Borderline Products between Bio-fertilizers/ Bio-effectors and Plant Protectants: The Role of Microbial Consortia

Abstract

Abstract:In the delicate normative balance, at European Union (EU) level of the borderline products (i.e., between plant protectants and bio-fertilizers/bio-effectors) containing microbial consortia (MC) instead of single microbial strains, the most relevant factors influencing the categorization of the products are the intention of use, the cell density and the mode of action. For the latter, the basic difference between the two types of products is that a plant protectant has a targeted activity on plant pathogens, while a bio-fertilizer acts indirectly by nourishing and fortifying the host plant (healthier plant), thus inducing a generalized resistance to the onset of pathological status, irrespective of its origin and nature. Case-studies are presented on the effectiveness of MC as bio-fertilizers/bio-effectors on different crops. Bio-fertilizers exhibit a double effect-biotic and abiotic, leading to the fortification of the crop plant linked to its more effective water and nutrient uptakes as well as to a generalized healthier status. This in turn leads to a higher resistance to diseases. In addition, bio-fertilizers play a relevant role on the reduction of environmental impacts due to chemical fertilizers, e.g., by facilitating the uptake of phosphorus (P), thus reducing the need of P fertilization. Although finding a scientifically-based balance between regulatory need and marketing constraint is not always an easy task, the availability of scientific advancements combined to common sense should help in describing positive effects and risk profiles of MC in agriculture.

Recent Advances in the Molecular Effects of Biostimulants in Plants: An Overview

“…Even though some authors classify microorganism inoculates as being biofertilizers [173][174][175][176], these could very well be referred to as biostimulants [7]. Fungi and bacteriabased biostimulants may have a role to play in mitigating the impacts of agricultural activity on the environment [177], such as positively influencing the soil biodiversity [178]. Moreover, microorganisms play a key role in the phyllosphere, rhizosphere and endosphere of plants increasing the availability of certain nutrients and facilitating their absorption, with the symbiosis between both being a key factor in their evolution [179].…”

Microbial Consortia versus Single-Strain Inoculants: An Advantage in PGPM-Assisted Tomato Production?

“…The agricultural use of biostimulants (BS) based on microbial inoculants or bioactive natural compounds, originating, e.g., from plant, seaweed, and compost extracts or plant and animal based protein hydrolysates with plant growth-promoting and strengthening potential but without significant input of nutrients, has a long history [1,2]. Seaweed and gelatine-based.…”

“…The commercial use of microbial BS in crop production was based initially on targeted selection of efficient single strain inoculants, starting with a first patent already in 1896 on Rhizobia to increase the atmospheric nitrogen fixation potential in leguminous plants [12]. Nowadays, numerous single-strain inoculants with biofertilizer functions are commercially available [1]. There is an increasing trend to use combination products based on microbial and nonmicrobial BS or microbial consortia, with the aim to exploit complementary or even synergistic interactions.…”

“…Examples comprise activation of phosphate solubilizing microorganisms in the absence of soluble P forms in soils, promotion of P mineralizers after supply of organic fertilizers or of chitinase-producing bacteria in response to proliferation of pathogenic fungi [13]. Various literature reviews claim that there is a clear trend showing the advantage of MCPs in comparison with single strain inoculants [1,14,18], but there are also contradictory reports [19] and particularly direct comparisons under real practice conditions are rare.…”

Maize Inoculation with Microbial Consortia: Contrasting Effects on Rhizosphere Activities, Nutrient Acquisition and Early Growth in Different Soils

“…Moreover, the composition of microbial consortia and non-microbial BS aims at the restoration of plant-beneficial, soil biological processes disturbed by soil degradation, intensive use of mineral fertilizers and chemical crop protection. This may apply for processes of nutrient cycling and mineralization, biological nitrogen fixation, nutrient mobilization and the pathogen suppressive potential in agricultural soils [4,7,8].…”