Masters Degrees (Genetics)

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Browsing Masters Degrees (Genetics) by Author "Antonov, Adrian Iordanov"

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    Transfer of leaf rust resistance genes from wild species to common wheat
    (Stellenbosch : Stellenbosch University, 1995) Antonov, Adrian Iordanov; Marais, G. F.; Stellenbosch University. Faculty of AgriSciences. Department of Genetics and Institute of Plant Biotechnology.
    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.