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

Orobanche cumana Wall., sunflower broomrape, is one of the major pests for the sunflower crop. Breeding for resistant varieties in sunflower has been the most efficient method to control this parasitic weed. However, more virulent broomrape populations continuously emerge by overcoming genetic resistance. It is thus essential to identify new broomrape resistances acting at various stages of the interaction and combine them to improve resistance durability. In this study, 71 wild sunflowers and wild relatives accessions from 16 Helianthus species were screened in pots for their resistance to broomrape at the late emergence stage. From this initial screen, 18 accessions from 9 species showing resistance, were phenotyped at early stages of the interaction: the induction of broomrape seed germination by sunflower root exudates, the attachment to the host root and the development of tubercles in rhizotron assays. We showed that wild Helianthus accessions are an important source of resistance to the most virulent broomrape races, affecting various stages of the interaction: the inability to induce broomrape seed germination, the development of incompatible attachments or necrotic tubercles, and the arrest of emerged structure growth. Cytological studies of incompatible attachments showed that several cellular mechanisms were shared among resistant Helianthus species.This study was performed in the frame of a 3-year project (ResODiv), funded by “Promosol” (the association of French Sunflower and Rapeseed Breeders for promoting these crops).Peer reviewe

Phenotyping of early stages of wild Helianthus species/ Orobanche cumana interaction towards the identification of new resistances

15th World Congress on Parasitic Plants, 30th June–5th July, Amsterdam, the Netherland.Orobanche cumana(the sunflower broomrape) is an obligate parasitic plant that specifically infects sunflower and is one of the main constraint of sunflower crop in Europe. Genetic resistance is the most efficient control of this parasitic weed illustrated by the breeding for resistant varieties in the past decades. However, more virulent broomrape populations are frequently emerging in many countries by overcoming the resistances introgressed in the cultivated sunflower varieties. Building durable resistance requires the combination of various resistance mechanisms and origins, named pyramidal resistance (Velasco et al., 2016), in contrast to vertical monogenic resistance. Searching for new and complementary broomrape resistance sources and mechanisms is hence a priority for sunflower breeding. Wild Helianthus species have been shown to provide such resources (Seiler and Jan, 2014). With this purpose, a screen of wild Helianthus species has been undertaken, through phenotyping of various stages of their interaction with the most virulent races of O. cumana: broomrape seed germination and haustorium formation using Helianthus root exudates, early stages (attachment and tubercle development) in mini-rhizotrons, and emerged shoots in pots. For early stages, a phenotyping tool in mini-rhizotrons (Louarn et al., 2016) has been optimised through the set-up of the nutritive solution, image acquisition using a nano-computer Raspberry/ cameraPi, and image analysis using Image J software. Sixty accessions (wild Helianthus andwild H. annuus) including H. grosseserratus, H. tuberosus, H. anomalus, H. divaricatus, H. bolanderi, H. argophyllus, H. petiolaris, H. praecox, H. debilis, H. nuttallii, H. strumosus and H. pauciflorusare being screened in the project. First results will be presented including cytological studies.Peer reviewe

DataSheet_2_Wild Helianthus species: A reservoir of resistance genes for sustainable pyramidal resistance to broomrape in sunflower.xlsx

Orobanche cumana Wall., sunflower broomrape, is one of the major pests for the sunflower crop. Breeding for resistant varieties in sunflower has been the most efficient method to control this parasitic weed. However, more virulent broomrape populations continuously emerge by overcoming genetic resistance. It is thus essential to identify new broomrape resistances acting at various stages of the interaction and combine them to improve resistance durability. In this study, 71 wild sunflowers and wild relatives accessions from 16 Helianthus species were screened in pots for their resistance to broomrape at the late emergence stage. From this initial screen, 18 accessions from 9 species showing resistance, were phenotyped at early stages of the interaction: the induction of broomrape seed germination by sunflower root exudates, the attachment to the host root and the development of tubercles in rhizotron assays. We showed that wild Helianthus accessions are an important source of resistance to the most virulent broomrape races, affecting various stages of the interaction: the inability to induce broomrape seed germination, the development of incompatible attachments or necrotic tubercles, and the arrest of emerged structure growth. Cytological studies of incompatible attachments showed that several cellular mechanisms were shared among resistant Helianthus species.Peer reviewe