[Estimation of efficiency of seed irradiation by thermal neutrons for inducing chromosomal aberration in M2 of cotton Gossipium hirsutum L].

Cytogenetic analysis of M2 plants after irradiation of cotton by thermal neutrons was performed in 56 families. In 40 plants of 27 M2 families, different abnormalities of chromosome pairing were found. These abnormalities were caused by primary monosomy, chromosomal interchange, and desynapsis. The presence of chromosome aberrations in some cases decreased meiotic index and pollen fertility. Comparison of the results of cytogenetics analysis, performed in M1 and M2 after irradiation, showed a nearly two-fold decrease in the number of plants with chromosomal aberrations in M2, as well as narrowing of the spectrum of these aberrations. The latter result is explained by the fact that some mutations are impossible to detect in subsequent generations because of complete or partial sterility of aberrant M1 plants. It was established that the most efficient radiation doses for inducing chromosomal aberrations in the present study were 15 and 25 Gy, since they affected survival and fertility of altered plant to a lesser extent.

[Estimation of the efficiency of seed irradiation by thermal neutrons for inducing chromosomal aberrations in M1 of cotton Gossypium hirsutum l].

Exposure of cotton seeds to thermal neutrons at doses of 15, 25, and 35 Gy was shown to induce many altered plants, including sterile and chimeric ones. Most of these phenotypic changes were shown to result from novel genomic, chromosomal, and desynaptic mutations. The presence of these mutations in the karyotype of M, plants often decreased meiotic index and pollen fertility. In translocation forms, the decrease in pollen fertility was caused by the prevalence of quadrivalents in form of rings and chains with adjacent segregation of chromosomes from the translocation complexes. Based on the shapes and sizes of multivalent associations, we performed preliminary localization of translocation breakpoints. A specific feature of the effect of thermal neuron irradiation in M1 was induction of numerous unique chromosomal aberrations, consisting in the appearance in the same plant of several types of mutations (genomic and chromosomal), exchange complexes in the same nucleus, and multiple exchanges involving three nonhomologous chromosomes.

[Evaluation of the effect of pollen irradiation on karyotype variability in M2 cotton plants]. / Otsenka vliianiia obluchennoi pyl'tsy na izmenchivost' kariotipa rastenii M2 khlopchatnika.

The karyotypes of biomorphologically abnormal cotton (Gossypium hirsutum L.) plants obtained in M2 after pollination with pollen irradiated at dose rates 10, 15, 20, and 25 Gy were studied. Various genomic and chromosomal mutations were detected in 57 M2 families. The primary monosomics isolated in M2 were found to be cytologically more stable and more viable, since they had higher meiotic indices, pollen fertility, and seed formation. In M2, a decrease in the number of plants with multiple karyotype aberrations and interchromosomal exchanges with high frequency of multivalent formation was observed. The multivalents had diverse patterns and types of chromosome segregation and translocation complexes. Their pollen fertility was higher than in translocants found in M1. Desynapsis often occurred in M2, including plants with chromosome deficiency or rearrangements. The variation in the number of univalents in various cells was found to result from different expression of synaptic genes. The results indicate stabilization of karyotypes, increase in cytologic stability and viability, and the absence of sterility in aberrant plants.

[Evaluation of the effect of pollen irradiation on karyotype variability in cotton plants]. / Otsenka vliianiia obluchennoi pyl'tsy na izmenchivost' kariotipa rastenii khlopchatnika.

The effect of pollen irradiation at dose rates of 10, 15, 20, and 25 Gy on variability in cotton plants Gossypium hirsutum L. was studied. The modified plants showed a reduced fertility, mainly caused by chromosomal rearragements and genomic mutations during meiosis. The genomic mutations involved primary and tertiary monosomics, monotelodisomics, and a haploid plant. The decrease in meiotic index and pollen fertility in the cotton aneuploids was related not only to aberrations in chromosome pairing but also to genetic features of the original plants. It was found that heterozygosity for interchromosomal exchanges found in M1 plants resulted in the formation of multivalent associations of chromosomes of various forms and types of segregation from translocation complexes. Another result was high variability in pollen fertility. An increase in irradiation dose rate caused an increase in the number of translocants with a high frequency of quadrivalents. The results suggest that the great diversity of forms observed in M1 after pollination with irradiated pollen is determined, first, by elimination of some chromosomes or their arms or the whole paternal genotype and second, by interchromosomal rearrangements. The high variability in pollen fertility of translocants hampers using this trait as a marker of heterozygosity for exchanges in cotton.

[Cytogenetic effects of the treatment of cotton seeds with thermal neutrons]. / Tsitogeneticheskii éffekt obrabotki semian khlopchatnika teplovymi neitronami.

After irradiation of cotton seeds with thermal neutrons, primary and tertiary monosomics and also plants with translocations were detected among offsprings M1 and M2. The interchanges had high frequency of multivalents at metaphase-I of meiosis. Genetic analysis of chlorophyll deficient cotton mutants has shown that recessive monogenic factors caused new mutations of the types xantha and viridis. New viridis mutant was also characterized by the heterozygosity of interchromosome translocations.