The effect of substitution of chromosome 5S1 of Aegilops longissima for its wheat homoeologues on spike morphology and on several quantitative traits

Each pair of homoeologous group 5 chromosomes of common wheat (Triticum aestivum) cv. Chinese Spring was replaced by the homoeologous pair 5S1 of Aegilops longissima. The resulting substitution lines were selected by the isozyme markers SKDH or TPI-2 as well as by the presence of 21 bivalents at meiosis. In lines lacking 5B, the alien chromosome could not compensate for the missing Ph1 allele, as was evident by multivalent formation at meiosis and by reduced fertility. In the absence of 5A, chromosome 5S1 not only failed to compensate for the occurrence of spike speltoidy but enhanced its expression. Chromosome 5S1 had a moderate dosage effect on reducing plant height and promoting earliness. When added to the genome of common wheat, this chromosome induced a considerable increase in grain weight, but it could not compensate for the absence of a pair of any of its homoeologues. Other yield components were negatively affected in both addition and substitution lines, as well as in other aneuploids. Grain protein percentage of the different lines was negatively related to their yield per spike. This rendered difficult the evaluation of genes for grain protein percentage. The implication of the obtained results on the use of alien genes for wheat improvement is discussed.Key words: substitution lines, wheat, Triticum aestivum, Aegilops longissima, alien chromosomes, quantitative traits.