A genetic linkage map of Physocarpus,a member of the Spiraeoideae (Rosaceae), based on RAPD,AFLP, RGA,SSR and gene specific markers

Physocarpus opulifolius is a deciduous shrub native to North America belonging to the Spiraeoideae subfamily of the Rosaceae. The cultivars ‘Luteus’ and ‘Diabolo’ are grown in gardens for their ornamental foliage, golden and purple respectively. We developed a linkage map of P. opulifolius with a view to detecting markers for the leaf colour genes, which are under major gene control. A total of 162 molecular markers (128 RAPDs, 27 AFLPs, three RGA, three STS markers and one SSR) and the leaf colour genes Pur and Aur were scored in the Physocarpus progeny and used to create a linkage map covering 586.1 cM over nine linkage groups. There was an average of 18.2 markers per linkage group and a mean linkage group length of 65.1 cM. Both leaf colour genes were mapped. This is the first reported linkage map of a member of the Spireaeoideae and the mapping of a small number of transferable markers has demonstrated its utility to comparative mapping, which will complement existing comparative mapping efforts in other rosaceous subfamilies.     

Inheritance of some morphological traits in grain amaranthus

Summary Intraspecific crosses involving five cultivars of Amaranthus hypochondriacus and two from A. caudatus were studied to investigate the inheritance of five morphological traits (seed coat colour, inflorescence colour, seedling colour, oval leaf mark and purple leaf mark). Seedling colour, inflorescence colour, seed coat colour and oval leaf mark segregated to a 3:1 ratio and therefore each was controlled by a single dominant gene. The purple leaf mark segregated in 9:7 ratio and hence may be controlled by two dominant genes. Simultaneous segregation for seed coat colour and inflorescence colour gave a ratio of 9:3:3:1. Similar genetic ratio was observed for the simultaneous segregation for oval leaf mark and inflorescence colour. It was suggested that each of these traits is controlled by independent genes.     

Inheritance of ‘domestication’ traits in bambara groundnut (Vigna subterranea (L.) Verdc.)

Controlled crosses in bambara groundnut were attempted between a range of thirty-six bambara groundnut landraces (thirty domesticated (V. subterranea var. subterranea) and six wild (V. subterranea var. spontanea)). Ten F₁ seed were produced. Of these, eight germinated producing F₂ populations. On seed set, four populations could be unambiguously confirmed as true crosses by F₃ seed coat colour. A single F₂ population, derived from a domesticated landrace from Botswana (DipC; female parent) crossed with a wild accession collected in Cameroon (VSSP11; male parent) was used to study a range of agronomic and domestication traits. These included; days to emergence, days to flowering, internode (fourth) length at harvest, number of stems per plant, leaf area, Specific Leaf Area (SLA), Carbon Isotope Discrimination (CID), 100 seed weight, testa colour and eye pattern around the hilum. On the basis of variation for internode length and stems per plant, 14 small F₃ families were selected and grown under field conditions to further investigate the genetic basis of the ‘spreading’ versus ‘bunched’ plant character, a major difference between wild and cultivated bambara groundnut. Results presented suggest that traits including leaf area, SLA, CID and 100 seed weight are controlled by several genes. In contrast, the variation for traits such as internode length, stems per plant, days to emergence and seed eye pattern around the hilum are likely to be under largely monogenic control. The results of this work are discussed in relation to the domestication of bambara groundnut.     

Reciprocal cross differences in a 6×6 diallel set of groundnut (Arachis hypogaea L.) in the F1 generation

Summary Reciprocal cross differences were studied in a 6×6 diallel full set comprising of thirty hybrid combinations of groundnut in the F₁ generation.Reciprocal cross differences were observed for growth habit in four pairs of crosses, for leaf colour, flower colour and stem pigmentation in two pairs of crosses each. It was observed that the inheritance of flower colour, stem pigmentation and testa colour which exhibited different shades of purple colour was likely to be governed by pleiotropic gene(s). Among the quantitative characters significantly positive reciprocal effects were observed in different crosses for number of mature pods per plant, weight of pods per plant and shelling percent. Marked reciprocal cross differences were observed for pod and kernel characters like pod filling, pod beak, pod constriction and testa colour.     

Development of a large population of activation-tagged mutants in an elite indica rice variety

In this study, we have generated more than 12,000 activation-tagged mutants in a high-yielding indica rice variety, 'BPT 5204', employing maize Ac/Ds system. Different transgenic plants obtained were analysed based on expression patterns of green fluorescence protein (GFP), red fluorescence protein (RFP), herbicide (Basta) tolerance and molecular analyses. T₁ seeds of pSQ5 and pSQ5-bar transgenics, when germinated separately on hygromycin (50 mg/L) and phosphinothricin (5 mg/L) containing medium, revealed a segregation of 3 tolerant : 1 susceptible plants. The germinal transposition frequency of Ds element in different T₂ progeny of rice plants was found to be about 18.0%. Different stable tagged mutants exhibited marked increases in plant height, number of tillers, leaf size, panicle size, seed size and number of grains per plant. The overall results indicate that the genes associated with these traits are upregulated by the enhancer element in activation-tagged mutants. As such, the various tagged mutant lines appear promising and serve as a valuable genetic resource for identification of key genes determining different agronomic traits of rice.     

Interspecific crosses inlinum

Summary Interspecific crosses were attempted between eleven species ofLinum, and those betweenL. usitatissimum, L. pallescens andL. africanum were successful. In these crosses the F₁ hybrid plants greatly exceeded the parental species in plant height, giving thereby greater length of fibre which could be of economic importance. The seed formation in the F₁ plants was considerably reduced. The blue flower colour was dominant over the white colour. Polyembryony was observed in the cross betweenL. usitatissimum andL. pallescens.     

Inheritance of siliqua orientation and seed coat colour in Brassica tournefortii

The inheritance of siliqua orientation and seed coat colour in Brassica tournefortii was investigated using four genotypes varying in these two characters. The F₁, F₂ and backcross generations of two crosses were used for studying the segregation pattern of the traits. The plants were classified for seed colour as having brown or yellow seeds and for siliqua orientation as having upright, semi‐spread or spread siliqua. Seed colour was found to be under monogenic control with brown being dominant over yellow. Siliqua orientation was under digenic polymeric gene action: upright siliqua was produced by the presence of two dominant genes and spread siliqua by two recessive genes. The absence of even a single dominant gene resulted in a third type of siliqua orientation, semi‐spread siliqua.     

Evidence for phenotypic assortative mating for flower colour in periwinkle

Two experiments were conducted with periwinkle, Catharanthus roseus, to determine the extent of natural outcrossing. Three white-flowered, fully self-fertile, monogenic recessive mutants, namely, dwarf, wavy leaf margin and curved leaf were used, together with their parental white-flowered variety, ‘Nirmal’, and a normal pink-flowered variety, PS-1. The extent of total outcrossing ranged from 43.4 to 79.3% among mutants. Outcrossing between white × white-flowered plants ranged from 28.3 to 65.3% and was two to four times greater than that between white × pink-flowered plants in the three mutants. The extent of out-crossing between white × pink-flowered plants was similar “02.2-15.0%” in all mutants and also similar to that in the normal white-flowered variety,‘Nirmal’(00.4%), where white × white flower out-crossing could not be estimated. There were no large differences in the number of seeds per fruit, percentage fruit set and germination percentage of seeds obtained from self, white × white and white × pink flower crosses made in the glasshouse. There were also no significant differences in the number of flowers produced by the genotypes used in the study. The observed higher frequency of white × white flower matings compared with white × pink flower matings appeared to be due to the constancy of flower colour exhibited by the butterfly pollinators Pachliopta hector and Catopsilia pyranthae during their flower visits. Observations made on the occurrence of natural self-pollination revealed that automatic self-pollination did not occur in periwinkle.     

Inheritance of black testa colour in lentil (Lens culinaris Medik.)

The inheritance of testa (seed coat) colour and interaction of cotyledon and testa colours were studied in seven crosses of lentil (Lens culinaris Medik.) involving parents with black, brown, tan or green testa and with orange, yellow or dark green cotyledons. Analysis of F₂ and F₃ seed harvested from F₁ and F₂ plants, respectively, revealed that although black testa is dominant over nonblack testa, its penetrance is not complete since both F₁ plants and heterozygous F₂ plants produced varying proportions of seeds with either black or nonblack testa. The F₂ populations of the crosses between parents with brown and tan, as well as brown and green, testa segregated in the ratio of 3 brown : 1 tan and 3 brown : 1 green, respectively, indicating monogenic dominance of brown testa colour over tan or green. The expression of testa colour was influenced by cotyledon colour when parents with brown or green testa are crossed with those having orange or green cotyledons. Thus F₂ seeds from these crosses with a green testa always had green cotyledons and never orange cotyledons. F₂ seeds from these crosses with a brown testa always had orange cotyledons and never green cotyledons. These results suggest diffusion of a soluble pigment from the cotyledons to the testa. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic Analysis of Morpho-Physiological Traits in Chickpea

The present study was conducted to investigate the genetic inheritance of morpho-physiological leaf traits in chickpea (Cicer arietinum L.). The experimental material comprised six generations, viz., two inbred parents, ‘T88’ and ‘Bold Seeded’, having contrasting leaf traits, and their derived F₁, F₂ and backcross of F₁ to either parent (B₁ and B₂). The experiment was randomized complete block design with three replications. Genetic parameters were estimated by generation mean analysis using all the six generations. Data were collected on individual plants within each family just before flowering on leaflet area (LA), number of leaflets per leaf (LL), rachis length (RL), and leaflet density (LD), which was calculated as number of leaflets per unit length of rachis. A simple additive-dominance model was found to be adequate to describe the inheritance of LL and LA, while dominance × dominance (i.e. [1]) and additive × dominance (i.e. [i]) interactions were also significant for RL and LD, respectively. Improvement or seed yield per plant may result from selection for LA by improving both RL and LL. Leaflet area may be included in the ongoing selection schemes, as a supplementary trait to increase the speed of improvement in seed yield per plant. Lanceolate leaflet shape was observed to be monogenically dominant over obovate leaflet shape, and segregated independently from purple/white flower color.     

Molecular mapping of genes involved in root hair formation in barley

In the presented study, the existing AFLP and SSR maps of barley were used to find chromosomal position of four genes controlling different stages of root hair development. Four barley mutants were used in the analysis: the root hairless mutant rhl1.b, mutant rhp1.b with root hair development blocked at the initial bulge formation, mutant rhi1.a with irregular pattern of sparsely located root hairs and mutant rhs1.a with very short root hairs. Each mutant was crossed with parents of ‘Steptoe’/‘Morex’ mapping population and F₂ progenies of crosses: mutant × ‘Steptoe’ and mutant × ‘Morex’ were analyzed for segregation of root hair phenotype and polymorphic AFLP and SSR markers. It was possible to map all the analyzed genes on barley chromosomes: rhl1 gene on the short arm of chromosome 7H, rhp1 gene on chromosome 1H, rhs1 locus in the pericentromeric region of chromosome 5H and rhi1 gene on the long arm of chromosome 6H. Subsequently, the Bulk Segregant Analysis and AFLP technique were used for saturation of the identified regions with new markers. The joint maps were constructed using as common points the SSR markers located in the target regions. Linkage maps of the regions around the four genes involved in the root hair formation in barley were composed of 8–11 markers and spanned over 16.1–49.0 cM. The distances between localized genes and the closest markers ranged from 1.0 to 3.8 cM. The identified chromosomal locations of genes can be used for their fine mapping and future map-based cloning.     

Inheritance of pigmentation and pod shape in winged bean

Summary The inheritance of five qualitative character differences in winged bean was studied in two crosses. All five character pairs were based on a single gene difference with complete dominance of purple over green stem colour, purple over green calyx colour, purple over green pod wing colour, purple specks over green pod and rectangular over flat pod shape. Linkage was observed between stem and calyx colour and also pod wing colour and pod specks.     

Inheritance of seed colour in Brassica campestris L. and breeding for yellow-seeded B. napus L.

Summary Seed colour inheritance was studied in five yellow-seeded and one black-seeded B. campestris accessions. Diallel crosses between the yellow-seeded types indicated that the four var. yellow sarson accessions of Indian origin had the same genotype for seed colour but were different from the Swedish yellow-seeded breeding line. Black seed colour was dominant over yellow. The segregation patterns for seed colour in F₂ (Including reciprocals) and BC₁ (backcross of F₁ to the yellow-seeded parent) indicated that the black seed colour was conditioned by a single dominant gene. Seed colour was mainly controlled by the maternal genotype but influenced by the interplay between the maternal and endosperm and/or embryonic genotypes. For developing yellow-seeded B. napus genotypes, resynthesized B. napus lines containing genes for yellow seed (Chen et al., 1988) were crossed with B. napus of yellow/brown seeds, or with yellow-seeded B. carinata. Yellow-seeded F₂ plants were found in the crosses that involved the B. napus breeding line. However, this yellow-seeded character did not breed true up to F₄. Crosses between a yellow-seeded F₃ plant and a monogenomically controlled black-seeded B. napus line of resynthesized origin revealed that the black-seeded trait in the B. alboglabra genome was possibly governed by two independently dominant genes with duplicated effect. Crossability between the resynthesized B. napus lines as female and B. carinata as male was fairly high. The sterility of the F₁ plants prevented further breeding progress for developing yellow-seeded B. napus by this strategy.     

Genetics of morphological traits in wild wheat,Triticum turgidum var.dicoccoides

Summary The mode of inheritance, linkage groups, and chromosomal location of 23 morphological and 4 biochemical traits were characterized in the wild tetraploid emmer wheat,Triticum turgidum var.dicoccoides. These traits were described and their mode of inheritance was determined by their segregation in four F₂ populations derived from crosses between four var.dicoccoides accessions and a tetraploiddurum cultivar. Linkage groups among the genes encoding for these traits were determined or postulated, and their chromosomal location was deduced by linkage to previously located genes. The genetic control of the following traits was characterized and is first reported here: black keel; hairy leaf sheath; hairy auricles; hairy rachilla; hairy kernel brush; obtuse flag leaf; and curved neck/peduncle. The linkage data indicated that developmentally-related genes tended to occur in clusters.     

Tree and fruit traits of progenies from the cross between (Annona cherimola Mill.?×?A. squamosa L.)?×?A. reticulata L. and approaches for the introgression of valuable genes from A. reticulata L.

Atemoya (Annona cherimola Mill. × A. squamosa L) and A. reticulata L. possess several contrasting foliage characteristics. Two hundred and fifty trispecies hybrids of atemoya and A. reticulata were therefore studied to investigate the inheritance of four foliage characteristics. Segregation for leaf colour (green or dark green), leaf angle (erect or drooping), leaf apex shape (rounded or pointed) and time of leaf fall (early or late or intermediate) into discreet phenotypic classes revealed that their inheritance followed simple Mendelian genetics. Based on phenotypes of parents and the segregating population, and the genetic ratios obtained, allelic symbols were assigned to four leaf characteristics. Duplicate dominant gene interaction governed the leaf colour and leaf position. Thus individuals with single or both the dominant genes (A-B-, A-bb, aaB-) produce green colour leaves and those with recessive genes (aabb) dark colour leaves. Likewise erect leaf individuals are C-D-, C-dd, ccD- and those with drooping leaves are ccdd. Further a single gene determined shape of leaf apex that was either rounded (Rr) or pointed (rr). Segregation of progenies for leaf fall into early (J ^E J ^E ), intermediate (J ^E J ^L ) and late (J ^L J ^L ) suggested that codominant alleles were responsible for time of leaf fall. The inheritance studies reported in this paper should guide in Annonaceous fruit breeding for foliage characteristics or could be used as selection criteria for those important traits with which they are associated.     

Genetics of novel corolla colours in periwinkle

Inheritance of a novel corolla colour in periwinkle [Catharanthus roseus (L) G. Don], viz. magenta, was studied by crossing an accession MJ, possessing this corolla colour, with cultivar Nirmal, possessing white corolla. The accession MJ was also crossed with another accession OR, possessing another novel corolla colour, viz. orange-red, to determine the relationship between genes governing magenta corolla and orange-red corolla. The F₁ plants of the cross MJ× Nirmal had pink corolla and red eye. In the F₂ generation, five kinds of corolla colours were observed: (i) pink corolla and red eye, (ii) rose corolla and red eye, (iii) magenta corolla and red eye, (iv) white corolla and red eye and (v) white corolla. The observed frequencies of the five kinds of plants fitted a ratio of 144:27:9:12:64. The progeny of the backcross, F₁ × MJ, segregated into three kinds of plants, (i) pink corolla and red eye, (ii) rose corolla and red eye and (iii) magenta corolla and red eye, in the ratio of 2:1:1, while the backcross, F₁ × Nirmal, segregated into two kinds of plants, (i) pink corolla and red eye and (ii) white corolla, in the ratio of 1:1. Two new genes (proposed symbols O^m and J) appeared to be involved in the determination of magenta and rose corolla colours. Interaction between four independent genes R, W, O^m and J, appeared to explain the observed segregation in the cross MJ × Nirmal. The F₁ plants of the cross MJ × OR had scarlet-red corolla and red eye. The segregation data of F₂ and backcross generations suggested that genes governing orange-red corolla and magenta corolla were allelic to each other. Two new and non-parental corolla colours viz., rose corolla and scarlet-red corolla, were observed in the progeny of the crosses of the present study.     

The Influence of Plant Developmental Stage on Expression of Resistance to leaf Rust (Puccinia recondita) in Two Near Isogenic Lines of Wheat

Cultivar ‘Thatcher’, and ‘Thatcher’ lines with Lr 21 and Lr 22 were studied against a number of races of Puccinia recondita for seedling and adult plant reaction. The study has established that Lr 21 and Lr 22 are genes effective against P. recondita at adult plant stage. It has also shown that these genes confer resistance against all races when plants are inoculated at boot leaf stage.     

Linkage relationships among loci controlling morphological traits in cowpea (Vigna unguiculata (L.) Walp.)

Summary Linkage among loci controlling various morphological traits in cowpea were determined using F₂ progenies. Data were collected on individual plants of four crosses segregating for several loci. Recombination estimates between the following pairs of loci were as follows: Sw (swollen vs normal stem base)-Fbc (cream vs green flower buds) (41±4.8%), Pu^s(purple vs green stems)-Cbr (cocoa-brown vs straw-yellow dry pods) (31±5.7%), Pu^p(purple vs green immature pods)-Cbr (30±5.7%), Pu^s-Pu^p (4±1.5%), Ndt (non-determinate vs determinate)-Pd (peduncle colour) (26±2.8%), Ndt-Hg (semi-erect vs erect plant type) (26±2.8%), P^t(purple vs green pod tips)-Bk (greyish-black vs straw-yellow dry pods) (19±2.4%) and Hg-Bpd (normal vs branching peduncle (24±9.5%). Four linkage groups (LG) were identified in these studies. The proposed LG I contained loci Sw and Fbc; LG II loci Pu^s, Pu^p, and Cbr; LG III loci Pd, Ndt, Gh, and Bpd; and LG IV loci P^tand Bk.     

Quantitative trait loci mapping of seed colour,hairy leaf,seedling anthocyanin,leaf chlorosis and days to flowering in F2 population of Brassica rapa L.

A diversity arrays technology (DArT) map was constructed to identify quantitative trait loci (QTL) affecting seed colour, hairy leaf, seedling anthocyanin, leaf chlorosis and days to flowering in Brassica rapa using a F₂ population from a cross between two parents with contrasting traits. Two genes with dominant epistatic interaction were responsible for seed colour. One major dominant gene controls the hairy leaf trait. Seedling anthocyanin was controlled by a major single dominant gene. The parents did not exhibit leaf chlorosis; however, 32% F₂ plants showed leaf chlorosis in the population. A distorted segregation was observed for days to flowering in the F₂ population. A linkage map was constructed with 376 DArT markers distributed over 12 linkage groups covering 579.7 cM. The DArT markers were assigned on different chromosomes of B. rapa using B. rapa genome sequences and DArT consensus map of B. napus. Two QTL (RSC1‐2 and RSC12‐56) located on chromosome A8 and chromosome A9 were identified for seed colour, which explained 19.4% and 18.2% of the phenotypic variation, respectively. The seed colour marker located in the ortholog to Arabidopsis thaliana Transparent Testa2 (AtTT2). Two QTL RLH6‐0 and RLH9‐16 were identified for hairy leaf, which explained 31.6% and 20.7% phenotypic variation, respectively. A single QTL (RSAn‐12‐157) on chromosome A7, which explained 12.8% of phenotypic variation was detected for seedling anthocyanin. The seedling anthocyanin marker is found within the A. thaliana Transparent Testa12 (AtTT12) ortholog. A QTL (RLC6‐04) for leaf chlorosis was identified, which explained 55.3% of phenotypic variation. QTL for hairy leaf and leaf chlorosis were located 0–4 cM apart on the same chromosome A1. A single QTL (RDF‐10‐0) for days to flowering was identified, which explained 21.4% phenotypic variation.     

Identification and inheritance of a partially dominant gene for yellow seed colour in Brassica napus

A yellow‐seeded doubled haploid (DH) line no. 2127‐17, derived from a resynthesized Brassica napus L., was crossed with two black‐seeded Brassica cultivars ‘Quantum’ and ‘Sprint’ of spring type. The inheritance of seed colour was investigated in the F₂, and BC1 populations of the two crosses and also in the DH population derived from the F1 of the cross ‘Quantum’× no. 2127‐17. Seed colour analysis was performed with the colorimeter CR‐300 (Minolta, Japan) together with a visual classification system. The immediate F1 seeds of the reciprocals in the two crosses had the same colour as the self‐pollinated seeds of the respective black‐ and yellow‐seeded female parents, indicating the maternal control of seed colour. The F1 plants produced yellow‐brown seeds that were darker in colour than the seeds of no. 2127‐17, indicating the partial dominance of yellow seed over black. In the segregating BC1 progenies of the two crosses, the frequencies of the black‐ and yellow‐seeded plants fit well with a 1 : 1 ratio. In the cross with ‘Quantum’, the frequencies of yellow‐seeded and black‐seeded plants fit with a 13 : 3 ratio in the F₂ progeny, and with a 3 : 1 ratio in the DH progeny. However, a 49 : 15 segregation ratio was observed for the yellow‐seeded and black‐seeded plants in the F₂ progeny of the cross with ‘Sprint’. It was postulated from these results that seed colour was controlled by three pairs of genes. A dominant yellow‐seeded gene (Y) was identified in no. 2127‐17 that had epistatic effects on the two independent dominant black‐seeded genes (B and C), thereby inhibiting the biosynthesis of seed coat pigments.