Development and characterization of a new sunflower source of resistance to race G of Orobanche cumana Wallr. derived from Helianthus anomalus.

Key message: A new OrAnom1 gene introgressed in cultivated sunflower from wild <bold>Helianthus anomalus</bold>confers late post-attachment resistance to<bold>Orobanche cumana</bold> race G and maps to a target interval in Chromosome 4 where two receptor-like kinases (RLKs) have been identified in the<bold>H. anomalus</bold>genome as putative candidates. Sunflower broomrape is a parasitic weed that infects sunflower (Helianthus annuus L.) roots causing severe yield losses. Breeding for resistance is the most effective and sustainable control method. In this study, we report the identification, introgression, and genetic and physiological characterization of a new sunflower source of resistance to race G of broomrape developed from the wild annual sunflower H. anomalus (accession PI 468642). Crosses between PI 468642 and the susceptible line P21 were carried out, and the genetic study was conducted in BC1F1, BC1F2, and its derived BC1F3 populations. A BC1F5 germplasm named ANOM1 was developed through selection for race G resistance and resemblance to cultivated sunflower. The resistant trait showed monogenic and dominant inheritance. The gene, named OrAnom1, was mapped to Chromosome 4 within a 1.2 cM interval and co-segregated with 7 SNP markers. This interval corresponds to a 1.32 Mb region in the sunflower reference genome, housing a cluster of receptor-like kinase and receptor-like protein (RLK-RLP) genes. Notably, the analysis of the H. anomalus genome revealed the absence of RLPs in the OrAnom1 target region but featured two RLKs as possible OrAnom1 candidates. Rhizotron and histological studies showed that OrAnom1 determines a late post-attachment resistance mechanism. Broomrape can establish a vascular connection with the host, but parasite growth is stopped before tubercle development, showing phenolic compounds accumulation and tubercle necrosis. ANOM1 will contribute to broadening the genetic basis of broomrape resistance in the cultivated sunflower pool and to a better understanding of the molecular basis of the sunflower-broomrape interaction. [ABSTRACT FROM AUTHOR]