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Update on sunflower broomrape situation in Spain: racial status and sunflower breeding for resistance

Melero-Vara, J.M., Domínguez, J., Fernández-Martínez, J.M.
Helia 2013 v.23 no.33 pp. 45-56
Helianthus annuus, Orobanche cernua, annuals, breeding lines, chromosomes, crops, crossing, dominant genes, epistasis, hybrids, inheritance (genetics), ovule culture, perennials, races, Spain
A review of the racial situation of Orobanche cumana in Spain and of several studies on sunflower resistance to broomrape is presented. In the nineties, populations of O. cumana attacking sunflower crops in Spain have evolved first towards the increase in frequency of race B simultaneous to the decrease of race A. Later, race E has appeared with increasing frequency. However, the subsequent change to resistant hybrids carrying the Or5 gene has prompted the recent appearance of a new race (race F) that overcomes this resistance gene, and is expanding mainly in southern Spain. Collections of cultivated P.I. accessions tested for resistance to races E or F indicated a low frequency of entries resistant or segregating for resistance. A low frequency of resistance was also observed in accessions of wild annual species. Among 18 species, only H. agrestis and H. anomalus showed full resistance to both races, whereas H. debilis ssp. cucumerifolius and H. exilis segregated. Lines breeding true for resistance, derived from H. anomalus, H. exilis and H. debilis have been produced. In contrast, inoculation of races E and F to wild perennials resulted in complete resistance in 74% of the species, and segregation for resistance to race F in 11%. The transference of resistance from wild perennial species into cultivated sunflower is, however, much more difficult than that of annuals. Embryo rescue and chromosome doubling techniques were often required. Although inheritance studies indicated dominance and one single gene involved in the resistance to races A and E in most crosses, two dominant genes, epistatic interactions and reversal in the dominance were observed in some cases.