Wheat leaf rust resistance in selected Triticum turgidum accessions

English: In wheat, the depletion of genes for rust resistance necessitates the search for alternative sources of diversity. Species related to wheat, e.g. Triticum turgidum, provide such a source of new and hopefully durable resistance genes to Puccinia triticina. In an effort to exploit this source, T. turgidum ssp. dicoccum var. arras, T. turgidum ssp. durum var. aestivum, T. turgidum ssp. durum var. murciense and T. turgidum ssp. polonicum, were crossed with the leaf rust-susceptible cultivar 8ST55. The F1 progeny from all crosses were susceptible in the adult-plant stage, suggesting recessivity of resistance. F2 tests indicated that two recessive genes may be responsible for resistance in T. turgidum ssp. dicoccum var. arras and T. turgidum ssp. durum var. aestivum, respectively. Segregation ratios suggested a single recessive gene in T. turgidum ssp. durum var. murciense. T. polonicum progeny deviated from both single and two-gene Mendelian models. To further characterize the resistance in T. turgidum, accessions were inoculated with six pathotypes (UVPrt2, 3, 5, 9, 13 and 17) of P. triticina. Since all were susceptible to UVPrt5 but resistant to the other isolates, it appeared that these accessions have race-specific (vertical) resistance to P. triticina. From fluorescence microscopy of resistance components it was found that prestomatal exclusion did not play a significant role. In T. turgidum ssp. dicoccum var. arras, T. turgidum ssp. durum var. aestivum and T. turgidum ssp. durum var. murciense early abortion of structures seemed important. T. turgidum ssp. polonicum and Morocco (control) had few, if any, early aborted structures and subsequent colonies were large in comparison to the other lines. T. turgidum ssp. dicoccum var. arras, T. turgidum ssp. durum var. aestivum and T. turgidum ssp. durum var. murciense showed varying degrees of host cell necrosis which is typical of a non-durable, hypersensitive response. No necrosis was detected in leaf rust colonies in T. furgidum ssp. polonicum. AFLP analysis was used to follow the introgression of resistance into domestic hexaploid wheat from T. turgidum ssp. dicoccum var. arras, the F1 hybrid and susceptible and resistant F2 plants. It was found that 12 AFLP markers were solely introgressed from T. turgidum ssp. dicoccum var. arras into the resistant F2 plants. Certain markers, however, introgressed from T. turgidum ssp. dicoccum var. arras were not present in all the resistant F2plants (although not present in the SST55 and the susceptible F2 progeny). This suggests that these markers are possible linked to either flanking regions of the introgressed segment or to only one of the two genes responsible for resistance. Contrary to what was expected, more polymorph isms were detected in tetraploid T. turgidum ssp. dicoccum var. arras than hexaploid SST55, suggesting an unequal contribution of genetic material from the respective parents in susceptible. and resistant F2 progeny. Furthermore, the frequency of introgression into F2 plants, especially into the resistant F2 progeny, was higher from T. turgidum ssp. dicoccum var. arras than from SST55. Further research is, however, necessary to fully evaluate the statistical significance of this data.