TY  - PRO
AU  - Naskidashvili,P.P.
AU  - Bedoshvili,D.
AU  - Dzidzishvili,R.R.
AU  - Naskidashvili,I.P.
AU  - Naskidashvili,M.P.
ED  - Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT)
ED  - 
TI  - Theoretical and practical importance of study of the hybrid necrosis
U1  - 633.1147 
PY  - 2004///
CY  - Tbilisi (Georgia)
PB  - CIMMYT
KW  - Crossbreeding
KW  - Morphogenesis
KW  - Necrosis
KW  - Phylogeny
KW  - Varieties
KW  - AGROVOC
KW  - Genotypes
KW  - CIMMYT
N1  - Abstract only
N2  - Study of hybrid population produced from crosses with Macha wheat has shown that in certain morphologically homogeneous lines within the same variety, occur the genotypes not containing dominant genes causing necrosis. Research has shown that the intensity of necrosis varies within the second generation. Depending on the parents, certain number ofthe segregated population plants perishes in the early stage of vegetation, certain number perishes later, and certain number is less damaged and fully develops. According to Hermsen, Dekaprelevich and Naskidashvili, segregation raties for necrosis in the second generation depends on the presense of the dominant genes responsible for the development of hybrid necrosis, on the genetic background and the presence of the modifier genes represented concurrently in the genotype. It was ascertained that the genotype of the first generation plants in the presence of the weak and extremely weak alleles does not develop the symptoms of necrosis, whereas the segregated plants of the second generation express the symptoms of necrosis. Such cases can be explained by the influence of the inhibitor genes represented in the genotype of the first generation plants. Extensive studies have proved that development of necrosis in hybrid generation is influenced by the duration of day, temperature, etc. It was noted that in cases when the parental forms carry weak or moderate alleles responsible for the development of necrosis, the first generation may escape its expression. In cases when necrosis in the parental forms is determined by strong alleles, the environment has little impact on the development of necrosis. Choice of parental forms for crosses is extremely important. For the crosses with Macha wheat a genotype without dominant gene Ne-2, responsible for the development of necrosis, or a genotype with the weak allele of such gene should be selected. The generation received from the latter should be cultivated on rich fertile soils and the hybrid population produced from it should be screened for the healthy plants. In the opinion of the certain group of researcher 's genotypes carrying strong alleles of the genes responsible for development of necrosis should be expelled from breeding programs, or at least the first generation grains should be subjected to the rated a-radiation (C 60) of 15-20 curie. Analyses of numerous hybrid combinations Of Macha wheat have proved that the best results are obtained when either the parental form used for crosses with Macha or Macha itself are the heterozygote organisms. The pair of the parental forms in such crossing pattern does not produce a lethal generation. While dealing with breeding and genetic aspects of hybrid necrosis understanding of physiological and biochemical mechanism of gene depression, responsible for such phenomenon, is essential. Analyses of segregating population proved the correlation of the stage of the necrosis expression and its intensity. The earlier necrosis is developed, the stronger is the impact of genes. Thus, the deeper is studied Macha and other genetic forms selected for breeding with Macha, the more effective and reliable will be the breeding results. Proceeding from the above mentioned, the study of necrosis is of a great practical and theoretical importance. There are a number of questions that have to be answered by studies on this problem. The following are considered as the current priorities: I. Identification of presence of all dominant necrosis genes in all species, all aboriginal variety-populations and all released varieties of wheat genus 2. Assassment of the dissemination area of necrosis genes, that bears the theoretical importance as an instrumentality for exploration and verification of the evolution of wheat family 3. As the disposal of the dominant necrosis genes proved to cause difficulties during breeding, production of mutants possessing recessive alleles through chemical mutagenesis is necessary. Establishment of the determinative symptoms of necrosis is necessary in order to simplify the process. It was proved through research that presence of the rare gene Ne-1, responsible for the development of necrosis in the genotype of Macha wheat, is related to phylogenesis and causes genetic isolation of this species
ER  -