Location: Northwest Irrigation and Soils Research2018 Annual Report
1. Identify molecular markers and their genetic map positions for priority sugar beet traits, including host plant resistance to curly top, root rots, and abiotic stresses. [NP301, C1, PS1B] 1.1. Whole genome re-sequencing of sugar beet public breeding line KDH13 for genetic variation analysis. 1.2. Identify a large representative set of single nucleotide polymorphism (SNP) markers for genotyping of mapping populations and germplasm. 1.3. Construct high density genetic linkage map to identify DNA markers closely linked to genes regulating resistance to curly top. 2. Improve germplasm screening procedures for host plant resistance, and incorporate disease management options into production practices through enhanced understanding of plant pathogen etiology and interactions with host resistance, pests, and abiotic stresses. [NP303, C3, PS3A] 2.1. Investigate curly top species variation and/or the presence of new curly top species in sugar beet. 2.2. Refine management strategies for curly top and pest control in sugar beet. 2.3. Establish the etiology and management options for an Athelia-like fungus associated with stored sugar beet roots. 2.4. Characterize and exploit the interaction of Rhizoctonia solani and Leuconostoc mesenteroides in sugar beet root rot to improve disease management options. 2.5. Determine the effect of rhizomania in the field on freeze damage to sugar beet roots in storage. 3. Identify novel sources of host plant resistance to diseases (curly top, rhizomania, and root rots), storage, and abiotic stresses (drought and frost), and incorporate them into adapted germplasm. [NP301, C1, PS1A]
Establish a research program to coordinate, interact and collaborate with university scientists to provide sustainable integrated disease and pest management strategies for sugar beet. New sugar beet germplasm with enhanced disease resistance and agronomic qualities will be developed, along with innovative and improved disease management strategies. Specific focus has been placed on alleviating crop losses due to curly top, rhizomania, root rots, spoilage during storage, and seedling frost injury. Genetic research will identify molecular markers associated with curly top resistance and establish their genetic map position. Understanding the etiology of pathogens associated with curly top, rhizomania, root rots, and storage losses, i.e., fungal decay, will lead to improved disease management options and screening methods. Using genetic methods with germplasm from the disease screening nurseries (curly top, rhizomania, Rhizoctonia-bacterial root rot, and storage), we will identify novel genes regulating traits of interest ultimately leading to public release of improved germplasm. New germplasm will be used by the sugar beet industry to enhance disease resistance and improve yields in commercial cultivars. The new genetic and pathogen knowledge generated will also allow our stakeholders to reduce losses by improved disease and postharvest storage management.
This is the final report for project 2054-21220-004-00D, which has been replaced by project 2054-21220-005-00D, "Development of Elite Sugar Beet Germplasm Enhanced for Disease Resistance and Novel Disease Management Options for Improved Yield." In support of Objective 1, the whole genome sequence of a breeding line (KDH13) that is resistant to beet curly top disease was sequenced. This was the first publicly released sugar beet genome sequence with resistance to beet curly top. This data is readily available so scientists can conduct in-depth genomic analysis to identify genes that regulate beet curly top. Differentially expressed genes due to infection with three strains of beet curly top virus were identified using the genomic sequence data in combination with RNA sequencing data. DNA markers from genic regions or genes that regulate beet curly top virus resistance were developed. Specifically, a large pool of differentially expressed gene-transcripts were identified from a gene family (CRK-8) that showed consistent overexpression due to infection with the three sugar beet curly top virus strains. Specific hybridity-test markers were developed to identify hybrids in the absence of morphological markers between parental lines. The deployment of these markers expedited the identification of hybrids as well as backcrossing between many parental lines. In Objective 2, a survey of beet curly top virus conducted in Kimberly, Idaho, from 2012 to 2015 determined that there was a shift from the severe strain of the virus being dominant in commercial sugar beet fields in 2006 to being undetectable at times from 2012 to 2015. A total of 11 beet curly top virus strains were identified, including the new Kimberly1 strain. The California/Logan, Colorado, and Worland beet curly top virus strains were found to predominate from 2012 to 2015 in commercial sugar beet fields. This shift in the dominate virus strains in commercial sugar beet fields demonstrated the need to include these virus strains when screening plants for resistance and developing new varieties. Seed and foliar insecticide treatments were investigated for the control of beet curly top virus in sugar beet. Poncho seed treatment was still fully effective at protecting plants from the beet curly top virus vector up to 59 days after planting. The pyrethroid foliar treatments tested were also effective at controlling the beet curly top virus vector when applied seven days before and after release of the vector. The seed and foliar treatments reduced symptoms by at least 22% and increased sugar yields at least 13%. Seed treatment is an effective way to supplement host resistance for early-season control of beet curly top virus in sugar beet. The pyrethroid foliar applications can be used to extend midseason control of curly top and reduce the potential for beet curly top virus to become resistant to the seed treatment. Disease problems in the field can negatively affect the storage of sugar beet roots, leading to multi-million dollar losses of recoverable sugar. The primary fungi associated with rot of sugar beet roots in storage were identified as Botrytis cinerea, Penicillium spp., and an Athelia-like sp. This research identified a new Penicillium species that was designated Penicillium cellarum Strausbaugh & Dugan. The primary fungal pathogen on roots in indoor piles was B. cinerea, but the incidence of the fungi in outdoor piles varied with location and year, and some outdoor piles had almost no fungal growth. These data emphasize that given the right location, mechanical control measures alone are adequate for managing fungal root rots even after 120 days in storage under ambient conditions. Additional research determined that the fungicides Propulse and Stadium effectively controlled fungal rots of sugar beet roots for up to 148 days in storage. Treated roots had 85 to 100% less fungal growth and had 14 to 46% less sucrose loss compared to untreated roots. Follow-up studies are being conducted to optimize application rates and methods for stored sugar beets. A thorough investigation of the interaction between Rhizoctonia solani and Leuconostoc was conducted. A total of 203 Leuconostoc isolates were collected from recently harvested sugar beet roots in southern Idaho and southeastern Oregon during 2010 and 2012. In pathogenicity field studies with a commercial sugar beet cultivar, all Leuconostoc isolates caused more rot when combined with R. solani than when inoculated alone both years. This synergistic interaction demonstrates that new management options for controlling this root disease problem need to address both Rhizoctonia solani and Leuconostoc. Rhizomania caused by beet necrotic yellow vein virus (BNYVV) is a major yield-limiting disease of sugar beet that also influences the ability of roots to resist freezing. Sugar beet roots from a BNYVV susceptible cultivar that was grown in a field with high levels of virus had no frozen tissue at -2 degrees Celsius (C), 7% to 63% frozen tissue at -3 degrees C and 63% to 90% frozen tissue at -4 degrees C. This same cultivar grown in a field with only a trace amount of virus has no frozen tissue at -3 degrees C and 13% to 27% frozen tissue at -4 degrees C. The BNYVV resistance cultivars did not have any significant frozen tissue until temperature decreased to -4 degrees C. Consequently, beet necrotic yellow vein virus will, not only lead to yield loss in susceptible sugar beet cultivars, but will also lead to more frozen root tissue even in some BNYVV resistant cultivars if the temperature decreases to -4 degrees C. Based on these observations, the air used to cool sugar beet roots in non-frozen piles throughout the winter should be greater than -3 degrees C to minimize sucrose loss. Related to Objective 3, a total of six new sugar beet germplasm has been released to public and private sugar beet breeders between 2014 and 2017. Two parental lines (KEMS-09 and KEMS-12) were released with high resistance to Rhizomania and powdery mildew. A homozygous doubled haploid line (KDH4-9) was released with differential resistance to curly top strains. Additionally, three parental lines (KEMS-6, KEMS6-600 and KEMS-08) with resistance to Cercospora leaf spot and Fusarium Yellows were released. New high sucrose elite germplasm (KPS24 and KPS25) were identified and used in hybridization schemes with other parental lines to combine important traits such as curly top resistance and bolting resistance. Fall planting of sugar beet will extend the growing season leading to higher sucrose yields but requires germplasm with both frost tolerance and bolting resistance. A mutant line (KEMS12-FP17) was identified as frost tolerant and bolting/flowering resistant. Only 28% of the plants of this mutant line bolted, while 100% of the commercial check cultivar bolted. This line will serve as a parental line for hybridization to combine bolting resistance and frost tolerance to other economically important traits such as high sucrose and disease resistance traits in commercial sugar beet cultivars.
1. Incidence and distribution of fungi in sugar beet storage piles. Fungal rots in sugar beet roots held in long-term storage can lead to millions of dollars in sucrose loss, but the incidence and distribution of fungal rots inside sugar beet piles and pathogenicity of some species is poorly understood. ARS researchers at Kimberly, Idaho, determined that the primary fungi associated with sugar beet storage rot in Idaho were Botrytis cinerea, Penicillium spp., and an Athelia-like sp. The Penicillium sp., P. cellarum, and the Athelia-like sp. were fungi first reported by this research group in earlier investigations. The primary fungal pathogen on roots in indoor piles was B. cinerea, but the incidence of the fungi in outdoor piles varied with location and year; however, almost complete control of fungal growth in some outdoor piles could be achieved with the combination of tarps, ventilation pipe, and finding a location with access to cool ambient air. These data emphasize that, given the right location, mechanical control measures alone are adequate for management of fungal root rots even after 120 days in storage under ambient conditions.
2. Rhizomania increases freezing damage on sugar beet roots in storage. Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) is a major yield-limiting disease of sugar beet that was found to also influence the roots' ability to resist freezing. When comparing roots grown in soil with high BNYVV levels compared with those grown with trace levels, ARS researchers at Kimberly, Idaho, determined that sugar beet roots of a BNYVV susceptible cultivar had more frozen tissue at both -3 degrees Celsius (C) (7% to 63% with high BNYVV and 0% with trace) and -4 degrees C (63% to 90% with high BNYVV and 13% to 27% with trace). No increase in frozen tissue occurred at higher temperatures or with BNYVV resistant cultivars. Consequently, BNYVV will not only lead to yield and sucrose loss in susceptible sugar beet cultivars, but also to more frozen root tissue as temperatures drop below -2 degrees C. Based on these observations, the air used to cool sugar beet roots in non-frozen piles throughout the winter should not drop below -2 degrees C to maximize sucrose retention.
3. Flowering resistance in sugar beet. Commercial sugar beet hybrid cultivars are bred as bolting resistant and usually do not get exposed to lower temperatures when planted in late spring. However, if the cultivars had bolting resistance and frost tolerance, they could be planted in the fall and have higher yield potential. ARS researchers in Kimberly, Idaho, identified a mutant line that could be planted in September in Kimberly, Idaho, survive the winter, and continue to grow in the spring. Only 28% of the plants bolted in the mutant line, while 100% of the plants bolted in the commercial check cultivar. This line provides a starting point to establish a combination of bolting resistance and frost tolerance in commercial sugar beet cultivars.
4. Resistance to Cercospora leaf spot and Fusarium Yellows in sugar beet. Cercospora leaf spot (CLS) is a yield-limiting sugar beet fungal disease that is prevalent in areas where relative humidity is conducive to fungal infection on leaves. ARS researchers in Kimberly, Idaho, in collaboration with sugar beet seed industry researchers, identified three breeding lines that had better tolerance to CLS compared to all current commercial cultivars. Additionally, the same breeding lines expressed high resistance to Fusarium yellows, a soil borne fungal disease. These lines may allow for better CLS and Fusarium yellows resistance in commercial sugar beet cultivars.