Project : USDA ARS

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Research Project: Genetic Enhancement of Sunflower Yield and Tolerance to Biotic Stress

Location: Sunflower and Plant Biology Research

2020 Annual Report

Objectives
OBJECTIVE 1: Develop and release sunflower germplasm and inbred lines with enhanced yield potential, desirable oil traits, or resistance to crop pests (insects and pathogens), along with effective molecular markers. Subobjective 1A: Develop genetic markers for Phomopsis, rust, and downy mildew resistance. Subobjective 1B: Characterize genetic and pathogenic variation in Phomopsis populations in North Central sunflower growing regions. Subobjective 1C: Evaluate diverse interspecific germplasm for resistance to Phomopsis, rust, and downy mildew. Subobjective 1D: Develop pre-breeding and advanced germplasm with novel traits or combinations of agronomically important traits. OBJECTIVE 2: Identify and characterize traits associated with resistance to insect pests and improved sunflower-pollinator interactions, and evaluate their effectiveness in insect management systems. Subobjective 2A: Evaluate susceptibility of sunflowers to insect pests and develop genetic markers for host plant resistance traits. Subobjective 2B: Assess variation and develop genetic markers for traits associated with pollinator visitation.

Approach
The economic impact of sunflower production in the United States is at least $1.5 billion per year. In the primary sunflower production areas, sunflower must compete with genetically-modified crops like corn and soybean that can be easier to produce or have more consistent yields. To maintain its position as a valuable rotational crop and ensure a consistent supply of heart-healthy oil, both maximum yield and consistency of yield must be improved. Losses from diseases and insect pests, along with related costs of management, are primary challenges for improving sunflower yields. Proposed research aims to improve resistance to diseases and insect pests and combine these traits with herbicide resistance, improved oil content and quality to create a more competitive crop. Specific objectives are to: (1) develop genetic markers for resistance to three major sunflower pathogens, (2) understand genetic and pathogenic variation for a disease that has recently increased in incidence and severity, (3) search for new sources of disease resistance from crop wild relatives of cultivated sunflower, (4) identify and characterize traits that will provide resistance to insect pests or improve sunflower-pollinator interactions (which positively contribute to yields), and (5) combine desired traits for pest resistance with other important agronomic traits to create superior germplasm. Success in these objectives will allow higher, more consistent yields and reduce costs of production, contributing to a stable supply of oil and non-oil sunflowers that supports profitable farming.

Progress Report
Subobjective 1A: Develop genetic markers for Phomopsis, rust, and downy mildew resistance. A population created in the prior year (HA 89 x HA 378) was advanced to F3 generation as a step towards quantitative trait loci (QTL) mapping of Phomopsis resistance. Mapping of a rust resistance gene from South African sunflower line KP199 was completed using phenotypic data from 130 F3 families tested for susceptibility to rust race 336. Linkage analysis of single nucleotide polymorphism (SNP) markers with rust phenotyping data placed the rust resistance gene, named R18, on sunflower chromosome 13 within an interval of 3.6 centimorgans. Pedigree selection was used to develop homozygous resistant germplasms. HA-R18 carrying rust R gene R17 and HA-R19 carrying rust R gene R18 were selected from two heterozygous South African sunflower lines, after testing against 11 common and virulent rust races, were shown to be resistant to eight and nine races, respectively. Subobjective 1B: Characterize population structure and genetic variation within and among populations of Phomopsis helianthi in the Northern Great Plains. The second and final year of Phomopsis isolate collection was completed. Across two years of sampling, a total of 300 stem lesions were collected from ten sunflower fields per state in North Dakota, South Dakota, and Minnesota. Three fields, located in Staples, Glyndon, and Crookston, Minnesota, were selected for hierarchical sampling of Phomopsis stalk lesions. Across all regional and hierarchical sampling, isolation of the fungal pathogen was successful for 374 stalk lesions and fungal DNA was successfully extracted for all isolated fungal samples. Species-specific primers were used to identify the Diaporthe species isolated from lesions, with 345 identified as Diaporthe helianthi, confirming this species is the most common cause of Phomopsis stem canker in the primary sunflower growing area of the United States. Of the remaining 29 samples, 24 were identified as D. gulyae, three lesion samples contained both D. helianthi and D. gulyae, and two were identified as the soybean stem canker species D. phaseolorum. DNA quantity and quality were evaluated and DNA from a total of 285 isolates from regional and hierarchical sampling were submitted for genotyping-by-sequencing. Subobjective 1C: Evaluate diverse interspecific germplasm for resistance to Phomopsis, rust, and downy mildew. The second year of field screening of 75 interspecific germplasms at two locations for resistance to Phomopsis stem canker was completed. Preliminary results identified lines with diverse genetic backgrounds for further testing. Replicated greenhouse screening for new sources of rust and downy mildew resistance genes against the most virulent races evaluated 128 interspecific germplasms. Preliminary results for rust resistance identified three promising lines with high levels of resistance and other germplasms segregating for resistance. Two germplasm lines were identified with total resistance to the most virulent downy mildew race and eight amphiploid lines derived from perennial species that were segregating for resistance. Subobjective 1D: Develop pre-breeding and advanced germplasm with novel traits or combinations of agronomically important traits. Nearly 4,000 nursery rows of high yield, high oil, disease, insect-, and herbicide-resistant sunflower experimental lines were grown in nurseries in Fargo, North Dakota, and Chile, with yield trials of experimental hybrids from these lines also grown at several locations throughout the sunflower growing region. Of these, we are in the process of developing release dockets for several Sclerotinia and Phomopsis resistant sunflower lines of both heterotic groups, downy mildew resistant lines, and early maturing lines suitable for double cropping in the southern and central plains, and late planting in the northern plains. Last year, insect resistant lines HA 488 with red sunflower seed weevil insect resistance, and HA 489 with resistance to banded sunflower moth were released. Both of these pests are common throughout the sunflower growing region, and the resistance is combined in these lines with other traits including high oleic acid, disease resistance, and herbicide tolerance. Subobjective 2A: Evaluate susceptibility of sunflowers to insect pests and develop genetic markers for host plant resistance traits. A second year of testing was completed on possible inbred line resistance to the red sunflower seed weevil. Using data from two years of artificial infestations with 30 weevils per plant, results showed 80% less seed damage for entry 14-121 (now HA 488) versus 13 previously released inbred lines. The use of HA 488 as a hybrid parent should permit reductions in seed weevil damage while maintaining compatibility with other management methods including insecticides. One additional year of data was collected on pericarp thickness from each of two existing mapping populations, and a second year of data on damage by seed-feeding caterpillars was collected for one population. Work on mapping the pericarp trait and testing its association with resistance to insect feeding is underway. Subobjective 2B: Assess variation and develop genetic markers for traits associated with pollinator visitation. Additional data were collected on floret size, the trait best associated with wild pollinator visitation in North Dakota, and seed size in a large mapping population. Across different locations and years, phenotypic traits were influenced primarily by genotype, secondarily by environment, with no significant genotype x environment effect. Seed and floret size exhibited a moderate phenotypic correlation, but quantitative trait loci (QTL) mapping indicates that the genetic bases for these two traits are mostly independent. This means that breeding for large seeds (required for confectionery sunflower) may be possible while preserving a moderate floret size, which promotes bee visitation and improved pollination.

Accomplishments
1. Genetic mapping of traits associated with pollinator visitation and yield quality in sunflowers. Pollination by wild bees increases yields of both oilseed and confection sunflowers. Because bees prefer sunflowers with shorter florets for easier nectar access, and seed size (length and width) is important in the confection sunflower market, ARS scientists in Fargo, North Dakota, and colleagues at University of Colorado-Boulder mapped genes associated with floret size and seed size in cultivated sunflowers. Though floret depth and seed length are correlated, trait mapping found the genetic bases for these two traits are largely independent. Markers developed for seed and floret size will improve private- and public-sector breeding by allowing easier selection of lines that are attractive to bees, but also have desirable seed size and shape for the confection sunflower market.

2. Mapping of Phomopsis stem canker resistance in sunflower. Phomopsis stem canker (PSC) is an emerging disease threatening global sunflower production but currently there are no effective fungicides and only limited genetic resistance. Incorporating genetic resistance is the most economical and sustainable strategy for disease management to effectively prevent crop loss. ARS scientists in Fargo, North Dakota, using marker-trait analysis discovered 15 quantitative trait loci (QTL) associated with PSC resistance on 11 sunflower chromosomes. Single nucleotide polymorphism (SNP) markers for the locations contributing to PSC resistance should allow marker-assisted selection for sunflower protected from this disease.

3. Development of sunflower lines with resistance to necrotrophic pathogens. Sclerotinia head and stalk rots, and Phomopsis stem canker, are prolific diseases in much of the U.S. sunflower production region, with large losses in yield and crop quality. ARS scientists in Fargo, North Dakota, along with researchers at South Dakota State University, North Dakota State University, and University of Colorado reviewed the literature and found a correlation of increased yearly precipitation and changing landscape use with increased Phomopsis stem canker incidence, but not Sclerotinia incidence. To reduce the presence of these major diseases in environments that are becoming wetter, ARS scientists also deployed resistance to these diseases via new inbred line germplasms, together with genes for herbicide tolerance, high oleic acid in the seed oil, downy mildew resistance, and high yield and oil content. Ten sunflower lines were released and registered with diversity in pedigree in order to provide a broad base of germplasm to industry breeders for incorporation of higher levels of necrotrophic pathogen resistance into modern sunflower hybrids.

4. Discovery and mapping of the two new rust resistance genes. Sunflower rust is a serious fungal disease in sunflower worldwide, with an increasing importance in North America due to new pathogen races. Because emergence of novel pathogen virulence has rendered most commercial sunflower hybrids susceptible to rust, there is a need to discover novel rust resistance genes for long-term management. ARS scientists in Fargo, North Dakota, have identified two sunflower lines, KP193 and KP199 introduced from South Africa, that are resistant to rust in a heterozygous condition. Mapping placed the two rust resistance genes, R17 from KP193 and R18 from KP199, on sunflower chromosome 13. Two homozygous resistant lines selected from KP193 and KP199 were developed with resistance to the most common and virulent rust races, providing valuable germplasms for use in breeding programs.

5. Wild sunflower as an alternate source of hydrocarbons. Increased attention has been given to the need for developing plant species as biorenewable sources of fuels, chemicals, feeds, and other important materials. These developments could reduce our nation's dependency on foreign sources of many strategic and essential materials. Perennial crop wild relatives of sunflower have been suggested as a potential source of hydrocarbons. Scientists from ARS in Fargo, North Dakota, and Baylor University found four perennial species from the Northern Great Plains had lower hydrocarbon content in the leaves compared to previous studies of annual species. However, there were individuals in some populations with useful levels of total hydrocarbons for breeding and selection, suggesting potential for wild perennial sunflowers to be developed as sources of renewable hydrocarbons.

U.S. DEPARTMENT OF AGRICULTURE

Sunflower and Plant Biology Research: Fargo, ND