Comparative Study of Bacillus -Based Plant Biofertilizers: A Proposed Index.

Simple Summary: Comparing different commercial biofertilizer products for their effects as biostimulants, as protectors of plants from drought and plant-pathogenic fungi, can be difficult due to the increasing number of bacteria available in the market. Using a panel of tests, we compared the effects of four commercial strains of the operational group Bacillus amyloliquefaciens to assess their ability to protect pepper plants and stimulate their growth. Then, we obtained numerical values that allow quick diagnoses when choosing a product to ensure that it has the greatest added value or when describing a new strain. The market for bacteria as agricultural biofertilizers is growing rapidly, offering plant-growth stimulants; biofungicides; and, more recently, protectors against extreme environmental factors, such as drought. This abundance makes it challenging for the end user to decide on the product to use. In this work, we describe the isolation of a strain of Bacillus velezensis (belonging to the operational group Bacillus amyloliquefaciens) for use as a plant-growth-promoting rhizobacterium, a biofungicide, and a protector against drought. To compare its effectiveness with other commercial strains of the same operational group, Bacillus amyloliquefaciens, we analyzed its ability to promote the growth of pepper plants and protect them against drought, as well as its fungicidal activity through antibiosis and antagonism tests, its ability to solubilize potassium and phosphates, and its ability to produce siderophores. Finally, we used a probit function, a type of regression analysis used to model the outcomes of analyses, to quantify the biostimulatory effectiveness of the different plant-growth-promoting rhizobacteria, developing what we have called the Agricultural Protection Against Stress Index, which allowed us to numerically compare the four commercial strains of the operational group Bacillus amyloliquefaciens, based on a Delphi method—a type of regression analysis that can be used to model a cumulative normal distribution—and integrate the results from our panel of tests into a single value. [ABSTRACT FROM AUTHOR]

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