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Basic elements of genetic architecture of heterosis in maize and details of using its in dihaploid breeding", dissertation for the degree of doctor habilitat of biological sciences


Author: Mihailov Mihail
Degree:doctor habilitat of biology
Speciality: 03.00.15 - Genetics
Year:2021
Scientific consultants: Vasile Botnari
doctor habilitat, associate professor (docent)
Galina Lupaşcu
doctor habilitat, professor, Institute of Genetics, Physiology and Plant Protection of the ASM
Institution: Institute of Genetics, Physiology and Plant Protection of the ASM

Status

The thesis was presented on the 4 November, 2021
Approved by NCAA on the 22 December, 2021

Abstract

Adobe PDF document – 1.08 Mb / in romanian
Adobe PDF document – 1.15 Mb / in russian

Thesis

CZU 633.15:[575.222.78:631.527](478)

Adobe PDF document 7.17 Mb / in russian
299 pages

Keywords

maize, heterosis, haploids, doubled haploids, breeding programs, biometrical genetics, quantitative traits, linkage, crossing-over

Summary

Thesis structure: introduction, 5 chapters, conclusions and recommendations, bibliography of 233 sources, 2 supplements, 215 pages of the main text (before bibliography), 37 figures, 47 tables. The results are published in 46 scientific works.

Aim of the work: to establish the basic elements of genetic architecture of heterosis in maize to optimize dihaploid breeding process oriented to creating high-productive inbred lines.

Objectives: to develop and apply the method of accounting for linkage in the evaluation of genetic parameters; develop and apply a dihaploid breeding scheme aimed at the most productive homozygous line from a simple hybrid.

Scientific novelty and originality. The new problems of biometric genetics have been solved: estimation of unbiased values of an average degree of dominance and polygenism criterion of quantitative traits; interval estimation of average linkage; genetic interpretation of the group statistics of manifestation of heterosis. The results obtained made it possible to establish some important aspects of the genetic nature of heterosis in maize: productivity heterosis is controlled by dominant and semi-dominant effects, and the dominance is almost unidirectional; the main part of the heterosis effect is distributed over several dozen loci, the average linkage between them corresponds to the statistically expected for a random arrangement of genes. Cis-regulation of crossing over in maize was detected. A new breeding method designed for the use of dihaploids was developed and tested on maize - the enriching-restoring breeding scheme, which contributed to an increase in the productivity of inbred lines by 30% in the 3rd breeding cycle.

The solved scientific problem consists in the scientific substantiation of a new direction in biometric genetics, based on the optimization of the calculation of the effects of genetic linkage, which led to the more accurate identification of the main elements of the genetic organization of maize heterosis, which allowed the elaboration of the enriching-restoring breeding scheme for double haploid plants, aimed at creating productive homozygous lines by accumulating favorable genes responsible for heterosis.

Theoretical significance: methods for evaluation of mean linkage and the linkage biases on genetic parameters expand the possibilities of biometric analysis of quantitative traits, since the accounting for linkage remains one of the least developed issues of biometric genetics. The methods developed here make it possible to obtain unbiased estimates of mean degree of dominance, due to the lack of which the question of the dominant or overdominant nature of heterosis has not yet been unambiguously resolved. The experimental results obtained here suggest the prevalence of dominant interactions in the heterosis effect in maize, being a strong argument for the theory of dominance. The parameter of normalized heterosis introduced here allows one to give a genetic interpretation of data on the group manifestation of heterosis. The detected effect of a homozygous background on the recombination frequency is not predicted by the existing crossover hypotheses and requires revision of its. The manifestation of some quantitative and qualitative traits in dihaploid lines is consistent with the theory of the compensation complex of genes.

Applicative value. The enriching-restoring breeding scheme allows create high-yielding inbred lines, and in the favorable case can lead to the fixation of heterosis. This scheme it is applicable to any cultures where doubled haploid lines can be obtained. The observed effect of a twofold increase in the recombination frequency between heterozygous loci against a homozygous background can solve the problem of inaccessible recombination variability.

Implementation of results: methods for producing dihaploid lines have been introduced into breeding practice and are used to create productive maize hybrids in the framework in cooperation with the institute “Porumbeni” and to create high-yielding inbred lines in Laboratory of Plant Genetic Resources, Institute of Genetics, Physiology and Plant Protection