Research Articles (Plant Science)

Permanent URI for this collectionhttp://hdl.handle.net/2263/1733

A collection containing some of the full text peer-reviewed/ refereed articles published by researchers from the Department of Plant Science

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Cyclitol metabolism is a central feature of Burkholderia leaf symbionts
(Wiley, 2023-02) Danneels, Bram; Blignaut, Monique; Marti, Guillaume; Sieber, Simon; Vandamme, Peter; Meyer, Marion; Carlier, Aurelien
The symbioses between plants of the Rubiaceae and Primulaceae families with Burkholderia bacteria represent unique and intimate plant–bacterial relationships. Many of these interactions have been identified through PCR-dependent typing methods, but there is little information available about their functional and ecological roles. We assembled 17 new endophyte genomes representing endophytes from 13 plant species, including those of two previously unknown associations. Genomes of leaf endophytes belonging to Burkholderia s.l. show extensive signs of genome reduction, albeit to varying degrees. Except for one endophyte, none of the bacterial symbionts could be isolated on standard microbiological media. Despite their taxonomic diversity, all endophyte genomes contained gene clusters linked to the production of specialized metabolites, including genes linked to cyclitol sugar analog metabolism and in one instance non-ribosomal peptide synthesis. These genes and gene clusters are unique within Burkholderia s.l. and are likely horizontally acquired. We propose that the acquisition of secondary metabolite gene clusters through horizontal gene transfer is a prerequisite for the evolution of a stable association between these endophytes and their hosts.
Calpurnia aurea (Aiton) benth extracts reduce quorum sensing controlled virulence factors in Pseudomonas aeruginosa
(MDPI Publishing, 2020-05-13) Cosa, Sekelwa; Rakoma, Jostina R.; Yusuf, Abdullahi Ahmed; Tshikalange, Thilivhali Emmanuel
Pseudomonas aeruginosa is the causative agent of several life-threatening human infections. Like many other pathogens, P. aeruginosa exhibits quorum sensing (QS) controlled virulence factors such as biofilm during disease progression, complicating treatment with conventional antibiotics. Thus, impeding the pathogen’s QS circuit appears as a promising alternative strategy to overcome pseudomonas infections. In the present study, Calpurnia aurea were evaluated for their antibacterial (minimum inhibitory concentrations (MIC)), anti-quorumsensing/antivirulence (AQS), and antibiofilm potential against P. aeruginosa. AQS and antivirulence (biofilm formation, swimming, and swarming motility) activities of plant extracts were evaluated against Chromobacterium violaceum and P. aeruginosa, respectively. The in vitro AQS potential of the individual compounds were validated using in silico molecular docking. Acetone and ethanolic extracts of C. aurea showed MIC at 1.56 mg/mL. The quantitative violacein inhibition (AQS) assay showed ethyl acetate extracts as the most potent at a concentration of 1 mg/mL. GCMS analysis of C. aurea revealed 17 compounds; four (pentadecanol, dimethyl terephthalate, terephthalic acid, and methyl mannose) showed potential AQS through molecular docking against the CviR protein of C. violaceum. Biofilm of P. aeruginosa was significantly inhibited by 60% using 1-mg/mL extract of C. aurea. Confocal laser scanning microscopy correlated the findings of crystal violet assay with the extracts significantly altering the swimming motility. C. aurea extracts reduced the virulence of pseudomonas, albeit in a strain- and extract-specific manner, showing their suitability for the identification of lead compounds with QS inhibitory potential for the control of P. aeruginosa infections.
Towards developing a metabolic-marker based predictive model for Phytophthora nicotianae tolerance in citrus rootstocks
(Springer, 2018-07) Sakupwanya, Masiyiwa Ngoni; Labuschagne, Nico; Loots, Mattheus Theodor; Apostolides, Zeno; nico.labuschagne@up.ac.za
Root rot of citrus trees caused by Phytophthora nicotianae is responsible for severe economic losses in citriculture. Use of resistant rootstocks is an effective method of managing this problem, however, breeding and selection of new citrus rootstocks is a time-consuming undertaking. The objective was to develop a method for the rapid assessment of rootstocks for P. nicotianae tolerance, using a metabolomics approach to identify metabolic markers for the phenotypic trait of tolerance. Sixteen citrus rootstocks were inoculated with P. nicotianae in the greenhouse for determination of relative tolerance/susceptibility. Healthy citrus roots from four tolerant and four susceptible rootstocks were used for metabolite analysis with the objective of identifying potential biomarkers. Organic solvent extractions of the roots were prepared and analysed by mass-spectrometry based liquid chromatography, which produced 367 ion features (retention time and m/z). Orthogonal partial least squares discriminant analysis of peak abundance using MarkerLynx software allowed for the identification of ion features that differentiate tolerant and susceptible rootstocks. Using descriptive and inferential statistics based on the ion features of uninoculated tolerant vs. susceptible rootstocks, applying logistic regression, 14 top markers were identified and two of them (22.03_259.0975 and 22.21_313.1445: retention time (rt) and mass to charge ratio (m/z) were accepted as potential metabolic markers. A model that can potentially predict tolerance in citrus rootstocks with >98% accuracy is presented.
Dung beetle activity improves herbaceous plant growth and soil properties on confinements simulating reclaimed mined land in South Africa
(Elsevier, 2018-12) Badenhorst, Jessica; Dabrowski, Jacqueline; Scholtz, Clarke H.; Truter, Wayne Frederick
Mining activities contribute greatly to economic growth and development in South Africa. However, post-mining soils have limited land-use potential due to low fertility, deficiency in organic matter content and poor physical, chemical, and microbiological properties. Dung beetles could potentially improve several aspects of soil degradation, complementing current rehabilitation efforts. Studies in relatively undisturbed soils of agro-ecosystems have found that dung burial introduces essential nutrients in dung to the plant root zone, which would otherwise remain on the soil surface and mostly volatilize in the absence of dung beetles. Furthermore, dung beetles create tunnels under dung pats, improving water infiltration rates, bulk density, soil aeration and pasture yields. The aim of the study was to determine whether these effects could be maintained on soil simulating reclaimed mined land, where very high rates of compaction may prevent tunnelling altogether. Three experimental treatments of dung + beetles (D + B), dung only (D) and control/no dung, no dung beetles (X) were applied twice over 2 years on 1 m3 experimental confinements. Various soil and herbaceous plant properties were assessed one and six months after each application of dung and beetles. Results obtained showed that water infiltration rate and plant biomass was significantly higher for all confinements containing dung beetles. Penetration resistance (soil strength) was significantly reduced for confinements with dung beetles. Magnesium and potassium levels in the soil were significantly higher for D + B treatments when compared to D and X treatments. In conclusion, results showed that dung beetles were able to maintain their activities in soils typical of reclaimed mine land, significantly improving soil properties and herbaceous plant growth. Incorporating the application of dung beetles to the conventional approach to rehabilitation has the potential to improve the efficacy of coal mine reclamation. This biological approach may also prove to be cost-effective over time as it provides a seasonal source of bioturbation, which does not disturb plant growth and reduces the requirements for soil rejuvenating tillage practices.
Effect of thyme oil vapours exposure on phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) genes expression, and control of anthracnose in ‘Hass’ and ‘Ryan’ avocado fruit
(Elsevier, 2017-10) Bill, Malick; Korsten, Lise; Remize, Fabienne; Glowacz, Marcin; Sivakumar, Dharini
The effect of thyme oil (96 μL L−1) vapours on the expression of phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) genes, and control of anthracnose was investigated in naturally infected ‘Hass’ and ‘Ryan’ avocado fruit stored for 21 d at 7–7.5 °C, and thereafter kept for 5 d at 20 °C, simulating the supply chain conditions. Exposure to thyme oil vapours prior to cold storage resulted in up-regulation of the PAL gene expression in both ‘Hass’ and ‘Ryan’ avocado when compared with untreated fruit and those treated with prochloraz®. The higher expression of PAL gene was observed in ‘Ryan’. Thyme oil vapours exposure resulted in the higher epicatechin content. At the same time, exposure to thyme oil vapours led to down-regulation of LOX gene expression in both cultivars. Thus, simultaneous up-regulation of PAL gene and down-regulation of LOX gene in avocados exposed to thyme oil vapours prior to cold storage was associated with higher epicatechin content in the fruit. Therefore, it can be concluded that postharvest application of thyme oil vapours increases anthracnose disease resistance in ‘Hass’ and ‘Ryan’ avocado fruit.
Amorfrutin-type phytocannabinoids from Helichrysum umbraculigerum
(Elsevier, 2017-11) Pollastro, Federica; De Petrocellis, Luciano; Schiano-Moriello, Aniello; Chianese, Giuseppina; Heyman, Heino Martin; Appendino, Giovanni; Taglialatela-Scafati, Orazio
Helichrysum umbraculigerum Less. has been reported to be a prolific producer of phytocannabinoids from the alkyl-, aralkyl-, normal-, and abnormal types. Investigation of an acetone extract from the aerial parts of the plant afforded two novel amorfrutin-type phytocannabinoids (3b, 4) and the new geranylated phloroglucinol 5a. The presence of cannabigerol (CBG, 1a) and its acidic precursor (pre-CBG, CBGA, 1b), previously reported from this plant, could not be confirmed, but the phenethyl analogue of CBG (Heli-CBG, 2a) and the methyl ester of its carboxylated version (2b) were isolated. Heli-CBG (2a) was assayed against a series of metabotropic (CB1 and CB2)- and ionotropic (thermo-TRPs) targets of phytocannabinoids, comparing its profile with the one of cannabigerol (CBG). A decreased affinity for cannabinoid receptor was observed, along with substantial retention of the thermo-TRP profile. The biogenetic relationships between the isoprenylated phenolics from H. umbraculigerum are discussed, highlighting the relevance of this species for biogenetic investigations on phytocannabinoids
Phylogenetic regionalization of marine plants reveals close evolutionary affinities among disjunct temperate assemblages
(Elsevier, 2017-09) Daru, Barnabas H.; Holt, Ben G.; Lessard, Jean-Philippe; Yessoufou, Kowiyou; Davies, T. Jonathan
While our knowledge of species distributions and diversity in the terrestrial biosphere has increased sharply over the last decades, we lack equivalent knowledge of the marine world. Here, we use the phylogenetic tree of seagrasses along with their global distributions and a metric of phylogenetic beta diversity to generate a phylogenetically-based delimitation of marine phytoregions (phyloregions). We then evaluate their evolutionary affinities and explore environmental correlates of phylogenetic turnover between them. We identified 11 phyloregions based on the clustering of phylogenetic beta diversity values. Most phyloregions can be classified as either temperate or tropical, and even geographically disjunct temperate regions can harbor closely related species assemblages. Geographic differences in sea surface temperatures account for more phylogenetic turnover than either water salinity or bathymetry. We also found a strong temperate-tropical gradient in evolutionary distinctiveness, with temperate phyloregions being the most evolutionarily unique. Our results highlight differences between the marine and terrestrial worlds, and suggest that the interplay between long-distance dispersal and phylogenetic niche conservatism played a central role in determining the contemporary distributions of seagrasses worldwide.
Integrating biogeography, threat and evolutionary data to explore extinction crisis in the taxonomic group of cycads
(Wiley Open Access, 2017) Yessoufou, Kowiyou; Daru, Barnabas H.; Tafirei, Respinah; Elansary, Hosam O.; Rampedi, Isaac
Will the ongoing extinction crisis cause a severe loss of evolutionary information accumulated over millions of years on the tree of life? This question has been largely explored, particularly for vertebrates and angiosperms. However, no equivalent effort has been devoted to gymnosperms. Here, we address this question focusing on cycads, the gymnosperm group exhibiting the highest proportion of threatened species in the plant kingdom. We assembled the first complete phylogeny of cycads and assessed how species loss under three scenarios would impact the cycad tree of life. These scenarios are as follows: (1) All top 50% of evolutionarily distinct (ED) species are lost; (2) all threatened species are lost; and (3) only all threatened species in each IUCN category are lost. Finally, we analyzed the biogeographical pattern of cycad diversity hotspots and tested for gaps in the current global conservation network. First, we showed that threatened species are not significantly clustered on the cycad tree of life. Second, we showed that the loss of all vulnerable or endangered species does not depart significantly from random loss. In contrast, the loss of all top 50% ED, all threatened or all critically endangered species, would result in a greater loss of PD (Phylogenetic Diversity) than expected. To inform conservation decisions, we defined five hotpots of diversity, and depending on the diversity metric used, these hotspots are located in Southern Africa, Australia, Indo-Pacific, and Mexico and all are found within protected areas. We conclude that the phylogenetic diversity accumulated over millions of years in the cycad tree of life would not survive the current extinction crisis. As such, prioritizing efforts based on ED and concentrating efforts on critically endangered species particularly in southern Africa, Australia, Indo-Pacific, and Mexico are required to safeguarding the evolutionary diversity in the cycad tree of life.
Evaluation of plant-produced Clostridium perfringens type D epsilon toxoid in a vaccine against enterotoxaemia in sheep
(AOSIS OpenJournals, 2017-04-25) Mokoena, Tinyiko; Chakauya, Ereck; Crampton, Michael; Weyers, Boet; Tselanyane, Malefa; Tsekoa, Tsepo; Chikwamba, Rachel
Enterotoxaemia (pulpy kidney) is a common bacterial disease of sheep caused by Clostridium perfringens type D epsilon toxin. It has mortality rates of up to 30% in non-vaccinated animals. Current vaccines from whole cell cultures are expensive to manufacture and can induce local inflammatory responses in sheep. They usually have reduced immunogenicity because of the difficulty of standardising the inactivation step in vaccine manufacturing. In the current study, we evaluated the safety and potency of a recombinant plant-made epsilon toxoid protein (r-Etox) as an affordable and safer alternative vaccine for developing countries. Results of injection site reactions, rectal temperature and toxin neutralisation test in single and prime– boost inoculations of mice, guinea pigs and sheep suggest that the product is not toxic to animals and could protect sheep against enterotoxaemia.
Aloe × Inopinata Gideon F.SM., N.R.Crouch & Oosth., (Asphodelaceae) [Aloe arborescens Mill. × Aloe chortolirioides A.Berger Var. Chortolirioides] : a nothospecies from the Barberton Centre of Endemism, Eastern South Africa
(Cactus and Succulent Society of America, 2016) Smith, Gideon F.; Figueiredo, Estrela; Crouch, Neil R.; Oosthuizen, Delia; Klopper, Ronell Renett
The natural hybrid between Aloe arborescens Mill. and A. chortolirioides A.Berger var. chortolirioides (Asphodelaceae) is here formally described as a nothospecies, A. ×inopinata Gideon F.Sm., N.R.Crouch & Oosth. The hybrid occurs at Kamhlabane, about 37 km [22 miles] east of Barberton, as well as at Twello 373JU in the Barberton district, Mpumalanga. It has been known in horticulture for many years, following the introduction of wild-sourced material by Gilbert W. Reynolds.
Testing the reliability of standard and complementary DNA barcodes for the monocot subfamily Alooideae from South Africa
(NRC Research Press, 2017-04) Daru, Barnabas H.; Van der Bank, Micelle; Bello, Abubakar; Yessoufou, Kowiyou
Although a standard DNA barcode has been identified for plants, it does not always provide species-level specimen identifications for investigating important ecological questions. In this study, we assessed the species-level discriminatory power of standard (rbcLa + matK) and complementary barcodes (ITS1 and trnH-psbA) within the subfamily Alooideae (Asphodelaceae), a large and recent plant radiation, whose species are important in horticulture yet are threatened. Alooideae has its centre of endemism in southern Africa, with some outlier species occurring elsewhere in Africa and Madagascar. We sampled 360 specimens representing 235 species within all 11 genera of the subfamily. With three distance-based methods, all markers performed poorly for our combined data set, with the highest proportion of correct species-level specimen identifications (30%) found for ITS1. However, when performance was assessed across genera, the discriminatory power varied from 0% for all single markers and combinations in Gasteria to 63% in Haworthiopsis, again for ITS1, suggesting that DNA barcoding success may be related to the evolutionary history of the lineage considered. Although ITS1 could be a good barcode for Haworthiopsis, the generally poor performance of all markers suggests that Alooideae remains a challenge. As species boundaries within Alooideae remain controversial, we call for continued search for suitable markers or the use of genomics approaches to further explore species discrimination in the group.
Effect of postharvest practices on the culturable filamentous fungi and yeast microbiota associated wit the pear carpoplane
(Elsevier, 2016-08) Volschenk, Quinton; Du Plessis, Erika Margarete; Duvenage, Francois J.; Korsten, Lise
Information regarding the filamentous fungi and yeast microbiota on pear surfaces is limited when compared to other fruits such as grapes and apples. The effect of commercial postharvest practices on pear fruit surface microbiota and species composition is not known, particularly in terms of the presence of postharvest pathogens and potential biocontrol microorganisms. Pear fruit were collected at harvest in the orchards of four commercial farms, after harvest at a communal pack house following chlorine drenching and after modified atmosphere storage. Microbiological analysis showed that during season one the fungal populations on pears from the four farms were significantly lower after CA storage when compared to populations of orchard pears, however during season two, the opposite trend was observed. The yeast populations were either significantly higher or similar after CA storage compared to the orchard pear counts during both seasons. Commercial drenching led to either an increase or reduction in the filamentous fungi and yeast populations, however a definite trend could not be observed. The postharvest practices decreased the number of viable morphologically different yeast and filamentous fungal species. A total of 16 yeast and 24 filamentous fungal species were isolated. A 76% dominance of Ascomycetes was observed. Known postharvest pathogens Penicilium commune and Penicillium crysogenum were present after CA storage. Potential known biocontrol organisms included Aureobasidium pullulans, Cryptococcus sp. and Sporobolomyces roseus. Knowledge generated could contribute to development of commodity-specific supply-chain management systems and biocontrol strategies based on scientific data to reduce pear fruit losses and for quality control purposes.
Antimicrobial resistance profiles of Salmonella spp. from agricultural environments in fruit production systems
(Mary Ann Liebert, 2016-09) Gomba, Annancietar; Chidamba, Lizyben; Korsten, Lise; lise.korsten@up.ac.za
Foodborne disease outbreaks involving fresh produce have increased in recent years. The risk of infection from contaminated food is worsened by the increased prevalence of antibiotic-resistant strains. This study evaluated the prevalence of antibiotic resistance in Salmonella isolates (n?=?263) from agricultural production systems through to the final packed product. Salmonella isolates were preliminarily identified by matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF MS) and API 20E and identities confirmed by invA gene polymerase chain reaction. Antimicrobial susceptibility was performed with 15 antimicrobial agents using the Kirby Bauer disk diffusion test. Of the 263 Salmonella isolates assessed, 59.3% were resistant to one or more antimicrobials. The most frequently detected resistance was against chloramphenicol and kanamycin (46.7%), trimethoprim sulfamethoxazole (28%), and streptomycin (14%), and the less frequently detected resistance was toward ampicillin (1.14%), amikacin (0.76%), and amoxicillin clavulanic acid (0.38%). Multiple antimicrobial resistance (MAR) (resistance to ?3 antibiotics) was found in 48.7% (76/156) isolates. The most common MAR phenotype was to chloramphenicol and trimethoprim/sulfamethoxazole kanamycin (43.6%). Resistance to chloramphenicol, kanamycin, or trimethoprim/sulfamethoxazole was only observed in MAR phenotypes. All isolates were susceptible to ceftiofur, cefoxitin, ceftriaxone, ciprofloxacin, nalidixic acid, gentamicin, and tetracycline. This study confirms the importance of fresh produce production environments as potential reservoirs and fresh produce as carriers of antibiotic-resistant Salmonella spp. with significant clinical importance. Further studies to evaluate the actual level of health risk from these pathogens should include characterization of the antibiotic resistance determinant genes among the isolates.
Systems genetics reveals a transcriptional network associated with susceptibility in the maize-gray leaf spot pathosystem
(Wiley, 2017-02) Christie, Nanette; Myburg, Alexander Andrew; Joubert, Fourie; Murray, Shane L.; Carstens, Maryke; Lin, Yao-Cheng; Meyer, Jacqueline; Crampton, Bridget Genevieve; Christensen, Shawn A.; Ntuli, Jean F.; Wighard, Sara S.; Van de Peer, Yves; Berger, David Kenneth; dave.berger@fabi.up.ac.za
We used a systems genetics approach to elucidate molecular mechanisms of maize responses to gray leaf spot (GLS) disease, caused by Cercospora zeina, a threat to maize production globally. Expression analysis of earleaf samples in a sub-tropical maize RIL population (CML444 X SC Malawi) subjected in field to C. zeina infection allowed detection of 20,206 expression QTLs (eQTL). Four trans-eQTL hotspots coincided with GLS disease QTLs mapped in the same field experiment. Co-expression network analysis identified three expression modules correlated with GLS disease scores. The module (GY-s) most highly correlated with susceptibility (r = 0.71; 179 genes) was enriched for the glyoxylate pathway, lipid metabolism, diterpenoid biosynthesis and responses to pathogen molecules such as chitin. The GY-s module was enriched for genes with transeQTLs in hotspots on chromosomes 9 and 10, which also coincided with phenotypic QTLs for GLS susceptibility. This transcriptional network has significant overlap with the GLS susceptibility response of maize line B73, and may reflect pathogen manipulation for nutrient acquisition and/or unsuccessful defense responses, such as kauralexin production by the diterpenoid biosynthesis pathway. The co-expression module that correlated best with resistance (TQ-r; 1498 genes) was enriched for genes with trans-eQTLs in hotspots coinciding with GLS resistance QTLs on chromosome 9. Jasmonate responses were implicated in resistance to GLS through co-expression of COI-1 and enrichment of genes with the GO term “cullin-RING ubiquitin ligase complex” in the TQ-r module. Consistent with this, JAZ repressor expression was highly correlated with GLS disease severity in the GY-s susceptibility network.
Spiny plants, mammal browsers, and the origin of African savannas
(National Academy of Sciences, 2016-09) Charles-Dominique, Tristan; Davies, T. Jonathan; Hempson, Gareth P.; Bezeng, Bezeng S.; Daru, Barnabas H.; Kabongo, Ronny M.; Maurin, Olivier; Muasya, A. Muthama; Van der Bank, Michelle; Bond, William J.
Savannas first began to spread across Africa during the Miocene. A major hypothesis for explaining this vegetation change is the increase in C4 grasses, promoting fire. We investigated whether mammals could also have contributed to savanna expansion by using spinescence as a marker of mammal herbivory. Looking at the present distribution of 1,852 tree species, we established that spinescence is mainly associated with two functional types of mammals: large browsers and medium-sized mixed feeders. Using a dated phylogeny for the same tree species, we found that spinescence evolved at least 55 times. The diversification of spiny plants occurred long after the evolution of Afrotherian proboscideans and hyracoids. However, it is remarkably congruent with diversification of bovids, the lineage including the antelope that predominantly browse these plants today. Our findings suggest that herbivore-adapted savannas evolved several million years before fire-maintained savannas and probably, in different environmental conditions. Spiny savannas with abundant mammal herbivores occur in drier climates and on nutrient-rich soils, whereas fire-maintained savannas occur in wetter climates on nutrient-poor soils.
Taxonomic notes on Acanthopsis Harv. (Acanthaceae, tribe Acantheae) : the group with trifid bracts
(Magnolia Press, 2017-02-10) Steyn, Hester Maria; Van Wyk, Abraham Erasmus (Braam)
In the southern African genus Acanthopsis, the morphology of the bracts is taxonomically useful at the species level. This contribution focuses on the taxonomy and conservation status of those members of the genus characterized by inflorescences with trifid bracts, all of which are confined to arid parts of the Northern Cape Province, South Africa. Three species (A. dregeana, A. glauca and A. tetragona) and four subspecies are recognised in this group. One new species (A. tetragona) with two subspecies (A. tetragona subsp. tetragona and A. tetragona subsp. pedunculata) and one new subspecies (A. dregeana subsp. longispina) are described. Identification keys to the species and infraspecific taxa of the group with trifid bracts are provided.
August Wulfhorst (1861-1936) and his overlooked contributions on the flora of Angola
(The Conservatory and Botanical Garden of the City of Geneva (CJBG), 2013-07-12) Figueiredo, Estrela; Smith, G.F. (Gideon Francois), 1959-; Nyffeler, Reto
August Wulfhorst (1861-1936), a German missionary attached to the Rheinische Missionsgesellschaft, collected material in omupanda (Amboland, Uukuanyama), which is located in present-day Angola. In the past, botanical collections from this area were wrongly proposed as originating from Namibia, so obscuring the occurrence of several taxa north of the borders of this former German colony, in Angola.
Phenolic content as an indicator of tolerance of cowpea seedlings to Sclerotium rolfsii
(Springer, 2017-10) Adandonon, Appolinaire; Regnier, Thierry; Aveling, T.A.S. (Terry)
The role of phenolics in plant tolerance to pathogen infection is well documented. The objective of the present preliminary investigation was to study phenolic metabolites involved in the tolerance or susceptibility of cowpea (Vigna unguiculata Walp.) cultivars to Sclerotium rolfsii Sacc. and to use their presence as a possible screening tool. Total, free acid, ester-bound and cell wall-bound phenolics of 10 cowpea cultivars were quantified. In healthy seedlings, the tolerant cultivars displayed the higher phenol content than the susceptible cultivars. In S. rolfsii infected seedlings, the highest increase was found from 48 h after inoculation. The net effect of inoculation was a 630 % increase in total phenolics (soluble and insoluble) in the stem of tolerant cultivars while the total phenolic content increased only by 212 % in the stems of susceptible cultivars. Two phytoalexins were detected. Although, no significant difference (P = 0.05) was detected among cultivars, in terms of free acid phenolics, the amount of ester-bound and cell wall-bound phenolics significantly increased, therefore demonstrating a similar trend to the one observed for the total phenolic content. These preliminary results showed that the presence of phenolics before and after S. rolfsii infection may be used as a rapid screening method for detection of tolerance to S. rolfsii damping-off and stem rot of cowpea.
A new antifungal eudesmanolide glycoside isolated from Sphaeranthus indicus Linn. (Family Compositae)
(Taylor and Francis, 2016-03) Mishra, Bhuwan B.; Kishore, Navneet; Tiwari, Vinod K.
A new antifungal eudesmanolide glycoside 11,13-dihydro-3-O-(β-digitoxopyranose)-7α- hydroxy eudasman-6,12-olide (2) in addition to known compounds 1 and 3, has been isolated from Sphaeranthus indicus Linn. Its structure was determined by spectral analysis (UV, IR, 1D and 2D NMR and mass spectrum).
A Eucalyptus bacterial wilt isolate from South Africa is pathogenic on Arabidopsis and manipulates host defences
(Wiley, 2011-04) Naidoo, Sanushka; Fouche-Weich, Joanne; Law, P.; Denby, K.J.; Marco, Y.; Berger, David Kenneth; dave.berger@fabi.up.ac.za
Ralstonia solanacearum, the causal agent of bacterial wilt, has been reported from Eucalyptus plantations in at least three countries in Africa. The lack of genomics resources in Eucalyptus species led us to develop and study a pathosystem between a previously characterized South African isolate and the model plant Arabidopsis thaliana. Ralstonia solanacearum BCCF401 isolated from a Eucalyptus grandis × Eucalyptus camaldulensis hybrid was shown to cause disease on A. thaliana ecotype Col-5. Arabidopsis genomics tools were exploited to investigate gene expression changes during wilt disease development, and thereby develop hypotheses that can be tested in Eucalyptus once genomics resources are available. Transcriptome analysis using 5000 A. thaliana ESTs was performed and revealed 141 genes that were differentially regulated by R. solanacearum infection (at a significance threshold of p < 0.03; Bonferroni corrected). A software tool ‘Rank Correlation Comparer’ was developed to compare expression profiles with Arabidopsis Affymetrix NASCArray data. High correlations were observed between the response of Arabidopsis plants to both Eucalyptus (BCCF401) and tomato (GMI1000) isolates of R. solanacearum, as well as to Pseudomonas syringae, Botrytis cinerea and treatment with abscisic acid. Basal defence responses in Col-5 in response to R. solanacearum were investigated by comparing the expression data following R. solanacearum infection to data after treatment with the Pathogen Associated Molecular Patterns (PAMP) flg22 and lipopolysaccharide, and the Type Three Secretion System deficient Pseudomonas syringae pv. tomato hrp− mutant. A subset of the genes which were induced by PAMPs were repressed by R. solanacearum infection, and vice versa, suggesting that these genes may be repressed or induced, respectively, by specific R. solanacearum effectors. We hypothesize that these genes represent targets of R. solanacearum effectors. The pending release of the Eucalyptus genome sequence will enable orthologues to be identified and these hypotheses to be tested in Eucalyptus trees.

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