Backcross breeding is commonly used for transfer of:
Backcrossing excels at transferring discrete, simply inherited traits governed by one or few genes where phenotype reliably identifies presence of donor allele. Disease resistance genes such as Sr2 for stem rust, Pi54 for blast, and Lr genes in wheat are typically dominant monogenic traits with major effect and high heritability, easily screened by inoculation in each backcross generation using pathogen isolates. Introgression of quantitative, polygenic traits like yield is inefficient because many loci would need simultaneous transfer, epistasis complicates selection, and linkage drag would i
Ref: Brar DS & Khush GS. Alien introgression in rice, Plant Molecular Biology 1997. Collard & Mackill 2008 MAS review