Dodonaea viscosa Jacq (Sapindaceae) is a medicinal plant with a worldwide distribution. The species has undergone enormous taxonomic changes which caused confusion amongst plant users. In Kenya, for example, two varieties are known to exist based on morphology, i.e., D. viscosa var. viscosa along the coast, and D. viscosa var. angustifolia in the Kenyan inland. These two taxa are recognized as distinct species in some reports. This prompted us to apply metabolomics to understand the relationship among naturally occurring populations of D. viscosa in Kenya, and to identify compounds that can assist in taxonomic delineation of the different varieties of D. viscosa from different parts of Kenya. The phytochemical variability of Kenyan D. viscosa var. angustifolia populations collected from four different geographical regions (Nanyuki, Machakos, Nairobi, and Narok) and one coastal D. viscosa var. viscosa (the Gazi) were analyzed by LC-MS using a metabolomics-driven approach. Four known compounds, two diterpenoids (dodonic acid (1), hautriwaic acid lactone (3), and two flavonoids (5,7,4′,5′-tetrahydroxy-3,6,2′-trimethoxyflavone (2) and catechin (4)) were isolated and purified from the Gazi coastal collection. The presence of these compounds and their relative abundance in other populations was determined by LC-MS analyses. Multivariate statistical analyses of LC-MS data was used for the visualization of the patterns of variation and identification of additional compounds. Eleven discriminant compounds responsible for separating chemometric clusters were tentatively identified. In an antimicrobial assay, hautriwaic acid lactone (3) and catechin (4) were the most active compounds followed by the extract from the coastal (Gazi) population. The clustering pattern of the five populations of D. viscosa suggested that the metabolite profiles were influenced by geo-environmental conditions and did not support the current classification of D. viscosa based on morphology. This study disputes the current classification of D. viscosa in Kenya and recommends revision using tools such as molecular phylogenetics.

Wildly grown in most regions of the world, Carissa edulis is a highly underutilised fruit with significant antioxidant characteristics. The phyto and physicochemical properties of C. edulis berries at different stages of ripening are evaluated in this work. Total flavonoids (TF), total phenolic content (TPC) and antioxidant activity were determined spectrophotometrically, while concentration of polyphenols was determined using liquid chromatography coupled to diode array detection and electrospray ionization mass spectrometry. Results showed that antioxidant activity was lowest (18.36 ± 0.12 mmol TE/g) in RS3 and decreased with TPC upon increased ripening. Conversely, TF increased with ripening progression with TF found to be highest in RS3 (5.92 ± 0.03 mg CE/g). Identified phenolic acids in C. edulis were quinic acid, protocatechuoyl-hexose, neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid and dicaffeoylquinic acid. Identified flavonoids included rutin, catechin, procyanidin dimer, procyanidin trimer, quercetin-3-O-glucosyl-xyloside, quercetin-3-O-robinobioside, quercetin-3-O-glucoside and quercetin-3-OH-3-methylglutaryl-glucoside. Physicochemical properties of C. edulis varied among samples with sugar/acid ratio of C. edulis ranging from 25.70 for RS1 to 50.36 for RS3. Ripening stage of C. edulis undoubtedly affects the phyto and physicochemical properties of C. edulis.

Zanthoxylum species are credited with various uses in ethnomedicine due to their rich metabolite composition. In Kenya, these include management of cancer and microbial related ailments. However, there are limited reports showing how the bioactivity of Kenyan Zanthoxylum species is linked to their phytochemical profiles. This study therefore aimed at examining the chemical variation among five Zanthoxylum species found in Kenya (Z. chalybeum, Z. gilletii, Z. holtzianum, Z. paracanthum and Z. usambarense) using metabolomics approaches and the anti-oxidant and antimicrobial activities of these species. In a Folin–Ciocalteu test, the phenolic content of the stem bark extracts of these species were 73.083–145.272 mg TAE/g, while the alkaloids (in bromothymol blue chromogenic test) and flavonoids (in aluminium chloride test) were found to be 152.39–207.19 mg ME/g, and 109.416–186.413 mg CE/g, respectively. These extracts also exerted strong antioxidant activities in the 2,2-iphenyl-1-picrylhydrazyl (DPPH) and ferric ion reducing antioxidant power assays. In a broth dilution assay, the extract of the stem bark of Z. holtzianum ability showed the highest antimicrobial activity, followed by Z. chalybeum stem bark extract. The activities were positively correlated to both flavonoids and alkaloids concentrations, while the concentration of phenolics had weak negative correlation to antimicrobial activities. A chemometric analysis of the liquid-chromatography mass spectrometry profiles led to grouping of the species into three clusters. This study illustrates the variation in the bioactivity of Zanthoxylum species based on metabolite composition and justifies the wide usage of Zanthoxylum species in Kenyan traditional medicinal practices. Graphical abstract

Citrus tristeza virus (CTV) causes economically important stem pitting in sensitive citrus types however the exact mechanisms of stem pitting development in citrus remain unclear. In this study, CTV infectious clones were used to study stem pitting induction in ‘Duncan’ grapefruit and ‘Mexican’ lime. A panel of open reading frame (ORF) replacement clones was generated focusing on the CTV ORFs implicated in stem pitting development and pathogenicity, namely p33, p18, p13 and p23. ORF replacements from severe- and mild-pitting CTV isolates were introduced into a mild-pitting infectious clone (genotype T36) to determine if stem pitting could be induced. A broad range of stem pitting outcomes were observed with ORF p18 (from isolate T3-KB) and ORF p23 (from isolate GFMS12-1.3) associated with enhanced stem pitting development. Metabolomic trends underlying the different stem pitting outcomes were further assessed by untargeted metabolite profiling. In each citrus host, the metabolite profiling identified statistically significant compounds that differed between stem pitting groups. These compounds were mainly phenolic acids and phenolic glycosides and are known to function as antioxidant and stress-signaling molecules. These metabolites can serve as targets for future time-course observations to potentially use mass spectrometry profiling to inform CTV management practices.

The paper is well structured and written, but in my opinion, it fails to make any substantial contributions to characterizing this plant. The work would have greatly benefited from an untargeted LC-MS approach using an accurate mass spectrometer.