The prospects for using haploinducers in maize breeding

Abstract

The discovery of spontaneous haploid plants and the development of ways to produce them in in vitro culture have set a new direction important for breeding and for theoretical research in reproductive biology. The frequency of spontaneous haploidy in cultivated plants is extremely low and does not exceed 0.01-0.1%, therefore, the search for sources and donors capable of stimulating haploidy in hybrid combinations is of current interest. Expansion of the search for new sources and donors of the haploinduction trait, the creation of new, more effective haploinducers contribute to the accumulation of scientific information and genetic sources, characterized by a high resource potential for selection and genetic research. The causеs of haploidy are not well understood yet. According to the available information, the genes localized in the qhir1, qhir11, qhir12 regions of chromosome 1 in maize are responsible for this process. The use of genes that stimulate haploinduction in maize in combination with the marker gene R1-nj responsible for anthocyanin coloration of the caryopsis and embryo, as well as genes A1 and B1, which are in control of the entire plant coloration, allowed the creation of haploinducer lines with a frequency of haploid stimulation up to 15%. Phenotypic expression of dominant alleles of the marker anthocyanin coloration genes in different parts of a hybrid plant, as well as in the caryopsis and embryo, contributes to the high-quality selection of haploid kernels in the cob due to the manifestation of recessive alleles of these genes at the haploid level. The presence of anthocyanin synthesis suppressor genes in siliceous maize (C1-I, C2-Idf, In1-D) restricts the use of the R1-nj gene in other representatives of siliceous maize. In order to overcome this problem, studies are underway to create other genotypes of haploinducers, which are not associated with the anthocyanin coloration of the caryopsis, but instead have other marker traits, such as the oil content in the kernel, the absence of ligules in the leaves, and root coloration in seedlings. The use of matroclinous and androclinous types of haploinduction allows breeders to obtain highly homozygous dihaploid maize lines, with both the maternal and paternal genomes. These achievements made it possible to cut five or more times the material and time inputs into the creation of inbred lines and their sterile analogs, accelerate the breeding of new maize hybrids, and signifi cantly improve the quality of seed production in terms of typicality and uniformity. The materials presented in the article should help breeders and geneticists to learn more about the innovative directions and problems of hybrid maize breeding.