A Rhizobacterium, Streptomyces albulus Z1-04-02, Displays Antifungal Activity against Sclerotium Rot in Mungbean

Abstract

Sclerotium rot causes damping-off and stem rot in seedlings and mature mungbeans, which negatively impacts cultivation. The use of a rhizobacterium to control soil-borne diseases is an alternative method to the excess use of synthetic fungicides; therefore, this study aims to screen rhizosphere actinobacteria with fungicidal activities against Sclerotium rolfsii, the pathogen that causes sclerotium rot in mungbeans. Primary screening showed that the Streptomyces sp. isolate Z1-04-02 displayed the highest effectiveness against S. rolfsii in dual culture plates, with a percentage inhibition of 74.28%. An assay containing enzymes that degrade cell walls, of the cell-free culture filtrate (CF) of Z1-04-02, showed that the activities of chitinase and β-1,3-glucanase were 0.0209 and 1.0210 U/mL, respectively, which was significantly higher than that of the control (media alone). The cell-free CF of Z1-04-02, incubated at 37 °C and 100 °C, using agar well diffusion, effectively inhibited the growth of S. rolfsii with inhibition percentages of 37.78% and 27.78%, respectively. Solid-phase microextraction (SPME) was applied to trap volatiles released from Z1-04-02 and gas chromatography–mass spectrometry (GC/MS); volatile antifungal compounds were tentatively identified as bicyclic monoterpene (1R)-(-)-myrtenal. The application of the cell-free CF, and the spore suspension of Z1-04-02, showed disease severity indexes (DSIs) of 12.5% and 8.25%, respectively, which were significantly lower than those showing inoculation by S. rolfsii alone. The identification of this strain by morphology, biochemistry tests, and 16s rDNA sequences revealed that Z1-04-02 was Streptomyces albulus. This finding revealed that S. albulus Z1-04-02 displayed diverse fungicidal activities against S. rolfsii, and it has the potential to act as a biological control agent in terms of inhibiting sclerotium rot in mungbeans.

Taxonomic Identification and Antagonistic Mechanism of Streptomyces Luomodiensis Sp. Nov. Against Phytopathogenic Fungi

“…These enzymes are responsible for catalyzing the hydrolysis of chitin and β-1,3-glucan, which are the major structural components of fungal cell walls. Accumulated data indicate that chitinases and β-1,3-glucanases produced by biocontrol microbes and plants can inhibit fungal growth [48,49]. The study conducted by Arora et al [45] showed that the chitinase and β-1,3-glucanase produced by Fluorescent pseudomonad can inhibit the growth of Rhizoctonia solani.…”

Taxonomic identification and antagonistic activity of Streptomyces luomodiensis sp. nov. against phytopathogenic fungi

“…These enzymes are responsible for catalyzing the hydrolysis of chitin and β-1,3-glucan, which are the major structural components of fungal cell walls. Accumulated data indicate that chitinases and β-1,3-glucanases produced by biocontrol microbes and plants can inhibit fungal growth ( Li et al, 2021 ; Ruangwong et al, 2022 ). The study conducted by Arora et al (2007) showed that the chitinase and β-1,3-glucanase produced by fluorescent pseudomonads can inhibit the growth of Rhizoctonia solani .…”

An update about plant growth promoting Streptomyces species

“…Oryza sativa (Rice) -Produce indole-3-acetic acid -Improves adventitious roots formation -Siderophore production [57] Streptomyces olivaceoviridis Triticum aestivum (Wheat) -Accelerates the emergence of adventitious roots -Enhances biosynthesis of gibberellin -Produces cytokinins [58] when compared to that of S. atrovirens, and therefore different effects of these species on plant growth were recorded. Similarly, Streptomyces albulus revealed that due to its antifungal activity against sclerotium rot in mungbean, it has the potential as a biocontrol agent [18]. Likewise, Streptomyces alfalfae XN-04 creates several siderophores, such as coelichelin, enterobactin, and mirubactin, which are influential plant growth promoters and disease suppressants [19].…”