2,4-Diacetylphloroglucinol producing Pseudomonas fluorescens JM-1 for management of ear rot disease caused by Fusarium moniliforme in Zea mays L

Abstract

Maize (Zea mays L.) is a major cereal crop grown in a large number of countries. Loss in maize yield due to biotic stresses including fungal phytopathogens is a matter of immense concern. Control measures applied for eradication of fungal phytopathogens in maize are not up to the mark and more often involve harsh chemical(s)/pesticide(s) that cause deleterious effects both in humans and soil biota. Greener alternatives, such as the use of rhizosphere microbes in the form of bioinoculants, have proven to be very successful in terms of enhancing crop yield and suppressing fungal phytopathogens. In the present study, fluorescent pseudomonads were isolated from the maize rhizosphere and monitored for their plant growth-promoting (PGP) and biocontrol activities against Fusarium moniliforme. Based on various PGP traits and biocontrol potential, isolate JM-1 was found to be most effective and as per 16S rRNA gene sequencing analysis was identified as Pseudomonas fluorescens. Further experiments showed that the biocontrol potential of JM-1 against ear rot fungus involved the production of antifungal compound 2,4-diacetylphloroglucinol (DAPG). When examined for antagonistic interaction under scanning electron microscopy (SEM), structural abnormality, hyphal lysis, and deformity in fungal mycelium were observed. In the pot experiment, application of talc-based JM-1 containing bioformulation (in pot trials) showed significant enhancement in maize growth parameters (including the seed number and weight) in comparison to control even in presence of the phytopathogen. Ear fresh weight, dry weight, number of seeds per plant, and 100-grain weight were found to increase significantly by 34, 34, 52, and 18% respectively, in comparison to control. P. fluorescens JM-1 can therefore be used as a bioinoculant for ear rot disease control and sustainably enhancing maize yield.

Supplementary information: The online version contains supplementary material available at 10.1007/s13205-022-03201-7.

Keywords: 2,4-DAPG; Biocontrol; Ear rot; Fluorescent pseudomonads; Maize; Metabolite; Pseudomonas.

Fig. 1

UV–Vis spectrum of fractioned metabolite (R_f 0.78) showing a tall peak at 270 nm

Fig. 2

FT-IR spectrum of TLC fractioned metabolite produced by P. fluorescens JM-1

Fig. 3

FT-IR spectrum of synthetic DAPG Source: https://spectrabase.com/spectrum/BuOXfva7g77

Fig. 4

SEM microphotographs (A and B) of F. moniliforme growth without the presence of antifungal metabolite (control) and (C and D) growth of F. moniliforme in presence of metabolite. Arrows indicate site of deformity

Fig. 5

Proposed mode of action for antifungal activity of 2,4-DAPG. A 1,4-DAPG targets asexual stages of the life cycle. It inhibits the process of sporogenesis and affects the motility and germination of the encysted zoospore. B Plasma membranes are more sensitive toward 2,4-DAPG. It causes alteration in structure and permeabilization of the plasma membrane. C In many fungi, due to 2,4-DAPG disorganization of cellular content and leakage occurs in hyphal tips. D Exposure of 2,4-DAPG influences fungal cell membrane formation by inhibiting the expression of cytochrome P450 14α-demethylase (CYP51) enzyme (see red arrow). CYP51 is responsible for the biosynthesis of ergosterol that helps in maintaining the fluidity of the lipid bilayer. E Vacuoles cover many physiological aspects of fungal cells. Exposure of 2,4-DAPG accelerates the rate of vacuolization or hypa space-filling by the vacuole. F 2,4-DAPG also acts as an uncoupler of oxidative phosphorylation and ATP synthesis. Acting as a proton ionophore it induces loss of mitochondrial membrane potential and increases oxygen consumption (respiration) but ATP synthesis cannot take place and hence growth is inhibited. Apart from this, due to 2,4-DAPG free radical leakage and the production of reactive oxygen species (ROS) occurs in the mitochondrion