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Rust and downy mildew (DM) are detrimental diseases in global sunflower (Helianthus annuus L.) production. Disease often results in yield loss and reduced seed quality. Host resistance to DM and rust is mediated by single dominant genes in sunflower. To better utilize genetic resistance, gene pyramiding is a common practice in crop breeding to extend the durability and longevity of resistance. Two confection sunflower germplasm lines, HA‐R20 (Reg. no. GP‐387, PI 702361) and HA‐R21 (Reg. no. GP‐388, PI 702362), were developed using the pedigree breeding method and DNA marker‐assisted selection and released by the USDA‐ARS Sunflower and Plant Biology Research Unit in collaboration with the North Dakota Agricultural Experiment Station in September 2022. HA‐R20 is an F3‐derived F4 confection restorer selection from the cross of HA‐DM2 and HA‐R8, carrying rust resistance genes R12 and R15 and DM resistance gene PlArg. HA‐R21 is an F3‐derived F4 confection maintainer selection from the cross of HA‐DM3 and HA‐R8, carrying rust resistance genes R13a and R15 and DM resistance gene Pl17. Disease reaction and marker testing for DM and rust confirmed that both germplasms harbor DM and rust R genes in the homozygous condition and are resistant to all DM and rust races identified in North America to date. These multiple disease‐resistant lines will provide the sunflower industry with durable disease‐resistant sources for the continued improvement of the crop. Core Ideas: Two confection sunflower germplasms, HA‐R20 and HA‐R21, were developed by marker‐assisted selection.HA‐R20 (R12/R15/PlArg) and HA‐R21 (R13a/R15/Pl17) harbor two rust and one downy mildew R genes each.Both lines have durable resistance to all rust and downy mildew races identified to date. [ABSTRACT FROM AUTHOR]

Downy mildew (DM), caused by the obligate pathogen Plasmopara halstedii (Farl.) Berl. & de Toni, is a worldwide yield‐limiting disease of sunflower (Helianthus annuus L.). To obtain durable DM resistance in sunflower hybrids, there is a need to stack new resistance genes into the best available germplasm. The DM resistance genes Pl8, Pl17, and Pl18 were recently fine mapped to sunflower chromosomes 13, 4, and 2, respectively. The current study pyramided these genes into a single genotype by marker‐assisted selection. Three oilseed sunflower germplasms, HA‐DM9 (Reg. no. GP‐381, PI 700009), HA‐DM10 (Reg. no. GP‐379, PI 700004), and HA‐DM11 (Reg. no. GP‐380, PI 700005), are dual DM‐resistant germplasm lines developed and have been released by the USDA‐ARS, Sunflower and Plant Biology Research Unit in collaboration with the North Dakota Agricultural Experiment Station in 2021. The three lines, HA‐DM9 (Pl8Pl8/Pl17Pl17), HA‐DM10 (Pl8Pl8/Pl18Pl18), and HA‐DM11 (Pl17Pl17/Pl18Pl18), each stacked two different DM genes, providing broad resistance to all P. halstedii races identified in North America and Europe so far, and can be used in sunflower breeding programs to enhance DM resistance. Core Ideas: Three oilseed sunflower germplasms with dual resistance to downy mildew were developed using marker‐assisted selection.HA‐DM9, HA‐DM10, and HA‐DM11 each pyramided two different downy mildew R genes.All germplasms exhibit resistance to all known downy mildew races identified in North America and Europe. [ABSTRACT FROM AUTHOR]

A five year field trial evaluated 71 oilseed sunflower, Helianthus annuus L., accessions, 32 breeding lines, and 25 interspecific crosses for resistance to infestation by naturally occurring populations of the banded sunflower moth, Cochylis hospes Walsingham (Lepidoptera: Tortricidae), in North Dakota. Germplasm with resistance to attack by the banded sunflower moth and subsequent larval feeding damage in the seeds was identified. PI 251902 had less than 10% feeding damage per head in all five years of testing and less than 6% in three of the five years. PI 372259 and PI 170401 exhibited 12% or less seed damage in three years of evaluation and PI 253776 had only 3% damage in two of the three years and was the least damaged in 2004. Four other accessions (PI 170385, PI 291403, PI 494859, and PI 505651) revealed resistance in three of five years. A number of the interspecific crosses which were retested based on earlier results showed reduced seed damage in 2003, but subsequently exhibited much greater damage the following year due to higher populations of banded sunflower moth. Hybrid 894 was earlier used by others as a susceptible check; however, in the current investigation, this hybrid consistently had the lowest average seed damage from C. hospes feeding among the germplasm evaluated. Results from this investigation indicate that there is potential for developing resistant genotypes with reduced feeding injury that will help sunflower producers reduce yield loss due to the banded sunflower moth. In addition, plant resistance can effectively be combined with delayed planting to decrease densities of C. hospes, thus reducing crop losses without disrupting the control of the larvae by parasitoids. [ABSTRACT FROM AUTHOR]