New sources of effective resistance genes to Fusarium wilt in flax (Linum usitatissimum L.) depending on temperature

Fusarium wilt caused mainly by fungus Fusarium oxysporum f. lini, is one of the most harmful and widespread diseases in flax. To increase the efficiency of breeding faber and oil flax plants resistant to the pathogen, the sufficient set of the parent plants possessing effective R-genes is necessary. Development of monogene-based resistant varieties will allow to reduce the time required fro breeding, and provide essential suppression of disease. In the present research we tested the resistance of world Linum usitatissimum L. gene pool specimens to highly aggressive Fusarium oxysporum f. lini monoisolates, and also studied haw the expressivity of R-genes was influenced by the temperature. The study was conducted in 2006-2010 using 28 collection flax specimens characterized by high resistance to F. oxysporum f. lini population. Also highly aggressive monoisolates and the most widespread races of the pathogen were used. To identify R-genes, the F2 plants from crossing studied specimens with the lines possessing known R-genes were tasted with monoisolate № 39 Fusarium oxysporum f. lini. To rank the specimens on fusarium wilt resistance, the tests were conducted in the nurseries and a climatic chamber at optimal temperature (26-28 °С), and the plant damage was estimated at early yellow ripeness or early development, respectively. A total of 16 specimens were shown to possess effective resistance genes. The other 12 specimens, when tested with different monoilolates, seemed not to be effectively resistant, moreover, their resistance decreased depending on an increased aggressiveness of some races of the pathogen due to weather conditions of the year. Hybridological analysis data were in line with phytopathological tests specifying genetic distinctions of specimens № 3896, l. 6 (Russia); Siciliana 285, l. 4 (Italy) and Honkej 21, l. 4 (China) with effective resistance genes Fu 4, Fu 7 and Fu 8, respectively. It was shown that at 26-28 °C during the seedlings-«herringbone» period an expressivity of resistance genes can decrease owing to increased aggressiveness of some races of the pathogen. At that, the effectiveness of Fu 7 gene was significantly influenced by the raised temperatures, whereas the effect of R-genes in the k-5657 (Minnesota, the USA) did not depend on the temperature. The found sources possessing various R-genes against fusarium wilt, when used in breeding, will help to avoid epiphytoty and to provide a sustainable flax production.