Genetic and physiological characterization of sunflower resistance provided by the wild-derived OrDeb2 gene against highly virulent races of Orobanche cumana Wallr

Abstract

Key message OrDeb2 confers post-attachment resistance to Orobanche cumana and is located in a 1.38 Mbp genomic interval containing a cluster of receptor-like kinase and receptor-like protein genes with nine high-confidence candidates. Abstract Sunflower broomrape is a holoparasitic angiosperm that parasitizes on sunflower roots, severely constraining crop yield. Breeding for resistance is the most effective method of control. OrDeb2 is a dominant resistance gene introgressed into cultivated sunflower from a wild-related species that confers resistance to highly virulent broomrape races. The objectives of this study were as follows: (i) locate OrDeb2 into the sunflower genome and determine putative candidate genes and (ii) characterize its underlying resistance mechanism. A segregating population from a cross between the sunflower resistant line DEB2, carrying OrDeb2, and a susceptible line was phenotyped for broomrape resistance in four experiments, including different environments and two broomrape races (FGV and GTK). This population was also densely genotyped with microsatellite and SNP markers, which allowed locating OrDeb2 within a 0.9 cM interval in the upper half of Chromosome 4. This interval corresponded to a 1.38 Mbp genomic region of the sunflower reference genome that contained a cluster of genes encoding LRR (leucine-rich repeat) receptor-like proteins lacking a cytoplasmic kinase domain and receptor-like kinases with one or two kinase domains and lacking an extracellular LRR region, which were valuable candidates for OrDeb2. Rhizotron and histological studies showed that OrDeb2 determines a post-attachment resistance response that blocks O. cumana development mainly at the cortex before the establishment of host-parasite vascular connections. This study will contribute to understand the interaction between crops and parasitic weeds, to establish durable breeding strategies based on genetic resistance and provide useful tools for marker-assisted selection and OrDeb2 map-based cloning.

Wild Helianthus species: A reservoir of resistance genes for sustainable pyramidal resistance to broomrape in sunflower

“…tardiflorus tested in this study did not induce germination, the exudates of the introgressed line DEB2 (with the resistance gene Or DEB2 introgressed from H. debilis subsp. tardiflorus ) induced germination ( Fernandez-Aparicio et al., 2022 ). This was probably because this specific resistance mechanism was not evaluated in the selection and introgression process aimed at developing the DEB2 line, in which only emerged broomrapes were phenotyped.…”

“…Five accessions were used as susceptible controls for the pot experiments in the first 2 assays (No. 1 to 2): NR5 (an inbred line carrying the gene HaOr5 that provides resistance to race E; Tang et al., 2003 ); Hybrid 2 ( Martín-Sanz et al., 2016 ), a commercial hybrid widely used in Southern Spain resistant to race F and susceptible to race G-GV (from Spain); P96, an inbred line resistant to races F and G-GV and susceptible to populations of race G from Eastern Europe ( Martín-Sanz et al., 2016 ); LP2 (an inbred line carrying the gene HaOr7 that confers resistance to race F and also incomplete resistance to populations of race G; Duriez et al., 2019 ), and Deb2 (an inbred line carrying the gene HaOr deb2 , and resistant to race G; Fernandez-Aparicio et al., 2022 ). In the assay No.…”

“…Nowadays, the most virulent races appeared in Eastern Europe and Spain, and were classified as G or H ( Antonova et al., 2013 ; Kaya, 2014 ; Martín-Sanz et al., 2016 ). Genetic studies have revealed other resistances such as QTL to races F and G ( Pérez-Vich et al., 2004 ; Louarn et al., 2016 ; Imerovski et al., 2019 ), or more recently single resistant genes to race G such as Or SII ( Martin-Sanz et al., 2020 ) and Or Deb 2 ( Fernandez-Aparicio et al., 2022 ). The only sunflower resistance gene identified so far is HaOr7 encoding for a Leucine-Rich-Repeat Receptor-Like Kinase ( Duriez et al., 2019 ).…”

“…However, in some studies, phenotyping was done in rhizotrons (small culture boxes) at early stages of resistance. Thus, it was shown that the HaOr7 resistance gene ( Duriez et al., 2019 ) and Or Deb2 ( Fernandez-Aparicio et al., 2022 ) led to resistance at the 2 nd stage leading to incompatible attachments for which vascular connections were not established. Tubercle necrosis was shown in the resistant line LR1 ( Labrousse et al., 2001 ; Louarn et al., 2016 ).…”

“…Incompatible attachments were associated with host defense responses at the tip of the haustorium, with an accumulation of phenolic compounds ( Echevarria-Zomeño et al., 2006 ). An encapsulation layer around the haustorium ( Dörr et al., 1994 ; Labrousse et al., 2001 ; Fernandez-Aparicio et al., 2022 ) and a gum-like substance deposition in host xylem vessels or the modifications of xylem cell walls preventing haustorium development and vascular connection, have been shown in some resistant accessions ( Dörr et al., 1994 ; Labrousse et al., 2001 ). Incompatible attachments were also associated with callose deposition, suberization, and protein cross-linking at the interface between parasite and host cells ( Echevarria-Zomeño et al., 2006 ).…”