S1 Plants Research Articles

Cytological characterization of an interspecific hybrid in <i>Jatropha</i> and its progeny reveals preferential uniparental chromosome transmission and interspecific translocation

Genetic variation in Jatropha curcas, a prospective biodiesel plant, is limited, and interspecific hybridization needed for its genetic improvement. Progeny from interspecific crosses between J. curcas and Jatropha integerrima can be used to improve agronomic characters and to increase oil content and yield. However, these hybrids have not been characterized cytologically. The present study was aimed at the analysis of chromosome behavior during meiosis and chromosome composition of S1 plants derived from an interspecific F1 hybrid using genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH). Bivalents that formed as a result of interspecific pairing were frequently observed, suggesting the presence of homoeologous chromosomes from the two species. Almost half of microspores were derived from the reduction division; GISH analysis indicated random transmission of the parent chromosomes to microspores. Male fertility measured as pollen staining with acetocarmine was 48.4%. In contrast, GISH analysis of S1 plants revealed preferential transmission of J. curcas chromosomes. We also found segment exchange between chromosomes of the two species (interspecific translocation) by GISH and FISH analyses. Introgression of J. integerrima chromosome segments into the J. curcas genome would help to improve Jatropha cultivars for mass production.

Using the Animal Model to Accelerate Response to Selection in a Self-Pollinating Crop.

We used the animal model in S0 (F1) recurrent selection in a self-pollinating crop including, for the first time, phenotypic and relationship records from self progeny, in addition to cross progeny, in the pedigree. We tested the model in Pisum sativum, the autogamous annual species used by Mendel to demonstrate the particulate nature of inheritance. Resistance to ascochyta blight (Didymella pinodes complex) in segregating S0 cross progeny was assessed by best linear unbiased prediction over two cycles of selection. Genotypic concurrence across cycles was provided by pure-line ancestors. From cycle 1, 102/959 S0 plants were selected, and their S1 self progeny were intercrossed and selfed to produce 430 S0 and 575 S2 individuals that were evaluated in cycle 2. The analysis was improved by including all genetic relationships (with crossing and selfing in the pedigree), additive and nonadditive genetic covariances between cycles, fixed effects (cycles and spatial linear trends), and other random effects. Narrow-sense heritability for ascochyta blight resistance was 0.305 and 0.352 in cycles 1 and 2, respectively, calculated from variance components in the full model. The fitted correlation of predicted breeding values across cycles was 0.82. Average accuracy of predicted breeding values was 0.851 for S2 progeny of S1 parent plants and 0.805 for S0 progeny tested in cycle 2, and 0.878 for S1 parent plants for which no records were available. The forecasted response to selection was 11.2% in the next cycle with 20% S0 selection proportion. This is the first application of the animal model to cyclic selection in heterozygous populations of selfing plants. The method can be used in genomic selection, and for traits measured on S0-derived bulks such as grain yield.

A new synthetic allotetraploid (A1A1G2G2) between Gossypium herbaceum and G. australe: bridging for simultaneously transferring favorable genes from these two diploid species into upland cotton.

Gossypium herbaceum, a cultivated diploid cotton species (2n = 2x = 26, A1A1), has favorable traits such as excellent drought tolerance and resistance to sucking insects and leaf curl virus. G. australe, a wild diploid cotton species (2n = 2x = 26, G2G2), possesses numerous economically valuable characteristics such as delayed pigment gland morphogenesis (which is conducive to the production of seeds with very low levels of gossypol as a potential food source for humans and animals) and resistance to insects, wilt diseases and abiotic stress. Creating synthetic allotetraploid cotton from these two species would lay the foundation for simultaneously transferring favorable genes into cultivated tetraploid cotton. Here, we crossed G. herbaceum (as the maternal parent) with G. australe to produce an F1 interspecific hybrid and doubled its chromosome complement with colchicine, successfully generating a synthetic tetraploid. The obtained tetraploid was confirmed by morphology, cytology and molecular markers and then self-pollinated. The S1 seedlings derived from this tetraploid gradually became flavescent after emergence of the fifth true leaf, but they were rescued by grafting and produced S2 seeds. The rescued S1 plants were partially fertile due to the existence of univalents at Metaphase I of meiosis, leading to the formation of unbalanced, nonviable gametes lacking complete sets of chromosomes. The S2 plants grew well and no flavescence was observed, implying that interspecific incompatibility, to some extent, had been alleviated in the S2 generation. The synthetic allotetraploid will be quite useful for polyploidy evolutionary studies and as a bridge for transferring favorable genes from these two diploid species into Upland cotton through hybridization.

Growth attributes of rapeseed varieties (Brassica campestris l.) in relation to sowing dates and weedings treatments

Context: To analyze the effect of sowing dates and weeding treatments on growth attributes such as total dry matter (TDM), leaf area index (LAI), net assimilation rate (NAR), crop growth rate (CGR), leaf area ratio (LAR) of three rapeseed (Brassica campestris L.) Objectives: The objective of the study was to identify the growth in relation to sowing dates and weed competition and identify the weeding number for better growth of rapeseed. Materials and Methods: This investigation was arranged as factorial experiment based on the split-split plot design with three replications. Four sowing dates were including 18 October (S1), 12 November (S2), 17 November (S3) and 3 December (S4) and three weeding treatments were no weeding (W0), one hand weeding (W1) and two hand weeding (W2) and three varieties viz., BINA Sarisha-5, BINA Sarisha-6 and BARI Sarisha-14 were investigated. Results: The results showed that, TDM, LAI, CGR, NAR and LAR were affected by sowing date and weeding treatments. The highest TDM, LAI and CGR were obtained in the first sowing and two weedings treatment. The highest NAR was found in S2 plants and W0 treatment. The highest LAR was found in S2 plants and W1 treatment. Conclusion: The results obtained in this study suggest that the first sowing and two weeding treatments are superior for the production of rapeseed. DOI: http://dx.doi.org/10.3329/jbs.v21i0.22519 J. bio-sci. 21: 51-59, 2013

Potential Sources of Resistance in U.S. Cucumis melo PIs to Crown Rot Caused by Phytophthora capsici

Phytophthora capsici is an aggressive pathogen that is distributed worldwide with a broad host range infecting solanaceous, fabaceous, and cucurbitaceous crops. Over the past two decades, increased incidence of Phytophthora blight, particularly in eastern states, has threatened production of many vegetable crops. Cucumis melo L. (honeydew and muskmelon), although especially susceptible to fruit rot, is also highly susceptible to crown rot. Currently, little is known about host resistance to P. capsici in C. melo. To assess crown rot resistance in C. melo seedlings, 308 U.S. PIs, and two commercial cultivars (Athena and Dinero) were grown under greenhouse conditions. Seedlings with three to four true leaves were inoculated with a five-isolate zoospore suspension (1 × 104 zoospores per seedling) at the crown and monitored for 6 weeks. All the susceptible control plants of Athena died within 7 days post-inoculation. The majority of the PIs (281 of 308) were highly susceptible to crown rot and succumbed to the disease rapidly and had less than 20% of the plants survive. Several PIs (PI 181748, PI 182964, and PI 273438) succumbed to crown rot earlier than the susceptible melon cultivars. Eighty-seven PIs selected on the basis of the first screen were re-evaluated and of these PIs, 44 were less susceptible than cultivars Athena and Dinero. Twenty-five of the 87 PIs were evaluated again and of these six PI, greater than 80% of the plants survived in the two evaluations. Disease development was significantly slower on these PIs compared with the susceptible checks. High levels of resistance in S1 plants of PI 420180, PI 176936, and PI 176940 were observed, which suggests that development of resistant germplasm for use in breeding programs can be accomplished. Further screening and careful selection within each of these PIs can provide a framework for the development of resistant germplasm for use in breeding programs.

AFLP and MSAP Analysis on Genetic Variation in Early Generations of Artificially Synthesized Brassica napus

In order to reveal pattern of genetic and epigenetic changes following allopolyploidization of A and C genomes in Brassica,AFLP(amplified fragment length polymorphism) was utilized to detect level of genome changes for S0 plants of cross A(Qinghai Dahuang×Zhonghua Jielan) and S0,S1 plants of cross B(Qinghai Dahuang×Zhongchi Jielan).Moreover,MSAP(me-thylation sensitive amplification polymorphism) was utilized to detect level of methylation changes for S0 plants of cross B.Five hundred and twenty three bands were amplified in S0 plants of cross A with 16 pairs of primer,nine out of these bands amplified showed significant differences between S0 and parents plants,mainly including deletion of seven parental restriction fragments and gain of two new fragments,accounting for 1.33% and 0.38% of total fragments,respectively.One thousand and ninety three bands were amplified in parental plants of B cross with 45 pairs of primer,only one from C genome out of these fragments lost in all S0 plants,accounting for 0.09% of total bands.In 16 S1 plants from the B9 plant,10 out of 1092 bands amplified showed varia-tions,consisting of the deletion of nine fragments from C genome and the gain of one new fragment.By MSAP approach,three loci with cytosine methylation changes were founded on A genome of S0 plants of B cross,which accounted for 1.37% of loci detected.In addition,a plant with flower color mutation in S0 generation of B cross was observed;we speculated that the flower color mutation was probably caused by genetic changes on C genome.This study provided theoretical informations for innovation of rapeseed germplasm by resynthesizing Brassica napus.

Homologous recombination in Arabidopsis seeds along the track of energetic carbon ions

Heavy ion irradiation has been used as radiotherapy of deep-seated tumors, and is also an inevitable health concern for astronauts in space mission. Unlike photons such as X-rays and γ-rays, a high linear energy transfer (LET) heavy ion has a varying energy distribution along its track. Therefore, it is important to determine the correlation of biological effects with the Bragg curve energy distribution of heavy ions.In this study, a continuous biological tissue equivalent was constructed using a layered cylinder of Arabidopsis seeds, which was irradiated with carbon ions of 87.5MeV/nucleon. The position of energy loss peak in the seed pool was determined with CR-39 track detectors. The mutagenic effect in vivo along the path of carbon ions was investigated with the seeds in each layer as an assay unit, which corresponded to a given position in physical Bragg curve. Homologous recombination frequency (HRF), expression level of AtRAD54 gene, germination rate of seeds, and survival rate of young seedlings were used as checking endpoints, respectively. Our results showed that Arabidopsis S0 and S1 plants exhibited significant increases in HRF compared to their controls, and the expression level of AtRAD54 gene in S0 plants was significantly up-regulated. The depth-biological effect curves for HRF and the expression of AtRAD54 gene were not consistent with the physical Bragg curve. Differently, the depth-biological effect curves for the developmental endpoints matched generally with the physical Bragg curve. The results suggested a different response pattern of various types of biological events to heavy ion irradiation. It is also interesting that except for HRF in S0 plants, the depth-biological effect curves for each biological endpoint were similar for 5Gy and 30Gy of carbon irradiation.

Changes in DNA methylation and transgenerational mobilization of a transposable element (mPing) by the Topoisomerase II inhibitor, Etoposide, in rice

BackgroundEtoposide (epipodophyllotoxin) is a chemical commonly used as an anti-cancer drug which inhibits DNA synthesis by blocking topoisomerase II activity. Previous studies in animal cells have demonstrated that etoposide constitutes a genotoxic stress which may induce genomic instability including mobilization of normally quiescent transposable elements (TEs). However, it remained unknown whether similar genetically mutagenic effects could be imposed by etoposide in plant cells. Also, no information is available with regard to whether the drug may cause a perturbation of epigenetic stability in any organism.ResultsTo investigate whether etoposide could generate genetic and/or epigenetic instability in plant cells, we applied etoposide to germinating seeds of six cultivated rice (Oryza sativa L.) genotypes including both subspecies, japonica and indica. Based on the methylation-sensitive gel-blotting results, epigenetic changes in DNA methylation of three TEs (Tos17, Osr23 and Osr36) and two protein-encoding genes (Homeobox and CDPK-related genes) were detected in the etoposide-treated plants (S0 generation) in four of the six studied japonica cultivars, Nipponbare, RZ1, RZ2, and RZ35, but not in the rest japonica cultivar (Matsumae) and the indica cultivar (93-11). DNA methylation changes in the etoposide-treated S0 rice plants were validated by bisulfite sequencing at both of two analyzed loci (Tos17 and Osr36). Transpositional activity was tested for eight TEs endogenous to the rice genome in both the S0 plants and their selfed progenies (S1 and S2) of one of the cultivars, RZ1, which manifested heritable phenotypic variations. Results indicated that no transposition occurred in the etoposide-treated S0 plants for any of the TEs. Nonetheless, a MITE transposon, mPing, showed rampant mobilization in the S1 and S2 progenies descended from the drug-treated S0 plants.ConclusionsOur results demonstrate that etoposide imposes a similar genotoxic stress on plant cells as it does on animal and human cells, which may induce transgenerational genomic instability by instigating transpositional activation of otherwise dormant TEs. In addition, we show for the first time that etoposide may induce epigenetic instability in the form of altered DNA methylation patterns in eukaryotes. However, penetrance of the genotoxic effects of etoposide on plant cells, as being reflected as genetic and epigenetic instability, appears to be in a strictly genotype- and/or generation-dependent manner.

Differentially expressed genes in dicamba‐resistant and dicamba‐susceptible biotypes

In an ongoing effort to investigate the mechanism of auxinic herbicide resistance in Kochia scoparia (kochia), polymerase chain reaction‐based cDNA suppression subtractive hybridization was used to identify genes that are differentially expressed between dicamba‐resistant (HRd) and dicamba‐susceptible (S1) kochia biotypes in response to herbicide treatment. Both the HRd and S1 adaptor‐ligated cDNAs were used in separate hybridizations in order to generate biotype‐specific clones. A total of 710 cDNAs, representing putative differentially expressed mRNAs, were isolated and subjected to further screening. The false‐positive cDNAs were removed by conducting two colony hybridizations and at least one Northern hybridization. Differential or biotype‐specific expression was confirmed for six clones each from the HRd and S1 plants. The S1‐related genes were constitutively expressed at higher levels than in the HRd plants, but none had significant sequence similarity to known genes. Among the HRd‐related genes, HRd‐88 had 42% amino acid sequence identity to a conserved domain within thiol peptidases, which might be involved in auxin‐regulated gene expression. The constitutively expressed and inducible (by the dicamba treatment) HRd‐39 had 40% identity and 60% similarity to a domain from the Fe(II)/α‐ketoglutarate‐dependent hydroxylase superfamily. The HRd‐39 gene product had the characteristics of an enzyme that is able to detoxify dicamba via oxidative hydroxylation and thus its overexpression might confer the dicamba resistance phenotype.

Evaluation of broad spectrum sources of resistance to Fusarium verticillioides and advanced maize breeding lines

The fungus Fusarium verticillioides is commonly associated with maize production in temperate regions of the world, producing ear rot and grain contamination by fumonisins. Genetic resistance is the best preventive action against fumonisin contamination, although at present no commercial maize hybrids are completely resistant. Several studies of the relationship between Fusarium and other species producing ear rot suggest that these fungal species interact in similar ways with the host plant. Consequently, host plant resistance to one pathogen could be associated with resistance to another. The aim of this study was to introduce sources of resistance to Fusarium spp. into maize inbred lines and to evaluate ear rot severity and fumonisin B1 contamination in advanced breeding lines and hybrids after artificial and natural infection with F. verticillioides. Two inbred lines (CO430 and MP420) with resistance to kernel infection by Fusarium graminearum and Aspergillus flavus, respectively, were crossed and backcrossed to susceptible inbred 1203. The BC1S1 progenies were evaluated for plant morphology and silk date and the selected S1 plants were self-pollinated. The S2 families were evaluated under artificial and natural infection with F. verticillioides. Selected S2 progenies were grown ear-to-row until S5-derived inbreds were developed. The S5 lines were evaluated under artificial and natural infection and used as males to produce single crosses. In both crosses, the mean ear rot of the S5 lines with the lowest ear rot was not significantly different from the resistant parent means. Significant progress was observed in the hybrids regarding ear rot performance: on average, ear rot severity decreased significantly from 23% in check hybrids to 5.3% in CO430-derived hybrids. Our results suggest that inbred lines bred for resistance to A. flavus and F. graminearum ear rot could be used to select advanced breeding lines with increased resistances to F. verticillioides ear rot.

Construction of intraspecific linkage maps, detection of a chromosome inversion, and mapping of QTL for constitutive root aerenchyma formation in the teosinte Zea nicaraguensis

The teosinte Zea nicaraguensis, a wild relative of maize, possesses a flooding tolerance-related trait: the formation of constitutive root aerenchyma under drained (non-flooded) soil conditions. A previous study suggested that the degree of constitutive aerenchyma formation varies within Z. nicaraguensis. The objectives of this study were to construct linkage maps, to determine the marker order in a region of chromosome 4 in which recombination between maize and Z. nicaraguensis is suppressed, and to identify quantitative trait loci (QTL) controlling constitutive root aerenchyma formation in two segregating populations of Z. nicaraguensis. A total of 236 simple sequence repeat (SSR) markers were screened for polymorphism in an S1 population of Z. nicaraguensis. Seventy-one polymorphic SSR markers were assigned to 10 chromosomes, and a linkage map was constructed covering 793.5 cM. In the S1 map, a paracentric inversion was detected on the long arm of chromosome 4; this rearrangement was confirmed in an S1 linkage map of a different Z. nicaraguensis accession. Composite interval mapping analysis in 96 S1 plants revealed QTL for aerenchyma formation on chromosomes 1 (bins 1.06–1.07) and 7 (bin 7.01), explaining 17 and 12% of the total phenotypic variance, respectively. The QTL on chromosome 1 was verified by using 156 S2 plants. Near-isogenic lines exhibiting the presence or absence of the aerenchyma QTL have been developed that should be useful for genetic and physiological analyses of root aerenchyma formation.

Eight cycles of recurrent selection for resistance to angular leaf spot in common bean

The genetic progress (GP) was evaluated after eight cycles of recurrent selection for resistance to angular leaf spot in common bean and indirect gain for yield and grain type. The base population (Cycle-0) was obtained from the diallel cross of seven lines with carioca grain and ten resistance sources. To obtain Cycle I, the most resistant S0 plants of Cycle 0 were intercrossed. The same procedure was adopted in the subsequent cycles. GP for resistance to the pathogen was estimated by the overall average of the progenies of each cycle in comparison with control Carioca MG and for productivity in comparison to the controls Carioca MG and Pérola. Lines of the first six cycles were used for grain type. No GP was detected for resistance to angular leaf spot. However, the indirect yield gain was 2.3% and 2.5% in the selection for grain type, with values similar to those obtained by direct selection for these traits.

Drought effect on photosynthetic activity, osmolyte accumulation and membrane integrity of two Cicer arietinum genotypes

Drought was induced in chickpea (Cicer arietinum L.) genotypes (ChK 3226 and ILC 3279) differing in yield capacity. Water stress (S1, RWC around 55–50%; S2, RWC ≤ 40%) drastically reduced stomatal conductance (gs) and net photosynthetic rate (PN) in both genotypes. ILC 3279 showed greater photosynthetic capacity (Amax) decreases. Maximum PSII photochemical efficiency (Fv/Fm), photochemical quenching (qP), total chlorophylls (Chls) and carotenoids (Cars) content showed stability in both genotypes under stress, but in S2 ILC 3279 presented an increase in basal fluorescence (F0) and a greater reduction in estimation of quantum yield of linear electron transport (Φe) than ChK 3226. Membrane damage evaluated by electrolyte leakage occurred earlier and was greater in ILC 3279. It also presented a decrease of total fatty acids (TFA) along drought, while in ChK 3226 greater amounts of TFA were observed in S1. In rehydration, PN of S1 plants completely recovered (ILC 3279) or remained slightly below control (ChK 3226). As regards S2 plants, ILC 3279 showed stronger PN and gs reductions than ChK 3226, despite both genotypes totally recovered Amax and chlorophyll (Chl) a fluorescence. ChK 3226 recovered more efficiently from membrane damage. Under control conditions, greater amounts of most of the studied soluble metabolites occurred in ChK 3226 plants. Malate and citrate decreased with water stress (S2) in both genotypes. Sucrose and pinitol (that had a higher concentration than sucrose in both genotypes) increased in ILC 3279 (S1 and S2), and decreased in ChK 3226 (S2). In ILC 3279 proline and asparagine followed similar patterns. Genotypes showed a similar shoot dry mass (DM) in control plants, but root DM was higher in ChK 3226. Drought reduced root and shoot DM in ChK 3226 already under S1, while in ILC 3279 root DM was unaffected by drought and shoot biomass decreased only in S2. Root/shoot ratio was always higher in ChK 3226 but tended to decrease under stress, while the opposite was observed in ILC 3279. No pods were obtained from control plants of both genotypes, or droughted ILC 3279 plants. ChK 3226 produced pods under S1 (higher yield) and S2. Under stress conditions, ChK 3226 was less affected in photosynthetic activity and membrane integrity, showing a better tolerance to drought. This agrees with the better yield of this genotype under water stress. Distinct strategies seem to underlie the different physiological responses of the two genotypes to water deficit. In spite of its significant solutes accumulation, ILC 3279 was more affected in photosynthetic activity and membrane integrity during water stress than ChK 3226, which showed better yield under drought. A relation could not be established between solutes accumulation of ILC 3279 and yield.

Parallel and interlaced recurrent selection (PAIRS): Demonstration of the feasibility of implementing PAIRS to improve complete and partial resistance to blast ( Magnaporthe grisea) and some other main traits in rice

The best generation for the evaluation and selection of a trait depends on its polygenic level and heritability. Little attention has been paid to integrating, in the same rice recurrent selection (RS) scheme, the separation of breeding generations. The option we propose is a new parallel and interlaced RS (PAIRS) scheme. We evaluated and selected earliness and grain size in the S0 generation, complete resistance to leaf blast in S1 plants, partial resistance to leaf and neck blast, earliness and yield components in S2 lines, gelatinization temperature, estimated by the extent of alkali spreading in S3 grains, and tolerance to rice delphacid ( Tagasodes orizicolus) mechanical injuries in S3 plants. Although this innovative scheme may seem complicated overall, this first application of PAIRS highlights that the improvement of every methodological step is very easy. Through a complete recurrent selection and genetic recombination cycle, we obtained good progress for grain length, partial resistance to leaf blast and gelatinization temperature (alkali spreading value), and excellent progress for targeted earliness, complete resistance to leaf blast, partial resistance to neck blast and yield. The population size and the number of plants or lines chosen were adequate and we can recommend them to partners.

Effects of salt stress on the expression of antioxidant genes and proteins in the model legume Lotus japonicus

Salt stress negatively affects many physiological processes in plants. Some of these effects may involve the oxidative damage of cellular components, which can be promoted by reactive oxygen species and prevented by antioxidants. The protective role of antioxidants was investigated in Lotus japonicus exposed to two salinization protocols: S1 (150 mM NaCl for 7 d) and S2 (50, 100 and 150 mM NaCl, each concentration for 6 d). Several markers of salt stress were measured and the expression of antioxidant genes was analyzed using quantitative reverse transcription–polymerase chain reaction and, in some cases, immunoblots and enzyme activity assays. Leaves of S1 plants suffered from mild osmotic stress, accumulated proline but noNa+, and showed induction of many superoxide dismutase and glutathione peroxidase genes. Leaves of S2 plants showed increases in Na+ and Ca2+, decreases in K+, and accumulation of proline and malondialdehyde. In leaves and roots of S1 and S2 plants, the mRNA, protein and activity levels of the ascorbate-glutathione enzymes remained constant, with a few exceptions. Notably, there was consistent up-regulation of the gene encoding cytosolic dehydroascorbate reductase, and this was possibly related to its role in ascorbate recycling in the apoplast. The overall results indicate that L. japonicus is more tolerant to salt stress than other legumes, which can be attributed to the capacity of the plant to prevent Na+reaching the shoot and to activate antioxidant defenses.

Full‐Sib Reciprocal Recurrent Selection with the Use of Doubled Haploids

ABSTRACTDoubled haploids are increasingly used in plant breeding, especially in maize (Zea mays L.) breeding. Their use can deeply change the interest of recurrent selection for the development of new hybrids. To show this, a full‐sib reciprocal recurrent selection scheme using doubled haploids (DH FS‐RRS) is proposed. Doubled haploid lines are derived from each population and they are then pair‐crossed, one line from one population being crossed to one line from the other population. After evaluation of the progenies, for each population, the parents of the best crosses are selected and intercrossed. As compared to the reciprocal recurrent selection using S0 plants (S0 FS‐RRS), DH FS‐RRS can be easily applied to maize in the absence of prolificacy. It is shown that, in the case of maize, for the same decrease in the effective population size and the same average number of plots per year, and with the use of winter nursery, the expected genetic advance per year for DH FS‐RRS can be 38.6% better than that for S0 FS‐RRS. The main advantage of DH FS‐RRS is to allow direct hybrid development.

Identification of AFLP and RAPD markers linked to anthracnose resistance in grapes and their conversion to SCAR markers

AbstractResistance to anthracnose or black spot (Elsinoe ampelina), a serious fungal pathogen in viticulture and table grape production, was investigated on 25 grape cultivars. Bioassays performed with culture filtrates produced by the pathogen revealed 14 resistant genotypes. In most plants resistance originated from Vitis labrucsa but also genotypes with V. rupestris and V. riparia × V. rupestris background showed resistance. Genetic analysis was conducted in F1, S1 and BC1 plants developed from various cultivars. In total, 326 F1 plants were evaluated, 172 genotypes proofed to be resistant, whereas 154 were susceptible to anthracnose. A Mendelian segregation ratio of 1 : 1 (χ2 = 0.30–0.65) indicating that anthracnose resistance is controlled by a single dominant gene. To facilitate the use of marker‐assisted selection in grape‐breeding PCR‐based markers were developed by random amplified polymorphic DNA and amplified fragment length polymorphism in bulk segregant analysis. Finally, OPB 151247 was developed as a sequence characterized amplified region marker being diagnostic for the locus of resistance to anthracnose in all resistant genotypes tested. Within the 25 grape cultivars OPB 151247 is diagnostic in the genetic background of both V. labrucsa and V. rupestris and V. riparia × V. rupestris.

English

  Genetic variation and correlations among traits within a Ghanaian bird-resistant pearl millet landrace population were investigated by evaluating S1 plants derived from the population, at two locations and for two years in Ghana. The objectives were to study genetic variation and correlations among traits in the population, determine the feasibility of selection and to suggest appropriate selection methods and selection indices for effective improvement. There was significant genetic variation for grain yield and most yield component traits, indicating that selection within the population would be feasible. Genetic variation was, however not significant for the percent incidence of downy mildew, implying that selection for improving resistance to the disease would not be effective. Heritabilities ranged from moderate to high (0.4- 0.73) for most traits, in view of which the use of recurrent selection methods, with progeny testing, could be effective for improvement of the population. Grain yield was observed to have significant phenotypic and genotypic correlations with days to 50% blooming and with earhead length, indicating that those two traits could be relied upon as selection indices for selection to improve grain yield. However, significant positive correlations were also observed between earhead length and plant height, which is undesirable, as plants with tall height tend to have a low harvest index and are also prone to lodging. In view of this, caution would be needed during selection, in order to achieve an improved population with good grain yielding ability and not very tall plant height.   Key words: Pearl millet, Ghanaian landrace, genetic variation, trait correlations, selection indices.

Discovery of an Amylose-free Starch Mutant in Cassava (Manihot esculenta Crantz)

One of the objectives of the cassava-breeding project at CIAT is the identification of clones with special root quality characteristics. A large number of self-pollinations have been made in search of useful recessive traits. During 2006 harvests an S1 plant produced roots that stained brownish-red when treated with an iodine solution, suggesting that it had lower-than-normal levels of amylose in its starch. Colorimetric and DSC measurements indicated low levels (3.4%) and an absence of amylose in the starch, respectively. SDS-PAGE demonstrated the absence of GBSS enzyme in the starch from these roots. Pasting behavior was analyzed with a rapid visco-analyzer and resulted in larger values for peak viscosity, gel breakdown, and setback in the mutant compared with normal cassava starch. Solubility was considerably reduced, while the swelling index and volume fraction of the dispersed phase were higher in the mutant. No change in starch granule size or shape was observed. This is the first report of a natural mutation in cassava that drastically reduces amylose content in root starch.

Development of NaCl-tolerant line in Chrysanthemum morifolium Ramat. through shoot organogenesis of selected callus line

Plants were regenerated successfully through shoot organogenesis of a NaCl-selected callus line of Chrysanthemum morifolium Ramat. cv. Maghi Yellow (a salt sensitive cultivar), developed through stepwise increase in NaCl concentration (0-100mM) in the MS medium. The stepwise increase in NaCl concentration from a relatively low level to cytotoxic level was found to be a better way to isolate NaCl-tolerant callus line, since direct transfer of callus to high saline medium was detrimental to callus survival and growth. The selected callus line exhibited significant increase in superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) activities compared to control callus (grown in medium devoid of NaCl). Stability of salt tolerance character of the selected callus line was checked by growing the calli in NaCl-free medium for 3 consecutive months followed by re-exposure to higher salinity stress (120mM NaCl). Among different growth regulator treatments, a combination of 5mgl(-1) TDZ (Thidiazuron) along with 0.25mgl(-1) NAA and 0.5mgl(-1) GA(3) was found to be the most effective for shoot organogenesis in selected callus line. The regeneration potential of the NaCl-tolerant callus ranged from 20.8% to 0% against 62.4% to 0% in control callus line. Under elevated stress condition (medium supplemented with 250mM NaCl), selected calli derived regenerants (S1 plants) exhibited significantly higher SOD and APX activities over both PC (positive control: control callus derived plants grown on MS medium devoid of NaCl) and NC (negative control: control callus derived plants subjected to 250mM NaCl stress) plants. In addition, the NC plants showed stunted growth, delayed root initiation, and had lesser number of roots as compared to S1 plants. Based on growth performance and antioxidant capacity, the S1 plants could be considered as NaCl-tolerant line showing all positive adaptive features towards the salinity stress. Further study on agronomic performance of these S1 plants under saline soil condition need to be undertaken to check the genetic stability of the induced salt-tolerance.