Effects of Arthrospira platensis Extract on Physiology and Berry Traits in Vitis vinifera

Biostimulation can prime elicitor induced resistance of grapevine leaves to downy mildew

Using plant defense elicitors to protect crops against diseases is an attractive strategy to reduce chemical pesticide use. However, development of elicitors remains limited because of variable effectiveness in the field. In contrast to fungicides that directly target pathogens, elicitors activate plant immunity, which depends on plant physiological status. Other products, the biostimulants, can improve certain functions of plants. In this study, the objective was to determine whether a biostimulant via effects on grapevine physiology could increase effectiveness of a defense elicitor. A new methodology was developed to study biostimulant activity under controlled conditions using in vitro plantlets. Both biostimulant and defense elicitor used in the study were plant extracts. When added to the culture medium, the biostimulant accelerated the beginning of plantlet growth and affected the shoot and root development. It also modified metabolomes and phytohormone contents of leaves, stems, and roots. When applied on shoots, the defense elicitor changed metabolite and phytohormone contents, but effects were different depending on whether plantlets were biostimulated or controls. Defense responses and protection against Plasmopara viticola (downy mildew agent) were induced only for plantlets previously treated with the biostimulant, Therefore, the biostimulant may act by priming the defense elicitor action. In this study, a new method to screen biostimulants active on grapevine vegetative growth was used to demonstrate that a biostimulant can optimize the efficiency of a plant defense elicitor.

Diversity of endophytic bacterial microbiota in grapevine shoot xylems varies depending on wine grape-growing region, cultivar, and shoot growth stage

Next-generation sequencing technology may clarify microbiota that are as yet poorly understood in the soil, the rhizosphere, and the phyllosphere of vineyards. To provide new information on the interaction between grapevine and microorganisms, we focused on the endophytic microbiota in grapevine. We performed endophytic microbiome analysis of the shoot xylems of four cultivars, Vitis vinifera cvs. Chardonnay, Pinot Noir, Cabernet Sauvignon, and Vitis sp. cv. Koshu, grown in eleven vineyards in Japan. The number of endophytic fungal species was small in the grapevine shoot xylems and could not be analyzed further, whereas a total of 7,019,600 amplicon sequences (46,642–285,003 per shoot xylem) and 1305 bacterial operational taxonomic units were obtained by analysis of the V3–V4 region of the bacterial 16S rRNA gene. Gammaproteobacteria was predominant in the shoot xylems at the shoot elongation stage irrespective of the cultivar, whereas Alphaproteobacteria and Oxyphotobacteria were predominant at véraison. Actinobacteria, Bacteroidia, Bacilli, and Clostridia were also detected in the shoot xylems. The endophytic bacterial microbiota in Koshu and Pinot Noir shoot xylems were similar irrespective of the grapevine-growing region. In contrast, the endophytic bacterial microbiota in Chardonnay and Cabernet Sauvignon showed diversity and complexity among grapevine-growing regions. Alpha diversity analysis revealed that Koshu shoot xylems had a higher diversity of endophytic bacterial microbiota than Pinot Noir, Chardonnay, and Cabernet Sauvignon shoot xylems, and that grapevine shoot xylems at the shoot elongation stage had a higher diversity of endophytic bacterial microbiota than those at véraison. Principal coordinate analysis (PCoA) demonstrated that the profiles of the endophytic bacterial microbiota in grapevine shoot xylems at véraison were relatively uniform compared with those at the shoot elongation stage. Multidimensional scaling analysis showed that the plots of all cultivars were generally apart from each other at the shoot elongation stage and then became close to each other at véraison. The plots of all grapevine-growing regions cultivating Koshu were close to each other, whereas those of grapevine-growing regions cultivating Chardonnay and Cabernet Sauvignon were apart from each other. The findings of this study suggest that the endophytic bacterial microbiota in grapevine shoot xylems varied depending on the cultivar and the grapevine-growing region even for the same cultivars, and that the microbiota fluctuated depending on the shoot growth stage.

Plant Biostimulants from Cyanobacteria: An Emerging Strategy to Improve Yields and Sustainability in Agriculture

Cyanobacteria can be considered a promising source for the development of new biostimulants as they are known to produce a variety of biologically active molecules that can positively affect plant growth, nutrient use efficiency, qualitative traits of the final product, and increase plant tolerance to abiotic stresses. Moreover, the cultivation of cyanobacteria in controlled and confined systems, along with their metabolic plasticity, provides the possibility to improve and standardize composition and effects on plants of derived biostimulant extracts or hydrolysates, which is one of the most critical aspects in the production of commercial biostimulants. Faced with these opportunities, research on biostimulant properties of cyanobacteria has undergone a significant growth in recent years. However, research in this field is still scarce, especially as regards the number of investigated cyanobacterial species. Future research should focus on reducing the costs of cyanobacterial biomass production and plant treatment and on identifying the molecules that mediate the biostimulant effects in order to optimize their content and stability in the final product. Furthermore, the extension of agronomic trials to a wider number of plant species, different application doses, and environmental conditions would allow the development of tailored microbial biostimulants, thus facilitating the diffusion of these products among farmers.