Browsing by Author "Veenstra, Amy"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Evaluation of southern African maize germplasm for phytoalexin accumulation following inoculation by Fusarium verticillioides
    (2017) Veenstra, Amy; Murray, Shane L; Rafudeen, Suhail
    Maize is a socially and economically important crop in Africa (and worldwide) that is severely affected by many fungal pathogens. The pathogen Fusarium verticillioides causes Fusarium ear rot in maize, a disease that greatly reduces quantity and quality of annual maize yields. The pathogen produces mycotoxins called fumonisins, which have been linked to adverse health effects in both humans and animals. Maize produces terpenoid phytoalexins, which are antimicrobial compounds that directly reduce the growth of many fungal pathogens including F. verticillioides. Two families of maize phytoalexins, termed kauralexins and zealexins, have been characterized. Key genes putatively involved in the biosynthetic pathway of these phytoalexins have been identified from the rice model and subsequent studies on maize. This research aimed to evaluate the correlation between phytoalexin accumulation and fungal growth in diverse southern African maize lines in response to F. verticillioides inoculation. Maize lines were inoculated with F. verticillioides using a seed soak inoculation method and grown in vitro for up to two weeks. The harvested tissue was analysed for fungal growth using quantitative PCR, putative phytoalexin biosynthetic gene expression using RT-qPCR and phytoalexin accumulation using gas-chromatography mass spectrometry. Furthermore, an endophyte growing in one of the maize lines was isolated and identified as Trichoderma asperellum. Trichoderma spp. are used as biocontrol agents against many fungal pathogens, although research on the specific antagonistic effect of T. asperellum on F. verticillioides is limited. Phytoalexin accumulation in maize containing endophytic T. asperellum was compared to maize inoculated with F. verticillioides. In vitro competition assays were performed to analyse the antagonistic effect of T. asprellum on F. verticillioides. Results from this study show that inoculation of maize lines with F. verticillioides induces the accumulation of total phytoalexins, and more specifically the accumulation of total kauralexins. Putative phytoalexin biosynthetic genes are also up-regulated in response to inoculation. Maize growing with a T. asperellum endophyte accumulated phytoalexins to the same levels as F. verticillioides, suggesting that T. asperellum induces a defence response that 'primes' the plant for further infection. In vitro competition assays between F. verticillioides and T. asperellum showed that T. asperellum significantly inhibits F. verticillioides growth. These results will aid in the identification of maize lines that can be bred with increased resistance to F. verticillioides with the goal to reduce F. verticillioides incidence in southern Africa. Furthermore, analysis of the efficacy of T. asperellum as an antagonist against F. verticillioides may provide another method for disease reduction in the field.
  • Thumbnail Image
    Item
    Open Access
    Transcriptomic Analysis of a Susceptible African Maize Line to Fusarium verticillioides Infection
    (2020-08-28) Lambarey, Humaira; Moola, Naadirah; Veenstra, Amy; Murray, Shane; Suhail Rafudeen, Mohamed
    Maize (Zea mays L.) is a staple crop providing food security to millions of people in sub Saharan Africa. Fusarium verticillioides, an important fungal pathogen, infects maize causing ‘Fusarium Ear Rot’ disease, which decreases maize kernel yield and the quality of the crop harvested. Currently, no African maize line is completely resistant to infection by F. verticillioides. This study investigated an African maize line, Zea mays CML144, infected with F. verticillioides. Analysis of morphological characteristics showed significant differences between mock-infected and infected plants. RNA-sequencing (RNA-seq) was conducted on plants 14 days post-inoculation to identify differentially expressed genes (DEGs) involved in F. verticillioides infection. Analysis of RNA-seq data revealed DEGs that were both significantly up- and down-regulated in the infected samples compared to the mock-infected control. The maize TPS1 and cytochrome P450 genes were up-regulated, suggesting that kauralexins were involved in the CML144 defense response. This was substantiated by kauralexin analyses, which showed that kauralexins, belonging to class A and B, accumulated in infected maize tissue. Gene ontology terms relating to response to stimulus, chemical stimulus and carbohydrate metabolic processes were enriched, and the genes belonging to these GO-terms were down-regulated. Quantitative real-time PCR was performed on selected DEGs and measurement of phytoalexin accumulation validated the RNA-seq data and GO-analysis results. A comparison of DEGs from this study to DEGs found in F. verticillioides (ITEM 1744) infected susceptible (CO354) and resistant (CO441) maize genotypes in a previous study, matched 18 DEGs with 17 up-regulated and one down-regulated, respectively. This is the first transcriptomic study on the African maize line, CML144, in response to F. verticillioides infection.