Genetics of resistance to cotton leaf curl disease in Gossypium hirsutum L. under field conditions

One hundred and forty two cotton germplasm lines were screened for cotton leaf curl virus symptoms in field evaluations during 2003, 2004, and 2005. Fifty cross combinations involving 30 of these lines classified resistant or susceptible were used for inheritance study of the disease. All the F(1) plants of crosses involving resistant x resistant, resistant x susceptible, and susceptible x resistant parents were resistant, indicating dominant expression of the disease resistance and there were no maternal or cytoplasmic effects detected from reciprocal hybridization. In 22 crosses, 4 types of segregation patterns were obtained in the F(2) generations. A good fit for 15 (resistant):1 (susceptible), 13 (resistant):3 (susceptible), 9 (resistant):7 (susceptible) ratios indicated digenic control of the trait with duplicate dominant, dominant inhibitory, and duplicate recessive epistasis, respectively. Three-gene control with triplicate dominant epistasis was obtained in one of the crosses. This segregation pattern, however, needs further confirmation due to smaller population size. The absence of complementary gene action was obtained in 1 susceptible x susceptible and 27 resistant x resistant crosses as their F(1)s were susceptible and resistant, respectively, and F(2) generation lacked segregation.     

Development of high-oleic,low-linolenic acid Ethiopian-mustard (Brassica carinata) germplasm

Seed oil of current zero erucic-acid germplasm of Ethiopian mustard ( Brassica carinata A. Braun) is characterized by a low concentration of oleic acid and high concentrations of linoleic and linolenic acids. Sources of increased oleic-acid (HO) and reduced linolenic-acid (LL) concentration have been developed separately in high erucic-acid germplasm. The objectives of the present research were to study the inheritance of the HO and LL traits in crosses HO x LL, and to develop HOLL recombinants, both in high erucic-acid and zero erucic-acid backgrounds. The HO mutant N2-3591 (about 20% oleic acid compared to 9% in conventional high erucic-acid materials), was reciprocally crossed with the LL lines N2-4961 and HF-186 (both with about 5% linolenic acid compared to 12% in standard high erucic-acid materials). Increased oleic acid concentration of N2-3591 was found to be controlled by alleles at one locus (Ol), whereas three different loci for reduced linolenic-acid concentration (Ln, Ln1 and Ln2) were identified in N2-4961 and HF-186. Crosses between N2-3591 and N2-4961 generated HOLL recombinants where levels of increased oleic-acid and reduced linolenic-acid were similar to those of the parents. However, a transgressive segregation for oleic acid was observed in crosses between N2-3591 and HF-186, where F(2) seeds with up to 29.7% oleic acid were obtained, in comparison to an upper limit of 25.1% in the N2-3591 parent grown in the same environment. The transgressive increased oleic-acid was expressed in the F(3) generation and was attributed to the presence of a second locus, designated Ol2. The transgressive trait was transferred to the zero erucic-acid line 25X-1, resulting in a zero erucic-acid germplasm with very high oleic-acid concentration (83.9% compared to 32.9% in 25X-1) and low linolenic-acid concentration (5.0% compared to 16% in 25X-1). Additionally, two other lines exhibiting different stable levels of increased oleic-acid (70.7% and 79.5%, respectively) and reduced levels of linolenic-acid (7.5% and 8.7%, respectively) were isolated.     

Mapping two functional domains of clathrin light chains with monoclonal antibodies

The two forms of clathrin light chains (LCA and LCB) or clathrin-associated proteins (CAP1 and CAP2) have presented an immunochemical paradox. Biochemically similar, both possess two known functional parameters: binding the clathrin heavy chain and mediating the action of an uncoating ATPase. All previously reported anti-CAP mAbs, however, react specifically with only CAP1 (Brodsky, F. M., 1985, J. Cell Biol., 101:2047-2054; Kirchhausen, T., S. C. Harrison, P. Parham, and F. M. Brodsky, 1983, Proc. Natl. Acad. Sci. USA, 80:2481-2485). Four new anti-CAP mAbs are reported here: two, C-7H12 and C-6C1, react with both forms; two others, C-10B2 and C-4E5, react only with the lower form. Sandwich ELISAs indicated that C-10B2, C-4E5, C-6C1, and C-7H12 react with distinct epitopes. Monoclonal antibodies C-10B2 and C-4E5 immunoprecipitate clathrin-coated vesicles (CCVs) and react with CAP2 epitopes accessible to chymotrypsin on the vesicle. These mAbs inhibit phosphorylation of CAP2 by endogenous CCV casein kinase II. In contrast, C-6C1 and C-7H12 react with epitopes that are relatively insensitive to chymotrypsin. CAP peptide fragments containing these epitopes remain bound to reassembled cages or CCVs after digestion. Immunoprecipitation and ELISAs demonstrate that C-7H12 and C-6C1 react with unbound CAPs but not with CAPs bound to triskelions or CCVs. The data indicate that the CAPs consist of at least two discernible structural domains: a nonconserved, accessible domain that is relevant to the phosphorylation of CAP2 and a conserved, inaccessible domain that mediates the binding of CAPs to CCVs.     

Effects of inter-subspecies hybridization of non-native <Emphasis Type="Italic">Monochamus alternatus alternatus</Emphasis> and native <Emphasis Type="Italic">M. a. endai</Emphasis> (Coleoptera: Cerambycidae) on the induction of larval diapause and adult body size

To evaluate the effects of Taiwanese Monochamus alternatus alternatus (Coleoptera: Cerambycidae) (T) on native M. a. endai populations (J) and pine wilt disease epidemics in Japan, the biological traits of reciprocally crossed lines between two subspecies were compared with parental lines. No significant differences were observed in egg viability among four crosses in the F1 generation. Hybridized lines had greater survival rates than inbred lines of the J × J cross. The incidence of larval diapause was lower in the inbred lines of M. a. alternatus (0.176 and 0.361) than in the inbred lines of M. a. endai (1.000). Hybridized lines showed a high diapause incidence of 0.896–1.000 in the F1 and F2 generations, indicating that diapause induction was dominant over nondiapause induction. Large numbers of ovarioles dominated over small numbers of ovarioles. Hybridized lines revealed greater adult body sizes than the inbred lines of parental subspecies in the F1 generation (heterosis), but not in the F2 generation. Heterosis in adult body size may contribute to pine wilt disease epidemics because of the greater oviposition rate and initial load of pathogenic nematodes. Two unlinked loci are estimated to control diapause induction. Gene introgression and the dynamics of nondiapause-inducing alleles are discussed.     

Abnormal genetic segregation associated with the presence of a Y. w+ chromosome in Drosophila melanogaster

We have observed an abnormal genetic segregation in the progeny of crosses between males of the F71 (y wa/Y.w+) strain and females of various strains carrying marker mutations on their chromosome 2. The Y.w+ chromosome, previously described as possibly being associated with a translocation of the 22D region of chromosome 2, was shown to carry the 21A1-22E4 tip of the 2L chromosome. One chromosome 2 of F71 had a deletion of this region. The abnormal genetic segregation observed in the progeny of different crosses can be explained both by the partial lethality (which becomes severe in some homogeneous genetic backgrounds) due to trisomy of the 21A1-22E4 chromosome 2 fragment and by the lethality associated with monosomy of this 21A1-22E4 segment.     

Regioselective cleavage of rings E and F in sarsasapogenin

Sapogenins from the 25R and 25S series show a marked difference on the E/F regioselectivity of the spiroketal cleavage with BF(3)/Ac(2)O. In contrast to the high yield of single E-ring cleavage products from diosgenin (3) and hecogenin (5), sapogenins of the 25R series (equatorial C-27 methyl), sarsasapogenin (1, 25S series, axial C-27 methyl) yields the corresponding acetyldihydropyran, (25S)-23-acetyl-22,26-epoxy-5beta-cholest-22-ene-3beta,16beta-diyl diacetate (8), two isomeric furostenes: (E)- and (Z)-(25S)-23-acetyl-5beta-furost-22-ene-3beta,26-diyl diacetate (9 and 10) and a third one bearing an additional acetyl group: (E)-(20S,25S)-20,23-diacetyl-5beta-furost-22-ene-3beta, 26-diyl diacetate (11). The structures of the compounds were unambiguously established using two dimensional NMR techniques. The lower E/F selectivity in the cleavage of 1 is attributed to steric hindrance resulting from the axial methyl in F ring on a beta elimination forming the dihydropyran double bond in the major product 8.     

A Temperature Effect on the Expression of Genotypic Differences in Flowering Induction in Antirrhinum majus

Three inbred lines of Antirrhinum majus and the F₁ generationsof crosses between them were scored for flowering time in ninegreenhouse and garden experiments. The inbreds fell into twogroups, the difference between which showed a marked interactionwith environments. The two lines (An 105, An 106) which weresimilar were earlier flowering than the third line (An 101)in those environments which produced generally early flowering,but were later than An 101 when the environmental conditionsled to late flowering. In all cases the F₁ generations wereat least as early as the earlier parent. Cabinet experiments identified temperature as the importantenvironmental factor when day length was kept constant at 16h. At 25°C, An 105 and An 106 were earlier than An 101 whileat 12°C, at which temperature the average flowering timewas much later, An 101 was earlier. The F₁ generations werelike An 105 and An 106 at 25°C but showed heterosis at 12°C. The differences in flowering time between genotypes were inall cases established by the time the first reproductive budsbecame visible (budding time). Thus a temperature differencewell outside the range of vernalizing temperatures is havinga striking effect on the phenotypic expression of genotypicdifferences determining the transition from vegetative to floweringdevelopment.     

Biological and genetic aspects of experimental hybrids from species of the Phyllosoma complex (Hemiptera: Reduviidae: Triatominae)

The present work is a thorough investigation of the degree of reproductive isolation between Meccus mazzottii and Meccus longipennis, Meccus picturatus, Meccus pallidipennis and Meccus bassolsae, as well as between M. longipennis and M. picturatus. We examined fertility and segregation of morphological characteristics in two generations of hybrids derived from crosses between these species. The percentage of pairs with (fertile) offspring was highest in the set of crosses between M. longipennis and M. picturatus, and lowest between M. mazzottii and M. picturatus. Most first-generation (F1) individuals from crosses involving M. mazzottii were morphologically similar to this species, while only F1 x F1 progeny of parental crosses between M. mazzottii and M. longipennis had offspring second generation that looked like M. mazzottii. The results indicate that different degrees of reproductive isolation apparently exist among the species of the Phyllosoma complex examined in this study. The biological evidence obtained in this study does not support the proposal that M. longipennis and M. picturatus are full species. It could indicate on the contrary, that both could be considered as subspecies of a single polytypic species. On the other hand, biological evidence supports the proposal that M. mazzottii is a full species.     

Linkage between loci controlling nodulation and testa variegation in peanut

Linkage of loci controlling nodulation (N(1)) and testa variegation (V) was studied for cultivated peanut (Arachis hypogaea L.). The lines M4-2 (nonnodulating, variegated; VVn(1)n(1)n(2)n(2)N(3)N(3)) and UF 487A (nodulating, nonvariegated; vvN(1)N(1)n(2)n(2)N(3)N(3)) were used as parents in the crosses M4-2 x UF 487A, M4-2 x (UF 487A x M4-2), and their reciprocals. Individual plants were evaluated for nodulation and testa variegation in the F(1), F(2), F(3), F(1)BC(1), and F(2)BC(1) generations. Data indicate that the N(1) and V loci are linked with calculated crossover percentage of 7.1%.     

Latent S alleles are widespread in cultivated self-compatible Brassica napus.

The genetic control of self-incompatibility in Brassica napus was investigated using crosses between resynthesized lines of B. napus and cultivars of oilseed rape. These crosses introduced eight C-genome S alleles from Brassica oleracea (S16, S22, S23, S25, S29, S35, S60, and S63) and one A-genome S allele from Brassica rapa (SRM29) into winter oilseed rape. The inheritance of S alleles was monitored using genetic markers and S phenotypes were determined in the F1, F2, first backcross (B1), and testcross (T1) generations. Two different F1 hybrids were used to develop populations of doubled haploid lines that were subjected to genetic mapping and scored for S phenotype. These investigations identified a latent S allele in at least two oilseed rape cultivars and indicated that the S phenotype of these latent alleles was masked by a suppressor system common to oilseed rape. These latent S alleles may be widespread in oilseed rape varieties and are possibly associated with the highly conserved C-genome S locus of these crop types. Segregation for S phenotype in subpopulations uniform for S genotype suggests the existence of suppressor loci that influenced the expression of the S phenotype. These suppressor loci were not linked to the S loci and possessed suppressing alleles in oilseed rape and non-suppressing alleles in the diploid parents of resynthesized B. napus lines.     

Effect of recombination in the parent populations on the means and combining ability variances in hybrid populations of maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.)

Recombination of selected genotypes plays a key role in plant breeding for generating new base populations. We investigated the influence of recombination in two parent populations on the means and combining ability variances of their hybrid population by (1) quantitative genetic theory and (2) experiments with maize. The two parent populations were founded by four early flint and four early dent inbred lines, respectively. Each population was studied in three generations: Syn-0, the four inbred lines themselves; Syn*-1, the six intrapool single crosses (SC); and Syn*-2, the three intrapool double crosses (DC). Four interpool hybrid populations were created: (1) all 16 SC and (2) all 36 DC were produced from generations Syn-0 and Syn*-1, respectively, (3) 168 biparental progenies (BIP) of type flint x dent (female x male), and (4) 168 BIP of type dent x flint were produced according to NC-design I with randomly sampled plants of generation Syn*-2. The half-sib and full-sib families obtained in this manner were evaluated for grain yield, dry matter concentration and plant height. According to theoretical results, differences in the population means of these hybrid populations indicate the presence of various types of epistasis. Changes in combining ability variances from SC to DC reflect different levels of parental inbreeding (F = 1 vs F = 0), whereas changes from DC to BIP only reflect the effects of recombination and are attributable to covariances between additive and dominance effects caused by linkage disequilibrium in the Syn-0 generations. The experimental results showed a significant decline in yield from DC to BIP due to a loss of gene combinations with favourable epistatic effects. Estimates of sigma(2)(GCA) attributable to flint or dent lines decreased or remained unchanged from SC to DC, but generally increased in the BIP populations. The consequences of these trends for developing improved interpool hybrids are discussed.     

Molecular mapping of rice blast resistance gene <Emphasis Type="Italic">Pi-1</Emphasis>(<Emphasis Type="Italic">t</Emphasis>) in the elite <Emphasis Type="Italic">indica</Emphasis> variety Samba mahsuri

Samba mahsuri (BPT 5204) is a cultivar of the medium slender grain indica variety of Oryza sativa grown across India for its high yield and quality. However, this cultivar is susceptible to several diseases and pests including rice blast. The analysis of near isogenic lines indicated the presence of a resistance gene, Pi-1(t) in the donor cultivar C101LAC which is highly resistant to the rice blast fungus Magnaporthe grisea (M. grisea). C101LAC was crossed with susceptible indica rice cultivar (BPT 5204) to generate the mapping population. A mendelian segregation ratio of 3:1 for resistant to susceptible F₂ plants using bulk segregation analysis confirmed the presence of a major gene pi-1(t) by simple sequence repeats marker RM224 to the highly virulent blast isolate DRR 001.     

Qualitative inheritance of water-stress induced apical sterility in wheat (Triticum aestivum)

Grain number per unit area is an effective component of grain yield in bread wheat. Water-stress induced apical sterility (tip sterility) reduces the number of grains and, consequently, the grain yield in semi-arid regions with a shortage of available water during the pre-anthesis period. Crosses between apical sterile and apical fertile varieties and selection lines were made and F1, BC1, and F2 populations were subjected to moderate water-stress to study the inheritance of this character. The F2 and BC1 plants were qualitatively categorised into two phenotypes and tested for monohybrid and dihybrid segregation hypotheses. All the spikes of F1 plants obtained from crosses between apical fertile and apical sterile varieties were fully fertile indicating apical fertility is dominant to apical sterility. The F2 segregation Results from crosses between apical fertile lines and Y82187 suggested two complementary dominant genes segregating independently were involved in tolerance to water-stress induced apical sterility. In other words, two dominant genes determine apical fertility in these crosses and if one of these loci is homozygous, recessive waterstress will induce apical sterility. One F2 population segregated for both apical sterility and vernalisation response. Semi-winter plants had more sterile spikelets and the result of chi-square test confirmed monhybrid segregation for vernalisation response.     

Biological aspects of crosses between Triatoma recurva (Stål), 1868 (Hemiptera: Reduviidae: Triatominae) and other members of the Phyllosoma complex

The degree of reproductive isolation between Triatoma recurva (Stål) (Hemiptera: Reduviidae: Triatominae) and the six species of the genus Meccus plus T. mexicana (Herrich‐Schaeffer) (Hemiptera: Reduviidae) was examined. Fertility and the segregation of morphological characteristics were examined in two generations of hybrids from crosses between these species. The percentage of couples with offspring (fertile) was low in the vast majority of sets of crosses, with the exception of that between T. recurva female and M. phyllosomus male. In all studied sets of crosses, no first‐ (F1) or second‐ (F2) generation individuals were morphologically similar to T. recurva but instead shared the morphology of the other parental species. A similar phenomenon was observed in the three successful sets of backcrosses. These results indicated that different recorded levels of reproductive fitness among T. recurva and the species of Meccus involved in this study, plus T. mexicana, are present and that they were apparently influenced by differing mechanisms of isolation. The presence of some degree of reproductive compatibility between studied triatomines of distinct genera (Meccus spp. and Triatoma spp.) reinforces the need for generic revision of the tribe Triatomini.     

Alteration of chromosome behavior and synchronization of parental chromosomes after successive generations in Brassica napus x Orychophragmus violaceus hybrids.

In an earlier study, the progenies of intergeneric hybrids Brassica napus (2n = 38) x Orychophragmus violaceus (2n = 24) were investigated in successive generations (F1-F4) for the cytological phenomenon of parental genome separation during mitotic and meiotic division. In the present study, inbred lines (F5-F8) derived from 1 such hybrid were characterized for morphology, chromosome pairing behaviour, and genome composition. One F5 plant (2n = 31) with slightly yellow petals and 12:19 and 15:16 segregation ratios in its pollen mother cells (PMCs) produced F6 plants with distinct morphological characteristics and wide variations in fertility and chromosome numbers (2n = 25-38). F7 and F8 lines with distinctive morphology and wide ranges in chromsome numbers were established. In PMCs of F7 plants from 4 F6 plants, 0-12 labelled chromosomes from O. violaceus, which predominantly appeared as bivalents, were identified by genomic in situ hybridization. They behaved synchronously with B. napus chromosomes during meiotic division. The results provide molecular cytogenetic evidence of the inclusion of O. violaceus chromosomes in the original hybrids and the cytology in the hybrids documented earlier. They also show that chromosome behaviour was altered and the parental chromosomes became synchronized after successive generations.     

The effect of pollen irradiation on segregation in spring barley crosses

Observations on the Ml, M2 and M3 generations from three barley crosses confirmed that pollen irradiation can cause deviations from expected segregation ratios for certain characters. The reduced fertility observed in the Ml and M2 generations of these crosses could be problematical in breeding programmes. It was of particular interest that at the highest dose rate used for the cross TS117 × Scots Bere there was no expression of the 6-row character, which is controlled by a recessive paternal factor.     

Segregation of restriction fragment length polymorphism in an interspecies cross of laboratory and wild mice indicates tight linkage of the murine IFN-beta gene to the murine IFN-alpha genes.

Southern blot analysis with murine (Mu) interferon (IFN)-alpha cDNA of restricted genomic DNA of three inbred strains of mice belonging to the species Mus musculus domesticus (BALB/c, C57BL/6, and DBA/2) revealed only a limited degree of polymorphism. For example, with HindIII there were only two polymorphic bands out of 14 hybridizing fragments. With Mu IFN-beta cDNA there was no polymorphism at all between BALB/c and C57BL/6 in DNA restricted with seven different enzymes. In contrast, HindIII-restricted DNA of an inbred strain of wild mice (M. spretus Lataste) hybridized with the IFN-alpha probe displayed a high degree of polymorphism compared with the three strains of laboratory mice and was also polymorphic when probed with IFN-beta cDNA. Although M. musculus domesticus and M. spretus Lataste represent different species, certain interspecies crosses are possible in the laboratory. This enabled us to follow segregation of restriction fragment length polymorphism in HindIII-restricted DNA obtained from 18 backcross progeny of a (DBA/2 X M. spretus)F1 X DBA/2 interspecies cross. There was complete coincidence between the segregation of parental (DBA/2) and (DBA/2 X M. spretus)F1-type IFN-beta and IFN-alpha restriction fragment length polymorphism, indicating tight linkage of the IFN-beta and IFN-alpha genes. In addition, in 15 of 18 progeny the segregation coincided with that of the brown locus on chromosome 4, in accord with previous results obtained with the IFN-alpha probe in strains derived from crosses between BALB/c and C57BL/6 mice. Thus, the Mu IFN-beta gene is tightly linked to the Mu IFN-alpha gene cluster on chromosome 4 near the brown locus.     

Partial interfertility between independently originated populations of the neo-allopolyploid <Emphasis Type="Italic">Mimulus peregrinus</Emphasis>

The reduction in genetic diversity in polyploid lineages, formed from whole-genome duplication of a few individuals, can affect their long-term evolutionary potential. Because most polyploids originate multiple times, secondary contact and gene exchange among independently formed polyploids can create novel genetic combinations and reduce the severity of genetic bottlenecks. However, independently originated polyploids may be reproductively isolated from each other due to genetic and chromosomal differences predating the polyploidisation event, or evolving subsequently in the dynamic genomes of young polyploid populations. Here we conducted experimental crosses to investigate the phenotype and interfertility between two independently originated populations of the allopolyploid Mimulus peregrinus (Phrymaceae). We found that individuals from the two populations are phenotypically distinct, but that inter- and intrapopulation crosses are not statistically different. Interpopulation crosses produce viable and fertile offspring, although our results suggest the existence of partial reproductive barriers in the form of reduced pollen viability. We found no difference in pollen viability between F1 and F2 generations. In contrast, we detected a reduction in floral and vegetative size, and in the proportion of plants that flowered, between F1 and F2 generations for both intra- and interpopulation crosses. Together, our results indicate that populations of independent origin can partially exchange genes, producing variable offspring, and that the phenotype of M. peregrinus may be unstable in the early generations. Natural selection on genetically based variation may be required for the evolution of more stable and fertile individuals of this nascent allopolyploid.     

Retention of D genome chromosomes in pentaploid wheat crosses

The transfer of genes between Triticum aestivum (hexaploid bread wheat) and T. turgidum (tetraploid durum wheat) holds considerable potential for genetic improvement of both these closely related species. Five different T. aestivum/T. turgidum ssp. durum crosses were investigated using Diversity Arrays Technology (DArT) markers to determine the inheritance of parental A, B and D genome material in subsequent generations derived from these crosses. The proportions of A, B and D chromosomal segments inherited from the hexaploid parent were found to vary significantly among individual crosses. F(2) populations retained widely varying quantities of D genome material, ranging from 99% to none. The relative inheritance of bread wheat and durum alleles in the A and B genomes of derived lines also varied among the crosses. Within any one cross, progeny without D chromosomes in general had significantly more A and B genome durum alleles than lines retaining D chromosomes. The ability to select for and manipulate this non-random segregation in bread wheat/durum crosses will assist in efficient backcrossing of selected characters into the recurrent durum or hexaploid genotype of choice. This study illustrates the utility of DArT markers in the study of inter-specific crosses to commercial crop species.     

Biological and genetic aspects of crosses between species of the genus Meccus (Hemiptera: Reduviidae Triatominae)

The degree of reproductive isolation between Meccus phyllosomus and the remaining five species of the genus Meccus, as well as between Meccus bassolsae and Meccus pallidipennis, Meccus longipennis and Meccus picturatus, was examined. Fertility and the segregation of morphological characteristics were examined in two generations of hybrids from crosses between these species. The percentage of couples with offspring (fertile) was high in the vast majority of sets of crosses, with the exception of that between ♀M. phyllosomus and ♂Meccus mazzottii. In sets of crosses involving M. bassolsae specimens, no first-generation (F1) individuals were morphologically similar to M. bassolsae, but instead shared the morphology of the other parental species. A similar phenomenon was observed in most sets of crosses involving M. phyllosomus. These results indicated that different degrees of reproductive isolation exist among the species of Meccus involved in this study. The biological evidence obtained in this study does not support the proposal that M. bassolsae is a full species. It could indicate that, on the contrary, it should be considered a subspecies of a single polytypic species. The biological evidence does support the proposal that M. phyllosomus is a full species.