Reverse Breeding: A Novel Tool for Crop Improvement

Hybrid vigor is the most important event in crop improvement, making F1 typically superior to either of their homozygous parents. The development of the best hybrid requires the evaluation of a large number of crosses derived from inbred lines. Breeders often confront considerable difficulties during evaluation due to the unpredictable nature of heterosis and characterization of heterozygotes. It leads to the loss of favorable alleles combinations in the next generation due to the segregation of genes. Apomixis is a way to preserve heterozygosity but has not been fully exploited in food crops due to mechanisms, i.e., apo-meiosis, parthenogenesis, and endosperm formation, which need to be operationalized and synchronized. However, reverse breeding seems to be a powerful and versatile technique to fix the heterozygous genotypes and develop complementary homozygous parental lines 170to reconstitute even better plant types than even original hybrid. Further, it also helps to develop homozygous chromosome substitution lines (CSL) and the construction of heterozygous inbred families (HIFs). Reverse breeding comprises selection of desirable heterozygous genotype, suppression of crossing over (CO), production of doubled haploids followed by selection, and crossing of complimentary lines through marker-assisted selection (MAS). Suppression of CO can be done using RNAi technology for the genes responsible for meiotic recombination or applying chemical compounds that inhibit recombination. Despite its potentiality, this technique is limited to diploid crops with basic chromosome number 12 or less and a high response to double haploid (DH) production. Besides, it necessitates standardization of protocol for suppression of meiotic CO.