Mónica Fernández-Aparicio, Lidia del Moral, Stéphane Muños, Leonardo Velasco & Begoña Pérez-Vich

Theoretical and Applied Genetics; Feb. 2022; vol. 135: 501–525

Key message

Or_Deb2 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. Or_Deb2 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 Or_Deb2 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 Or_Deb2, and a susceptible line was phenotyped for broomrape resistance in four experiments, including different environments and two broomrape races (F_GV and G_TK). This population was also densely genotyped with microsatellite and SNP markers, which allowed locating Or_Deb2 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 Or_Deb2. Rhizotron and histological studies showed that Or_Deb2 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 Or_Deb2 map-based cloning.

See https://link.springer.com/article/10.1007/s00122-021-03979-9

Fig.1: Linkage map of sunflower chromosome (Chr) 4 containing the Or_Deb2 gene. The ORS prefix denote SSR marker loci; the SFW prefix, SNP marker loci mapped by Bowers et al. (2012); the AX prefix, SNP marker loci from the 600 k AXIOM® array developed at LIPME-INRAE (Toulouse, France); and the Iasnip prefix SNP markers developed in this study from sunflower NB-LRR resistance gene candidates. Left figure: complete map; right figure: refined map of the Or_Deb2 region. The cumulative distances in centiMorgans are shown at the left of each map