Achievements in sunflower breeding for resistance to broomrape

Parasitic plant broomrape (Orobanche cumana Wallr.) is a major problem in sunflower (Helianthus annuus L.) production. Yield losses can be up to 100% when susceptible genotypes are grown. Eight known races of broomrape in sunflower have been identified and designated by letters from A to H. Five races have been identified (A, B, C, D and E) in the past, while more virulent races have recently appeared in the countries around the Black Sea and Spain. The race E has been predominant in Serbia for many years, although in some places a new race has appeared. Broomrape can be confined using chemical control, but growing resistant genotypes appears to be the most efficient and reliable way of control. The sources of resistance have mainly been found in the wild species of the genus Helianthus. Sunflower resistance to broomrape is controlled by Or genes. The system of resistance control depends on the race of broomrape and sources of resistance material. Over the last five decades, significant results have been achieved in sunflower breeding for the resistance to broomrape. Five dominant genes (Or1-Or5), which provide resistance to five races of broomrape (A-E), have been identified, establishing a set of five differential lines. The set was later supplemented with lines resistant to race F. Intensive work has been done at the Institute of Field and Vegetable Crops (IFVC) on: (1) finding the source of resistance towards races which overcome races E and F, in the wild species and cultivated sunflower, (2) determining the gene effects and mode of inheritance of this trait; as well as (3) research on the molecular level, focused on finding markers closely linked to Or genes. Genotypes were tested in naturally infested fields in Serbia, where race E is fully dominant; Spain, where race F is predominant; and in Romania and Turkey, where very virulent races (over race F) of broomrape are present. The results have indicated that several genotypes were selected as potentially resistant or highly tolerant to virulent races of broomrape present in these locations. Intensive research on the molecular level was focused on the development of specific DNA markers, in order to facilitate and accelerate the introduction of resistance into cultivated sunflower. By comparing the molecular profile of resistant and susceptible genotype, a polymorphism was observed on LG3 of the SSR map. The identification of closely related molecular markers will facilitate the introgression of the gene into different sunflower lines. Another way to control broomrape is the cultivation of sunflower hybrids tolerant to imidazolinone herbicides. This measure solves the problem of broomrape regardless of its racial composition.