Plant Protection Institute, Hungarian Academy of Sciences, 1525 Budapest, PO Box 102, HungaryBackground and objectives
Wheat leaf rust caused by Puccinia recondita is an important disease of wheat in many parts of the world. The main strategy of controlling of wheat leaf rust is now to breed resistant cultivars. However, resistance of cultivars can be easily impaired because of the physiological specialization of pathogen. From year to year new races/pathotypes can appear in the rust population which are able to infect the cultivars, which have previously been resistant earlier. This is the reason that data surveys are important for resistance breeders.

Materials and methods
Field studies and the collection of wheat leaf rust samples from year to year have been carried out in all experimental wheat nurseries and wheat growing areas in Hungary. The leaf rust pathotypes were identified using 15 near-isogenic host differentials. The determination of virulence genes in rust population and finding the effective resistance genes against leaf rust were done using 41 Lr near-isogenic lines. The wheat lines with single genes for resistance to leaf rust were tested for reaction to 12 isolates of leaf rust in growth cabinets at 10C as well as at 25C.

Results and conclusions
In the last five years leaf rust has occurred yearly and even in 1994-1995 was strongly widespread and reached epidemic levels. There was major a change in the rust population in Hungary. Four important races (Nr.12, Nr.58, Nr. 61 and Nr.77) were determined from Hungarian wheat leaf rust population. Analysis data showed that race Nr. 61 and Nr. 12 prevailed from 1993 to 1997, while, earlier, race Nr.77 had been dominant. Twelve virulence pathotypes of the races were detected using 15 near-isogenic lines as differentials. Isolates of main races differentiated into groups according to their reaction on line with Lrl 5 and Lr 21. Frequencies of virulence to lines with Lr 2c, Lr 3, Lr 3bg, Lr 3ka, Lrl 2, Lrl 3, Lrl 4a, Lrl 4b, Lrl 5, Lrl 7, Lrl 8, Lr 20, Lr 22, Lr 26, Lr 32, Lr 34, Lr 35, Lr 37 and LrB resistance genes were about 80-100%. Among them Lr 3 and Lr 26 are present most frequently in Hungarian cultivars, which is the reason that these cultivars were strongly infected by leaf rust in the recent years. In this period the frequencies of virulence to lines with Lr l, Lr 2a, Lr 2b resistance genes decreased, were lower than in previous years. No virulence was found to resistance genes Lrg, Lrlg, Lr 24, Lr 28, Lr 29, Lr 38, LrW.

We found that a number of resistance genes were influenced by temperature, e.g. the line with Lrl 8 was resistant at low temperature (10C), whereas the lines with Lrl0 and Lr23 resistance genes were resistant only at high temperature (25C). It was shown, that the virulence of leaf rust populations changed considerably in Hungary from 1993 to 1997. It appears that the virulence spectrum of leaf rust population in Hungary is currently similar to those of eastern European countries and differs from that in France and Italy [1].

1. Bartos P, Walther U, 1997. Proceedings of Conference. 11-13. November, 1997. Praha, Czech Republic, pp. 91-92