Transfer of leaf rust resistance genes from wild species to common wheat

Antonov, Adrian Iordanov (1995)

Thesis (M. Sc. Agric.) -- University of Stellenbosch, 1995.

Thesis

ENGLISH ABSTRACT: A wild species collection that consists of 928 accessions which represent 27 species of the genus Triticum (877 accessions) and 12 species of the genus Thinopyrym (51 accessions) was screened for resistance to leaf rust. The initial screening was done with an inoculum mix of the 5 pathotypes UVPrt2, UVPrt3, UVPrt8, UVPrt9 and UVPrt13. A total of 231 accessions (222 from the genus Triticum and 9 from Thinopyrum) proved to be resistant/moderately resistant to all races. An attempt was made to determine the following with regard to each resistant accession: (i) Can it be crossed successfully with common or tetraploid wheat? (ii) Is the resistance expressed sufficiently in the presence of the wheat genomes? (iii) Is it possible to transfer the resistance into wheat genomes? Seventy nine accessions have not yet been crossed successfully while the remaining 143 (representing 20 species) were crossed with common wheat or tetraploid wheat, depending on the ploidy level of the wild parent. The interspecific hybrids mostly had distinct phenotypes or were validated by doing root tip chromosome counts. A number of transfer attempts failed in the F1 as a result of one of the following: Suppression or irregular expression of the resistance (60 accesions of T. monococcum, T. turgidum, T. timopheevii, T. syriacum, T. triunciale, T. triaristatum, T. ovatum, T. sharonense, T. searsii, T. longissimum, T. crassum, T. cylindricum and T. dichasians), the formation of embryoless seeds or poor F1 viability (7 accessions). In 76 hybrids the resistance is fully expressed and these are now in a various stages of backcrossing to wheat. In some instances the chromosome number of the hybrids had to be doubled beforehand to ensure fertility during backcrossing. Thus far, the hybridization programme succeeded in producing: hybrid F1's with 21 accessions, B1F1's with 13 accessions, B2F1's with 16 accessions, B3F1's with 15 accessions, B4F1's with 6 accessions and B5F1's with 2 accessions. The most advanced generations (B3F1, B4F1 and B5F1) represent the following 11 Triticum species: T. turgidum (AABB), T. timopheevii (AAGG), T. speltoides (SS), T. sharonense (SS), T. kotschii (UUSS), T. peregrinum (UUSS), T. columnaris (UUMM), T. macrochaetum (UUMM), T. ovatum (UUMM) and T. triaristatum 4x (UUMM). A hexaploid or near hexaploid wheat background has been restored in 17 cross combinations. The species sources of the 76 successful combinations were retested with the individual leaf rust pathotypes. In view of the abundant resistance detected among the Triticum accessions, it was decided not to attempt crosses with the resistant Thinopyrum accession at this stage.

AFRIKAANSE OPSOMMING: 'n Wilde-spesie versameling bestaande uit 928 aanwinste, wat 27 spesies van die genus Triticum (877 aanwinste) en 12 spesies van die genus Thinopyrum insluit (51 aanwinste), is getoets vir blaarroesweerstand. Die aanvanklike sifting is gedoen met 'n inokulum-mengsel van 5 blaarroes-patotipes, te wete, UVPrt2, UVPrt3, UVPrt8, UVPrt9 en UVPrt13. 'n Totaal van 231 aanwinste (232 uit die genus Triticum en 9 uit die genus Thinopyrum) is gevind om matig bestand tot bestand te wees teen al die rasse. 'n Poging is aangewend om die volgende vas te stel met betrekking tot al die bestande aanwinste: (i) Kan dit suksesvol verbaster word met gewone of tetraploïede koring? (ii) Word die weerstand in die basters voldoendc uitgedruk in die teenwoordigheid van die koringgenome? (iii) Sal dit moontlik wees om die weerstand oor te dra na koringchromosome? Nege-en-sewentig aanwinste kon tot dusver nog nie suksesvol met koring gekruis word nie terwyl die oorblywende 143 (verteenwoordigend van 20 spesies) wet gekruis is met gewone of tetraploïede koring, afhangende van die ploïedievlak van die skenkerouer. Die interspesie-basters het meesal duidelik uitkenbare fenotipes ge-openbaar of kon bevestig word by wyse van wortelpuntchromosoomtellings. 'n Aantal verbasteringspogings het in die F1 gefaal vanweë een van die volgende redes: Onderdrukking of ongereelde uitdrukking van die weerstand (60 aanwinste van T. monococcum, T. turgidum, T. timopheevii, T. syriacum, T. triunciale, T. triaristatum, T. ovmum, T. sharonense, T. searsii, T. longissimum, T. crassum, T. cylindricum en T.dichasians), die vorming van embrio-lose sade of lae lewenskragtigheid van die F1 (7 aanwinste). In 76 basters is die weerstand volledig uitgedruk en hierdie materiaal verkeer tans in verskillende stadia van terugkruising na koring. In sommige gevalle moes die chromosoomgetalle van die basters vooraf verdubbel word ten einde vrugbaarheid tydens terugkruising te verseker. Tot dusver kon die verbasteringsprogram die volgende daarstel: Baster F1's vanaf 21 aanwinste, T1F1's vanaf 13 aanwinste, T2F1's vanaf 16 aanwinste, T3F1's vanaf 15 aanwinste, T4F1 's vanaf 6 aanwinste en T5F1 's vanaf 2 aanwinste. Die mees gevorderde generasies (T3F1, T4F1 en T5F1) verteenwoordig die volgende 11 Triticum spesies: T. turgidum (AABB), T. timopheevii (AAGG), T. speltoides (SS), T. sharonense (SS), T. kotschii (UUSS), T. peregrinum {UUSS), T. columnaris (UUMM), T. macrochaetum (UUMM), T. ovatum (UUMM) en T. triaristatum 4x (UUMM). 'n Heksaploïede of naby-heksaploïede koring-agtergrond is reeds herstel in 17 kruisingskombinasies. Die weerstand in die spesiesbronne is ook gekontroleer deur elkeen te hertoets met die indiwiduele blaarroespatotipes. Vanweë die rykdom van weerstandsgene wat onder die Triticum aanwinste gevind is, is daar besluit om voorlopig nie die bestande Thinopyrum-aanwinste te benut nie.

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