Wheat leaf rust resistance in selected Triticum turgidum accessions

Abstract

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.

Afrikaans: Na aanleiding van die afname in bruikbare roesweerstandsgene in koring is dit noodsaaklik om nuwe bronne van variasie te soek.· Spesies verwant aan broodkoring, soos bv. Triticum turgidum, kan 'n waardevolle bron van nuwe en moontlik volhoubare weerstand teen Puccinia triticina wees. In 'n poging om hierdie bron te ontgin is T. turgidum ssp. dicoccum var. arras, T. turgidum ssp. durum var. aestivum, T. turgidum ssp. durum var. murciense en T. turgidum ssp. polonicum . gekruis met SST55, In blaarroesvatbare koringkultivar. Die F1 nageslag van alle kruisings was vatbaar in die volwasseplantstadium, wat 'n aanduiding was van resessiewe weerstand. Die F2 populasies het gesegregeer in weerstandbiedende en vatbare plante. Segregasiedata het getoon dat twee resessiewe gene moontlik verantwoordelik was vir weerstand in onderskeidelik T. turgidum ssp. dicoccum var. arras en T. turgidum ssp. durum var. aestivum. 'n Enkel resessiewe geen het moontlik weerstand in T. turgidum ssp. durum var. murciense bemiddel. T. turgidum ssp. polonicum-nageslag se segregasie data het afgewyk van beide die 7:9 en 1:3 Mendeliese verhoudings. Ten einde weerstand in T. turgidum te karakteriseer is aanwinste geïnokuleer met ses patotipes (UVPrt2, 3, 5, 9, 13 en 17) van P. triticina. AI die spesies was vatbaar vir UVPrt5, maar bestand teen die ander isolate. Hierdie interaksie tussen gashere en isolate is bewys dat die aanwinste slegs oor rasspesifieke (vertikale) weerstand beskik. Met f1uoressensie-mikroskopie van weerstandskomponente is gevind dat prestomatale uitsluiting nie 'n rol in weerstand speel nie. By T. turgidum ssp. dicoccum var. arras, T. turgidum ssp. durum var. aestivum en T. turgidum ssp. dicoccum var. murciense was die vroeë abortering v~n swamstrukture belangrik. In T. turgidum SSp. polonicum en Morocco (kontrole) is enkele, indien enige, vroeë aborsies opgemerk en swamkolonies was groot in vergelyking met die ander drie spesies. T. turgidum ssp. dicoccum var. arras, T. turgidum ssp. durum var. aestivum en T. turgidum ssp. dicoccum var. murciense het wisselende grade van gasheerselnekrose, tipies van hipersensitiewe en nie-volhoubare bestandheid, getoon. Geen nekrose kon by blaarroeskolonies in T. turgidum ssp. polonicum waargeneem word nie. AFLP analise is gebruik om die introgressie van weerstand vanaf T. turgidum ssp. dicoccum var. arras na kommersiële heksaploïede koring, hul F1, en weerstandbiedende en vatbare F2 nageslag te volg. In die studie is gevind dat 12 AFLP merkers eksklusief van T. turgidum ssp. dicoccum var. arras oorgedra is na bestande F2 plante. Sekere van die merkers afkomstig vanaf T. turgidum ssp. dicoccum var. arras was nie teenwoordig in al die weerstandbiedende F2 nageslag nie (alhoewel hulle nie teenwoordig was in SST55 of die vatbare F2 nageslag nie). Dit kan wees dat die merkers gekoppel is aan een van die aangrensende gebiede van die oorgedraagde segment, of slegs aan een van die twee gene verantwoordelik vir weerstand. In teenstelling met wat verwag is, is meer polimorfismes opgemerk in die tetraploïde T. turgidum ssp. dicoccum var. arras as in heksaploïede SST55, moontlik as gevolg van 'n hoë graad van verskil tussen hulle. Verder is die introgressie-frekwensie in die F2 plante hoër vanaf T. turgidum ssp. dicoccum var. arras as vanaf SST55, wat aandui dat 'n onewe bydrae van genetiese materiaal van die respektiewe ouers oorgedra is na die vatbare en weerstandbiedende F2 nageslag. Verdere navorsing is egter nodig om die statistiese betekenisvolheid van die data te evalueer.