小麦品种群体的细胞学研究

对９个小麦品种群体进行了细胞学观察。结果表明,４．５３％的细胞含有至少一对不配对的染色体,２．３１％的细胞里,染色体偏离正常的数目。显然,这种自然的不规则性可能导致非整倍体后代的产生。３．５７％的细胞发生了易位,群体的２．２２％为单体植株。     

Genetic studies in dioecious melandrium. I

Sex-linked and sex-influenced inheritance are of interest because of their relation to the still intriguing problem of sex detrmination. Genes involved in the formation of the sex organs are regarded to be sex-determining genes. These genes may be present in all chromosomes including the sex-chromosomes. Other genes present in the sex-chromosomes, but not involved in sex determination, are the sex-linked genes. A mutation for narrow leaves we came across in ourM. ablum material is regarded as a case of sex linkage. Also the certation effect observed inM. album andM. dioicum must have been caused by genes on the sex-chromosomes. In both cases, however, it is not altogether unikekely, that the genes, regarded as sex-linked ones, actually take in the process of sex-determination.Sex-determining genes might influence the effect of other genes, that are therefore called sex-influenced genes. We observed a number of such sex-influenced characters inMelandrium.InM. album, female plants are, on the whole, larger than male plants, having larger stems and leaves. The petals, however, are larger in male plants, except in families with very broad petals. The leaves and petals are narrower in female plants than in male ones, except in families with very broad leaves and families with broad petals, where the difference in shape was no longer present. Usually, slightly more anthocyanin is formed in male plants than in females both in petals and the green parts. More glandular hairs were observed on male plants than on female ones.Insofar the observations were made inM. dioicum the same results were obtained.We regard these phenomena to be an expression of the different physiological conditions in female and in male plants, these conditions being provoked by the sex-determinging genes and more favourable for vegetative growth in female than in male plants.     

Genetic studies of frost resistance in wheat

Summary Genetic studies of frost resistance were performed on various wheat varieties using diallel, F₂ monosomic and substitution analysis.A six-parental cross including reciprocals was carried out, and F₁ hybrids and their parents were used for the freezing tests under controlled conditions. Both the general combining ability (GCA) and the specific combining ability (SCA) were significant, indicating additive and non-additive gene action in the inheritance of frost resistance. The high GCASCA ratio revealed a preponderance of additive genetic variance. No significant reciprocal differences were found between the reciprocal crosses. The variance/covariance graphical analysis indicated the partial dominance of frost sensitivity. Frost sensitive varieties had the largest number of dominant genes, while frost resistant varieties had the highest proportion of recessive genes. The magnitude of the additive component of variation was higher than that of the dominance component, and the overall measure of the degree of dominance was smaller than one, so average dominance is incomplete. The increasing and decreasing alleles are not equally frequent at all loci. In this set of wheat varieties the values of narrow and broad heritability are relatively high.F₂ monosomic analysis of the winter wheat variety Arthur crossed with the monosomics of Chinese Spring revealed that the average frost resistance of all the 21 monosomics was lower than that of the disomic. F₂ monosomic hybrids 5A, 2B, 4B and 5D proved to be relatively frost resistant, while monosomics 3A, 3B and 6D were the most sensitive.The control of frost resistance in the set of chromosome substitution lines of the variety Cheyenne into Chinese Spring (with the exception of 2B) indicated that the genes responsible for the frost resistance of Cheyenne are localised in chromosomes 5A, 7A, 4B, 5B, 4D and 5D.The genetic basis of frost resistance and problems of analysis are discussed.     

Genetic dissection of grain yield in bread wheat. I. QTL analysis

Grain yield forms one of the key economic drivers behind a successful wheat (Triticum aestivum L.) cropping enterprise and is consequently a major target for wheat breeding programmes. However, due to its complex nature, little is known regarding the genetic control of grain yield. A doubled-haploid population, comprising 182 individuals, produced from a cross between two cultivars ‘Trident’ and ‘Molineux’, was used to construct a linkage map based largely on microsatellite molecular makers. ‘Trident’ represents a lineage of wheat varieties from southern Australia that has achieved consistently high relative grain yield across a range of environments. In comparison, ‘Molineux’ would be rated as a variety with low to moderate grain yield. The doubled-haploid population was grown from 2002 to 2005 in replicated field experiments at a range of environments across the southern Australian wheat belt. In total, grain yield data were recorded for the population at 18 site-year combinations. Grain yield components were also measured at three of these environments. Many loci previously found to be involved in the control of plant height, rust resistance and ear-emergence were found to influence grain yield and grain yield components in this population. An additional nine QTL, apparently unrelated to these traits, were also associated with grain yield. A QTL associated with grain yield on chromosome 1B, with no significant relationship with plant height, ear-emergence or rust resistance, was detected (LOD ≥2) at eight of the 18 environments. The mean yield, across 18 environments, of individuals carrying the ‘Molineux’ allele at the 1B locus was 4.8% higher than the mean grain yield of those lines carrying the ‘Trident’ allele at this locus. Another QTL identified on chromosome 4D was also associated with overall gain yield at six of the 18 environments. Of the nine grain yield QTL not shown to be associated with plant height, phenology or rust resistance, two were located near QTL associated with grain yield components. A third QTL, associated with grain yield components at each of the environments used for testing, was located on chromosome 7D. However, this QTL was not associated with grain yield at any of the environments. The implications of these findings on marker-assisted selection for grain yield are discussed.     

Defective kernel mutants of maize. I. Genetic and lethality studies

A planting of 3,919 M₁ kernels from normal ears crossed by EMS-treated pollen produced 3,461 M₁ plants and 3,172 selfed ears. These plants yielded 2,477 (72%) total heritable changes; the selfed ears yielded 2,457 (78%) recessive mutants, including 855 (27%) recessive kernel mutants and 8 (0.23%) viable dominant mutants. The ratio of recessive to dominant mutants was 201:1. The average mutation frequency for four known loci was three per 3,172 genomes analyzed. The estimated total number of loci mutated was 535 and the estimated number of kernel mutant loci mutated was 285. Among the 855 kernel mutants, 432 had a nonviable embryo, and 59 germinated but had a lethal seedling. A sample of 194 of the latter two types was tested for heritability, lethality, chromosome arm location and endosperm-embryo interaction between mutant and nonmutant tissues in special hyper-hypoploid combinations produced by manipulation of B-A translocations. The selected 194 mutants were characterized and catalogued according to endosperm phenotype and investigated to determine their effects on the morphology and development of the associated embryo. The possibility of rescuing some of the lethal mutants by covering the mutant embryo with a normal endosperm was investigated. Ninety of these 194 mutants were located on 17 of the 18 chromosome arms tested. Nineteen of the located mutants were examined to determine the effect of having a normal embryo in the same kernel with a mutant endosperm, and vice versa, as compared to the expression observed in kernels with both embryo and endosperm in a mutant condition. In the first situation, for three of the 19 mutants, the mutant endosperm was less extreme (the embryo helped); for seven cases, the mutant endosperm was more extreme (the embryo hindered); and for nine cases, there was no change. In the reverse situation, for four cases the normal endosperm helped the mutant embryo; for 14 cases there was no change and one case was inconclusive.