No abstract

During the last years in Rostov region of Russian Federation highly virulent biotypes of broomrape have propagated, affecting both hybrids of foreign breeding, and the native sunflower assortment, which used to be resistant earlier. Apart from that, the resistance of some known European sunflower types to broomrape races had disappeared, which testifies about the presence of the races F, G, H in the region at least. Consequently, the search of the sources of resistance is urgent.14 samples of annual and 27 of perennial wild sunflower from the collection of Kuban experimental station VIR were tested for resistance to the most virulent broomrape population. From the annual species only H. petiolaris had weak degree of affection (1-3 tubercles/plant), while the other were affected to a high degree. The majority of perennial sunflower samples have shown the immunity.Perennial wild species of the sunflower of the same name that were used earlier in the research of Ruso et al. (1996) as resistant species against the Spanish populations of broomrape, show resistance also to high virulent O. cumana, which had propagated in the Rostov region of the Russian Federation.The immunity to broomrape of the studied wild perennial sunflower samples is not related to the absence of stimulating effect of root exudations on the seeds of the parasite. The immunity is more likely connected to physiologicalbiochemical features of cortex root cells.

Broomrape (Orobanche cumana Wallr.) is a parasitic plant that feeds on sunflower roots. In recent years, a new, aggressive race designated as race F (called biotype D in Russia) has spread drastically in Spain. The aim of our work was to find donors of resistance to this biotype, to study heredity of this trait and to develop new sunflower inbred lines combining F-race broomrape resistance with other valuable traits. Preliminary resistance tests showed that practically all VNIIMK-released and prospective inbred lines are susceptible to the new broomrape race, with only VK-623 exhibiting resistance. Consequently, we tested all breeding materials obtained from VK-623 as a parental line as well as all F 1 hybrids. All F 1 hybrids were susceptible to the new race, indicating that the resistance was recessive. Among the tested breeding material, resistant plants were encountered with different rates. Fifteen resistant plants were found in the progeny of two F 3 morphologically different plants from a hybrid combination 14B × (VK-623 × VK-616). After testing, all of them were transplanted and self-pollinated. Their progeny proved their resistance in the next year tests. As a result, two new prospective inbred sunflower lines were developed, which exhibited resistance to broomrape races C and D. However, as the recessive character of the obtained resistance creates some difficulties in commercial sunflower hybrid breeding, we shall continue to look for new dominant resistance genes donors among the sunflower samples.

Sunflower downy mildew caused by Plasmopara halstedii (Farl.) Berl. et de Toni is a destructive and widespread disease. More than 50 races of P. halstedii have been recorded worldwide. In 2020, in the Russian Federation (Zernogradsky district, Rostov region), a globally new race 337 was identified for the first time. The pathogen was identified on the plants of a foreign sunflower hybrid bearing the resistance gene Pl₆. According to the five-digit racial nomenclature, its virulence profile was determined as 337 53. It is the first P. halstedii race recorded in the Russian Federation that simultaneously infects all differential lines of the 3^rd triplet, i.e., HA-R4, HA-R5 and HA-335. The sunflower lines RHA-274, 803-1, PSC8, RHA-419 and RHA-340 were resistant to it. All the collected isolates of the new race were susceptible to the fungicide mefenoxam.

After a long period (about 30 years) without broomrape problems in sunflower fields, intensive infestations were observed in some parts districts of Northern Caucasus. Virulence of the pathogen populations from some regions of Northern Caucasus was compared with those of race F from Spain and a mixture of races F, G, H from the European part of Turkey. It was shown that the broomrape populations from Northern Caucasus have heterogeneous structure. The populations Svetlogradskaya, collected in 2005, and Morozovskaya, collected in 2006, were most virulent. The first has the virulence comparable to one from Turkey and it is a mixture of nonvirulent and virulent races for the studied sunflower genotypes. Race F predominates in the mixture and has a there is an admixture (although insignificant) of more virulent individuals. The population Privolnenskaya from 2003 collection, is a mixture of different races also, but it is less virulent, containing race E and some insignificant admixture of more virulent individuals (most likely race F).