ASSOCIATION BETWEEN GENE LR34 FOR LEAF RUST RESISTANCE AND LEAF TIP NECROSIS IN WHEAT

Durable resistance to leaf rust (Puccinia recondita Roberge ex Desmaz. f. sp. tritici) in bread wheat (Triticum aestivum L.) cultivars is known to result from the interaction of Lr34 with other minor additive genes that are effective in the adult growth state. The Lr34 gene seems to be present in several CIMMYT germplasm-derived Mexican cultivars that display temperature- and light-sensitive seedling responses similar to those displayed by near-isogenic 'Thatcher' lines that contain Lr34. Adult plants of these two Thatcher lines and all Mexican cultivars postulated to carry Lr34 display resistance to leaf rust and exhibit leaf tip necrosis symptoms. This study was conducted to determine whether Lr34 and a gene or genes for leaf tip necrosis are linked. The simultaneous presence of Lr34 and leaf tip necrosis in the two Thatcher near-isogenic lines and Mexican cultivars was confirmed by evaluating F2 plants or F3 lines obtained from various intercrosses. Lr34 and leaf tip necrosis were inherited together in a population of 117 F3 lines obtained from the cross of leaf rust resistant 'Jupateco 73R' (carrying Lr34 and leaf tip necrosis) with its susceptible counterpart 'Jupateco 73S'. Linkage or pleiotropism was also evident in the crosses of six Lr34-carrying Mexican cultivars with 'Siete Cerros 66' (which does not have Lr34). The gene for leaf tip necrosis, designated Ltn, could be used as a marker for Lr34.