Browsing by Author "Nkomo, Mbukeni"

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    Biocontrol Potential of Bacillus subtilis and Bacillus tequilensis against Four Fusarium Species
    (MDPI, 2023) Baard, Vejonepher; Bakare, Olalekan Olanrewaju; Daniel, Augustine Innalegwu; Nkomo, Mbukeni; Gokul, Arun
    The use of biological control agents as opposed to synthetic agrochemicals to control plant pathogens has gained momentum, considering their numerous advantages. The aim of this study is to investigate the biocontrol potential of plant bacterial isolates against Fusarium oxysporum, Fusarium proliferatum, Fusarium culmorum, and Fusarium verticillioides. Isolation, identification, characterization, and in vitro biocontrol antagonistic assays of these isolates against Fusarium species were carried out following standard protocols. The bacterial endophytes were isolated from Glycine max. L leaves (B1), Brassica napus. L seeds (B2), Vigna unguiculata seeds (B3), and Glycine max. L seeds (B4). The bacterial isolates were identified using 16S rRNA PCR sequencing. A phylogenetic analysis shows that the bacterial isolates are closely related to Bacillus subtilis (B1) and Bacillus tequilensis (B2–B4), with an identity score above 98%. All the bacterial isolates produced a significant amount (p < 0.05) of indole acetic acid (IAA), siderophores, and protease activity. In vitro antagonistic assays of these isolates show a significant (p < 0.05) growth inhibition of the fungal mycelia in the following order: F. proliferatum > F. culmorum > F. verticillioides > F. oxysporum, compared to the control. The results suggest that these bacterial isolates are good biocontrol candidates against the selected Fusarium species
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    Effects of acidic and alkaline electrolyzed water treatments on the volatilomics and proteomics changes in fresh-cut apple during storage
    (Royal Society of Chemistry, 2025) Caleb, Oluwafemi James; Belay, Zinash A.; Nkomo, Mbukeni
    Electrolyzed water (EW) has shown potential to decontaminate and maintain the quality of fresh-cut apple; however, the underlying response of the product to this treatment remains unclear. Thus, this study aims to identify the possible quality regulation mechanisms of acidic electrolyzed water (AEW) and alkaline electrolyzed water (ALEW) treatments on fresh-cut ‘Granny Smith’ apples via volatile organic compound (VOC) and qualitative proteomics analysis during storage at 2 °C for 10 days. The results identified 43 VOCs, including 10 esters, 9 alcohols, 9 alkanes, 8 carboxylic acids, 6 ketones, and 1 aldehyde. The distribution of VOCs was significantly affected by the pretreatment conditions; fresh-cut apple treated with AEW was characterised by the highest number of esters, alcohols, and carboxylic acids, whereas samples treated with ALEW exhibited predominantly carboxylic acids, alcohols, and alkanes in comparison to control (untreated) samples. Ethyl dodecanoate, which was identified only in the ALEW samples on each sampling day, had the highest concentration among all the individual VOCs. The proteomics results showed that a total of 3434, 3401, and 3313 proteins were identified on day 3, 6, and 10, respectively, across all samples. Until day 6 of storage, no significant differences were observed among the samples. Notably, on day 6, “M16C_associated domain-containing protein” was shown to be unique to the control samples. KH type-2 domain-containing protein, methylenetetrahydrofolate reductase (MTHFR), and 1,4-alpha-glucan branching enzyme were unique proteins identified after AEW treatment at day 6 and 10 of storage. No unique protein was identified for the ALEW samples. These results provide the first report of the proteomic and volatilomic changes associated with EW-treated fresh-cut apple during storage. Data are available via ProteomeXchange with identifier PXD056621. © 2025 RSC.
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    Exogenous p-coumaric acid improves salvia hispanica l. Seedling shoot growth
    (MDPI Open Access Journals, 2019) Nkomo, Mbukeni; Gokul, Arun; Keyster, Marshall; Klein, Ashwil
    p-Coumaric acid (p-CA) belongs to a family of natural esters of hydroxycinnamic acid compounds that have been shown to modulate plant growth and metabolism. In this study, we investigated the effect of exogenous p-CA on plant growth, reactive oxygen species (ROS)-induced oxidative damage, photosynthetic metabolism, osmolyte content and changes in superoxide dismutase (SOD) enzymatic activity.
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    p-Coumaric acid differential alters the ion-omics profile of chia shoots under salt stress
    (MDPI, 2024) Badiwe, Mihlali; Nkomo, Mbukeni; Niekerk, Lee-Ann
    p-Coumaric acid (p-CA) is a phenolic compound that plays a crucial role in mediating multiple signaling pathways. It serves as a defense strategy against plant wounding and is also presumed to play a role in plant development and lignin biosynthesis. This study aimed to investigate the physiological and ionomic effect of p-CA on chia seedlings under salt stress. To this end, chia seedlings were supplemented with Nitrosol® containing 100 μM of p-CA, 100 of mM NaCI, and their combined (100 mM NaCI + 100 μM p-CA) solutions in 2-day intervals for a period of 14 days along with a control containing Nitrosol® only. The treatment of chia seedlings with 100 mM of NaCI decreased their growth parameters and the content of the majority of the essential macro-elements (K, P, Ca, and Mg), except for that of sodium (Na). The simultaneous application of p-CA and a salt stress treatment (p-CA + NaCI) alleviated the effect of salt stress on chia seedlings’ shoots, and this was indicated by the increase in chia biomass. Furthermore, this combined treatment significantly enhanced the levels of the essential microelements Mg and Ca. In summary, this brief report is built on the foundational work of our previous study, which demonstrated that p-CA promotes growth in chia seedlings via activation of O2 −. In this brief report, we further show that p-CA not only promotes growth but also mitigates the effects of salt stress on chia seedlings. This mitigation effect may result from the presence of Mg and Ca, which are vital nutrients involved in regulating metabolic pathways, enzyme activity, and amino acid synthesis.
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    Piperonylic acid alters growth, mineral content accumulation and reactive oxygen species-scavenging capacity in chia seedlings
    (Oxford University Press, 2022) Nkomo, Mbukeni; Gokul, Arun; Ndimba, Roya
    p-Coumaric acid synthesis in plants involves the conversion of phenylalanine to trans-cinnamic acid via phenylalanine ammonia-lyase (PAL), which is then hydroxylated at the para-position under the action of trans-cinnamic acid 4-hydroxylase. Alternatively, some PAL enzymes accept tyrosine as an alternative substrate and convert tyrosine directly to p-coumaric acid without the intermediary of trans-cinnamic acid. In recent years, the contrasting roles of p-coumaric acid in regulating the growth and development of plants have been well-documented. To understand the contribution of trans-cinnamic acid 4-hydroxylase activity in p-coumaric acid-mediated plant growth, mineral content accumulation and the regulation of reactive oxygen species (ROS), we investigated the effect of piperonylic acid (a trans-cinnamic acid 4-hydroxylase inhibitor) on plant growth, essential macroelements, osmolyte content, ROS-induced oxidative damage, antioxidant enzyme activities and phytohormone levels in chia seedlings. Piperonylic acid restricted chia seedling growth by reducing shoot length, fresh weight, leaf area measurements and p-coumaric acid content. Apart from sodium, piperonylic acid signifcantly reduced the accumulation of other essential macroelements (such as K, P, Ca and Mg) relative to the untreated control. Enhanced proline, superoxide, hydrogen peroxide and malondialdehyde contents were observed. The inhibition of trans-cinnamic acid 4-hydroxylase activity signifcantly increased the enzymatic activities of ROS-scavenging enzymes such as superoxide dismutase, ascorbate peroxidase, catalase and guaiacol peroxidase. In addition, piperonylic acid caused a reduction in indole-3-acetic acid and salicylic acid content. In conclusion, the reduction in chia seedling growth in response to piperonylic acid may be attributed to a reduction in p-coumaric acid content coupled with elevated ROS-induced oxidative damage, and restricted mineral and phytohormone (indole-3-acetic acid and salicylic) levels.