Toward breeding for disease resistance using weak alleles inducing hybrid weakness

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Synthetic hexaploid wheat (AABBDD genome) is produced through crossing tetraploid wheat (AABB genome) with a D-genome progenitor Aegilops tauschii, and available for common wheat breeding to introduce agronomically useful genes from Ae. tauschii. However, abnormal growth phenotypes are sometimes observed in the interspecific hybrids induced by epistatic interaction between the AB and D genomes. The objective of the present study is confirmation of increased disease resistance in synthetic hexaploids showing weak phenotype of hybrid weakness. The results revealed that the enhanced disease resistance was significantly observed in the synthetic wheat lines with weak hybrid chlorosis, although no significant difference was found between the weak hybrid chlorosis-exhibiting plants and wild-type plants in the F_2 population between the normal and hybrid chlorosis lines of synthetic wheat. These observations suggested that trade-off could be established between increase in disease resistance and inhibition of plant growth vigor, and that weak allele for the hybrid chlorosis is available for wheat breeding to produce enhanced disease-resistance varieties.