A comparison of monosomic and disomic substitution lines in the chromosomal location of leaf rust resistance genes in tetraploid wheats

[摘要] English: Two sets of aneuploids were employed and compared to localize adult plantleaf rust resistance genes in tetraploid wheat accessions. One set was thehexaploid Chinese Spring (CS) A- and B-genome monosomics (2n=6x-1=41,AABBDD) and the other the tetraploid Langdon durum D-genome disomiesubstitutions (2n=4x-2+2=28). The tetraploid accessions (2n=4x=28, AABB) 104(Triticum turgidum subsp. dicoccum var. arras) and 127 (T. turgidum subsp.durum var. aestivum) were selected as leaf rust-resistant after evaluating 353Triticum accessions. To study the chromosomal locations of the resistance genes, crosses weremade between the complete sets of aneuploids (maternal parents) and theaccessions. From both crosses F1 hybrids were used for meiotic chromosomeanalysis and to select monosomic plants for F2 segregation analysis. In thecross of the CS AB-genome monosomics with resistant lines, F1monopentaploid plants (2n=5x-1=34, AABBD) were selected. In the othercrosses of the resistant accessions with the substitution lines, F1 doublemonosomic plants were selected with 13 bivalent and two univalentchromosomes during metaphase I. The F2 segregates of selfed monosomicplants were inoculated at the flag leaf stage with pathotype UVPrt2 of Pucciniatriticina. The CS monosomic analysis showed that in accession 104 a Lr gene occurs onchromosome 1A. Another gene in the accession was localized on chromosome6B by Langdon durum substitution analysis. The second gene in this accessioncould not be localized from CS analysis since the F1 monopentaploid hybrid ofthat cross was sterile making the F2 segregation analysis incomplete. The genelocalized on chromosome 1A in accession 104 by the CS analysis could not belocalized by the substitution analysis owing to the presence of a suppressorgene brought from the 0 chromosome of substitution line 101 A. In accession127 the resistance gene was located on chromosome 4A using the two sets ofaneuploids. The study indicated that the tetraploid O-genome substitution lines are morecommendable stocks than the hexaploid CS monosomics for chromosomalmapping of leaf rust resistance genes in tetraploid wheats. The trustworthinessof the tetraploid cytogenetic stocks is that the F1 double monosomic hybridsresulting from crossing with the tetraploid did not show sterility or poorgermination. These would furnish complete F2 segregation analysis. Besides, therelatively few numbers of chromosomes in the F1 hybrids would ease meioticchromosome analysis. However, it would be necessary to consider the CSmonosomic stocks during gene interaction from D-genome chromosomes ofcertain substitution lines on genes present on the A- or B-genomechromosomes of the tetraploid wheat under study. The analysis of variance of important agronomic traits in the substitution linessuggested that three substitution aneuploids namely 202B, 707 A and 707Bwere phenotypically divergent when compared to the other lines and therecurrent parent. These lines are reportedly backcrossed for 12 generations toLangdon. It appears, however, that further backcrossings to the recurrentparent and further targeted selections are necessary to increase traits such asplant height, number of spikelets per spike, kernel weight, and seed yield in line202B. The same selection schemes are required to improve the number ofspikelets per spike, number of kernels per spike, kernel weight, and seed yieldin line 707B. Additionally traits such as number of spikelets per spike, kernelweight and seed yield require further improvement in line 707 A. The pathanalysis revealed true associations of seed yield with kernel weight and headingdate. This association was also supported by a simple correlation analysis. Thedirect path value of the path coefficient analysis exposed kernel weight as a keyselection criterion to improve seed yield in the substitution aneuploids. Thealternate path values further indicated selection for kernel weight would bringsimultaneous selection of improved number of kernel per spike, spikelets perspike and plant height.

[发布机构] University of the Free State