| dc.description.abstract | Cotton (Gossypium spp), a globally traded commodity, encounters numerous obstacles during the cultivation of both Upland (G. hirsutum) and Pima (G. barbadense) varieties. Fusarium oxysporum f.sp. vasinfectum race 4 (Fov4), is a virulent pathogen towards Pima cotton with a unique soil inhabiting lifestyle which makes managing disease difficult. Current disease management predominately utilizes fungicides for transporting disease-free seed, while biological controls are largely under-utilized. The introduction focuses on current research utilizing volatile organic compounds (VOC) from various antagonistic bacteria as biological controls against phytopathogens, including Fusarium oxysporum species. Two research objectives were aimed at identifying unique combinations of antagonistic bacteria capable of improving Fov4 inhibition with only VOCs. Fov4 inhibition by VOCs was investigated using bacteria isolated from cotton rhizosphere and bulk soil. Using partitioned petri dishes to physically separate all interested organisms, bacteria, Fov4, and Pima cotton, effects of bacterial VOCs were investigated. Combinations of Bacillus Rz141 with Streptomyces HC658, and Paenibacillus ELP529 with Brevibacillus Rz160, increased VOC inhibition to 26% and 27%, respectively. Suppression by VOCs extended to Fov4-infected Pima cotton resulting in symptom reduction. The third research objective was to identify differences in Fov4 genome compared to Fusarium oxysporum f.sp. vasinfectum race 1, which can help understand host specificity and virulence in Fov races. A putatively identified multi-facilitator superfamily transporter showed differential expression in Fov4 during infection of Pima cotton. A null mutant was generated and further characterized. Growth comparisons of wild type and mutant showed significant difference when grown on NaCl (p<0.05). Additional differences were seen in conidiation and pigment production, but no change in pathogenicity to Pima cotton when compared to wild type. Based on characterization results, this putative MFS transporter was named Fusarium oxysporum sodium related transporter-1 (FoSRT1). In summary, research showed that soil bacteria VOCs have the potential as biocontrols for their ability to suppress Fov4 growth and Pima cotton infection. The influence of NaCl on Fov4 growth was shown, but unknown is why this gene was differentially expressed during infection. This body of work shows the importance of abiotic and biotic soil characteristics which contribute to Fov4 growth and virulence. | |
