Biological Control Efficacy of Indigenous Antagonistic Bacteria Isolated from the Rhizosphere of Cabbage Grown in Biofumigated Soil against Pythium aphanidermatum Damping-Off of Cucumber

Abstract

Soil biofumigation is a widely used farming practice for soil-borne disease management in vegetable crops. Soil biofumigation is the practice of the incorporation of fresh plant materials from the members of the Brassicaceae family into the soil which release antimicrobial volatile organic compounds (VOCs), namely glucosinolates and their hydrolysis products. However, the VOCs may affect non-target beneficial soil biota including microbial biocontrol agents (MBAs) due to their broad-spectrum toxicity. In this study, native antagonistic rhizobacteria were isolated from cabbage plants grown in biofumigated fields and their potential in the management of Pythium aphanidermatum cucumber damping-off was evaluated with and also without biofumigation using cabbage leaf residue. A total of 20 morphologically distinct, culturable bacterial strains were recovered from the rhizosphere soil of cabbage cultivated in a biofumigated field, with the largest fraction of the isolates belonging to the genus Bacillus. The other bacterial genera isolated were Pseudomonas, Serratia, Stenotrophomonas, Microbacterium and Priestia. Of the 20 bacterial isolates, Pseudomonas aeruginosa B1-SQU, Pseudomonas indica B2-SQU, Serratia marcescens B3-SQU and Pseudomonas brenneri B4-SQU exhibited inhibitory activity against P. aphanidermatum in a co-culture assay. The deformation and shrinkage of P. aphanidermatum hyphae due to diffusible antimicrobial compounds from these bacterial strains were witnessed through scanning electron microscopy. A biofilm was formed by these bacterial strains in vitro and they exhibited compatibility with each other; however, they had no significant plant growth promotion effect on cucumber. These bacterial strains significantly reduced damping-off in cucumber under greenhouse conditions when applied to soil singly, but failed to show a significant effect when combined with biofumigation treatment, though the bacterial population in the soil was maintained at higher levels. Soil biofumigation alone was also not effective in suppressing the damping-off of cucumber. Gas chromatography–mass spectrometry analysis revealed that 1-butanol, n-butyl butyrate and butyl acetate were the predominant VOCs in the soil amended with cabbage leaf residue. The results suggest that soil biofumigation with cabbage leaf residue has no significant effect on P. aphanidermatum under high inoculum levels; furthermore, it affects the efficiency of the bacterial antagonists in controlling damping-off in cucumber.

Rice Weevil (Sitophilus oryzae L.) Gut Bacteria Inhibit Growth of Aspergillus flavus and Degrade Aflatoxin B1

“…SEM analysis of A. flavus hyphae sampled from the inhibition zone in a dual culture assay plate showed aberrant morphologies, including wrinkling of the surface, shrinkage, and distortion. Similar findings were reported by Al-Daghari et al [ 56 ] when P. aphanidermatum , the damping-off pathogen of cucumber, was co-cultivated with antagonistic strains of Serratia marcescens and Pseudomonas spp. Likewise, shrinkage of P. aphanidermatum mycelium was observed when the oomycete was co-cultured with an antagonistic fungus, Aspergillus terreus [ 57 ].…”

“…However, in this study, silane, trimethyl(1-methyl-1-propenyl)-, (E)-, silane, tetramethyl-, and pentamethyldisilane were identified as major compounds produced by B. subtilis RWBG1. Similarly, Al-Daghari et al [ 56 ] reported that an antagonistic strain of P. aeruginosa B1-SQU obtained from cabbage rhizosphere, which showed inhibitory activity against P. aphanidermatum , produced 1-Butanol, 3-methyl- (syn: Isopentanol/Isoamyl alcohol) and dimethyl disulfide as the major compounds. Al-Rashdi et al [ 86 ] showed that P. aeruginosa PC5 obtained from Prosopis cineraria produced dimethyl disulfide as the major VOC, followed by n-hexadecanoic acid and di-tert-butyl decarbonate, whereas 1-decanol was identified as the major component in this study.…”

“…In contrast, the volatiles from B. firmus RWGB3 were not effective against A. flavus. The production of VOCs is recognized as an important mechanism by which antagonistic bacterial isolates suppress plant pathogenic fungi [ 41 , 42 , 56 , 83 , 84 , 85 , 86 ]. These VOCs are gaseous, lipophilic, low-molecular-weight (<300 Da) compounds [ 87 ] that disrupt fungal cell membranes, leading to the leakage of cell contents and, eventually, cell death [ 88 , 89 ].…”

Biocontrol Potential of Trichoderma Ghanense and Trichoderma Citrinoviride toward Pythium aphanidermatum

“…ON113866), was part of a fungal culture collection of the Department of Plant Sciences (Sultan Qaboos University, Muscat, Oman). It was obtained from our previous studies [49]. On petri dishes containing potato dextrose agar (PDA) medium (Thermo Fisher Scientific, Waltham, MA, USA), the fungal pathogen's pure culture was transferred and incubated at a temperature of 25 ± 2 • C for further experiments.…”

Comparative study of root and soil microbiological activity in individual and co-cultivation of cabbage (Brassica oleraceae L. var. capitata L.)

“…Изследването на ризосферната почвена микробна общност и нейната връзка с основна-та почвена микробна общност е от решаващо значение за поддържане на здравето и плодородието на почвата и подобряване на добивите от селскостопански култури. Общо 20 морфологично различни, култивирани бактериални щама са възстановени от ризосферната почва на зеле, култивирано в биофумигирано поле, като най-голямата част от изолатите принадлежат към род Bacillus, а другите изолирани бактериални родове са Pseudomonas, Serratia, Stenotrophomonas, Microbacterium и Priestia (Al-Daghari et al, 2023). При изследване на ризосферната микрофлора на диво зеле (Brassica oleracea L.) Gols et al (2023) установяват, че гъбичните общности се различават по-силно отколкото бактериалните общности.…”