Identification and fine mapping of <Emphasis Type="Italic">Pi33</Emphasis>, the rice resistance gene corresponding to the Magnaporthe grisea avirulence gene <Emphasis Type="Italic">ACE1</Emphasis>

Rice blast disease is a major constraint for rice breeding. Nevertheless, the genetic basis of resistance remains poorly understood for most rice varieties, and new resistance genes remain to be identified. We identified the resistance gene corresponding to the cloned avirulence gene ACE1 using pairs of isogenic strains of Magnaporthe grisea differing only by their ACE1 allele. This resistance gene was mapped on the short arm of rice chromosome 8 using progenies from the crosses IR64 (resistant) × Azucena (susceptible) and Azucena × Bala (resistant). The isogenic strains also permitted the detection of this resistance gene in several rice varieties, including the differential isogenic line C101LAC. Allelism tests permitted us to distinguish this gene from two other resistance genes [Pi11 and Pi-29(t)] that are present on the short arm of chromosome 8. Segregation analysis in F₂ populations was in agreement with the existence of a single dominant gene, designated as Pi33. Finally, Pi33 was finely mapped between two molecular markers of the rice genetic map that are separated by a distance of 1.6 cM. Detection of Pi33 in different semi-dwarf indica varieties indicated that this gene could originate from either one or a few varieties.Communicated by D.J. Mackill     

Inheritance of photoperiod-induced flowering in three photoperiodic lines of Aeschynomene americana L.

Summary Induction of flowering by photoperiod was studied in the parental, F₁, F₂, and reciprocal backcross generations of crosses between three photoperiod-responsive Aeschynomene americana L. lines. Generation means appeared additive. Analysis with Mather and Jinks' scaling tests showed little or no epistasis and indicated that an additive-dominance model was adequate. Partitioning components of variation revealed that nearly all variation was additive genetic with dominance and environmental variation negligible. An additive genetic model with two loci, each with two alleles and all alleles having equal net effect, was tested using Power's partitioning method. Results demonstrated that the model fit the data and that there is a major additive genetic system controlling flowering in these crosses, with minor genetic and environmental influences present. Selection for flowering at a desired day length should be feasible.Accepted by A.R. HallauerFlorida Agricultural Experiment Station, Journal Series No. 9251     

Inheritance and mapping of embryo sac abortion in hybrid between Indica and Japonica rice (Oryza sativa L.)

A doubled haploid (DH) population derived from anther culture of F₁’s between an Indica var. Zhai-Ye-Qing 8 and a Japonica var. Jing-Xi17 as well as two backcross populations derived from this DH population were used to investigate inheritance of the embryo sac abortion at early megagametogenesis occurring in Indica/Japonica rice crosses. Two major loci, dominant and complementaryesa-1 andesa-2, located on chromosomes 6 and 12 respectively, were detected. Genetic analysis indicated that embryo sac fertility is mainly regulated by the gametophytic genotype at these two loci.     

Genetic aspects of wheat gliadin proteins

Inheritance of gliadin components unique to three different varieties of common wheat (Triticum aestivum L.) was studied in F₁ and F₂ seeds of intervarietal crosses using protein patterns obtained by polyacrylamide gel electrophoresis in aluminum lactate buffer (pH 3.2). The patterns of F₁ seeds of the crosses Cheyenne × Justin and INIA 66R × Justin evidenced all the bands present in the patterns of the parents; band intensities reflected gene dosage levels dependent on whether the contributing parent was maternal or paternal in accordance with the triploid nature of endosperm tissue. Most of the gliadin components examined segregated in accordance with control by a single dominant gene, but in two instances single bands in the one-dimensional electrophoretic patterns segregated in the F₂ as expected if controlled by two genes. A method of two-dimensional electrophoresis was developed that resolved these apparently single bands into two components each, which could segregate independently. Linkage analysis provided evidence of codominant alleles and closely linked genes coding for gliadin protein components in both coupling and repulsion situations. The gliadin protein components seem to be coded for by clusters of genes located on chromosomes of homoeologous groups 1 and 6 in hexaploid wheats.Reference to a company or product name does not imply approval by the U.S. Department of Agriculture to the exclusion of others which may also be suitable.     

Expression instability and genetic disorders in transgenicNicotiana plumbaginifolia L. plants

The ease of integrative transformation with foreign genes and the extent of their expression and stability in successive generations determine the applicability of direct gene transfer. InNicotiana plumbaginifolia, one to ten copies of foreign DNA were integrated into the plant genome, resulting in simple to complex patterns of integration. Genetic analysis showed that in more than 50% of the cases, this DNA inserted at two or more loci in the genome. Of the 156 crosses performed between F₁ monogenic transformants, only eight combinations showed linkage of the inserted neomycin phosphotransferase genes (npt). The following instability events were registered: physical loss, alterations in the initial segregation rates in successive meiotic generations observed in either selfing or crossing (reduction or increase in number of segregating loci) and genomic disorders in crosses between transformants. Among them of particular interest were the discordant segregation values observed between corresponding R₁ and F₁ progenies in up to 9% of the evaluated transformants. In addition, 5% of the transformants showed a phenotypic loss of resistance. In the F₃ generation, 5 out of 15 transformants exhibited instability, which was transmitted to the F₄ generation. Further increases in instability rates were observed with higher numbers of insertion loci and in crosses between independent transgenic plants, reaching 100% when a trigenic partner was involved.N. plumbaginifolia exhibited more instability thanN. tabacum under equivalent experimental conditions. The molecular bases of such instability events are discussed in relation to DNA methylation, co-suppression and genomic imbalance.     

Comparative efficiency of four selection methods for deriving high-yielding lines in mungbean [Vigna radiata (L.) Wilczek]

The comparative efficiency of four selection methods, viz., honeycomb (HC), pedigree selection (PS), single-seed descent (SSD) and the bulk method (BM), was assessed in three crosses of mungbean. The lines derived by each method, along with check varieties, were yield-tested in a compact family block design in F₅ and F₆ generations during summer and kharif of 1990. On the basis of the mean of the lines, the range, the number of superior lines over the best check, and the proportion of the top 10% lines in all the crosses and generations, the honeycomb method exhibited superiority over PS, SSD and BM for yield per plant and its component traits. PS, SSD and BM did not differ from each other. The honeycomb and SSD methods were found suitable for deriving superior lines for seed yield and pods per plant in mungbean.     

Genetic basis of low-temperature-sensitive sterility in indica-japonica hybrids of rice as determined by RFLP analysis

 Low-temperature-sensitive sterility (LTSS) has become one of the major obstacles in indica-japonica hybrid rice breeding. In this study, we determined, using RFLP markers, the genetic basis of LTSS in two populations derived from crosses between indica and japonica parents, the BC₁F₁ of 3037/02428//3037 and the F₂ of 3037/02428. The fertility segregation in the two populations under low-temperature conditions was used as a measurement of the temperature sensitivity of the various genotypes in the populations. A RFLP survey of bulked extremes from the BC₁F₁ population identified three genomic regions, two on chromosome 1 and one on chromosome 12, that were likely to contain genes for LTSS (or Ste loci). One-way ANOVA and QTL analysis using a total of 19 markers from these three genomic regions resolved three Ste loci in the BC₁F₁ population and two Ste loci in the F₂ population. On the basis of chromosomal location these loci were distinct from those governing wide-compatibility identified in previous studies. Two- and three-way ANOVA showed that these loci acted essentially independent of each other in conditioning LTSS. The main mode of gene action was an interaction between the indica and the japonica alleles within each locus. For each respective locus this resulted in a drastic fertility reduction in the heterozygote state relative to the homozygote state. The results have significant implications in indica-japonica hybrid rice breeding programs. Received : 10 April 1996 / Accepted: 2 June 1997     

Chloroplast DNA inheritance in theStellaria longipes complex (Caryophyllaceae)

Inheritance of chloroplast DNA (cpDNA) was examined in F₁ progenies derived from three crosses and three corresponding reciprocal crosses betweenStellaria porsildii andS. longifolia. Chloroplast DNA restriction fragments were analyzed using methods of nonradioactive digoxigenin-11-dUTP labeling and chemiluminescent detection with Lumi-Phos 530. Distinct interspecific restriction fragment polymorphisms were identified and used to demonstrate the mode of cpDNA inheritance. Mode of cpDNA inheritance differed among crosses. Two crosses in whichS. porsildii, SP2920-21, was the maternal parent exhibited three different types of plastids, maternal, paternal and biparental, among the F₁ hybrids, suggesting a biparental cpDNA inheritance and plastid sorting-out inStellaria.     

Studies on protein content and yield levels in rice

Summary Crosses between low and high protein varieties revealed the dominance of low protein over high protein content. The number of desirable segregants with the double combination of high protein and yield were scored in each generation. The increasing frequency of desirable segregants from the F₂ to the F₃ generation in all the crosses increase the chances of selecting desirable recombinants for propagating improved rice varieties. Hybridisation followed by selection may help in developing varieties with high protein content and superior yield potential.     

A diallel analysis of heterosis in elite hybrid rice based on RFLPs and microsatellites

Hybrid rice has contributed significantly to the dramatic increase of rice production in the world. Despite this, little attention has been given to studying the genetic basis of heterosis in rice. In this paper, we report a diallel analysis of heterosis using two classes of molecular markers: restriction fragment length polymorphisms, (RFLPs) and microsatellites. Eight lines, which represent a significant portion of hybrid rice germ plasm, were crossed in all possible pairs, and the F₁s were evaluated for yield and yield component traits in a replicated field trial. The parental lines were surveyed for polymorphisms with 117 RFLP probes and ten microsatellites, resulting in a total of 76 polymorphic markers well-spaced in the rice RFLP map. The results indicated that high level heterosis is common among these crosses: more than 100% midparent and 40% better-parent heterosis were observed in many F₁s, including some crosses between maintainer lines. Heterosis was found to be much higher for yield than for yield component traits, which fits a multiplicative model almost perfectly. Between 16 and 30 marker loci (positive markers) detected highly significant effects on yield or its component traits. Heterozygosity was significantly correlated with several attributes of performance and heterosis. Correlations based on positive markers (specific heterozygosity) were large for midparent heterosis of yield and seeds/panicle and also for F₁ kernel weight. These large correlations may have practical utility for predicting heterosis.     

RFLP mapping of the genes controlling hybrid breakdown in rice (Oryza sativa L.)

 Complementary recessive genes hwd1 and hwd2 controlling hybrid breakdown (weakness of F₂ and later generations) were mapped in rice using RFLP markers. These genes produce a plant that is shorter and has fewer tillers than normal plants when the two loci have only one or no dominant allele at both loci. A cultivar with two dominant alleles at the hwd1 locus and a cultivar with two dominant alleles at the hwd2 locus were crossed with a double recessive tester line. Linkage analysis was carried out for each gene independently in two F₂ populations derived from these crosses. hwd1 was mapped on the distal region of rice genetic linkage map for chromosome 10, flanked by RFLP markers C701 and R2309 at a distance of 0.9 centiMorgans (cM) and 0.6 cM, respectively. hwd2 was mapped in the central region of rice genetic linkage map for chromosome 7, tightly linked with 4 RFLP markers without detectable recombination. The usefulness of RFLP mapping and map information for the genes controlling reproductive barriers are discussed in the context of breeding using diverse rice germplasm, especially gene introduction by marker-aided selection.     

Genetic Structure of Blastocerus dichotomus Populations in the Paraná River Basin (Brazil) Based on Protein Variability

The population structure of 147 marsh deer (Blastocerus dichotomus) from three areas in the Paraná River basin, Brazil, was studied by observing protein polymorphism at 17 loci. Six loci were polymorphic and 11 monomorphic. The proportion of polymorphic loci (P) was 35.29% and the average heterozygosity (H) was 6.31%. Wright's F_ST indicated that only 4.9% of the total variation in allelic frequencies was due to genetic differences between the three groups. The high value of F_IS (0.246) indicated inbreeding in the marsh deer. Genetic distance values (D = 0.014–0.051) showed little divergence between the three areas. We suggest that probable mechanisms accounting for the genetic structure are female phylopatry and polygyny and also that inbreeding has resulted from decreasing areas of wetland leading to isolation, overhunting, and diseases transmitted by cattle.     

Sex-restricted non-Mendelian inheritance of mouse Chromosome 11 in the offspring of crosses between C57BL/6J and (C57BL/6J × DBA/2J)F1 mice

We report on the observation of sex-restricted, non-Mendelian inheritance over a region of mouse Chromosome (Chr) 11, occurring in the offspring of crosses between two commonly used Mus musculus-derived inbred strains, C57BL/6J and DBA/2J. In the surviving backcross progeny of reciprocal matings between (C57BL/6J × DBA/2J)F₁ hybrids and the C57BL/6J parental strain, we observed the preferential appearance of C57BL/6J alleles along a region of Chr 11. The deviation from Mendelian predictions was observed only in female offspring from both reciprocal backcrosses, and not in males from either cross. The sex-specificity of the observed non-Mendelian inheritance points to an explanation based on embryonic or neonatal lethality. Our data add to previously obtained evidence for a Chr 11 locus or loci with sex-specific and allele-specific effects on viability. Received: 19 December 1997 / Accepted: 10 June 1998     

Differentiation and classification of parental lines and favorable genic interactions affecting F1 fertility in distant crosses of rice (Oryza sativa L.)

 This study was intended to investigate the extent of genetic differentiation in parental lines of rice hybrids and to analyze the genetic basis underlying the fertility phenomenon in distant crosses. Two subsets of rice material (111 entries in total) were used, including 81 doubled-haploid (DH) lines and 30 Indica and Japonica rice varieties or lines (as a control). The DH lines was derived from a heterotic Indica/Japonica cross (Gui630/02428) by anther culture. The materials in the control represent a broad spectrum of the Asian cultivated rice gene pool including landraces, primitive cultivars, historically important cultivars, modern elite cultivars, super rice and parents of superior hybrids. In accordance with the NC II design, 57 out of the DH lines were test-crossed to two important wide compatibility lines: photoperiod-sensitive genetic male sterile (PGMS) line N422s and thermo-sensitive genetic male sterile (TGMS) line Peiai64s. The F₁s and their parents, 182 entries in total, were examined for the performance of seven traits in a replicated field trial. All the rice materials was surveyed for polymorphisms using 92 RFLP markers selected from two published molecular marker linkage maps. Genotypes of the F₁ hybrids at the molecular-marker loci were deduced from the parental genotypes. The analysis showed that there were two types of genetic differentiation in the two subsets of rice material; that is, qualitative differentiation in the control and quantitative differentiation in the DH lines. In addition, favorable genic interactions (both intra- or inter-locus) contributed to better increase the fertility in hybrids of distant crosses through incorporation of a wide-compatibility line as the female parent. Favorable genic interactions can be applied in hybrid rice breeding programs by selecting parents with an appropriate extent of genetic differentiation. Received: 5 June 1997 / Accepted: 10 September 1997     

Unilateral incompatibility as a major cause of skewed segregation in the cross between Lycopersicon esculentum and L. pennellii

Skewed segregations are frequent events in segregating populations derived from different interspecific crosses in tomato. To determine a basis for skewed segregations in the progeny of the cross between Lycopersicon esculentum and L. pennellii, monogenic segregations of 16 isozyme loci were analyzed in an F₂ and two backcross populations of this cross. In the F₂, 9 loci mapping to chromosomes 1, 2, 4, 9, 10 and 12 exhibited skewed segregations and in all cases there was an excess of L. pennellii homozygotes. The genotypic frequencies at all but one locus were at Hardy-Weinberg equilibria. In the backcross populations, all except two loci exhibited normal Mendelian segregations. No post-zygotic selection model could statistically or biologically explain the observed segregation patterns in the F₂ and backcross populations. A pre-zygotic selection model, assuming selective elimination of the male gametophytes during pollen function (i.e., from pollination to karyogamy), could adequately explain the observed segregations in all three populations. The direction of the skewed segregations in the F₂ population was consistent with that expected based on the effects of unilateral incompatibility reactions between the two species. In addition, the chromosomal locations of 5 of the 9 markers that exhibited skewed segregations coincided with the locations of several known compatibility-related genes in tomato. Multigenic unilateral incompatibility reactions between L. esculentum pollen and the stigma or style of L. pennellii (or its hybrid derivatives) are suggested to be the major cause of the skewed segregations in the F₂ progeny of this cross.     

Genetic variation amongst viviparid snails in the genus Mekongia (Prosobranchia: Viviparidae) in Thailand

Allozyme variation in viviparid snails from the genus Mekongia in Thailand were examined across the different species, subspecies and geographical locations (river drainage systems). Using horizontal starch gel electrophoresis, 11 presumed allozyme loci (eight polymorphic) from eight enzyme systems were screened. Heterozygosity was moderately low (Hexp = 0.000–0.109, mean = 0.037). One population of Mekongia pongensis (Nong Khai) was monomorphic at all 11 examined loci in contrast to the other two populations, suggesting bottleneck within this population. Populations were more differentiated in the Mekongia sphaericula complex (F_ST = 0.587) than in either the Mekongia swainsoni complex (F_ST = 0.161) or M. pongensis species (F_ST = 0.073). Mekongia sphaericula sphaericula and Mekongia sphaericula extensa exhibited fixed allele differences at two loci, a high genetic distance (D = 0.265–0.300) and a potential polyphyletic relationship, suggesting two distinct lineages (species).     

Genetically idiosyncratic responses of Drosophila melanogaster populations to selection for improved learning ability

To what extent is adaptive evolution over short timescales repeatable? To address this question, we studied the performance of crosses between replicate Drosophila melanogaster lines previously subject to selection for improved learning response in the context of oviposition substrate choice. Of the 10 pairwise F₁ crosses among the five selection lines, four performed in the original learning assay similarly to the parental lines, whereas the remaining six showed learning scores significantly below the average of the parental lines. In particular, four F₁ crosses (three involving the same line) showed no detectable learning, on a par with unselected control lines. This indicates that the response to selection in some lines involved allelic substitutions at different loci. Additional assays of crosses between two selection lines indicated that the loss of performance in hybrids generalized to another type of learning assay, and held for both short‐ and long‐term memory. Joint analysis of first‐ and second‐generation crosses between these two lines supported the hypothesis that the response to selection in these different lines was based on the spread of recessive alleles at different loci. These results show that the evolutionary trajectories of populations of the same origin subject to uniform selection may sometimes diverge over very short evolutionary timescales.     

Inheritance of the photoperiodically induced cold acclimation response in Cornus sericea L., red-osier dogwood

Summary Cold acclimation responses of latitudinal ecotypes of Cornus sericea L. (C. stolonifera Michx.) and F₁, F₂ and BC₁ hybrid progenies were measured under natural photoperiod conditions in St. Paul, MN and artificially shortened photoperiods in the glass-house. The 65 °N and 62 °N ecotypes (Alaska and Northwest Territories, respectively) were characterized by a short night length for hardiness induction, the 42 °N ecotype (Utah A and B) by a long night length for hardiness induction, while the F₁ was intermediate to the parents. Results from reciprocal crosses indicated there was no significant unilateral maternal influence on cold acclimation. Acclimation responses of the F₂ were highly variable but generally ranged between the parental extremes. However, three individuals from the 42 ° × 62 °N crosses exhibited greater cold resistance than the northern parent on two successive freezing test dates. F₂ plants were also found with less freezing resistance than the southern parent. Backcrosses to the southern parent produced progeny with acclimation patterns resembling that of the southern parent and were significantly less hardy than the F₂ in early freezing tests.Scientific Journal Series Paper No. 12,075 of the Minnesota Agricultural Experiment Station     

Genetic variability in Plantago species in relation to their ecology

Summary Genetic variation in leaf and inflorescence morphology and in generative development within the species Plantago major has been analysed by means of crosses between members of two different subspecies. The variable characters chosen are supposed to be important for determining the ecological differences between the subspecies and other ecotypes. The analyses of F₂'s indicated that a substantial number of loci controlling the above mentioned characters are situated near the Pgm-1 locus, forming a gene complex. This gene complex can exist in at least three different forms in ssp. pleiosperma, ssp. major lawn type and ssp. major roadside type, respectively. In addition, some important factors for ecotypic differentiation are situated in the neighbourhood of the Got-1 locus and in a linkage group containing three other allozyme loci. These linkages between allozyme loci and fitness-affecting loci can explain the restriction of some enzyme alleles to a particular subspecies.Grassland Species Research Group Publication No. 50     

Genetic bases for protein polymorphism in Fundulus heteroclitus (L.). I. Lactate dehydrogenase (Ldh-B), malate dehydrogenase (Mdh-A), glucosephosphate isomerase (Gpi-B), and phosphoglucomutase (Pgm-A)

Electrophoretic analysis has shown populations of F. heteroclitus to possess variants at four enzyme-coding loci: Ldh-B, Mdh-A, Gpi-B, and Pgm-A. Based on the phenotypic distribution in the F₁ generation, each variant segregates as an autosomally inherited codominant allele. A pairwise comparison of the expected phenotypic classes among these loci showed no evidence of strong linkage; however, weak linkage could not be ruled out. Despite the considerable genetic divergence of populations from the geographical extremes of this species, offspring resulting from crosses between individuals from these localities show viabilities similar to those found for crosses of local populations.This work was supported by NSF Grants GB 37548 and DEB 76-19877 and by grant from the National Geographic Society. A. R. P. is an NIH trainee supported by a training grant (No. HD00139) to the Deartment of Biology.This is contribution No. 959 of the Department of Biology, Johns Hopkins University.