Investigation of Fusarium Stalk and Kernel Rot Diseases in Field Crops
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Fusarium verticillioides is a fungal pathogen of row crops, such as maize and sugarcane, and produces the toxic secondary metabolite, fumonisin B1 (FB1). The first topic of this research was aimed to isolate and characterize the Pokkah boeng pathogen through morphological, physiological, and molecular analyses. Pokkah boeng is a serious disease of sugarcane, which can lead to devastating yield losses in cropproducing regions; however, there is still uncertainty about the causal agent of the disease. Sugarcane-colonizing fungi were isolated in Fujian, China and assayed for cell wall degrading enzyme capabilities. Five isolates were identified for further analysis. ITS sequencing revealed that these five strains are Fusarium, Alternaria, Phoma, Phomopsis, and Epicoccum. The Fusarium isolate was further identified as F. verticillioides after Calmodulin and EF-1 gene sequencing and microscopic morphology study. Pathogenicity assay confirmed that F. verticillioides was directly responsible for disease on sugarcane. Co-inoculation of F. verticillioides with other isolated fungi did not lead to a significant difference in disease severity, refuting the idea that other cellulolytic fungi can increase disease severity as an endophyte. For the second topic, a Next-generation sequencing (NGS) experiment was performed to investigate novel genes downstream of MADS-box transcription factors (TFs). With NGS data obtained from F. verticillioides wild type and MADS-box TF mutant samples, a computational network-based analysis was used to predict downstream genetic subnetwork modules,associated with FB1 production. These subnetworks were subsequently analyzed in silico, and five genes hypothesized as putative hub genes were subjected to functional characterization. Modification of RAS GTPase (SNG3), cyanate lyase (SNG4) and methyltransferase (SNG5) resulted in a significant reduction in FB1 biosynthesis. Conversely, mutation of the 50S ribosome-binding GTPase (SNG1) led to an increase in FB1 production compared to the wild-type. Fitness of the Sng3, Sng4, and Sng5 genedeletion strains was not adversely affected on V8, defined liquid (DL), and PDA media. With focus on Sng3 and Sng5 strains, a gene expression study was performed to investigate the transcriptional regulatory directionality of neighboring genes in the two subnetworks. Expression of three neighboring genes (FVEG_06215, FVEG_07056, and FVEG_00035) were significantly altered in the Sng3 mutant, furthering the possibility of a hub role for FVEG_02390 in subnetwork A. Gene expression analysis of Subnetwork B in Sng5 demonstrated that FVEG_11168 plays an important role in transcription of neighboring genes (FVEG_07056 and FVEG_06215). Further study into FB1 regulatory pathways is needed to improve our understanding of the F. verticillioides pathogenesis.
Hilton, Angelyn Elizabeth (2016). Investigation of Fusarium Stalk and Kernel Rot Diseases in Field Crops. Master's thesis, Texas A&M University. Available electronically from