Concepts and applications of foliar spray for microbial inoculants

Abstract

Damages of the (agro)ecosystem by extensive use of chemical fertilizers and pesticides, the global dying of bee populations possibly linked to pesticide spraying, and stricter regulations for pesticide use together with successful use of microbials in IPM programs are pushing on the development and commercialization of new microbial products and a large and growing biostimulants and biocontrol market. This review focuses on microbial inoculants including bacteria, fungi, and viruses used as biostimulant or biocontrol agent for foliar application and covers all important steps from inoculant development to successful field application. Topics presented comprise typical spraying equipment including the importance of the spraying process and relating effects, furthermore formulation development including classification and adjuvants, and thirdly regulatory aspects as currently applied or under discussion. Microbial inoculants for foliar spray reported in scientific literature are summarized and contrasted with selected commercial products. Special attention is given to factors most important in microbial spray: (a) type of active ingredient (bacteria, fungi, viruses), (b) mode of action (ingestion, contact, competition), (c) interaction with the plant leaf surface, (d) droplet size in terms of microbe concentration and leaf coverage, and (e) environmental conditions during spraying. Finally, we want to emphasize that timely administration is of utmost importance for successful spraying and maximum efficacy. This might be supported by weather stations and disease/pest models as an important step towards precision farming.

A review on the plant microbiome: Ecology, functions, and emerging trends in microbial application

“…Experiments adding lipo-chitooligosaccharides (LOCs) isolated from rhizobia to formulations [99] or adapting the growth medium of an inoculant to increase exopolysaccharides (EPS) and polyhydroxybutyrate (PHB) content in the formulation [100] increased for instance the PGP-effects. The mechanisms of bacterial additives are not yet understood, while surfactants adjust droplet size and rheological properties, reduce drift and improve adhesion to hydrophobic cuticular surfaces [101]. Macrobeads that encapsulate PGPB provide a humid environment as well as nanoparticles, which improve adhesion of PGPB to roots [102], [103].…”

Role of Dominant Phyllosphere Bacteria with Plant Growth–Promoting Characteristics on Growth and Nutrition of Maize (Zea mays L.)

“…While much is known regarding phyllosphere-associated bacteria possessing different PGP characteristics, few studies have exploit these properties to improve maize growth and nutritional status. In the last years, application of phyllospheric PGPB as biostimulants to promote plant growth has been studied on some plants including wheat, Arabidopsis, and strawberry (Chinnadurai et al 2009;Esitken et al 2010, Mwajita et al 2013Batool et al 2016;Saleem et al 2017, Preininger et al 2018.…”

The Great Five—an artificial bacterial consortium with antagonistic activity towards Pectobacterium spp. and Dickeya spp.: formulation, shelf life, and the ability to prevent soft rot of potato in storage

“…In contrast, the GF strains formulated as wettable powders and stored at 8°C survived for a period of 12 months without a significant drop in cell numbers. Most of the bioformulations currently available on the market have a declared shelf life of 1 year, with minimum of 3 months and up to 6 years in case of selected spore-based products (Arora and Mishra 2016;Preininger et al 2018). Suggested storage conditions include freezing (− 20°C), cooling (4-10°C), or room temperature depending on the type of formulation and its content.…”