Research on resistance to sunflower broomrape: an integrated vision

Abstract

-Sunflower broomrape (Orobanche cumana Wallr.) parasitization on sunflower was first observed at the end of the 19th century and has continued since then jeopardizing sunflower cultivation in many areas of Europe and Asia. A distinctive characteristic of the O. cumana-sunflower parasitic system is that it is mainly governed by a genefor-gene interaction. This determines complete resistance in the host controlled by dominant alleles at a single locus, which facilitates the management of the resistance for hybrid seed production. But on the other hand avirulence in the parasite is also controlled by dominant alleles at a single gene. Monogenic, dominant resistance exerts a strong selection pressure on the parasite that maximizes the probability of overcoming resistance mechanisms in a short period of time. This has in fact resulted in a number of physiological races that periodically surpass all the available resistance sources. The spread of populations to new areas and the subsequent hybridization between populations is another mechanism creating genetic diversity in sunflower broomrape and allegedly recombination of avirulences genes. After more than one century of coexistence, genetic resistance to broomrape in sunflower has to be focused under an integrated approach that considers not only the characterization of resistance mechanisms in the host, but also the genetic and physiological bases of avirulence in the parasite. From the perspective of genetic resistance in sunflower, most important is not relying only on single dominant genes, but following instead pyramiding strategies. These should give priority to combining complementary mechanisms of resistance under both qualitative (vertical) and quantitative (horizontal) genetic control. These aspects are discussed in the paper. Keywords:Avirulence genes / broomrape / genetic resistance / Orobanche cumana / sunflower Résumé -Recherche de résistance à l'orobanche chez le tournesol : une vision intégrée. Le parasitisme de l'orobanche du tournesol (Orobanche cumana Wallr) a été observé à la fin du 19 e siècle et a continué depuis lors, mettant en péril la culture du tournesol dans de nombreuses régions d'Europe et d'Asie. Une caractéristique spécifique de l'interaction O.cumana-Tournesol est qu'elle est principalement régie par une interaction gène pour gène. Elle détermine une résistance totale de l'hôte contrôlée par des allèles dominants à un seul locus, ce qui facilite la gestion de la résistance pour la production de semences hybrides. Mais d'un autre côté, l'avirulence du parasite est également contrôlée par les allèles dominants d'un seul gène. Monogénique et dominante, la résistance exerce une forte pression de sélection sur le parasite qui maximise la probabilité de surmonter les mécanismes de résistance dans un court laps de temps. Cela a en fait abouti à un certain nombre de races physiologiques d'orobanche qui contournent régulièrement toutes les sources de résistance disponibles. La propagation des populations en de nouveaux lieux et l'hyb...

Broomrape Threat to Agriculture

“…Co-existing non-weedy populations might represent an additional source of genetic variation for weedy populations by hybridization (Thorogood et al 2009;Velasco et al 2016)…”

“…This is best demonstrated in the case of sunflower. O. cumana is so far the only broomrape species in which monogenic resistance was identified in sunflower soon after the onset of the O. cumana problem and was widely exploited in sunflower breeding (Velasco et al 2016). As a drawback, this wide exploitation over large areas of these highly resistant hybrids imposed high selection pressure on the O. cumana populations, leading to the development of races (see Molinero-Ruiz et al 2015).…”

Association mapping for broomrape resistance in sunflower

“…Their development was possible due to the existence of good sources of resistance, especially in wild Helianthus species, with monogenic inheritance in most cases ( Fernández-Martínez et al., 2015 ; Cvejić et al., 2020 ). Genetic resistance to broomrape was introduced into sunflower in the early breeding programs in the former USSR in the first years of the 20th century ( Velasco et al., 2016 ). However, the introduction of new resistance sources was followed by the appearance of new physiological races of the parasite that overcame resistance ( Fernández-Martínez et al., 2015 ).…”

Assessment of the Genetic Structure and Diversity of Orobanche cumana populations from Turkey Using Simple Sequence Repeat Markers

“…Changes in broomrape populations in many countries over the past 15 years have resulted in the formation of new races (G and H) (Skoric et al, 2021). There are totally eight races of O. cumana and various countries commonly reported F, G, and H races (Kaya, 2014) Although it has been reported that molecular marker studies on genetic diversity, population structure, racial identification, gene flow, and virulence genetic mechanisms for broomrape populations are not sufficient (Velasco et al, 2016); Recently, studies of molecular markers with highly informative markers have been increasing. Molecular markers are predominantly selected for genetic characterization studies due to having advantages like their abundance in number, unaffected characteristics by environmental factors, or the developmental stage of plants.…”