Pairs Of Reciprocal Crosses Research Articles

Field Evaluation of Experimental Maize Hybrids for Resistance to the Fall Armyworm (Lepidoptera: Noctuidae) in a Warm Temperate Climate.

The polyphagous fall armyworm (FAW), Spodoptera frugiperda, has become an invasive pest worldwide in recent years. To develop maize germplasm with multiple pest resistance and understand genetic inheritance, 12 experimental hybrids (six pairs of reciprocal crosses) with diverse genetic backgrounds and four commercial checks were examined for FAW resistance in 2013 and 2014. The experiment utilized a randomized complete block design with four replications as the block factor. FAW injury on maize plants was assessed at 7 and 14 d after the artificial infestation at the V6 stage, and predatory arthropod taxa and abundance on maize seedlings were recorded 7 d after the infestation. Spodoptera frugiperda resistance varied significantly among the 16 hybrids. Two reciprocal crosses ('FAW1430' × 'Oh43' and 'CML333' × 'NC358') showed the least FAW injury. Eleven arthropod predators [i.e., six coleopterans, three hemipterans, earwigs (dermapterans), and spiders (or arachnids)] were also recorded; the two most common predators were the pink spotted ladybeetle, Coleomegilla maculata, and the insidious flower (or minute pirate) bug, Orius spp. Predator abundance was not correlated to FAW injury but varied greatly between 2013 and 2014. Principal component analysis demonstrated that, when compared with FAW resistant (or Bt-transgenic) checks ('DKC69-71', 'DKC67-88', and 'P31P42'), five pairs of the reciprocal crosses had moderate FAW resistance, whereas a pair of reciprocal crosses ('NC350' × 'NC358' and NC358 × NC350) showed the same FAW susceptibility as the non-Bt susceptible check 'DKC69-72'. Both parents contributed similarly to FAW resistance, or no maternal/cytoplasmic effect was detected in the experimental hybrids.

Genomic Architecture of Hybrid Male Sterility in a Species Without Sex Chromosomes (Tigriopus californicus, Copepoda: Harpacticoida).

Sterility among hybrids is one of the most prevalent forms of reproductive isolation delineating species boundaries and is expressed disproportionately in heterogametic XY males. While hybrid male sterility (HMS) due to the "large X effect" is a well-recognized mechanism of reproductive isolation, it is less clear how HMS manifests in species that lack heteromorphic sex chromosomes. We evaluated differences in allele frequencies at approximately 460,000 SNPs between fertile and sterile F2 interpopulation male hybrids to characterize the genomic architecture of HMS in a species without sex chromosomes (Tigriopus californicus). We tested associations between HMS and mitochondrial-nuclear and/or nuclear-nuclear signatures of incompatibility. Genomic regions associated with HMS were concentrated on a single chromosome with the same primary 2-Mbp regions identified in one pair of reciprocal crosses. Gene Ontology analysis revealed that annotations associated with spermatogenesis were the most overrepresented within the implicated region, with nine protein-coding genes connected with this process found in the quantitative trait locus of chromosome 2. Our results indicate that a narrow genomic region was associated with the sterility of male hybrids in T. californicus and suggest that incompatibilities among select nuclear loci may replace the large X effect when sex chromosomes are absent.

Genome-Wide Association Study in Pseudo-F2 Populations of Switchgrass Identifies Genetic Loci Affecting Heading and Anthesis Dates.

Switchgrass (Panicum virgatum) is a native prairie grass and valuable bio-energy crop. The physiological change from juvenile to reproductive adult can draw important resources away from growth into producing reproductive structures, thereby limiting the growth potential of early flowering plants. Delaying the flowering of switchgrass is one approach by which to increase total biomass. The objective of this research was to identify genetic variants and candidate genes for controlling heading and anthesis in segregating switchgrass populations. Four pseudo-F2 populations (two pairs of reciprocal crosses) were developed from lowland (late flowering) and upland (early flowering) ecotypes, and heading and anthesis dates of these populations were collected in Lafayette, IN and DeKalb, IL in 2015 and 2016. Across 2 years, there was a 34- and 73-day difference in heading and a 52- and 75-day difference in anthesis at the Lafayette and DeKalb locations, respectively. A total of 37,901 single nucleotide polymorphisms obtained by exome capture sequencing of the populations were used in a genome-wide association study (GWAS) that identified five significant signals at three loci for heading and two loci for anthesis. Among them, a homolog of FLOWERING LOCUS T on chromosome 5b associated with heading date was identified at the Lafayette location across 2 years. A homolog of ARABIDOPSIS PSEUDO-RESPONSE REGULATOR 5, a light modulator in the circadian clock associated with heading date was detected on chromosome 8a across locations and years. These results demonstrate that genetic variants related to floral development could lend themselves to a long-term goal of developing late flowering varieties of switchgrass with high biomass yield.

Using next-generation RNA sequencing to identify imprinted genes.

Genomic imprinting is manifested as differential allelic expression (DAE) depending on the parent-of-origin. The most direct way to identify imprinted genes is to directly score the DAE in a context where one can identify which parent transmitted each allele. Because many genes display DAE, simply scoring DAE in an individual is not sufficient to identify imprinted genes. In this paper, we outline many technical aspects of a scheme for identification of imprinted genes that makes use of RNA sequencing (RNA-seq) from tissues isolated from F1 offspring derived from the pair of reciprocal crosses. Ideally, the parental lines are from two inbred strains that are not closely related to each other. Aspects of tissue purity, RNA extraction, library preparation and bioinformatic inference of imprinting are all covered. These methods have already been applied in a number of organisms, and one of the most striking results is the evolutionary fluidity with which novel imprinted genes are gained and lost within genomes. The general methodology is also applicable to a wide range of other biological problems that require quantification of allele-specific expression using RNA-seq, such as cis-regulation of gene expression, X chromosome inactivation and random monoallelic expression.

Utilization of weedy rice for development of japonica hybrid rice ( Oryza sativa L.)

Two representative weedy rice lines, three typical japonica varieties and three typical indica varieties were used for 6 pairs of reciprocal crosses. The morphological traits of twelve F 1 hybrid lines, their parents and four elite cultivars were investigated for heterosis over mid-parent (HM), over parent (HP) and competitive heterosis (CH) analysis. Traits detected in weedy rice lines seemed larger than those in cultivars and excellent heterosis was produced in weedy rice crossing with japonica rice. Although weedy rice kept closer relationships with japonica rice compared to indica rice. But the heterosis of reciprocal crosses between weedy rice and japonica was closed to those of crosses between indica rice and japonica rice. In six of one hundred and eighteen weedy rice lines, the fertility restore gene for BT type cytoplasmic male sterility (BT-CMS) were detected. Weedy rice was very valuable germplasm resources with the abundant polymorphism. Meanwhile, the disadvantage, lodging, shattering and incompact plant type, should be modified by hybridization, backcross and multiple cross with japonica rice. Although it is difficult to use weedy rice directly, weedy rice may be available to breed both male sterile line and restorer line through improvement, developing japonica hybrid rice.

Meiotic transmission of Drosophila pseudoobscura chromosomal arrangements.

Drosophila pseudoobscura harbors a rich gene arrangement polymorphism on the third chromosome generated by a series of overlapping paracentric inversions. The arrangements suppress recombination in heterokaryotypic individuals, which allows for the selective maintenance of coadapted gene complexes. Previous mapping experiments used to determine the degree to which recombination is suppressed in gene arrangement heterozygotes produced non-recombinant progeny in non-Mendelian ratios. The deviations from Mendelian expectations could be the result of viability differences between wild and mutant chromosomes, meiotic drive because of achiasmate pairing of homologues in heterokaryotypic females during meiosis, or a combination of both mechanisms. The possibility that the frequencies of the chromosomal arrangements in natural populations are affected by mechanisms other than adaptive selection led us to consider these hypotheses. We performed reciprocal crosses involving both heterozygous males and females to determine if the frequency of the non-recombinant progeny deviates significantly from Mendelian expectations and if the frequencies deviate between reciprocal crosses. We failed to observe non-Mendelian ratios in multiple crosses, and the frequency of the non-recombinant classes differed in only one of five pairs of reciprocal crosses despite sufficient power to detect these differences in all crosses. Our results indicate that deviations from Mendelian expectations in recombination experiments involving the D. pseudoobscura inversion system are most likely due to fitness differences of gene arrangement karyotypes in different environments.

Evidence of apomixis in hemisexual dogroses, Rosa section Caninae

All members of Rosa section Caninae, dogroses are polyploid and characterized by their unbalanced meiosis, which in most cases leads to a pronounced morphological influence from the maternal parent. In a previous investigation on a pair of reciprocal crosses between two species in this section, Rosa dumalis and R. rubiginosa (2n=35), nine offspring plants (approximately 10%) did not receive any of the 21 RAPD markers present in the respective pollen parent. This was interpreted as a possible occurrence of apomixis. These nine plants have now been subjected to a further study with additional markers. Thirteen new RAPD markers showed the same result as in the previous investigation: none of the nine plants inherited any of the pollen donor markers. The reproducibility of the RAPD markers was checked by mixing DNA samples to obtain a series of artificial hybrids between the two parent plants. Twelve RAPD markers gave the expected result, whereas one marker appeared only 50% of the time. In addition, pollen viability, mean number of seeds per hip, mean seed weight, and mean weight of fruit flesh per hip have been studied on the four progeny groups: R. dumalis×R. rubiginosa plants which received pollen donor markers (PM plants), R. dumalis×R. rubiginosa plants which did not receive any pollen donor markers (NPM plants), R. rubiginosa×R. dumalis PM plants and R. rubiginosa×R. dumalis NPM plants. A canonical discriminant analysis based on these four reproductive characters separated the four progeny groups. There were significant differences between the two PM groups in all investigated characters, and also between the PM and the NPM groups in pollen viability. The result from the RAPD markers together with the differences in pollen viability between the PM and NPM progeny groups is taken as an indication that apomixis occurs within the Caninae section.

Variation and Inheritance in Hemisexual Dogroses, Rosa Section Caninae

ABSTRACTDogroses, Rosa sect. Caninae (x=7, 2n=28, 35 or 42) grow wild in the Scandinavian countries. Hips from this section have a particular aroma and are used in Sweden for making a traditional dessert dish, rose hip soup. Commercial production has recently been initiated with field-grown selections from the Balsgård rose hip breeding program. The species are often used as rootstocks for ornamental roses and some of them could also be a potential source of resistance for e.g. blackspot. All species within the section have a unique meiosis with 7 bivalents regardless of ploidy level. Viable pollen cells contain 7 chromosomes and egg cells 21, 28 or 35 chromosomes. In a study of a pair of reciprocal crosses between R. dumalis X R. rubiginosa (both 2n=35), molecular RAPD markers showed that all 78 progeny plants inherited almost all of the seed-parent specific marker. In contrast, only half of the pollen-specific markers were transmitted to any of the progenies. Most of the pollen-specific markers were found in 75–90% of the progenies, but there was also one marker that was only found in 50% of the progenies and three markers that only appeared in 2–4 plants. The study also showed that the species were genetically very similar. Nine progeny plants have never received any of the pollen-specific markers and these plants were subjected to an extended study with additional molecular markers. Reproductive characters as pollen viability, amount and weight of seeds and fruit weight variables were studied on all the progeny plants. Pollen viability was approx 25% in the parent plants whereas the hybrid progenies had a pollen viablity of 0–10%. Of the nine progeny plants which lacked pollen-specific RAPD markers even in this extended study, seven had a pollen viability close to that found in their seed-parents. This suggests that facultative apomixis occurs in this section, but it is difficult to quantify its contribution to the already low genetic variability.

Morphological and RAPD markers show a highly skewed distribution in a pair of reciprocal crosses between hemisexual dogrose species, Rosa sect. Caninae

The dogroses, Rosa sect. Caninae, are polyploid and characterized by their unique meiosis with an unequal number of chromosomes in the male and female gametes. The pollen cells have 7 chromosomes and the egg cells 21, 28 or 35 depending on the ploidy level of the species. The resulting matroclinal inheritance was studied with both morphological and molecular markers in a pair of reciprocal crosses between R. dumalis and R. rubiginosa (2n=35). A canonical discriminant analysis based on seven morphological characters showed only a minor overlapping between the two progeny groups. In addition, the R. dumalis×R. rubiginosa offspring were more heterogeneous than the offspring from the reciprocal cross in each of the characters analysed. Eleven RAPD markers specific for the R. dumalis parent and 10 RAPD markers specific for the R. rubiginosa parent were scored in the offspring. Each of the offspring exhibited either all, or all-but-one, of the seed parent markers. The average number of pollen donor markers found in the offspring was 3.2 (R. dumalis×R. rubiginosa) and 2.7 (R. rubiginosa×R. dumalis). About half of the pollen donor markers were never transmitted to the progeny. This is, to our knowledge, the first time the highly skewed chromosome distribution in Rosa sect. Caninae has been demonstrated with statistically evaluated morphological data and with molecular markers.

Predominant Paternal Transmission of the Mitochondrial Genome in Cucumber

Segregation analyses of restriction fragment length polymorphisms (RFLPs) in cucumber revealed one paternally inherited Pstl genomic clone, possibly from either the mitochondrial (mt) or chloroplast (cp) genome. Polymorphisms in the mtDNA were identified with clones apocytochrome B and atp9. No polymorphisms were detected in the cpDNA using restriction enzymes that recognize 6 and 4 bp sequences. Two pairs of reciprocal crosses were made between individual plants of the breeding line Gy14 and cultivar Wisconsin SMR18 with USDA plant introduction 432860. A nuclear RFLP was biparentally inherited and established the hybrid origin of all progenies. For 68 of 70 progenies (97%), the mt genome of cucumber showed paternal transmission. Two hybrid plants possessed both parental fragments for one of the two polymorphic probe enzyme combinations, likely due to mitochondrial heterogeneity in the pollen parent.

A genetic analysis of low‐temperature‐sensitive sterility in indica‐japonica rice hybrids

AbstractLow‐temperature‐sensitive sterility has become one of the major obstacles in indica–japonica hybrid rice breeding. The objectives of this paper were to evaluate the extent of the fertility reduction and to determine the genetic basis of low‐temperature‐sensitive sterility. Seventeen varieties were crossed in various ways to produce 21 F1s including 16 indica‐japonica hybrids. Fertility of the F1s and their parents was examined under both high and low temperature conditions. Considerable reduction in spikelet fertility was observed under low‐temperature conditions in the majority of the indica–japonica hybrids having at least one wide compatibility parent. However, the extent of fertility reduction varied greatly, depending on the parental genotypes. Data from five pairs of reciprocal crosses indicated that the cytoplasm had no effect on fertility reduction. The more‐or‐less bimodal distribution of the fertility segregation of one BC1F1 and two F2: populations under low‐temperature conditions suggested that the low‐temperature‐sensitive sterility was controlled by only one or a few genes. It was also shown that the low‐temperature‐sensitivity is not related to wide compatibility. We conclude that it is possible to develop indica‐japonica hybrids with wide compatibility and also insensitivity to the low‐temperature conditions.

DNA fingerprint variability within and among parental lines and its correlation with performance of F1 laying hens

Genetic diversity within and among nine pure lines of Beijing White Leghorn chickens was determined by DNA fingerprinting using human ministatellite probes 33.6 and α-globin 3'HVR, as well as bacteriophage M13. Within lines similarity coefficients ranged from 0.497 to 0.628, significantly higher than that within a sample of white chicken from a local market. Relationships among lines were established by clustering analysis based on inter-line coefficients of difference calculated from DNA fingerprints of pooled DNA. A complete diallel crossing among the nine pure lines was conducted. By using linear correlation analysis, it was found that the maximum distance between parental lines was positively correlated with egg number, egg production, survival rate and their corresponding heterosis percentages within a pair of reciprocal crosses. Similar relationships were found where only the higher of the reciprocal crosses were used in the analysis. It was also shown that similarity coefficients within a sire line or dam line were positively correlated with 40-week egg number and its heterosis percentage and the heterosis percentage for 40-week egg production, but negatively correlated with the 40-week survival rate of the cross-bred populations.

Inheritance and Agronomic Performance of the Waxless Character in Brassica napus L.

AbstractA mutant of oilseed rape (B. napus L.) with waxless leaves was discovered in 1988. Three pairs of reciprocal crosses were made between the mutant (Wl) and 3 normal wax layered lines (Nwl). By the summer planting in Kunming and Wenjiang and the autumn planting in Wenjiang, it was confirmed that the Wl character is completely dominant to the normal opposite Nwl. Chi‐square tests revealed that the segregation ratios of Wl to Nwl among B1 and F2 plants fit to 1:1 and 3:1, respectively, i.e. the assumption of one gene pair. The yield of 12 hybrids, which were derived fom Wl and some Nwl lines, exceeded the check control ‘Zhong You 821’, a best cultivar in Chinese production by 19.31 % on the average. When the seedling had 3–4 leaves, both phenotypes can be accurately determined visually on the field. This material possesses potential value for studies of the genetics and breeding, as a prominent genetic marker in B. napus.

Genetic Control of Glycinebetaine Level in Barley1

The accumulation of betaine (glycinebetaine, N,N,N‐trimethylglycine) in water‐ or salt‐stressed barley (Hordeum vulgare L.) plants may be a metabolic adaptation to stress. We investigated the inheritance of betaine level using genotypes varying in betaine content. Shoots of unstressed plants grown in growth chambers were assayed for betaine at the three‐leaf stage. Analyses of four pairs of reciprocal crosses indicated that neither maternal nor cytoplasmic effects were significant but that there may be some dominance of the low betaine trait. An incomplete diallel made with eight low‐ and five high‐betaine parents indicated that general combining ability accounted for the majority (74.6%) of genetic effects, suggesting a largely additive trait. Additive, dominance, and epistatic components of heritability were estimated by generation mean analysis of the parental, F1, F2, and backcross generations of a single high‐ × low‐betaine cross. This analysis also showed that betaine accumulation was a predominantly additive trait. Narrow‐sense heritability values for the trait were 0.53 and 0.63 from midparent‐offspring regression and generation mean analysis, respectively. The level of betaine accumulation in barley is a nuclear, predominantly additive trait of relatively high narrow‐sense heritability. Therefore, evaluation of the adaptive significance of betaine in water and salt‐stressed plants should be possible using an isopopulation approach.

Inheritance of glutenin subunits in F1 seeds of reciprocal crosses between European hexaploid wheat cultivars

Ten pairs of reciprocal crosses have been made between wheat cultivars which show differences in their glutenin subunit compositions. The F1 seed glutenin subunit composition was studied by means of polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS). The results indicate that all the high molecular weight (HMW) and medium molecular weight (MMW) subunits (from 133,000 to 65,000 daltons) are transmitted to the F1 seed generation from the parental cultivars. In accordance with the triploid nature of the heterozygous endosperm (3n) and with the maternal and paternal gene dosage ratio (2∶1) in the endosperm itself, a significant effect of maternal parent is registered when comparing pairs of reciprocal seeds. Genes coding for the glutenin subunits are expressed whatever their doses are (one, two, or three) in the hybrid endosperm; thus the glutenin subunits inheritance is consistent with the co-dominant type.For one pair of the reciprocal crosses, two MMW parental bands (MW: 71,000 and 66,000) seemed absent in the F1 seed patterns while a new band with an intermediate, apparent MW (68,000) appears. This phenomenon was observed when the glutenins analyzed by electrophoresis were previously separated from other endosperm proteins, and not when they were directly extracted from the ground seed. We assume that the extraction can cause interactions between moieties attached to the subunits and lead to the formation of a complex having an intermediate electrophoretic mobility.

Inheritance of Resistance to Permethrin in Culex pipiens quinquefasciatus1

The mode of inheritance of resistance to permethrin was studied in 2 strains of the southern house mosquito selected with the d-trans and d-cis isomers of this pyrethroid. Resistance was found to be co dominant (D = −0.014 to 0.14) in the d-trans-selected strain, and partially recessive (D = −0.15 to −0.35) in the d-cis-selected strain. The similarity of dominance values (D) in each pair of reciprocal crosses indicates a lack of sex linkage. Dose response lines for the backcross progeny (F1 ♂×S♀) were significantly different from those which might be expected on the basis of single gene inheritance, leading to the conclusion that permethrin resistance in this mosquito is of polyfactorial origin.

Genetic control of seed proteins in wheat

Electrophoretic profiles of crude protein extracts from seed of F1 hybrids and reciprocal crosses among diploid, tetraploid and hexaploid wheats were compared with those of their respective parental species. The electrophoretic patterns within each of three pairs of reciprocal crosses, T.boeoticum X T.urartu, T.monococcun X T. urartu and T.dicoccum X T. araraticum, were different from one another but were identical with those of their respective maternal parents. Protein bands characteristic of the paternal parents were missing in F1 hybrid seed suggesting that the major seed proteins in wheat were presumably regulated by genotype of the maternal parent rather than by the seed genotype. However, in another three pairs of reciprocal crosses, T.boeoticum X T. durum, T.dicoccum X T.aestivum and T. zhukovskyi x T. aestivum, protein bands attributable to the paternal parents were present in the F1 hybrid seeds indicating that the seed proteins were not always exclusively regulated by the maternal genotype. The expression of paternal genomes is presumably determined by dosage and genetic affinity of the maternal and paternal genomes in the hybrid endosperm. The maternal regulation of seed protein content is probably accomplished through the maternal control over seed size. The seed protein quality may, however, depend upon the extent of expression of the paternal genome.

Study on inheritance of resistance to root aphid, Pemphigus bursarius, in lettuce

SUMMARYThe inheritance of resistance to lettuce root aphid, Pemphigus bursarius, was studied in lettuce using the Wellesbourne cultivars Avondefiance and Avoncrisp as resistant parents and Borough Wonder and Webb's Wonderful as aphid‐susceptible parents. All four cultivars were crossed in all possible combinations including reciprocals and the response to root aphid of plants in the P1F1F2 and BC generations was assessed using apterae of P. bursarius from the lettuce cv. Iceberg. Resistance to attack was clearly inherited and the parents appeared to be homozygous for their resistance or susceptibility. In the F1 generation, however, in all crosses between resistant and susceptible parents, segregation into susceptible, resistant and some slightly less resistant plants occurred. This and the highly significant differences in segregation between pairs of reciprocal crosses in the F1 and other generations indicate that the inheritance of resistance to root aphid is controlled by extra‐nuclear factors. Modifying genes might also be involved but there appears to be no linkage of root aphid resistance with resistance to downy mildew, for which the Wellesbourne lettuces were bred.

Genetic and environmental control of foetal and placental growth in the mouse

SUMMARYBirth weight was recorded in the first and second litters of six inbred strains of mice and of all possible crosses between them. The mean birth weight of F1young was significantly greater than that of inbred young in most cases; in no case were they significantly lighter than inbred young at birth.Foetal weight and placental weight were recorded on the 17th daypost coitumin the first litters of four strains and of two pairs of reciprocal crosses. F1foetuses were 13–16% heavier than inbred foetuses on crossing four strains. F1placentae were about 15% heavier than inbred placentae on crossing three strains. Crossbreeding did not affect placental weight in the fourth strain. The significance of these findings is discussed.Analyses of data from individual strains and crosses showed that foetal weight was affected by the number of implants in the same uterine horn and independently by the number in the whole litter. The two independent effects, local and systemic respectively, tended to decrease foetal weight as litter size increased. The independent local effect of litter size on placental weight was different and tended to increase placental weight slightly as the number of implants in the same uterine horn increased.Three different instances of maternal effects on foetal and placental growth were observed.The effects of the litter and the mother on foetal growth are discussed in relation to the physiological basis of environmental variation in pre-natal growth.

THE PROBLEM OF DIFFERENCES OF OFFSPRING IN RECIPROCAL CROSSES OF DROSOPHILA

1. To test for the existence of maternal effects in Drosophila melanogaster, approximately isogenic stocks of Dichaete, pyd, vg, M-3, M-4 were prepared. Reciprocal crosses were made between each stock and Dichaete, and between Dichaete and non-Dichaete siblings. The results, as indicated by posterior dorso-central (i.e., average number of dorsocentral bristles per hemithorax), of the Dichaete progeny show that no significant differences arose within six pairs of reciprocal crosses. The reciprocal crosses of four other pairs of experiments yielded significant differences in bristle indices. Two of these pairs were alike in type of crosses, but different in type of culture method. The sign of the differences in bristle indices was reversed in these two sets of experiments, the progeny with the higher indices coming from Dichaete mothers in one case, and from Dichaete fathers in the other.2. Tests of homogeneity show that within crosses, all bottles of which have had identical treatment, di...