Resistance to <Emphasis Type="Italic">Cucumber green mottle mosaic virus</Emphasis> in <Emphasis Type="Italic">Cucumis sativus</Emphasis>

Cucumber green mottle mosaic virus (CGMMV) is a severe threat for cucumber production worldwide. At present, there are no cultivars available in the market which show an effective resistance or tolerance to CGMMV infection, only wild Cucumis species were reported as resistant. Germplasm accessions of Cucumis sativus, as well as C. anguria and C. metuliferus, were mechanically infected with the European and Asian strains of CGMMV and screened for resistance, by scoring symptom severity, and conventional RT-PCR. The viral loads of both CGMMV strains were determined in a selected number of genotypes using quantitative RT-PCR. Severe symptoms were found following inoculation in C. metuliferus and in 44 C. sativus accessions, including C. sativus var. hardwickii. Ten C. sativus accessions, including C. sativus var. sikkimensis, showed intermediate symptoms and only 2 C. sativus accessions showed mild symptoms. C. anguria was resistant to both strains of CGMMV because no symptoms were expressed and the virus was not detected in systemic leaves. High amounts of virus were found in plants showing severe symptoms, whereas low viral amounts found in those with mild symptoms. In addition, the viral amounts detected in plants which showed intermediate symptoms at 23 and 33 dpi, were significantly higher in plants inoculated with the Asian CGMMV strain than those with the European strain. This difference was statistically significant. Also, the amounts of virus detected over time in plants did not change significantly. Finally, the two newly identified partially resistant C. sativus accessions may well be candidates for breeding programs and reduce the losses produced by CGMMV with resistant commercial cultivars.     

<Emphasis Type="Italic">Rf4</Emphasis> has minor effects on the fertility restoration of wild abortive-type cytoplasmic male sterile <Emphasis Type="Italic">japonica</Emphasis> (<Emphasis Type="Italic">Oryza sativa</Emphasis>) lines

Wild abortive (WA)-type cytoplasmic male sterility (CMS) has been exclusively used for breeding three-line hybrid indica rice, but it has not been applied for generating japonica hybrids because of the difficulties related to breeding japonica restorer lines. Determining whether the major restorer-of-fertility (Rf) gene used for indica hybrids can efficiently restore the fertility of WA-type japonica CMS lines may be useful for breeding WA-type japonica restorer lines. In this study, japonica restorer lines for Chinsurah Boro II (BT)-type CMS exhibited varying abilities to restore the fertility of ‘WA-LiuqianxinA’, which is a WA-type japonica CMS line. Additionally, Rf genes for WA-type CMS were identified in the BT-type japonica restorers. Meanwhile, ‘C9083’, which is a BT-type japonica restorer, exhibited a limited ability to restore the fertility of WA-type japonica CMS lines, and a genetic analysis revealed that the fertility restoration was controlled by one locus. The Rf gene was mapped to an approximately 370-kb physical region and was identified as Rf4. Furthermore, Rf gene dosage effects and the temperature influenced the fertility restoration of WA-type japonica CMS lines. This study is the first to confirm that Rf4 has only minor effects on the fertility restoration of WA-type japonica CMS lines. These results may be relevant for the development of WA-type japonica hybrids.     

Molecular breeding for resistance to black rot [<Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">campestris</Emphasis> (Pammel) Dowson] in <Emphasis Type="Italic">Brassicas</Emphasis>: recent advances

The Brassicas are affected by several diseases, of which black rot, Xanthomonas campestris pv. campestris (Pam.) Dowson (Xcc), is one of the most widespread and devastating worldwide. The black rot bacteria causes systemic infection in the susceptible plants and penetrate the plants through the hydathodes or wounds. Typical disease symptoms are ‘V’ shaped necrotic lesions appearing from the leaf margins with blackened veins. Periodic outbreaks of the black rot pathogen have occurred worldwide, especially in the continental regions, where high temperatures and humidity favor the incidence of disease occurrence causing huge yield loss. The challenge to control the losses in vegetable brassicas production is made more difficult by the adverse climatic changes and evolution of new pathogenic races. The development of black rot resistant hybrids/varieties is the most reliable long term practical solution for effective disease control. Identification of new resistant genetic resources, tightly linked markers with resistance loci and QTL mapping would facilitate the breeding programme for black rot resistance. Information regarding genetics of resistance and mapping of resistance genes/QTLs will accelerate the marker assisted resistance breeding in brassica crops against Xcc. In future we need to identify the race specific candidate genes for and their validation through transgenics and gene expression. Moreover, it is imperative to identify functional markers for resistance genes through identification of R gene families and their relationship with resistance expression. This comprehensive review will help the researchers working in this area to understand the dynamics of black resistance breeding and to formulate future breeding strategies.     

Identification of genetic sources with attenuated <Emphasis Type="Italic">Tomato chlorosis virus</Emphasis>-induced symptoms in <Emphasis Type="Italic">Solanum</Emphasis> (section <Emphasis Type="Italic">Lycopersicon</Emphasis>) germplasm

The whitefly-transmitted Tomato chlorosis virus (ToCV) (genus Crinivirus) is associated with yield and quality losses in field and greenhouse-grown tomatoes (Solanum lycopersicum) in South America. Therefore, the search for sources of ToCV resistance/tolerance is a major breeding priority for this region. A germplasm of 33 Solanum (Lycopersicon) accessions (comprising cultivated and wild species) was evaluated for ToCV reaction in multi-year assays conducted under natural and experimental whitefly vector exposure in Uruguay and Brazil. Reaction to ToCV was assessed employing a symptom severity scale and systemic virus infection was evaluated via RT-PCR and/or molecular hybridization assays. A subgroup of accessions was also evaluated for whitefly reaction in two free-choice bioassays carried out in Uruguay (with Trialeurodes vaporariorum) and Brazil (with Bemisia tabaci Middle-East-Asia-Minor1—MEAM1?=?biotype B). The most stable sources of ToCV tolerance were identified in Solanum habrochaites PI 127827 (mild symptoms and low viral titers) and S. lycopersicum ‘LT05’ (mild symptoms but with high viral titers). These two accessions were efficiently colonized by both whitefly species, thus excluding the potential involvement of vector-resistance mechanisms. Other promising breeding sources were Solanum peruvianum (sensu lato) ‘CGO 6711’ (mild symptoms and low virus titers), Solanum chilense LA1967 (mild symptoms, but with high levels of B. tabaci MEAM1 oviposition) and Solanum pennellii LA0716 (intermediate symptoms and low level of B. tabaci MEAM1 oviposition). Additional studies are necessary to elucidate the genetic basis of the tolerance/resistance identified in this set of Solanum (Lycopersicon) accessions.     

Resistance to late blight (<Emphasis Type="Italic">Phytophthora infestans</Emphasis>) in ten wild <Emphasis Type="Italic">Solanum</Emphasis> species

Nineteen accessions of the tuber-bearing species Solanum berthaultii, S. chacoense, S. leptophyes, S. microdontum, S. sparsipilum, S. sucrense, S. venturii, S. vernei and S. verrucosum were tested for their resistance to late blight in two years of field experiments. Plants were artifically inoculated with zoospores of race 1.2.3.4.5.7.10.11 and the development of the disease was followed. Resistance ratings, calculated as the areas under the disease progress curves (ADPC), demonstrated a high resistance in all accessions except in S. sparsipilum, S. leptophyes and their interspecific hybrid. Segregations suggest that major genes for resistance are present in S. sucrense and S. venturii, and may also play a role in S. verrucosum. It is not yet certain wether the resistance of the other accessions is comparable to the partial and durable resistance of S. tuberosum cultivars like Pimpernel, as inheritance and mechanism have yet to be established. However, segregations suggesting the presence of single major genes with complete dominance were not found in these other accessions. Tuber initiation in the field occurred in only one accession, S. tuberosum ssp. andigena, and maturity of the clones was not related to their resistance. In the other accessions maturity types could not be assessed, as the clones require short day conditions for tuber initiation.     

Sources of resistance to <Emphasis Type="Italic">Phytophthora</Emphasis> root rot within the genus <Emphasis Type="Italic">Beta</Emphasis>

Phytophthora root rot caused by Phytophthora drechsleri Tucker is one of the most devastating sugar beet diseases in tropical areas. To identify genetic resources resistant to this disease, an aggressive isolate of P. drechsleri was selected. Then, a screening method was optimized based on the standard scoring scales of 1–9 (1: no symptoms, 9: complete plant death). Finally, 19 sugar beet lines, three cultivars, and 14 accessions of the wild species Beta vulgaris subsp. maritima, B. macrocarpa, B. procumbens, and B. webbiana were evaluated for resistance to the most aggressive isolate of P. drechsleri by using the optimized method (inoculum included 20 g of rice seed together with superficial wound creation). The isolates of P. drechsleri had significant variation in aggressiveness, and Kv10 was the most aggressive isolate on the susceptible variety Rasoul. The lines O.T.201-15, SP85303-0 (resistant check), and S2-24.P.107 had the lowest disease index with scores of 3.09, 3.13, and 3.27 respectively; they were categorized into the resistant group. The interaction between isolates and genotypes was not significant, which indicated the same response of each genotype to different isolates. Investigating the resistance of different generations of sugar beet revealed that progeny selection would be an effective method for increasing the resistance level of breeding materials to P. drechsleri. Among the wild species, the accession 9402 belonging to B. macrocarpa and the accession 7234 of B. vulgaris subsp. maritima had the lowest disease index (2.29 and 2.60, respectively) and were categorized into the resistant group.     

Functional markers delimiting a <Emphasis Type="Italic">Medicago</Emphasis> orthologue of pea symbiotic gene <Emphasis Type="Italic">NOD3</Emphasis>

Symbiotic gene mutated in the pea (Pisum sativum L.) line RisfixC is a determinant of the number of symbiotic root nodules. In parallel to a sharp increase in nodule number, its mutational inactivation brings about the insensitivity of nodulation to the ambient nitrate level (Nts trait). Using the established localization to the SYM2-NOD3 region of the pea linkage group I, functional PCR markers were developed for the orthologous region on the chromosome 5 of the model species Medicago truncatula. Owing to the conservation of the binding regions of the designed primers, pea orthologues were successfully amplified with 60% of the primer pairs tested. When applied to a mapping pea population from the cross of the line RisfixC x Afghanistan L1268 (sym2), the new markers allowed to localize the supernodulation mutation within 2.5 cM confidence interval in the pea genome. The placement of the functional markers on the M. truncatula chromosome 5 confined the orthologous gene location to eight overlapping BACs spanning approximately 710 kbp (positions 37,755,678–38,467,472). The narrowed list of the annotated Medicago genes in combination with the published data on their symbiotic and nitrate regulation can be used for the candidate gene identification, together with the requirements imposed by the known function in nodule number initiation and nitrate sensing. In addition, the new markers are applicable for tracking the RisfixC allele in breeding programmes aimed at the improvement of symbiotic performance.     

Obtainment of an intergeneric hybrid between <Emphasis Type="Italic">Forsythia</Emphasis> and <Emphasis Type="Italic">Abeliophyllum</Emphasis>

Forsythia suspensa and F. ‘Courtaneur’ were used as female parents to cross with Abeliophyllum distichum in 2011 and an intergeneric hybrid of F. suspensa × A. distichum was obtained, though with very low seed set. The morphological characteristics, flower fragrance and volatile organic compounds of flowers were analysed. The intergeneric hybrid had intermediate morphological characteristics of both parents and flower fragrance and was confirmed as a true intergeneric hybrid by amplified fragment length polymorphism (AFLP) markers. Compared with its mother parent (F. suspensa), flowers of the intergeneric hybrid are pale yellow with delicate fragrance. Volatile organic compounds of flowers were retrieved by purge-and-trap techniques, and determined by gas chromatography and mass spectrometry (GC–MS). The main volatile organic components of F. suspensa were isoprenoids, while the main volatile organic components of A. distichum and the hybrid of F. suspensa × A. distichum were aliphatics. To determine the time and the site of intergeneric hybridizing barriers occured, the pollen tubes’ behavior after pollination was observed under fluorescence microscopy. It was found that significant pre-fertilization incompatibility existed in intergeneric crossing combinations [F. ‘Courtaneur’ (Pin) × A. distichum (Thrum) and F. suspensa (Pin) × A. distichum (Thrum)], and only a few pollen tubes of A. distichum penetrated into the ovaries of Forsythia. In our research, an intergeneric hybrid between Forsythia and Abeliophyllum was obtained for the first time, which will provide a solid foundation for expanding the flower color range of Forsythia and breeding fragrant-flowered cultivars.     

Transformation of <Emphasis Type="Italic">Campanula</Emphasis> by wild type <Emphasis Type="Italic">Agrobacterium rhizogenes</Emphasis>

Compact growth is an important quality criterion in horticulture. Many Campanula species and cultivars exhibit elongated growth which is suppressed by chemical retardation and cultural practice during production to accommodate to the consumer’s desire. The production of compact plants via transformation with wild type Agrobacterium rhizogenes is an approach with great potential to produce plants that are non-GMO. Efficient transformation and regeneration procedures vary widely among both plant genera and species. Here we present a transformation protocol for Campanula. Hairy roots were produced on 26–90% of the petioles that were used for transformation of C. portenschlagiana (Cp), a C. takesimana × C. punctata hybrid (Chybr) and C. glomerata (Cg). Isolated hairy roots grew autonomously and vigorously without added hormones. The Cg hairy roots produced chlorophyll and generated plantlets in response to treatments with cytokinin (42 µM 2iP) and auxin (0.67 µM NAA). In contrast, regeneration attempts of transformed Cp and Chybr roots lead neither to the production of chlorophyll nor to the regeneration of shoots. Agropine A. rhizogenes strains integrate split T-DNA in T_L- and T_R-DNA fragments into the plant genome. In this study, regenerated plants of Cg did not contain T_R-DNA, indicating that a selective pressure against this T-DNA fragment may exist in Campanula.     

New sources of resistance to <Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> in <Emphasis Type="Italic">Capsicum annuum</Emphasis>

Background

Cucumber mosaic virus (CMV) is the most serious virus disease affecting chilli (Capsicum annuum L.) worldwide and the absence of natural resistance makes management of CMV outbreaks difficult. The characterization of improved sources of resistance to CMV in chilli would facilitate the development of commercially acceptable chilli varieties with adequate levels of CMV resistance. A total of 30 chilli genotypes were evaluated for their reaction to CMV in field and artificial inoculated conditions during 2010-2011 and 2011-2012. Large differences were observed among genotypes for disease incidence, severity indexes, and yield losses. Based on observed data, genotype CA23 (Noakhali) was identified as resistant, while CA12 (Comilla-2) was categorized as moderately resistant to CMV both in natural and inoculated conditions. Enzyme-linked immunosorbent assay absorbance values of samples taken from CMV-infected leaves corresponded well with visible viral symptoms for these genotypes. The identified C. annuum CA23 and CA12 genotypes represent previously undescribed and potentially useful sources of CMV resistance.

     

Identification of the <Emphasis Type="Italic">S</Emphasis> locus core sequences determining self-incompatibility and <Emphasis Type="Italic">S</Emphasis> multigene family from draft genome sequences of radish (<Emphasis Type="Italic">Raphanus sativus</Emphasis> L.)

The S core and its flanking sequences were identified from two independent draft genome sequences of radish (Raphanus sativus L.). After gap-filling with PCR, the S core regions and full-length S receptor kinase (SRK) genes from two radish genomes were obtained. Phylogenetic analysis of the SRK genes clearly showed that one S core region belonged to the class I S haplotypes, but the other was included in the class II S haplotypes. Three sequences showing homology with known transposable elements were identified in the core regions, and one intact copia-type long terminal repeat (LTR)-retrotransposon containing a 4125-bp open reading frame (ORF) was identified in the class I S haplotype. A total of 61 genes showing homology with the SRK genes were identified from two draft genome sequences. Among them, the RsKD1 showed the highest homology with the SRK genes. There was 90% nucleotide sequence identity between the RsKD1 and RsSRK1 genes in the kinase domains. The phylogenetic tree of SRK genes and 13 most closely related homologs showed that all homologs were more closely related to the class II SRK genes than to the class I SRKs. Physical mapping of radish SRK-homologous genes and their B. rapa orthologs showed that two radish homologs and their B. rapa orthologs were tightly linked to the SRK genes in radish and B. rapa genomes. Sequence information about multiple SRK-homologs identified in this study would be helpful for designing reliable primer pairs for faithful PCR amplification of the SRK alleles, leading to improvement of the S haplotyping system in radish breeding programs.     

Analysis of population structure and genetic diversity reveals gene flow and geographic patterns in cultivated rice (<Emphasis Type="Italic">O. sativa</Emphasis> and <Emphasis Type="Italic">O. glaberrima</Emphasis>) in West Africa

To fully exploit the diversity in African rice germplasm and to broaden the gene pool reliable information on the population genetic diversity and phenotypic characteristics is a prerequisite. In this paper, the population structure and genetic diversity of 42 cultivated African rice (Oryza spp.) accessions originating from West Africa (Benin, Mali and Nigeria, Liberia etc.) were investigated using 20 simple sequence repeats (SSR) and 77 amplified fragment length polymorphisms (AFLP). Additionally, field trials were set up to gain insight into phenotypic characteristics that differentiate the genetic populations among rice accessions. The analysis revealed considerably high polymorphisms for SSR markers (PIC mean?=?0.78) in the germplasm studied. A significant association was found between AFLP markers and geographic origin of rice accessions (R?=?0.72). Germplasm structure showed that Oryza sativa accessions were not totally isolated from Oryza glaberrima accessions. The results allowed identification of five O. glaberrima accessions which grouped together with O. sativa accessions, sharing common alleles of 18 loci out of the 20 SSR markers analyzed. Population structure analysis revealed existence of a gene flow between O. sativa and O. glaberrima rice accessions which can be used to combine several interesting traits in breeding programs. Further studies are needed to clarify the contributions of this gene flow to valuable traits such as abiotic and biotic stresses including disease resistance.     

Development of RAPD and ISSR derived SCAR markers linked to <Emphasis Type="Italic">Xca1Bo</Emphasis> gene conferring resistance to black rot disease in cauliflower (<Emphasis Type="Italic">Brassica oleracea</Emphasis> var. <Emphasis Type="Italic">botrytis</Emphasis> L.)

Black rot caused by Xanthomonas campestris pv. campestris (Xcc) (Pam.) is the most devastating disease of cauliflower (Brassica oleracea var. botrytis L.; 2n = 2x = 18), taking a heavy toll of the crop. In this study, a random amplified polymorphic DNA (RAPD) and inter simple sequence repeat (ISSR) derived sequence characterized amplified region (SCAR) markers linked to the black rot resistance locus Xca1bo were developed and evaluated as a screening tool for resistance. The RAPD marker OPO-04₈₃₃ and ISSR marker ISSR-11₆₃₅ were identified as closely linked at 1.6 cM distance to the black rot resistance locus Xca1bo. Both the markers OPO-04₈₃₃ and ISSR-11₆₃₅ were cloned, sequenced and converted into SCAR markers and validated in 17 cauliflower breeding lines having different genetic backgrounds. These SCAR markers (ScOPO-04₈₃₃ and ScPKPS-11₆₃₅) amplified common locus and showed 100% accuracy in differentiating resistant and susceptible plants of cauliflower breeding lines. The SCAR markers ScOPO-04₈₃₃ and ScPKPS-11₆₃₅ are the first genetic markers found to be linked to the black rot resistance locus Xca1bo in cauliflower. These markers will be very useful in black rot resistance marker assisted breeding.     

Genetic mapping of resistance to <Emphasis Type="Italic">Puccinia hordei</Emphasis> in three barley doubled-haploid populations

The success of breeding for barley leaf rust (BLR) resistance relies on regular discovery, characterization and mapping of new resistance sources. Greenhouse and field studies revealed that the barley cultivars Baronesse, Patty and RAH1995 carry good levels of adult plant resistance (APR) to BLR. Doubled haploid populations [(Baronesse/Stirling (B/S), Patty/Tallon (P/T) and RAH1995/Baudin (R/B)] were investigated in this study to understand inheritance and map resistance to BLR. The seedlings of two populations (B/S and R/B) segregated for leaf rust response that conformed to a single gene ratio (\({\text{X}}_{1:1}^{2}\) = 0.12, P > 0.7 for B/S and \({\text{X}}_{1:1}^{2}\) = 0.34, P > 0.5 for R/B) whereas seedlings of third population (P/T) segregated for two-gene ratio (\({\text{X}}_{1:1}^{2}\) = 0.17, P > 0.6) when tested in greenhouse. It was concluded that the single gene in Baudin and one of the two genes in Tallon is likely Rph12, whereas gene responsible for seedling resistance in Stirling is Rph9.am (allele of Rph12). The second seedling gene in Tallon is uncharacterized. In the field, APR was noted in lines that were susceptible as seedlings. A range of disease responses (CI 5–90) was observed in all three populations. Marker trait association analysis detected three QTLs each in populations B/S (QRph.sun-2H.1, QRph.sun-5H.1 and QRph.sun-6H.1) and R/B (QRph.sun-1H, QRph.sun-2H.2, QRph.sun-3H and QRph.sun-6H.2), and four QTLs in population P/T (QRph.sun-6H.2, QRph.sun-1H.2, QRph.sun-5H.2 and QRph.sun-7H) that significantly contributed to low leaf rust disease coefficients. High frequency of QRph. sun-5H.1, QRph. sun-6H.1, QRph. sun-1H.1, QRph. sun-2H.2, QRph. sun-6H.2, QRph. sun-7H (based on presence of the marker, closely associated to the respective QTLs) was observed in international commercial barley germplasm and hence providing an opportunity for rapid integration into breeding programmes. The identified candidate markers closely linked to these QTLs will assist in selecting and assembling new APR gene combinations; expectantly this will help in achieving good levels of durable resistance for controlling BLR.     

Expression of the <Emphasis Type="Italic">Ga1-s</Emphasis> gametophyte factor in <Emphasis Type="Italic">shrunken2</Emphasis> sweet corn

Outcrossing is an important problem in specialty maize (Zea mays L.) that can be prevented by using gametophyte factors, such as Ga1-s, which preserve maize plants from pollen contamination. Our objective was to check if the gametophyte factor Ga1-s can protect sweet corn homozygous for sh2 in an efficient and stable way. We combined Ga1-s and sh2 by crossing two popcorn and three sweet corn inbred lines, respectively, in a North Carolina Design II, followed by an ear-to-row breeding program with selection for sh2 phenotype and absence of outcrossing. The released inbred lines homozygous for Ga1-s and sh2 were used for obtaining five hybrids that were evaluated for outcrossing and agronomic performance. Our results show that the gametophyte factor Ga1-s effectively protects the sh2 plants and that this effect was stable across environments. However, the agronomic performance of these inbred lines must be improved. Popcorn donors and sweet corn receptors of Ga1-s were unevenly represented in the released Ga1-s / sh2 inbred lines, suggesting that the viability of sh2 is affected by the genotypes involved. Therefore, breeders should pay attention to the choice of donors of Ga1-s that favors the viability of sh2.     

Effects of introgressions from <Emphasis Type="Italic">Festuca pratensis</Emphasis> on winter hardiness of <Emphasis Type="Italic">Lolium perenne</Emphasis>

Previous studies reported that some genotypes with introgressed Festuca chromosome segment(s) in Lolium genome showed enhanced winter hardiness compared to Lolium. The aim of this study was to search comprehensively for the Festuca pratensis chromosome regions affecting winter hardiness-related traits when introgressed into the Lolium perenne genome. Association between F. pratensis introgression and winter hardiness-related traits (fall and winter hardiness indexes, early-spring dry matter yield, and freezing tolerance) were screened in the diploid introgression populations (n = 203) that had some F. pratensis chromosome segments introgressed. Eighty-four intron markers corresponding to unique rice genes randomly distributed across the genome were used for genotyping. Winter hardiness of almost all plants in the introgression populations was lower than that of the F. pratensis and triploid hybrid parents, but the average was higher than that of L. perenne. A significant positive effect of F. pratensis introgression on early-spring dry matter yield was detected on chromosome 7. This quantitative trait locus (QTL) was confirmed by linkage analysis using a backcross population with F. pratensis introgression in the target region of chromosome 7. However, the contribution of the newly identified QTL was rather small (6.7–9.6%), suggesting that superior winter hardiness of F. pratensis compared to L. perenne is conferred by multiple small-effect QTLs. We also detected a previously unreported negative effect of Festuca introgression on winter hardiness. Newly obtained QTL information in this study would contribute to the design of Festuca/Lolium hybrid breeding.     

Resistance screening of breeding lines and commercial tomato cultivars for <Emphasis Type="Italic">Meloidogyne incognita</Emphasis> and <Emphasis Type="Italic">M. javanica</Emphasis> populations (Nematoda) from Ethiopia

Soil and root samples were collected from major tomato growing areas of Ethiopia during the 2012/2013 growing season to identify root-knot nematode problems. DNA-based and isozyme techniques revealed that Meloidogyne incognita and M. javanica were the predominant Meloidogyne species across the sampled areas. The aggressiveness of different populations of these species was assessed on tomato cultivars Marmande and Moneymaker. The two most aggressive populations of each species were selected and further tested on 33 tomato genotypes. The resistance screening and mechanism of resistance was performed after inoculation with 100 freshly hatched (<24 h) second-stage juveniles (J2). Eight weeks after inoculation the number of egg masses produced on each cultivar was assessed. For the resistance mechanism study, J2 penetration and their subsequent development inside the tomato roots were examined at 1, 2, 4 and 6 weeks after inoculation. On both cultivars Marmande and Moneymaker all M. incognita and M. javanica populations formed a high number of egg masses indicating highly aggressive behaviour. Populations from ‘Jittu’ and ‘Babile’ for M. incognita and ‘Jittu’ and ‘Koka’ for M. javanica were selected as most aggressive. None of the 33 tomato genotypes were immune for these M. incognita and M. javanica populations. However, several tomato genotypes were found to have a significant effect on the number of egg masses produced indicating possible resistance. For M. javanica populations there were more plants from cultivars or breeding lines on which no egg masses were found compared to M. incognita populations. The lowest number of egg masses for both populations of M. incognita was produced on cultivars Bridget40, Galilea, and Irma while for M. javanica it was on Assila, Eden, Galilea, Tisey, CLN-2366A, CLN-2366B and CLN-2366C. Tomato genotypes, time (weeks after inoculation) and their interaction were significant sources of variation for J2 penetration and their subsequent development inside the tomato roots. Differential penetration was found in breeding lines such as CLN-2366A, CLN-2366B and CLN-2366C, but many of the selected tomato genotypes resistance for the tested M. incognita and M. javanica populations were expressed by delayed nematode development. Therefore, developing a simple screening technique to be used by local farmers or extension workers is crucial to facilitate selection of a suitable cultivar.     

Mapping of new resistance (<Emphasis Type="Italic">Vr2</Emphasis>, <Emphasis Type="Italic">Rm1</Emphasis>) and ornamental (<Emphasis Type="Italic">Di2</Emphasis>, <Emphasis Type="Italic">pl</Emphasis>) Mendelian trait loci in peach

Peach powdery mildew is one of the major diseases of the peach. Various sources of resistance to PPM have thus been identified, including the single dominant locus Vr2 carried by the peach rootstock ‘Pamirskij 5’. To map Vr2, a linkage map based on microsatellite markers was constructed from the F₂ progeny (WP²) derived from the cross ‘Weeping Flower Peach’ × ‘Pamirskij 5’. Self-pollinations of the parents were also performed. Under greenhouse conditions, all progenies were scored after artificial inoculations in two classes of reactions to PPM (resistant/susceptible). In addition to Vr2, WP² segregated for three other traits from ‘Weeping Flower Peach’: Rm1 for green peach aphid resistance, Di2 for double-flower and pl for weeping-growth habit. With their genomic locations unknown or underdocumented, all were phenotyped as Mendelian characters and mapped: Vr2 mapped at the top of LG8, at 3.3 cM, close to the CPSCT018 marker; Rm1 mapped at the bottom of LG1, at a position of 116.5 cM, cosegregating with the UDAp-467 marker and in the same region as Rm2 from ‘Rubira’^®; Di2 mapped at 28.8 cM on LG6, close to the MA027a marker; and pl mapped at 44.1 cM on LG3 between the MA039a and SSRLG3_16m46 markers. Furthermore, this study revealed, for the first time, a pseudo-linkage between two traits of the peach: Vr2 and the Gr locus, which controls the red/green color of foliage. The present work therefore constitutes a significant preliminary step for implementing marker-assisted selection for the four major traits targeted in this study.     

Hybrids of <Emphasis Type="Italic">Passiflora</Emphasis>: <Emphasis Type="Italic">P. gardneri</Emphasis> versus <Emphasis Type="Italic">P. gibertii,</Emphasis> confirmation of paternity,morphological and cytogenetic characterization

Two new varieties of interspecific hybrids of Passiflora have been developed from the cross between P. gardneri versus P. gibertii, both registered under the Passiflora Society International. Twelve putative hybrids were analyzed. Hybridization was confirmed using RAPD and SSR markers. Primer UBC11 (5′-CCGGCCTTAC-3′) generated informative bands. Primer SSR Pe75 has amplified species-specific fragments and a heterozygote status was observed with two parent bands 300 and 350 bp. The molecular markers generated have been analyzed for the presence or absence of specific informative bands. Based on the morphological characterization, we have identified two hybrid varieties: P. ‘Gabriela’ and P. ‘Bella’. P. ‘Gabriela’ produced flowers in bluish tones, bluish petals on the adaxial and abaxial faces, light blue sepals on the adaxial and light green on the abaxial faces, corona with the base of filaments in intense lilac color and white apex. P. ‘Bella’ produced flowers in lilac tones, intense lilac petals on the adaxial and abaxial faces, dark lilac sepals with whitish edges on the adaxial and light green on the abaxial faces, corona with the base of filaments in intense lilac color and white apex. The cytogenetic analysis verified that the hybrids have the same chromosomal number as the parents (2n = 18); the formation of bivalents between the homeologous chromosomes (n = 9) was observad, leading to regular meiosis, which allows the sexual reproduction and use of these hybrids in breeding programs.