Registration of Oilseed Sunflower Germplasms HA‐BSR6, HA‐BSR7, and HA‐BSR8 Highly Resistant to Sclerotinia Basal Stalk Rot and Downy Mildew

Sclerotinia basal stalk rot (BSR) and downy mildew (DM) are agronomically important diseases of sunflower (Helianthus annuus L.) worldwide. Three sunflower germplasm lines, HA‐BSR6 (Reg. no. GP‐353, PI 685019), HA‐BSR7 (Reg. no. GP‐354, PI 685020), and HA‐BSR8 (Reg. no. GP‐355, PI 685021), were developed with dual resistance to both BSR and DM. Their resistance to BSR was transferred from the wild annual sunflower H. praecox subsp. runyonii Engelmann & A. Gray (Heiser) (PI 468853), and DM resistance was introgressed from inbred line HA 458 possessing the Pl17 gene. The germplasms were tested for BSR resistance in inoculated field trials in multiple locations over 4 yr. All three germplasm lines showed significantly higher BSR resistance (p < 0.05) than the recurrent parent and the checks across environments, with a 4‐yr mean disease incidence (DI) ranging from 1.2 to 4.8%, while ‘Cargill 270’ (susceptible hybrid check) and HA 89 (recurrent parent) had DI of 36.1 and 31.0%, respectively, and HA 441 (resistant inbred check) and ‘Croplan 305’ (resistant hybrid check) had DI of 19.5 and 11.6%, respectively. Whole genome scan using genotyping‐by‐sequencing revealed the presence of H. praecox subsp. runyonii chromosome segments in HA‐BSR6, HA‐BSR7, and HA‐BSR8, which are potentially associated with BSR resistance. Phenotypic evaluation identified DM resistance in all three germplasm lines, with flanking DNA markers confirming the presence of the Pl17 gene in the lines. These germplasm lines can be used in sunflower breeding programs for pyramiding both BSR and DM resistance genes.