtPDF1.2, and AtVSP1) after stress application, suggesting that VvNAC1 is an important regulatory component of the plant signalling defence cascade. Collectively, these results provide evidence that VvNAC1 could represent a node of convergence regulating grapevine development and stress responses, including defence against necrotrophic and biotrophic pathogens.