Project Number: 5402-21220-006-00
Project Type: Appropriated

Start Date: Jul 27, 2003
End Date: Jul 26, 2008

Objective:
Objective 1: Develop and distribute enhanced germplasm with high agronomic performance and strong resistance to sugar beet disease, primarily focusing on resistance to Rhizoctonia solani and Cercospora beticola, but with effort on resistance to other important sugar beet pathogens. Objective 2: Characterize the biology and interaction of major sugar beet pathogens (esp. Cercospora beticola, Rhizoctonia solani, and Fusarium oxysporum) and potential biocontrol agents with sugar beet to provide new information that will facilitate development of sugar beet with greater disease resistance and assist in the development of improved and innovative management principles. Objective 3: Evaluate, characterize, and utilize available genetic resources (esp., in the USDA-ARS NPGS Beta PI germplasm collection) and determine the genetic diversity within sugar beet and pathogen populations, to better understand and manage important pathogens of sugar beet, and to produce enhanced germplasm more rapidly and more efficiently to meet the changing needs of seed companies and the growers they serve.

Approach:
Objective 1 We will focus on resistance to Rhizoctonia root rot and Cercospora leaf spot, which are evaluated at Fort Collins via annually created artificial epiphytotics. A lesser effort will be placed on collaborative efforts with other public scientists and breeders working on other pests and diseases. As potential sources of disease resistance are discovered, they will be crossed into agronomically acceptable genepools using traditional breeding methods with progeny testing. We have obtained high sucrose populations from different sources. It is very possible that relaxation of selection pressure might reduce the linkage disequilibrium responsible for phenotypic expression of the trait of interest, especially when that trait is multigenic. We will use resistance to Rhizoctonia solani as an experimental trait and examine the potential shift in phenotypic expression after three cycles of population increase with and without disease pressure. Objective 2 We will transform Cercospora beticola with a modified version of green fluorescent protein (GFP) in order to better observe interactions between the fungus and sugar beet leaves without requiring destructive sampling. Transformed Cercospora will be used to monitor the infection process and to allow real time observation in the laboratory. Research on the use of fungal agents as biological control agents for soil-borne disease of sugar beet will focus on control of Rhizoctonia solani, both in the seedling stage, and in the mature plant. A collection of isolates of Trichoderma spp. with biological control activity on other crops will be used, as will isolates collected from sugar beets and from beet field soil. Interactions of sugar beet pathogens with other crops will be investigated by examining the potential for sugar beet pathogens, particularly Rhizoctonia solani and Fusarium oxysporum, to colonize live plant tissue of rotation crops, and the ability to saprophytically colonize dead plant tissue to allow survival or increased inoculum production in the absence of the sugar beet host. Objective 3 Fungicide resistance research will focus on the genetics of benzimidazole resistance in Cercospora beticola. Since research with other Ascomycetes has demonstrated that benzimidazole resistance is generally associated with mutations in the -tubulin gene, we hypothesize that resistance in C. beticola will be due to similar mutations. Accessions well characterized within GRIN on geographic origin, morphological characteristics, and response to various Beta pathogens will be used to address a more basic question on the dynamics of biodiversity - Does selection of a diverse core collection based on one set of descriptors ensure that this will be a diverse collection when evaluated with another set of descriptors? Further research will involve investigations of genetic variability in sugar beet pathogens and tests for genetic markers, factors, or genes important in the plant-pathogen interaction. While Fusarium oxysporum isolates frequently have host specificity, there are reports that indicate that F. oxysporum that infect beets may be a diverse group.