Genetic variation in F<Subscript>2</Subscript> populations and their potential in the improvement of grain yield in tef (<Emphasis Type="Italic">Eragrostis tef</Emphasis>)

Tef is a staple cereal of Ethiopia in high demand by consumers. In order to cope up with this high consumer demand, productivity per unit of land must increase through the development and use of high-yielding varieties. To this effect, the National Tef Research Project has long been striving towards the development of high yielding varieties through direct selection from germplasm and concentrating favourable alleles through hybridization and selection, despite the tedious crossing technique. The objective of this study was to assess the degree of genetic variation in F₂ populations of tef as a basis for improving grain yield. F₂ populations from 12 crosses and their parents were grown at the Debre Zeit Agricultural Research Center, Ethiopia, and assessment was made on eight traits on individual plant basis. Eleven of the 12 crosses showed substantial genetic variation for grain yield and its components, indicating the potential for improvement through selection. Moreover, grain yield, plant weight and yield related traits showed moderate to high heritability values (17–80%). In all the crosses, tiller number, panicle weight, yield per panicle and panicle length showed significant (P ≤ 0.05) and positive association with grain yield. Considering the degree of genetic variation and heritability values, emphasis should be given to selected crosses in an effort to developing high-yielding tef varieties.     

Heritability and genetic advance in recombinant inbred lines of tef (Eragrostis tef)

Recombinant inbred lines (RILs) of the tef cross Kaye Murri × Fesho were evaluated for nine quantitative traits at three locations in the central highlands of Ethiopia during the 1998/99 main season in order to estimate the genetic coefficient of variation (GCV), heritability and genetic advance expected from selection. Highly significant differences were obtained among the RILs for all traits studied. Grain yield, panicle weight and yield per panicle showed a relatively high GCV (12–16%). A comparatively high heritability was obtained from days to heading (31%) followed by panicle length (25%) and grain yield (23%). Moderate amounts of heritability values were obtained for panicle weight and yield per panicle. High genetic advance as percent of the mean were obtained from grain yield (16%), yield per panicle (12%) and panicle weight (10%) at5% selection intensity, which indicated the possibility of improving these traits. Several RILs were identified that have exceeded the better yielding parent at all locations. Grain yield showed a strong positive association (r = 0.26–0.70) with shoot biomass, lodging index, panicle length, plant height, panicle weight and yield per panicle. Overall, the present results showed a) the availability of genetic variance for some useful traits in the RILs for exploitation through selection, b) the existence of significant genotype × location interaction that indicated the need to test inbred populations in more environments, and c)the availability of superior inbred lines for further breeding work. This revised version was published online in August 2006 with corrections to the Cover Date.     

Resynthesizing <Emphasis Type="Italic">Brassica napus</Emphasis> from interspecific hybridization between <Emphasis Type="Italic">Brassica rapa</Emphasis> and <Emphasis Type="Italic">B. oleracea</Emphasis> through ovary culture

Using three varieties of Brassica rapa, cv. Hauarad (accession 708), cv. Maoshan-3 (714) and cv. Youbai (715), as the maternal plants and one variety of B. oleracea cv. Jingfeng-1 (6012) as the paternal plant, crosses were made to produce interspecific hybrids through ovary culture techniques. A better response of seed formation was observed when ovaries were cultured in vitro at 9–12 days after pollination on the basal MS and B5 media supplemented with 6-benzylaminopurine (BA) and naphthylacetic acid (NAA). The best response was observed for cross 714×6012 with the rate of seeds per ovary reaching 43.0%. Seeds for cross 715×6012 showed the best germination response (66.7%) on the regeneration medium (MS+1.0 mg l^–1 BA+0.05 mg l^–1 NAA). In all three cross combinations, good response in terms of root number and length of plants was observed on the root induction medium (MS+1.0 mg l^–1 BA+0.1 mg l^–1 NAA). A better response was observed for the regenerated plants cultured for 14 days than for 7 days. The ovary-derived plants with well-developed root system were hardened for 8 days and their survival rate reached over 80%. Cytological studies showed that the chromosome number of all plants tested was 19 (the sum of both parents), indicating that these regenerated plants were all true hybrids of B. rapa (n = 10) × B. oleracea (n = 9). The regenerated plants were doubled with colchicine treatment, and the best response in the crosses 708×6012, 714×6012 and 715×6012 was observed when treated with 170 mg l^–1 colchicine for up to 30 h and their doubling frequency reached 52, 56 and 62%, respectively.     

Production and characterization of inter-sectional hybrids between <Emphasis Type="Italic">Kalanchoe spathulata</Emphasis> and <Emphasis Type="Italic">K. laxiflora</Emphasis> ( = <Emphasis Type="Italic">Bryophyllum crenatum</Emphasis>)

The genus Kalanchoe is currently divided into section Kalanchoe and section Bryophyllum, and there has been no successful report on the production of inter-sectional hybrids. Therefore, reciprocal crosses were made between Kalanchoe spathulata (sect. Kalanchoe) and K. laxiflora (sect. Bryophyllum) in order to obtain basic information on the reproductive barriers between these two sections. The seeds were aseptically germinated in vitro and the plants were grown in greenhouse till flowering. When K. spathulata was used as a maternal donor, 39 out of 80 plants showed intermediate characteristics between K. spathulata and K. laxiflora. In contrast, no plants were obtained in the reverse crosses. Hybridity of these plants was confirmed by flow cytometric analysis, chromosome numbers and RAPD analysis. Bulbil formation on the leaf margin as one of the conspicuous characteristics of K. laxiflora was not observed in the hybrids. Some of the hybrid lines showed some pollen fertility, but failed to yield viable seeds by self-pollination or backcross-pollination. Successful production of the inter-sectional hybrid between the two species suggests that they are not so distantly related as considered previously.     

Production of intergeneric hybrid plants between <Emphasis Type="Italic">Sandersonia aurantiaca</Emphasis> and <Emphasis Type="Italic">Gloriosa rothschildiana</Emphasis> via ovule culture (Colchicaceae)

Intergeneric hybrid plants between Colchicaceous ornamental plants, Sandersonia aurantiaca and Gloriosa rothschildiana, have successfully been produced via ovule culture. After 5 days of reciprocal cross-pollination, a few pollen tubes were observed in the ovary. Although seeds were obtained in both reciprocal cross-combinations, they did not germinate under ex vitro conditions. Ovules with placental tissues isolated 14 days after cross-pollination of S. aurantiaca × G. rothschildiana were cultured on a medium containing 0.01 mg l^–1 each of -naphthaleneacetic acid (NAA) and 6-benzyladenine (BA), on which 41.5% of ovules swollen and produced callus-like structures within 10 weeks. When such swollen ovules were transferred to a medium containing 0.1 mg l^–1 each of NAA and BA, 7.5% of the initially cultured ovules produced rhizome-like structures within 6 weeks. Among the rhizome-like structures, those derived from two independent ovules (3.7% of the initially cultured ovules) produced multiple shoots following transfer to a medium containing 0.25 mg l^–1 NAA and 2.5 mg l^–1 BA. Multiple shoot-derived plantlets were established on a plant growth regulator-free medium, and they were successfully transplanted to pots. Early verification of their hybridity was accomplished by flow cytometry (FCM) analysis, chromosome observation and rDNA analysis.     

<Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of faba bean <Emphasis Type="Italic">(Vicia faba</Emphasis> L.) using embryo axes

A system for the production of transgenic faba bean by Agrobacterium-mediated transformation was developed. This system is based upon direct shoot organogenesis after transformation of meristematic cells derived from embryo axes. Explants were co-cultivated with A. tumefaciens strain EHA105/pGlsfa, which harbored a binary vector containing a gene encoding a sulphur rich sunflower albumin (SFA8) linked to the bar gene. Strain EHA 101/pAN109 carrying the binary plasmid containing the coding sequence of a mutant aspartate kinase gene (lysC) from E. coli in combination with neomycinphosphotransferase II gene (nptII) was used as well. The coding sequences of SFA8 and LysC genes were fused to seed specific promoters, either Vicia faba legumin B4 promoter (LeB4) or phaseolin promoter, respectively. Seven phosphinothricin (PPT) resistant clones from Mythos and Albatross cultivars were recovered. Integration, inheritance and expression of the transgenes were confirmed by Southern blot, PCR, enzyme activity assay and Western blot.     

A simple,rapid and reliable bioassay for evaluating seedling vigor under submergence in <Emphasis Type="Italic">indica</Emphasis> and <Emphasis Type="Italic">japonica</Emphasis> rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Submergence is a major stress causing yield losses particularly in the direct-seeded rice cultivation system and necessitates the development of a simple, rapid and reliable bioassay for a large scale screening of rice germplasms with tolerance against submergence stress. We developed two new bioassay methods that were based primarily on the seedling vigor evaluated by the ability of fast shoot elongation under submerged conditions, and compared their effectiveness with two other available methods. All four bioassay methods using cultivars of 7 indica and 6 japonica types revealed significant and consistent cultivar differences in seedling vigor under submergence and/or submergence tolerance. Japonica cultivars were more vigorous than indica cultivars, with Nipponbare being the most vigorous. The simplest test tube method showed the highest correlations to all other methods. Our results suggest that seedling vigor serves as a submergence avoidance mechanism and confers tolerance on rice seedlings to flooding during early crop establishment. A possible relationship is discussed between seedling vigor based on fast shoot elongation and submergence tolerance defined by recovery from submergence stress.     

Genetic analysis reveals a dominant <Emphasis Type="Italic">S</Emphasis> locus and an <Emphasis Type="Italic">S</Emphasis> suppressor locus in natural self-compatible <Emphasis Type="Italic">Brassica napus</Emphasis>

A self-incompatible (SI) line, S-1300, and its maintainer 97-wen135, a self-compatible (SC) line, were used to study the inheritance of maintenance for self-incompatibility in B. napus. The ratio of SI plants to SC plants from S-1300 × 97-wen135 F₂ and (S-1300 × 97-wen135) × 97-wen135 was 346:260 and 249:232, fitting the expected ratio of 9:7 and 1:1, respectively. Based on these observations, here we propose a genetic model in which two independent loci, S locus and S suppressor locus (sp), are predicted to control the inheritance of maintenance for self-incompatibility in B. napus. The genotypes of S-1300 and 97-wen135 are S ₁₃₀₀ S ₁₃₀₀ sp ₁₃₀₀ sp ₁₃₀₀ and S ₁₃₅ S ₁₃₅ sp ₁₃₅ sp ₁₃₅ , respectively. S ₁₃₅ is dominant to S ₁₃₀₀ , but coexistence of sp ₁₃₀₀ and sp ₁₃₅ fails to suppress S locus. Both S ₁₃₀₀ and S ₁₃₅ can be suppressed by sp ₁₃₅ , while sp ₁₃₀₀ can suppress S ₁₃₅ but not S ₁₃₀₀ . The model contains two characteristics: that a dominant S locus exists in self-compatible B. napus, and that co-suppression will occur when sp loci are heterozygous. The model has been validated by the segregation of S phenotypes in the (S-1300 × 97-wen135) × S-1300, the progenies of SC S-1300 × 97-wen135 F₂ plants and DH population developed from S-1300 × 97-wen135 F₁. This is the first study to report co-suppression of S suppressor loci in B. napus. The genetic model will be very useful for developing molecular markers linked to maintenance for self-incompatibility and for dissecting the mechanism of SI/SC in B. napus.     

Genetic analysis of resistance to <Emphasis Type="Italic">soil-borne wheat mosaic virus</Emphasis> derived from <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

Genetic Analysis of Resistance to Soil-Borne Wheat Mosaic Virus Derived from Aegilops tauschii. Euphytica. Soil-Borne Wheat Mosaic Virus (SBWMV), vectored by the soil inhabiting organism Polymyxa graminis, causes damage to wheat (Triticum aestivum) yields in most of the wheat growing regions of the world. In localized fields, the entire crop may be lost to the virus. Although many winter wheat cultivars contain resistance to SBWMV, the inheritance of resistance is poorly understood. A linkage analysis of a segregating recombinant inbred line population from the cross KS96WGRC40 × Wichita identified a gene of major effect conferring resistance to SBWMV in the germplasm KS96WGRC40. The SBWMV resistance gene within KS96WGRC40 was derived from accession TA2397 of Aegilops taushcii and is located on the long arm of chromosome 5D, flanked by microsatellite markers Xcfd10 and Xbarc144. The relationship of this locus with a previously identified QTL for SBWMV resistance and the Sbm1 gene conferring resistance to soil-borne cereal mosaic virus is not known, but suggests that a gene on 5DL conferring resistance to both viruses may be present in T. aestivum, as well as the D-genome donor Ae. tauschii.     

Identification of RAPD markers linked to the rust (<Emphasis Type="Italic">Uromyces fabae</Emphasis>) resistance gene in pea (<Emphasis Type="Italic">Pisum sativum</Emphasis>)

Summary Two RAPD markers linked to gene for resistance (assayed as pustule number cm⁻² leaf area) to rust [Uromyces fabae (Pers.) de Bary] in pea (Pisum sativum L.) were identified using a mapping population of 31 BC₁F₁ [HUVP 1 (HUVP 1 × FC 1] plants, FC 1 being the resistant parent. The analysis of genetics of rust resistance was based on the parents, F₁, F₂, BC₁F₁ and BC₁F₂ generations. Rust resistance in pea is of non-hypersensitive type; it appeared to be governed by a single partially dominant gene for which symbol Ruf is proposed. Further, this trait seems to be affected by some polygenes in addition to the proposed oligogene Ruf. A total of 614 decamer primers were used to survey the parental polymorphism with regard to DNA amplification by polymerase chain reaction. The primers that amplified polymorphic bands present in the resistant parent (FC 1) were used for bulked segregant analysis. Those markers that amplified consistently and differentially in the resistant and susceptible bulks were separately tested with the 31 BC₁F₁ individuals. Two RAPD makers, viz., SC10-82₃₆₀ (primer, GCCGTGAAGT), and SCRI-71₁₀₀₀ (primer, GTGGCGTAGT), flanking the rust resistance gene (Ruf) with a distance of 10.8 cM (0.097 rF and LOD of 5.05) and 24.5 cM (0.194 rF and a LOD of 2.72), respectively, were identified. These RAPD markers were not close enough to Ruf to allow a dependable maker-assisted selection for rust resistance. However, if the two makers flanking Ruf were used together, the effectiveness of MAS would be improved considerably.     

Genetic and histological characterization of a novel recessive genic male sterile line of <Emphasis Type="Italic">Brassica napus</Emphasis> derived from a cross with <Emphasis Type="Italic">Capsella bursa</Emphasis>-<Emphasis Type="Italic">pastoris</Emphasis>

In a previously made cross Brassica napus cv. Oro (2n = 38) × Capsella bursa-pastoris (2n = 4x = 32), one F₁ hybrid with 2n = 38 was totally male sterile. The hybrid contained no complete chromosomes from C. bursa-pastoris, but some specific AFLP (amplified fragment length polymorphism) bands of C. bursa-pastoris were detected. The hybrid was morphologically quite similar to ‘Oro’ except for smaller flowers with rudimentary stamens but normal pistils, and showed good seed-set after pollination by ‘Oro’ and other B. napus cultivars. The fertility segregation ratios (3:1, 1:1) in its progenies indicated that the male sterility was controlled by a single recessive gene. In the pollen mother cells of the male sterile hybrid, chromosome pairing and segregation were normal. Histological sectioning of its anthers showed that the tapetum was multiple layers and was hypertrophic from the stage of sporogenic cells, and that the tetrads were compressed by the vacuolated and disaggregated tapetum and no mature pollen grains were formed in anther sacs, thus resulting in male sterility. The possible mechanisms for the production of the male sterile hybrid and its potential in breeding are discussed.     

Ploidy level studies on the <Emphasis Type="Italic">Dioscorea cayenensis</Emphasis>/<Emphasis Type="Italic">Dioscorea rotundata</Emphasis> complex core set

The Guinea yams, Dioscorea cayenensis Lam. and D. rotundata Poir. (D. cayenensis–D. rotundata complex), represent a highly important crop, widely distributed in the humid and semi-humid tropics. The ploidy levels of 170 accessions of the core set of Guinea yams from West African countries was determined using flow cytometry with propidium iodide staining. One hundred and eight of the genotypes were found to be tetraploid, 47 were hexaploid and five were octoploid. One mixoploid individual containing tetraploid and hexaploid nuclei was also detected. A deeper analysis considering each separate taxon revealed that while for D. rotundata the majority of individuals were tetraploid, for D. cayenensis this ploidy level was not detected in any of the accessions. Also, no association between ploidy level and place of cultivation was found for the evaluated germplasm. The obtained data is highly valuable for breeding programs of Guinea yam, especially for the optimization of future hybridization experiments directed to the genetic improvement of this economically important crop.     

Hybrid performance for yield and yield components in cardamom (<Emphasis Type="Italic">Elettaria cardamom</Emphasis> Maton)

Cardamom is an important high value spice crop. Hybrid breeding is discussed for some time, but there is no information for cardamom. Eight genetically diverse cardamom lines were crossed in a diallel to evaluate the performance of hybrids and determine heterosis over mid-parent, better-parent and standard control for yield and yield components. The study was undertaken for a period of 3 years from 1988 to 2001 (Experiment I). Hybrids generally showed good overall performance for most of the characteristics compared with parents. Ten of the 56 hybrids significantly out-yielded the standard control (RR 1). Substantial mid-parent (MPH), better-parent (BPH) and standard (SH) heterosis were observed for the majority of the characteristics studied. Further evaluation of selected hybrids for yield and disease resistance during 2002–2007 (Experiment II) led to the identification of two cross combinations (CCS 1 × NKE 19 and RR 1 × NKE 12) with high yield and mosaic resistance. The study revealed that cardamom hybrids with high yield potential, desirable quality characteristics and mosaic resistance can be developed from appropriate parents through heterosis breeding. This is the first report of heterosis in cardamom for yield and yield contributing characteristics.     

Genetics of resistance to <Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> in <Emphasis Type="Italic">Cucumis sativus</Emphasis> var. <Emphasis Type="Italic">hardwickii</Emphasis> R. Alef

The genetics of resistance to Cucumber mosaic virus (CMV) in Cucumis sativus var. hardwickii R. Alef, the wild progenitor of cultivated cucumber was assessed by challenge inoculation and by natural infection of CMV. Among the 31 genotypes of C. sativus var. hardwickii collected from 21 locations in India the lowest mean percent disease intensity (PDI) was recorded in IC-277048 (6.33%) while the highest PDI was observed in IC-331631 (75.33%). All the four cultivated varieties (DC-1, DC-2, CHC-1 and CHC-2) showed very high PDI and susceptible disease reaction. Based on mean PDI, 8 genotypes were categorized as resistant, 13 as moderately resistant, 9 as moderately susceptible and one as susceptible. A chi-square test of frequency distribution based on mean PDI in F₂ progenies of six resistant × susceptible crosses revealed monogenic recessive Mendelian ratio 1(R):3(S) to be the best fit. This monogenic recessive model was further confirmed by 1(R):1(S) ratio as the best fit for back cross with resistant parent and no fit for either 3:1 or 1:1 in the back cross with the susceptible parent. The results revealed that CMV resistance in C. sativus var. hardwickii was controlled by a single recessive gene. Considering the cross compatibility between C. sativus var. hardwickii and cultivated cucumber, the resistance trait can be easily transferred to cultivated species through simple backcross breeding.     

A cytoplasmic-nuclear male-sterility system derived from a cross between <Emphasis Type="Italic">Cajanus cajanifolius</Emphasis> and <Emphasis Type="Italic">Cajanus cajan</Emphasis>

Cytoplasmic-nuclear male-sterility is an important biological tool, which has been used by plant breeders to increase yields in cross-pollinated cereals and vegetables by commercial exploitation of the phenomenon of hybrid vigor. In legumes, no such example exists due to the absence of an economic way of mass pollen transfer from male to female parent. Pigeonpea [Cajanus cajan (L.) Millsp.], however, is a different legume where a moderate level of insect-aided natural out-crossing (25–70%) exists and it can be used to produce commercial hybrid cultivars, if an efficient and stable cytoplasmic-nuclear male-sterility (CMS) system is available. This paper reports the development of a stable CMS system (ICP 2039A), derived from an inter-specific hybrid of Cajanus cajanifolius, a wild relative of pigeonpea, with a cultivar ICP 11501. Using this genetic material, designated as the A₄ cytoplasm, a number of fertility restorers and maintainers have been developed. The best short-duration experimental pigeonpea hybrid ICPH 2470 produced 3205 kg ha⁻¹ grain yield in 125 days, exhibiting 77.5% advantage over the control cultivar UPAS 120. At present, all the important biological systems necessary for a successful commercial hybrid breeding program are available in pigeonpea and the package of this technology has been adopted by private seed sector in India for the production and marketing of hybrid varieties.     

Molecular markers linked to <Emphasis Type="Italic">Bn</Emphasis>;<Emphasis Type="Italic">rf</Emphasis>: a recessive epistatic inhibitor gene of recessive genic male sterility in <Emphasis Type="Italic">Brassica napus </Emphasis>L.

7–7365AB is a recessive genic male sterile (RGMS) two-type line, which can be applied in a three-line system with the interim-maintainer, 7–7365C. Fertility of this system is controlled by two duplicate dominant epistatic genes (Bn;Ms3 and Bn;Ms4) and one recessive epistatic inhibitor gene (Bn;rf). Therefore an individual with the genotype of Bn;ms3ms3ms4ms4Rf_ exhibits male sterility, whereas, plant with Bn;ms3ms3ms4ms4rfrf shows fertility because homozygosity at the Bn;rf locus (Bn;rfrf) can inhibit the expression of two recessive male sterile genes in homozygous Bn;ms3ms3ms4ms4 plant. A cross of 7–7365A (Bn;ms3ms3ms4ms4RfRf) and 7–7365C (Bn;ms3ms3ms4ms4rfrf) can generate a complete male sterile population served as a mother line with restorer in alternative strips for the multiplication of hybrid seeds. In the present study, molecular mapping of the Bn;Rf gene was performed in a BC₁ population from the cross between 7–7365A and 7–7365C. Bulked segregant analysis (BSA) and amplified fragment length polymorphism (AFLP) technique was used to identify molecular markers linked to the gene of interest. From a survey of 768 primer combinations, seven AFLP markers were identified. The closest marker, XM5, was co-segregated with the Bn;Rf locus and successfully converted into a sequence characterized amplified region (SCAR) marker, designated as XSC5. Two flanking markers, XM3 and XM2, were 0.6 cM and 2.6 cM away from the target gene, respectively. XM1 was subsequently mapped on linkage group N7 using a doubled-haploid (DH) mapping population derived from the cross Tapidor × Ningyou7, available at IMSORB, UK. To further confirm the location of the Bn;Rf gene, additional simple sequence repeat (SSR) markers in linkage group N7 from the reference maps were screened in the BC₁ population. Two SSR markers, CB10594 and BRMS018, showed polymorphisms in our mapping population. The molecular markers found in the present study will facilitate the selection of interim-maintainer.     

Genetics of grain yield and other agronomic characters in t'ef (Eragrostis tef Zucc Trotter). II. The triple test cross

The normal and selfed families of the triple test cross were employed to detect gene action in t'ef for grain yield and other useful agronomic characters in the breeding programme. Cultivars Kay Murri and Fesho were used as L₁ and L₂ testers, respectively. Eight randomly selected cultivars and two released varieties (DZ-01-354 and DZ-01-196) were crossed with the testers L₁, L₂ and L₃ (the F₁ of L₁ × L₂). In the case of the selfed families, 14 cultivars and two released varieties were used for crossing with the testers. The normal families were grown on an Inceptisol developed from volcanic ash whilst the selfed families were grown on a pellic Vertisol at the Debre Zeit Agricultural Research Centre, Ethiopia. The rainfall during the experimental season was 463 mm. Epistasis was detected for grain yield, yield per panicle, panicle weight, plant weight, harvest index, tiller number, panicle length, culm diameter, days to heading and days to maturity in the normal families of the triple test cross (TTC) of t'ef. Similarly the characters grain yield, yield per panicle, panicle weight, plant height, panicle length, days to heading and days to maturity showed epistasis in the selfed families of the TTC. Epistatic interaction was not important for shoot biomass and for harvest index (for the transformed data) in this family. Therefore, both the normal and selfed families of the TTC were in agreement with regard to detecting epistasis for grain yield, yield per panicle, panicle weight, panicle length, days to heading and days to maturity. Significant additive (D) and dominance (H) components were estimated for the characters in both families, although the magnitudes might have been inflated due to epistasis. The dominance component for panicle length was unimportant in both families of the TTC and as a result the additive components were not biased. In general, the additive, dominance and epistatic components were important in t'ef. Since the crop is self-fertilized only the additive and additive × additive terms are important to develop pure breeding varieties. Therefore, selection for superior segregants should start in advanced generations as homozygosity increases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic diversity evaluation of a loquat (<Emphasis Type="Italic">Eriobotrya japonica</Emphasis> (Thunb) Lindl) germplasm collection by SSRs and <Emphasis Type="Italic">S</Emphasis>-allele fragments

Loquat (Eriobotrya japonica (Thunb.) Lindl.) is a minor Rosaceae fruit of growing interest as an alternative to the main fruit crops. In this context, the selection of new cultivars to satisfy the market demand will request the suitable characterization of the available germplasm. In this work, genetic relationships among 83 loquat accessions from different countries belonging to the European loquat germplasm collection, held at the Instituto Valenciano de Investigaciones Agrarias (IVIA) in Moncada (Spain) were evaluated using microsatellites and S-allele fragments. A total of nine single sequence repeats (SSRs) from Malus and Eriobotrya genera revealed 53 informative alleles and the S-RNases consensus primers detected 11 self-incompatibility putative alleles. The combined data allow to distinguish unambiguously 80 out of the 83 accessions studied. Unweighted pair-group method (UPGMA) cluster and principal coordinates analysis (PCoA), based on Dice’s genetic distance, generally grouped genotypes according to their geographic origins and pedigrees. Discrepancies and similarities of the results obtained with other variability analysis, based on pomological traits or molecular markers, on the same loquat collection are discussed.     

Development and characterisation of a <Emphasis Type="Italic">Brassica carinata</Emphasis> inbred line incorporating genes for low glucosinolate content from <Emphasis Type="Italic">B. juncea</Emphasis>

The presence of high levels of sinigrin in the seeds represents a serious constraint for the commercial utilisation of Ethiopian mustard (Brassica carinata A. Braun) meal. The objective of this research was the introgression of genes for low glucosinolate content from B. juncea into B. carinata. BC₁F₁ seed from crosses between double zero B. juncea line Heera and B. carinata line N2-142 was produced. Simultaneous selection for B. carinata phenotype and low glucosinolate content was conducted from BC₁F₂ to BC₁F₄ plant generations. Forty-three BC₁F₄ derived lines were selected and subject to a detailed phenotypic and molecular evaluation to identify lines with low glucosinolate content and genetic proximity to B. carinata. Sixteen phenotypic traits and 80 SSR markers were used. Eight BC₁F₄ derived lines were very close to N2-142 both at the phenotypic and molecular level. Three of them, with average glucosinolate contents from 52 to 61 micromoles g⁻¹, compared to 35 micromoles g⁻¹ for Heera and 86 micromoles g⁻¹ for N2-142, were selected and evaluated in two additional environments, resulting in average glucosinolate contents from 43 to 56 micromoles g⁻¹, compared to 29 micromoles g⁻¹ for Heera and 84 micromoles g⁻¹ for N2-142. The best line (BCH-1773), with a glucosinolate profile made up of sinigrin (>95%) and a chromosome number of 2n = 34, was further evaluated in two environments (field and pots in open-air conditions). Average glucosinolate contents over the four environments included in this research were 42, 31 and 74 micromoles g⁻¹ for BCH-1773, Heera and N2-142, respectively. These are the lowest stable levels of glucosinolates reported so far in B. carinata.     

Genetic mapping of AFLP markers in Japanese bunching onion (<Emphasis Type="Italic">Allium fistulosum</Emphasis>)

Summary The first genetic linkage map of Japanese bunching onion (Allium fistulosum) based primarily on AFLP markers was constructed using reciprocally backcrossed progenies. They were 120 plants each of (P₁)BC₁ and (P₂)BC₁ populations derived from a cross between single plants of two inbred lines: D1s-15s-22 (P₁) and J1s-14s-20 (P₂). Based on the (P₂)BC₁ population, a linkage map of P₁ was constructed. It comprises 164 markers – 149 amplified fragment length polymorphisms (AFLPs), 2 cleaved amplified polymorphic sequences (CAPSs), and 12 simple sequence repeats (SSRs) from Japanese bunching onion, and 1 SSR from bulb onion (A. cepa) – on 15 linkage groups covering 947 centiMorgans (cM). The linkage map of P₂ was constructed with the (P₁)BC₁ population and composed of 120 loci – 105 AFLPs, 1 CAPS, and 13 SSRs developed from Japanese bunching onion and 1 SSR from bulb onion – on 14 linkage groups covering 775 cM. Both maps were not saturated but were considered to cover the majority of the genome. Nine linkage groups in P₂ map were connected with their counterparts in P₁ map using co-dominant anchor markers, 13 SSRs and 1 CAPS.