TRANSFER OF LEAF RUST RESISTANCE FROMAEGILOPS SPELTOIDESTOTRITICUM AESTIVUM

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Abstract
Five accessions of Aegilops speltoides resistant to race 5 of leaf rust were crossed and backcrossed four or five times to wheat cultivars Manitou and Neepawa. The resistance transferred from each accession to the recurrent parents appeared to be controlled by one incompletely dominant gene. Since a majority of resistant lines show complete chromosome pairing when heterozygous and segregate in a monofactorial ratio of 3 resistant to 1 susceptible, the Aegilops genes must be on wheat chromosomes. The present experiment shows that if extensive homoeologous chromosome pairing occurs in the F1hybrids, introgression can occur directly from a diploid into a hexaploid. The origin of polyploids in the Triticum-Aegilops polyploid complex is briefly discussed, and it is stressed that polyploidy is closely and inversely related to introgression. Whether introgression or polyploidy is going to occur depends largely on the genomic relationships and the extent of chromosome pairing in the F1hybrid.