Breeding efforts in crops have been largely confined to the exploitation of genetic variation available within the primary gene pool, resulting in a narrow genetic base. Introgression as a breeding scheme has been remarkably successful for an array of inheritance and molecular studies in food crops. Crop wild relatives (CWRs), landraces, and exotic germplasm offer great potential for introgression of novel variation not only to widen the genetic base of the elite gene pool for continuous incremental gains over breeding cycles but also to discover the cryptic genetic variation hitherto. Introgression lines are specialized populations derived through advanced backcrossing, which are nearly isogenic to the recurrent parent and contain only a small fraction from the donor parent. These populations are much more efficient for QTL identification and fine mapping followed by studying QTL × environment interaction due to their homozygous nature as compared to the conventional populations3.

The two sets of introgression lines of Gossypium hirsutum × Gossypium barbadense were used to dissect the QTL stability of three fiber quality traits (fiber length, strength and micronaire) across environments using 551 simple sequence repeat markers selected from a high-density genetic map. Background-independent (BI) and stably expressed (SE) quantitative trait loci (QTLs) were identified using these two sets of introgression lines across multiple environments. Genetic background more greatly affected fiber quality traits than environmental factors. Sixty-one SE- QTLs, including two BI-QTLs, were novel and 48 SE-QTLs, including seven BI-QTLs, were previously reported4.

Quantitative trait loci (QTLs) were mapped for mineral element content in 96 introgression lines derived from a cross between the elite Korean Oryza sativa japonica cultivar “Hwaseong” and the wild rice Oryza rufipogon (IRGC105491). The population was grown in two locations, and the Fe, Zn, Mn, and Ca contents of the brown rice were measured. Six QTLs were identified on chromosomes 6, 8, and 10, and all Oryza rufipogon alleles increased trait values1.

Breeding progress in most crops has relied heavily on the exploitation of variation within the species, a process that is destined to fail once the supply of novel variants has been exhausted. Accessing a crop’s secondary gene pool, as represented by its wild relatives, has the potential to greatly expand the supply of usable genetic variation. Thus, introgression is emerging as an important source of novel genetic variation, alongside standing variation and mutation. The current resurgence of interest in introgression breeding can be expected to result in the increased deployment of exotic genes in commercial cultivars.2

REFERENCES:

1. ADEVA, C., YUN, Y.T., SHIM, K.C., LUONG, N.H., LEE, H.S., KANG, J.W., KIM, H.J. AND AHN, S.N., 2023, QTL Mapping of mineral element contents in rice using introgression lines derived from an interspecific cross. Agron. 13(1):76.

2. HAO, M., ZHANG, L., NING, S., HUANG, L., YUAN, Z., WU, B., YAN, Z., DAI, S., JIANG, B., ZHENG, Y. AND LIU, D., 2020, The resurgence of introgression breeding, as exemplified in wheat improvement. Front. Plant Sci, 11: 252.

3. PRATAP, A., DAS, A., KUMAR, S. AND GUPTA, S., 2021, Current perspectives on introgression breeding in food legumes. Front. Plant Sci., 11:589189.

4. XIAO, X., LIU, R., GONG, J., LI, P., LI, Z., GONG, W., LIU, A., GE, Q., DENG, X., LI, S. AND CHEN, Q., 2023, Fine mapping and candidate gene analysis of qFL-A12-5: a fiber length-related QTL introgressed from Gossypium barbadense into Gossypium hirsutum. Theor. Appl. Genet. 136(3):48.