Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 2.38

MARKER-ASSISTED SELECTION WITH SSRs AND AFLPs TARGETED TO LEAF RUST AND POWDERY MILDEW IN WHEAT

M. MACCAFERRI*, M.C. SANGUINETI*, F. ROTONDO*, R. TUBEROSA*, A. DE MONTIS**, E. DE AMBROGIO**

*) Department of Agroenvironmental Science and Technology (DiSTA), Via Fanin 44, 40127 Bologna, Italy

**) Società Produttori Sementi Bologna, Divisione Ricerca, Via Macero 1, 40050 Argelato, Italy

wheat, leaf rust, powdery mildew, marker-assisted selection

In wheat, marker-assisted selection (MAS) for pyramiding disease resistance genes is now feasible thanks to the recent development of a range of molecular tools; in particular, the development of wheat varieties characterised by durable resistance to leaf rust (Puccinia recondita f.sp. tritici) and powdery mildew (Blumeria graminis f. sp. tritici) is a major objective of wheat breeding. In Europe and in Italy, Lr9 and Lr24 for leaf rust and Pm4b and Pm13 for powdery mildew proved to be effective resistance genes. Dominant STSs (Sequence Tagged Sites) are already available for Lr9, Lr24 and Pm13 but are not fully informative as to the genetic constitution of segregating materials, thus limiting MAS efficiency. Our objectives were to screen mapped SSRs and to generate new AFLPs tightly linked to each one of the four selected resistance genes. Four experimental F₃ populations, each segregating for one of the four resistance genes, are being used to develop new diagnostic molecular markers. Preference was given to co-dominant AFLP markers or to AFLP band linked to susceptibility.

As to Lr9, microsatellite markers mapped on the distal regions of 6BL were not informative, thus, new AFLP markers were generated in a bulk segregant analysis experiment. About 15,000 AFLP loci were screened for polymorphism on the two contrasting bulks (made by 15 and 11 susceptible and resistant F₃ families. The AFLP screening yielded 26 bands putatively associated to Lr9: 5 of them appeared associated with susceptibility, 20 with resistance and 1 locus showed codominance. The relatively high frequency of loci associated to resistance could be ascribed to the different structural features of the wheat and Ae. umbellulata chromosome segments involved in the translocation (Zhang et al. 1998, Theor Appl Genet 96: 69-75). AFLP markers SseGA/MseCAG-200, SseGA/MseTCT-185, SseTC/MseTAG-210 (associated to susceptibility) showed no recombination events with Lr9 over 26 F₃ families. The codominant SseAT/MseCTA-410/405 was also validated for tight linkage.

As to Lr24, four informative microsatellite probes were identified on the distal region of chr. 3DL: WMS38, WMS314, WMS664 and WMS645. The probe WMS645 showed a codominant polymorphism, while each of the WMS38, WMS314, and WMS664 loci showed a null allele associated in coupling with the resistance gene, most probably because of the nucleotide divergence between the distal region of wheat 3DL and the introgressed one.

As to Pm4b (distal region of chr. 2L), probes WMS382, WMS311 and WMS846 produced a dominant polymorphism associated to Pm4b resistance allele. Association was detected also for the probe WMS991(codominant marker), but three families, over the 30 tested, showed a recombination event.

As to Pm13, about 13,500 AFLP fragments screened in BSA yielded 36 differential AFLP markers, with 16 of them associated to susceptibility and 12 further validated for tight association to Pm13.