Production Of Inbred Lines Research Articles

Identification, Elucidation and Deployment of a Cytoplasmic Male Sterility System for Hybrid Potato.

Recent advances in diploid F1 hybrid potato breeding rely on the production of inbred lines using the S-locus inhibitor (Sli) gene. As a result of this method, female parent lines are self-fertile and require emasculation before hybrid seed production. The resulting F1 hybrids are self-fertile as well and produce many undesirable berries in the field. Utilization of cytoplasmic male sterility would eliminate the need for emasculation, resulting in more efficient hybrid seed production and male sterile F1 hybrids. We observed plants that completely lacked anthers in an F2 population derived from an interspecific cross between diploid S. tuberosum and S. microdontum. We studied the antherless trait to determine its suitability for use in hybrid potato breeding. We mapped the causal locus to the short arm of Chromosome 6, developed KASP markers for the antherless (al) locus and introduced it into lines with T and A cytoplasm. We found that antherless type male sterility is not expressed in T and A cytoplasm, proving that it is a form of CMS. We hybridized male sterile al/al plants with P cytoplasm with pollen from al/al plants with T and A cytoplasm and we show that the resulting hybrids set significantly fewer berries in the field. Here, we show that the antherless CMS system can be readily deployed in diploid F1 hybrid potato breeding to improve hybridization efficiency and reduce berry set in the field.

Production of hybrid potatoes: Are heterozygosity and ploidy levels important?

It has been proposed that maximizing heterosis for yield in potato may be achieved by maximizing heterozygosity and associated intra and interlocus interactions. Tetraploids offer more opportunities to create such interactions than diploids hence the general observations that tetraploids are higher yielding than diploids. Consequently, efforts have been made to increase heterozygosity in tetraploids by introgressing allelic diversity from other Solanum species into cultivated potato. However, conventional potato breeding is difficult because the cultivated potato is an autotetraploid with tetrasomic inheritance and it comprises highly heterozygous individuals which suffer inbreeding depression upon selfing; breeding at the tetraploid level is slow and less efficient than at diploid level. At the diploid level, it is possible to breed for and fix traits under recessive genetic control; it is nearly impossible to do so at the tetraploid level. There is also rapid response to selection due to greater variation in diploids than tetraploids. Consequently, there have been efforts to convert potato from an asexually propagated tetraploid crop into an inbred seed-propagated diploid; this is by production of inbred lines through selfing of the tetraploids to assemble desirable combinations of genes in the inbreds. These efforts are at the experimental stages and a lot of research needs to be done before they are confirmed. Because currently there is little experimental evidence to support superiority of the inbred seed-propagated diploid strategy, it appears the theory that heterosis for yield in potato may be achieved by maximizing heterozygosity and associated intra and interlocus interactions remain unchallenged; these interactions are more in tetraplods than in diploids. This paper therefore looks at genetic basis of yield heterosis in cultivated potato and the role of heterozygosity and ploidy level in production of hybrid potatoes.

Features of development and reproduction of transgenic flax

Primary transformants carrying a genetic construct with the chimeric gfp-tua6 gene were obtained using biolistic transformation of hypocotyl explants of flax variety Vasilek. Viable modified plants were used as a basis for the production of inbred lines with confirmed inheritance of introduced genetic construct in three generations. The characteristics of phenological growth stages, plant height, number of bolls and meiosis were studied for transgenic plants. A comparison of transformed lines based on reproduction years revealed a significant decrease of seed production in one line. Meiotic analysis of this line at metaphase I and anaphase I stages was conducted. The percentage of cells with impaired meiosis was highest in transgenic plants of the line with the lowest seed production. Thus, the nonspecific incorporation of genetic construct into the flax genome using biolistic transformation impairs meiosis to a different extent and it is the main reason for unequal reproducibility of transgenic flax. The production of stably reproducing transgenic lines requires systematic analysis of meiosis.

Genetic distance among doubled haploid maize lines and their testcross performance under drought stress and non-stress conditions

In contrast to conventional inbreeding that takes up to seven generations to develop inbred lines, the doubled haploid (DH) technology allows production of inbred lines in two generations. The objectives of the present study were to: (a) evaluate testcross performance of 45 doubled haploid lines under drought stress and non-stress conditions (b) estimate heritabilities for grain yield and other traits and (c) to assess the genetic distance and relationship among the DH lines using 163,080 SNPs generated using genotyping-by-sequencing (GBS). The 45 hybrid and five checks were evaluated using a 10 × 5 alpha lattice in six drought stress and nine well-watered environments in Kenya, Uganda, and Tanzania. Differences in trait means between the drought stress and well-watered conditions were significant for all measured traits except for anthesis date. Genetic variances for grain yield, grain moisture, plant height and ear height were high under well-watered environments while genetic variance for anthesis date, root lodging and stalk lodging were high under drought stress environments. Combined analyses across drought stress and well-watered environments showed that ten top hybrids produced 1.6–2.2 t/ha grain yield under well-watered condition and 1–1.4 t/ha under drought stress condition higher than the mean of the commercial checks. Genetic distance between pairwise comparisons of the 38 of the 45 DH lines ranged from 0.07 to 0.48, and the overall average distance was 0.36. Both cluster and principal coordinate analysis using the genetic distance matrix calculated from 163,080 SNPs showed two major groups and the patterns of group was in agreement with their pedigree. Thirteen (13) of the best hybrids are currently in National Performance Trials testing, an important step towards commercialization in Kenya, Tanzania and Uganda.

Trends of pollen production and tassel area index in yellow lines, hybrids and blue corn landraces

Studies on pollen amount play significant role either in selection or seed production. The results of our two-year-long experiments suggest that both cropyear and genotype influence the pollen production of inbred lines. Data confirm those of Fonseca et al. (2003) that TAI can be used for the prediction of pollen amount. Pollen is an important vector of gene flow in maize (Luna et al., 2001). With their large height (for example by Santo D. Blue ≈ 425 cm) and abundant pollen amounts special blue varieties can play as markers in the studies of GMO (genetically modified organism) versus conventional cultivation, co-cultivation, since the blue colour as a dominant feature can make their detection easy.

Selection, hybridization and genome manipulation in Siluroidei

Resume Selection, hybridization, and gcnome manipulation in the Siluroidei is reviewed. Selection topics include strain evaluation, qualitative traits, quantitative traits, mass selection, farnily selection, inbreeding, and crossbreeding. Hybridization is discussed with reference to culture traits. Genome manipulation technologies - sex reversal, gynogenesis, androgenesis, polyploidization, and gene transfer - are considered with application to genctic improvernent of Siluroidei. Strains of ictalurid catfish Vary significantly for traits such as growth, disease resistance, harvestahility, reproduction, body conformation and carcass yield. Growth of domestic strains can be 250% greater than that of wild strains. Strain differences have also been identified for clariid, bagrid, and silurid catfishes. Mass selection has increascd growth rate by up to 30%. Heritability estimates predict a rcsponse to selection for the traits of diseasc resistance and tolcrance to low oxygen Icvels. Crossbreeding strains of Ictalurus punctatus have improved growth, diseasc resistance and reproductive performance. Two generations of inbreeding depresscd body weight of I. punctatus as much as 30%. and can reducc viability and reproductive performance. Hybridization of I. punctatus X I. furcatus has resulted in a 20% increase in growth. Traits for tolerance to oxygen deficit, feed conversion, disease resistance, harvestability, and carcass yicld were also irnproved. Interspecific, intergeneric, and intcrfamilial hyhrids have bccn made with clariid fishes; heterotic growth was indicated. Hybridization has also been used to combine desirable traits of parental species. Sex reversal of I. punctatus using estrogen treatment followcd by progeny testing can result in monosex, all-male populations. Gynogenesis and androgenesis are approaches to production of inbred lines of catfish, but thus far have limited application in aquaculture. Polyploidization has been applied in several ictalurid, silurid, and clariid fishes, but predicted improvements in performance have not been realized. Gene transfer has been accomplished in I. punctatus and Clarias gariepinus using microinjection and electroporation; the foreign genes have been expressed and inherited. Transgenic I. punctatus containing salmonid growth hormone genes grew 20-40% faster than controls.

Production of androgenetic diploid rainbow trout.

Haploid androgenesis was induced in rainbow trout (Salmo gairdneri) when eggs were irradiated with 60Co gamma radiation prior to fertilization. Diploidy was restored to the androgenetic haploid zygotes by suppression of first cleavage division using hydrostatic pressure. Peak survival in the androgenetic diploid lots (32.5-38.9 percent of control) occurred when a pressure shock of 9000 pounds per square inch lasting from one to three minutes was applied to the eggs 345 minutes post-fertilization. Chromosomal analysis confirmed diploidy in the androgenetic individuals and suggested that YY rainbow trout are viable to at least the "eyed stage" of development. Inheritance patterns at two loci confirmed all-paternal inheritance. The relatively high yields of completely homozygous androgenetic rainbow trout and the potential for the use of androgenesis in the production of inbred lines and in genetic studies indicate that androgenesis may become a valuable tool in fish research and breeding.

The inheritance of partial self-compatibility in Brassica oleracea L. inbreds homozygous for different S-alleles

In a study of partial self-compatibility in Brassica oleracea, flower number, seeded siliqua and seed production were recorded on self and cross-pollinated inflorescences of 32 progenies obtained by inter-crossing and selfing 8 plants homozygous for the incompatibility alleles S2, S5, S15 and S45.Progeny differences for both self-and out-cross seed production could be largely attributed to G.C.A. effects which were essentially uncorrelated. For cross-pollinated inflorescences heterosis was also important. Significant differences were found for selfed seed set and its two components, the proportion of flowers producing seeded siliquae and the numbers of seed per seeded siliqua, between parents with the same S-allele which could not be attributed to S-genotype alone. No evidence of increased self-compatibility in particular S-allele heterozygotes (mutual weakening) could be found.Outcross seed production depended primarily on the numbers of seeds set per seeded siliqua while self seed production was largely determined by the proportion of flowers which produced seeded siliqua. It is suggested that this is a key character for the production of inbred lines with reduced partial self-compatibility.

The production of inbred lines of brussels sprouts with dominant S-alleles

The best sources of Brussels sprout inbred lines with both good agronomic characters and high self-incompatibility are likely to be cultivars of reasonably good agronomic type which have not been too intensively selected. Comparison of three cultivars of different agronomic quality showed that the cultivars of poor and moderate quality had about 55% of plants with a dominant S-allele, but the most highly selected cultivar had only 25% of such plants. A programme of S-allele screening is suggested which incorporates the minimum number of tests required to determine whether or not a particular plant has a dominant S-allele. A survey of S-alleles present in commercial F1 hybrids showed that the frequency of dominant S-alleles was only 19% in hybrids released prior to the end of 1971, but was 50% in hybrids released since 1971.

The Effect of Inbreeding on Reproductive Fitness of S. C. W. Leghorns

THE reproductive fitness of an animal may be defined as the number of its offspring reaching breeding age. When all birds in a breeding flock are given an equal opportunity to reproduce themselves, in the sense that the beginning and duration of the hatching season are held constant and that no young are culled, wide variation in reproductive fitness exists.This variation is of particular importance in the production of inbred lines, where selection for fitness may have to be practiced in order to prevent the reproductive rates from decreasing below replacement levels. Should the variation in fitness be dependent on the variation in the degree of homozygosity of either the parents or the offspring (thus producing differential rates of elimination), the accuracy of computed increases in homozygosity under inbreeding (the inbreeding coefficients) may be brought into question. The present study is designed to throw some light on this question, .