RESUMO
Leaf rust is one of the most significant diseases of wheat worldwide. In Argentina, it is one of the main reasons for variety replacement that becomes susceptible after large-scale use. Some varieties showed durable resistance to this disease, including Buck Manantial and Sinvalocho MA. RILs (Recombinant Inbred Lines) were developed for each of these varieties and used in genetics studies to identify components of resistance, both in greenhouse inoculations using leaf rust races, and in field evaluations under natural population infections. In Buck Manantial, the APR gene LrBMP1 was associated with resistance in field tests. In crosses involving Sinvalocho MA, four genes were previously identified and associated with resistance in field testing: APR (Adult Plant Resistance) gene LrSV1, the APR genetic system LrSV2 + LrcSV2 and the ASR (All Stage Resistance) gene LrG6. Using backcrosses, LrBMP1 was introgressed in four commercial susceptible varieties and LrSV1, LrSV2 + LrcSV2 and LrG6 were simultaneously introgressed in three susceptible commercial varieties. The use of molecular markers for recurrent parent background selection allowed us to select resistant lines with more than 80% similarity to commercial varieties. Additionally, progress towards positional cloning of the genetic system LrSV2 + LrcSV2 for leaf rust APR is reported.
RESUMO
KEY MESSAGE: A complementary gene to LrSV2 for specific adult plant leaf rust resistance in wheat was mapped on chromosome 4BL, tightly linked to Lr12 / 31. LrSV2 is a race-specific adult plant leaf rust (Puccinia triticina) resistance gene on subdistal chromosome 3BS detected in the cross of the traditional Argentinean wheat (Triticum aestivum) variety Sinvalocho MA and the experimental line Gama6. The analysis of the cross of R46 [recombinant inbred line (RIL) derived from Sinvalocho MA carrying LrSV2 gene and the complementary gene Lrc-SV2 identified in the current paper] and the commercial variety Relmo Siriri (not carrying neither of these two genes) allowed the detection of the unlinked complementary gene Lrc-SV2 because the presence of one dominant allele of both is necessary to express the LrSV2-specific adult plant resistance. Lrc-SV2 was mapped within a 1-cM interval on chromosome 4BL using 100 RILs from the cross Sinvalocho MA × Purple Straw. This genetic system resembles the Lr27+31 seedling resistance reported in the Australian varieties Gatcher and Timgalen where interacting genes map at similar chromosomal positions. However, in high-resolution maps, Lr27 and LrSV2 were already mapped to adjacent intervals on 3BS and Lrc-SV2 map position on 4BL is distal to the reported Lr12/31-flanking microsatellites.