Abstract:In 1995-2004 we investigated leaf rust virulence in Slovakia on Thatcher near isogenic lines (NILs) with genes Lr1, Lr2a, Lr2b, Lr2c, Lr3a, Lr9, Lr10, Lr11, Lr15, Lr17, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. According to reaction of leaf rust isolates resistance genes Lr9 and Lr19 were completely effective to all examined pathotypes in all years. The resistance genes Lr24 and Lr28 were also completely effective to all examined pathotypes till the year 2001. In the year 2001 we detected 20% and 10% virulent isolates on NILs Lr24 and Lr28, respectively. According to the reaction of investigated isolates from the territory of Slovakia on NILs, resistance genes Lr2c, Lr3a, Lr11, Lr17, Lr21, Lr23 and Lr26 were mostly ineffective. During the 1994-2004 period we detected 16 races of leaf rust (races 2, 2SaBa, 6, 6SaBa, 12, 12SaBa, 14, 14SaBa, 57, 57SaBa, 61, 61SaBa, 62SaBa, 77, 77SaBa, 77/57SaBa). The most frequently determined races were 61SaBa and 77SaBa, which occurred in all years. Among frequently determined races we can assign race 12SaBa as well. According to the field tests in 2001-2004 good resistance to leaf rust was displayed by the cvs Arida (Lr13, Lru), Eva (Lr3, Lru) and Solara (Lru).

In 2005, 2006 and 2008 the virulence of wheat leaf rust population was studied on Thatcher near-isogenic lines with Lr1, Lr2a, Lr2b, Lr2c, Lr3a, Lr9, Lr10, Lr13, Lr15, Lr17, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. Samples of leaf rust (141 in total) were obtained from different parts of Slovakia. Resistance gene Lr9 was effective to all tested isolates except three isolates from 2008. No virulence was found to Lr19 and genes Lr24 and Lr28 were also highly effective. Low incidence of virulence to Lr2a was observed. Sixty-five winter wheat cultivars registered in Slovakia were tested with seven leaf rust isolates in the greenhouse. Cultivar Bona Dea was the most resistant of all.

In 1997–1998 virulence of the leaf rust population was studied on near isogenic Thatcher lines with the genes for resistance Lr1, Lr2a, Lr2b, Lr2c, Lr3, Lr9, Lrll, Lr15, Lr/7, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28, and on the standard differentials Mala­ koff, Carina, Brevit, Webster, Loros, Mediterranean, Hussar, Democrat and the supplemental cultivar Salzmtinder Bartweizen. All 55 analyzed rust samples were avirulent on Lr9, Lr19, Lr24 and Lr28.On the standard differentials, races 61SaBa, 77SaBa, 77/57SaBa, 2SaBa, 77, 12SaBa, 62SaBa, 6, 6SaBa and 14 were determined. Races 61SaBa and 77SaBa (77/57SaBa) prevailed in both years. Races 6 and 6SaBa were found for the first time. The effectiveness of leaf rust resistance genes in registered cultivars under field conditions in variety trials is discussed.

Virulence of the wheat leaf rust populations of 1999 and 2000 from Slovakia was studied on Thatcher near-isogenic lines (NILs) with genes Lr1, Lr2a, Lr2b, Lr2c, Lr3a, Lr9, Lr10 (only in 2000), Lr11, Lr15, Lr17, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. Seven pathotypes were determined from 36 rust samples in 1999, and 17 pathotypes from 45 rust samples in 2000. The frequency of virulence on Lr1, Lr2a and Lr2b was relatively low, and there was no virulence on Lr9, Lr19, Lr24 and Lr28. The frequency of virulence on Lr2c, Lr15, Lr23 and Lr26 varied between 53.0 and 97.8%. All isolates were virulent on Lr3, Lr11, Lr17 and Lr21. The identified pathotypes conformed with races 61SaBa, 57SaBa, 12SaBa, 6SaBa, 77SaBa, 6, 61 and 2SaBa. In 1999 races 61SaBa, 77SaBa and 57SaBa prevailed, in 2000 races 61SaBa, 57SaBa, 12SaBa, 6SaBa and 77SaBa were prevalent. Data on the reactions of 18 cultivars and advanced lines to six rust isolates of 2000 representing different pathotypes and to one isolate from the collection (race 14) are presented.