Location: Soil Management and Sugarbeet Research
2019 Annual Report
Objectives
Objective 1: Identify novel resistance genes to major sugar beet fungal pathogens and sugar beet cyst nemotode within sugar beet genetic resources, especially its crop wild relatives; introgress the discovered novel sources of resistance into sugar beet germplasm for release; incorporate evaluation and characterization data into the Germplasm Resources Informaiton Network (GRIN) database; and screen sugar beet germplasm and commerical lines for major fungal pathogens.
Sub-objective 1A: Introgress novel sources of resistance to major pathogens into sugar enhanced beet germplasm for release.
Sub-objective 1B: Screen 64 selected accessions of Beta vulgaris subspecies maritima (B.v. subsp. maritima) using single nucleotide polymorphic (SNP) markers linked to resistance genes. Confirm the resistance to these important diseases and begin to introgress novel sources of resistance into sugar beet germplasm for release.
Objective 2: Identify and characterize genetic interactions, biochemical pathways, and metobolic processes that control interactions between sugar beet and fungal pathogens, for more efficacious disease resistance selection and improved germplasm for breeding programs, and to provide pratical disease management recommendations for sugar beet producers.
Sub-objective 2.A: Screen sugar beet germplasm with the newly discovered pathogen, Fusarium secorum, to identify resistance to the disease caused by this pathogens, Fusarium yellow decline, and to compare resistance in these sugar beet populations to the more traditional disease, Fusarium yellows primarily caused by Fusarium oxysporum f. sp. betae. (Webb)
Sub-objective 2.B: Using metabolomic profiling, characterize the biological pathways that are induced during susceptible and resistant interactions with F. oxysporum f. sp. betae and F. secorum.
Approach
The sugar beet research within the Soil Management and Sugar Beet Research Unit contributes to the broader, national sugar beet research effort by USDA-ARS. Our research focuses on sugar beet disease because they remain an important source of pre- and post-harvest crop and sugar losses throughout the United States and internationally. Although advances have been made effective tools for managing important diseases are lacking. The pathogenic fungi Rhizoctonia and Fusarium and the sugar beet cyst nematode have particular economic importance because they are among the major limiting factors for sugar beet production nationwide. As part of a national sugar beet improvement program, we will apply a focused approach to enhance crop improvement methods and produce resistant germplasm through increased understanding of sugar beet genetics, some of its major pathogens, and its wild relatives. This project will exploit increased understanding of sugar beet/pathogen interactions and improve the understanding of pathogen diversity. We will use this knowledge to more quickly and cost effectively select disease resistant germplasm and develop superior disease management strategies. The breeding and pathology components of the project are focused on enhanced sugar beet germplasm through increased understanding of important sugar beet diseases and their epidemiology. This is especially crucial in diseases for which there is no chemical protection or where crop protectants are being phased out.
Progress Report
Objective 1: The unit has made continued progress with sequencing the high coverage sugarbeet germplasm obtained from colleagues in Germany, Spain, and within ARS. Much of the germplasm is sequenced to identify variability in the genome of the three species of Patellifolia. This is useful because Patellifolia is a wild relative of beta vulgaris and a possible source of disease resistance for domesticated sugar beets. The sequences were aligned to an established reference genome in Beta vulgaris and also analyzed as a de novo assembly. Each of these methods resulted in the identification of thousands of candidate single nucleotide polymorphisms (SNPs) that can be used to evaluate diversity. Specifically, work focused on: 1) estimating the extent of differentiation and admixture among the three described species, and 2) estimating the provenance of accessions that lack geo-referenced information by using genetic assignment tests with geo-referenced samples provided by collaborators. This work will continue beyond the 60-month research project, and the results are being used to support collection management. Also, progress has been made in identifying and describing the morphology of binucleate Rhizoctonia, a new isolate of fungal disease of sugar beet.
Objective 2: In the first year of our new project, studies have been initiated to screen sugarbeet germplasm for resistance to the novel sugar beet disease, Fusarium yellowing decline. In preliminary studies, we screened six known Fusarium yellows susceptible sugar beet genotypes with 7 isolates of F. secorum and compared virulence\disease severity to three previously reported Fusarium isolates. During this work, we confirmed identification of all isolates via morphological characterization, as well as phylogenetic relationships to the previously described Fusarium population from sugar beet. Surprisingly we discovered that some isolates previously described as F. oxysporum f. sp. betae were actually the novel pathogen F. secorum. Likewise, another group of isolates also previously identified as F. oxysporum f. sp. betae were actually F. commune. Taken together, these data suggest that F. secorum is more widespread than previously thought and that it may actually have been causing Fusarium yellows and not only Fusarium yellowing decline. Screening of resistant sugar beet germplasm is currently in progress and is approximately 50% completed.
Accomplishments
1. Identified a new genus and species that causes Fusarium disease of sugar beet. Several species of Fusarium can cause disease in sugar beet often causing significant economic loss in the field and in post-harvest storage. In order to better manage the disease, it is important to correctly identify the species of Fusarium that is actually contributing to disease symptoms. Previous research had indicated that Fusarium oxysporum (F. oxysporum) were the main cause of disease in sugar beet. ARS scientists in Fort Collins, Colorado, discovered that isolates previously identified as F. oxysporum are actually a newer species of Fusarium that was recently identified (F. secorum). It was also discovered that another isolate previously identified as F. oxysporum is actually a different species that has not been previously associated with sugar beet (F. commune). Inoculation of sugar beet with differing genetic backgrounds demonstrated that all of these isolates have a significant range of disease severity and symptom development depending on the cultivar in question. Proper identification of the Fusarium species that cause disease in sugar beet will enable identification of genetic sources of disease resistance, and will benefit breeders in the development of more robust varieties of sugarbeet.
