Location: Northwest Irrigation and Soils Research
2019 Annual Report
Objectives
1. Develop genetic markers that will allow for marker-assisted breeding; develop superior sugar beet germplasm with priority traits, such as high sucrose and resistance to various diseases; and release improved breeding materials, including doubled haploid lines, inbred lines, and genetic mapping populations.
1.1. Develop elite germplasm with curly top, Rhizoctonia crown and root rot (RCRR), Cercospora leaf spot (CLS), and storage rot resistance, and high sucrose and low impurities. (Eujayl, Strausbaugh)
1.2. Conduct whole genome sequencing of elite germplasm lines for genetic variation analysis for RCRR resistance. (Eujayl, Strausbaugh)
1.3. Establish a large complement of single nucleotide polymorphism (SNP) markers for genotyping mapping populations and germplasm for curly top and RCRR resistance. (Eujayl, Strausbaugh)
2. Dissect disease development pathways and host-pathogen interactions, and design improved disease management strategies and screening procedures in sugar beet.
2.1. Investigate the interaction between the most common Leuconostoc van Tiegham haplotypes and the various genetic subgroups of R. solani. (Strausbaugh)
2.2. Investigate the use of RNA interference (RNAi) for the control of Beet curly top virus (BCTV). (Strausbaugh, Eujayl)
2.3. Develop additional management strategies for curly top and pest control in sugar beet. (Strausbaugh)
Approach
The proposed research is a coordinated cooperative effort between USDA-ARS, university scientists, and industry partners which will improve sucrose yield in sugar beet production. Elite sugar beet germplasm will be developed to increase sucrose content, while reducing impurities and improving disease resistance and management options for Beet curly top virus (BCTV), Rhizoctonia solani, and storage rot fungi. The first objective is non-hypothesis research focused on improving or identifying novel traits of interest, releasing elite germplasm with these traits, and sequencing lines to map and develop markers for these traits. Genetic markers will allow for marker-assisted breeding and release of superior sugar beet germplasm. Backcrossing, mass selection, and recurrent selection will be used to produce populations and lines with disease resistance, low impurities, and high sucrose content. Doubled haploid lines from this germplasm will be used to produce hybrids and segregating populations for genetic mapping. Whole genome sequencing will be conducted using PacBio technology and optical mapping. This effort will be complemented with gene expression profiling via RNA-Seq and Iso-Seq to identify differentially expressed genes caused by R. solani infection. A large complement of single nucleotide polymorphism (SNP) markers for genotyping mapping populations and germplasm for curly top and Rhizoctonia crown and root rot resistance will be developed. If additional sources of high sucrose or disease resistance are needed, additional high sucrose parental lines and plant introduction accessions will be screened. The second objective is hypothesis driven research which advances our knowledge of disease development and interactions to improve disease management strategies and screening procedures in sugar beet production. The interaction between Leuconostoc and R. solani will be investigated, since Leuconostoc haplotypes will possibility vary in their ability to create more root rot through a synergistic interaction with genetic subgroups of R. solani. Root inoculations in field studies will be conducted with bacterial isolates representing the predominant haplotypes for L. mensenteroides and L. pseudomesenteroides and R. solani isolates representative of the diversity present in anastomosis groups found in sugar beet. Five weeks after inoculation, rotted tissue will be measured and the pH associated with that tissue will be established. Isolations from the leading edge of the rot from randomly selected roots will be conducted to complete Koch’s postulates. Based on the results from the interaction studies, fungal-bacterial combinations exhibiting the synergistic interaction will be evaluated further through inhibition and enzyme assays. To improve management options for BCTV, the use of RNA interference (RNAi) and foliar insecticides will be investigated. If RNAi proves successful, RNAi will also be investigated for the control of R. solani.
Progress Report
Substantial progress was made on both project objectives in FY19. For Objective 1, significant progress was made with the development of genetic markers and superior sugar beet germplasm with priority traits. New hybrids and populations were developed via crossing doubled haploid lines carrying either Rhizoctonia or Beet curly top virus (BCTV) resistance. Additionally, lines with resistance to Cercospora leaf spot were hybridized to BCTV resistant lines to develop populations with multiple traits. Hybrids were self-pollinated to produce populations for genetic mapping and elite germplasm selection. Gene pyramiding for BCTV resistance was started by crossing different BCTV resistances sources guided by the dataset of differentially expressed genes. Mutant breeding line (KEMS12-FP17) proved to be frost tolerant and survived over winter in Idaho without bolting in two seasons of experiments. This line is a potential genetic source of winter-beet germplasm and has been hybridized to other breeding lines to incorporate the non-bolting trait into BCTV resistance and high sucrose parental lines. DNA markers were used to genotype this line. DNA markers differentiating between the non-bolting mutant line from mother plants were identified. F2 mapping population was developed to genetically map the non-bolting trait in public germplasm. Substantial progress has been made with whole genome sequencing of elite germplasm lines for genetic variation analysis of Rhizoctonia crown and root rot resistance.
For Objective 2, significant progress was made on dissecting disease development pathways, host-pathogen interactions, and designing improved disease management strategies. The interaction of various Leuconostoc haplotypes versus a genetically diverse range of R. solani strains was investigated. Under Sub-objective 2.1, the synergistic interaction between any Leuconostoc strain and the R. solani AG-2-2 IIIB strains allowed for the most rot to occur. Root tissue pH was 6.2 to 6.4 with < 2 millimeter of rot and 4.0 to 4.2 in tissue with >30 millimeter of rot. Individually, both the bacterial (Leuconostoc) and fungal (R. solani) strains primarily led to minor rot (8 millimeter or less) that was not significantly different from the non-inoculated water check (0 millimeter). On the other hand, 19 of the 20 treatments with the most rot were R. solani-Leuconostoc combination treatments. Both the isolation data and tissue pH suggest Leuconostoc spp. and subsequent bacterial and yeast contaminants were present in the rotted root tissue. However, without R. solani AG-2-2 strains being present when internal rot initiates, Leuconostoc strains did very little damage. Under Sub-objective 2.2, primers and dsRNA protocols were established to investigate the use of RNA interference (RNAi) for the control of BCTV. An initial small experiment in the greenhouse had promising results and will be increased to a full-scale study once the new greenhouse is available in 2020. Under Sub-objective 2.3, different insecticide chemistries were investigated for the management of curly top and pests on sugar beet. Seven insecticide chemistries were compared for their ability to manage curly top, versus two commercial products and a non-treated check. Some chemistries could significantly reduce curly top symptoms compared to the non-treated check, but none of the chemistries provided similar control and yield as the commercial products. A natural infestation of black bean aphids allowed control of this pest to be evaluated versus the different chemistries as well. As expected, the commercial seed treatment, Poncho, provided excellent aphid control, but unexpectedly the Truvia (a sugar substitute from the grocery store) also provided a significant reduction in the percentage of plants with aphid colonies. Truvia likely does not have a future for aphid control on sugar beets since good chemistries already exist for aphid control. However, our University of Idaho collaborator will investigate the possibility of utilizing Truvia for aphid control in organic and home owner production systems.
Accomplishments
1. Synergistic interaction of Rhizoctonia and Leuconostoc leads to rot in sugar beet. Late season Rhizoctonia root rot in sugar beet can lead to complete yield loss in Idaho. Previous research indicated that the most severe damage occurred when Leuconostoc was also present. Studies were conducted by ARS researchers in Kimberly, Idaho, to better understand the interaction of this fungus and bacteria. Both isolations and tissue pH suggest late season sugar beet root rot is primarily associated with Leuconostoc and secondary organisms; however, damage was minor unless both Rhizoctonia and Leuconostoc were present when internal rot initiates. Thus, if adequate resistance to Rhizoctonia is present in sugar beet, little or no rot will be caused by Leuconostoc or other secondary organisms. These results emphasize the need for incorporating good Rhizoctonia resistance into commercial sugar beet cultivars.
Review Publications
Strausbaugh, C.A. 2018. Incidence, distribution, and pathogenicity of fungi causing root rot in Idaho long-term sugar beet storage piles. Plant Disease. 102(11):2296-2307. https://doi.org/10.1094/PDIS-03-18-0437-RE.
Strausbaugh, C.A. 2019. Commercial sugar beet cultivars evaluated for rhizomania resistance and storability in Idaho, 2017. Plant Disease Management Reports. 13:CF048.
Strausbaugh, C.A. 2019. Experimental sugar beet cultivars evaluated for rhizomania resistance and storability in Idaho, 2017. Plant Disease Management Reports. 13:CF049.
Strausbaugh, C.A., Hellier, B.C. 2019. Beet curly top resistance in USDA-ARS Plant Introduction Lines, 2018. Plant Disease Management Reports. 13:CF050.
Strausbaugh, C.A., Fenwick, A.L. 2019. Beet curly top resistance in USDA-ARS Ft. Collins germplasm, 2018. Plant Disease Management Reports. 13:CF051.
Strausbaugh, C.A., Wenninger, E.J. 2019. Foliar insecticides for the control of curly top in Idaho sugar beet, 2018. Plant Disease Management Reports. 13:CF052.
Strausbaugh, C.A., Hellier, B.C. 2018. Rhizomania and storage rot resistance in USDA-ARS plant introduction lines evaluated in Idaho, 2017. Plant Disease Management Reports. 12:CF155.
Strausbaugh, C.A., Fenwick, A.L. 2018. Ft. Collins sugar beet germplasm evaluated for rhizomania and storage rot resistance in Idaho, 2017. Plant Disease Management Reports. 12:CF154.
Dugan, F.M., Strausbaugh, C.A. 2019. Catalog of Penicillium spp. causing blue mold of bulbs, roots, and tubers. Mycotaxon. 134(1):197-213. https://doi.org/10.5248/134.197.
Eujayl, I.A., Strausbaugh, C.A. 2018. Kimberly sugar beet germplasm evaluated for rhizomania and storage rot resistance in Idaho, 2017. Plant Disease Management Reports. 12:CF153.
Eujayl, I.A., Strausbaugh, C.A. 2018. Beet curly top resistance in USDA-ARS Kimberly germplasm lines evaluated in Idaho, 2017. Plant Disease Management Reports. 12:CF152.
