Characterization ofLr34,a Major Gene Conferring Nonhypersensitive Resistance to Wheat Leaf Rust

Abstract

Wheat leaf rust resistance gene Lr34 is claimed to contribute to durability of resistance in wheat cultivars in combination with other genes for resistance. We compared the effect of Lr34 with that of Lr12 and Lr13 (all in Thatcher background) and with the partial resistance of Akabozu and BH1146. Seedlings of all lines displayed a compatible infection type. Lr34 increased latency period and decreased infection frequency, especially at low temperature. The gene caused a small but significant increase in early abortion of sporelings. The number of haustoria per sporeling 42 h after inoculation was reduced significantly, but this was not associated with papilla formation. In adult plants the effect of Lr34 was much clearer. In the flag leaf Lr34 decreased infection frequency and increased latency period. Many infection units did not develop further than the stage in which they caused pale (nonhypersensitive) flecks. Also at the microscopic level we found no increased hypersensitivity due to Lr34. Lr34 shared features both with Lr13 and with the genes for partial resistance in Akabozu and BH1146. The main difference with Lr13 was the association of the latter with chlorosis at the macroscopic level and cell necrosis at the microscopic level. Lr34 and the partial resistance in Akabozu and BH1146 are based on reduced rates of haustorium formation in the early stages of infection, in association with no or relatively little plant cell necrosis. However, the reduction of haustorium formation in Thatcher-Lr34 appeared to be due to a low rate of intercellular hyphal development and not to papilla formation as in Akabozu and BH1146. We argue that Lr34 should be considered a major gene conferring partial resistance sensu Parlevliet.