Abstract
The most common leguminous plants’ diseases are caused by soil-borne pathogens leading to important economic losses worldwide. Strains L1 and L8, belonging to Aureobasidium pullulans species, were tested in vitro and in vivo as biocontrol agents (BCAs) against Rhizoctonia solani (Rs1) (AG-4) and as plant growth promoters (PGPs). The non-volatile metabolites produced by L1 and L8 strains inhibited the pathogen mycelial growth by 87.9% on average, with no significant differences between the two strains. The lower pathogen diametric growth inhibition was displayed by both yeasts’ volatile metabolites (VOCs) that significantly reduced the colony growth of R. solani, and similarly to the control, with an average of 10.5%. By in vivo assay, L1 and L8 strains showed the ability to control the pathogen virulence probably through the biofilm formation around the bean and soybean plant roots, as confirmed by scanning electron microscope (SEM) analysis. The spectroscopic analysis highlighted the composition of non-volatile compounds: complex carbohydrates (pullulan), degrading enzymes, siderophores and antifungals (aureobasidins). Moreover, the ability of L1 and L8 strains to stimulate the bean and soybean plant roots, stems, and leaves growth was investigated, showing that these yeasts could have an application not only as BCAs but also as plant growth biostimulator.
Highlights
Rhizoctonia solani represents one of the principal soil-borne pathogens that can attack a wide range of plant species, mainly leguminous plants, causing seed decay, dampingoff, hypocotyl rot, and web blight (Thiessen and Woodward 2012; Müller Schmidh et al 2018)
Rhizoctonia solani isolate (Rs1) used in the present experiments was obtained from symptomatic bean plants (Phaseolus vulgaris L.) grown in an experimental field located in Cadriano (Bologna, Italy), molecularly identified, and deposited to Criof mycological collection
A. pullulans L1 and L8 strains revealed the capability to control a soil-borne pathogen of bean and soybean plants, such as R. solani
Summary
Rhizoctonia solani represents one of the principal soil-borne pathogens that can attack a wide range of plant species, mainly leguminous plants, causing seed decay, dampingoff, hypocotyl rot, and web blight (Thiessen and Woodward 2012; Müller Schmidh et al 2018). Yeasts show similar mechanisms of action against soil-borne fungal plant pathogens and plant’s aerial parts pathogens (El-Tarabily and Sivasithamparam 2006). Their ability to multiply rapidly, to produce antifungal diffusible metabolites, and cell wall-degrading enzymes (CWDEs) (Kohl et al 2019), is a hallmark for potential application as soil BCAs and plant growth promoters (PGPs). The efficacy of volatile and nonvolatile metabolites, produced by A. pullulans strains L1 and L8 in inhibiting growth and enzymatic activity of the soil-borne pathogen R. solani of bean and soybean plants, was assayed in vitro.
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