Diversity of <Emphasis Type="Italic">Xylella fastidiosa</Emphasis> host suitability among siblings from a non-traditional interspecific <Emphasis Type="Italic">Prunus</Emphasis> cross

Ten F₂ clones from an initial hybridization of Prunus webbii?×?Prunus persica cv Harrow Blood were evaluated under greenhouse conditions for their reaction to Xylella fastidiosa subsp. fastidiosa strain M23 during two growing seasons. Clonal accessions used for the study were selected on the basis of horticultural diversity, and were a small subset of trees from a large F₂ population. Foliar symptoms of M23-inoculated trees were monitored weekly throughout the 20-week growth period. Clones were then sampled for bacterial titer determinations. With the exception of parental accession Harrow Blood, all clones yielded measurable titer; however, almond leaf scorch disease symptoms were never observed in five of the ten sibling clonal accessions. Vegetative bud break and bloom phenology data collected from field-grown mother trees over a 7 year period as well as leaf morphology characters of the clonal accessions were examined for associations with bacterial titers of inoculated clones using a principal components analysis. No clear associations were noted, with small sample size limiting the predictive ability of the analysis.     

Generation of interspecific hybrids between <Emphasis Type="Italic">Trifolium vesiculosum</Emphasis> and <Emphasis Type="Italic">T. alexandrinum</Emphasis> using embryo rescue

Interspecific hybrids were developed between Trifolium alexandrinum cultivar Wardan × Trifolium vesiculosum and T. alexandrinum cultivar BL1 × T. vesiculosum through embryo rescue, as the crosses failed to set seed under natural conditions. Trifolium vesiculosum was used as a donor/male parent in this study as it is reported to possess tolerance to stem rot and high forage yield. Fertilization in crossed florets of the crosses was manifested from the recovery of swollen ovaries (< 7.80%) and confirmed from the presence of one degenerated ovule in most (> 93.00%) of the swollen ovaries. The hybrid embryos at various developmental stages (heart, torpedo and cotyledonary) were rescued at a frequency of 2.56% from Wardan × T. vesiculosum and 6.12% from BL1 × T. vesiculosum. Differentiation occurred only in the cotyledonary stage embryos, resulting in 17 putative interspecific hybrid plantlets. The assessment of plantlet hybridity through SSR markers (for the alleles inherited from the donor parent), micromorphological leaf traits (leaf texture and stomata) and morphological characters (plant height, leaflet length and width) confirmed production of two interspecific hybrids designated as AV1 and BV3 representing both the crosses. AV1 displayed moderate resistance and BV3 was resistant to stem rot.     

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 of interspecific hybrids between <Emphasis Type="Italic">Lilium longiflorum</Emphasis> and <Emphasis Type="Italic">L. lophophorum</Emphasis> var. <Emphasis Type="Italic">linearifolium</Emphasis> via ovule culture at early stage

Interspecific hybridization was carried out between Lilium longiflorum and L. lophophorum var. linearifolium by using the cut style method of pollination, as a contrast, intraspecific hybridization between L. longiflorum ‘Gelria’ and L. longiflorum was also made, but no mature seeds and offspring were obtained from the two combinations under in vivo condition. Ovules excised from each carpel 5–35 days after pollination (DAP) were cultured on B5 or half-strength B5 medium containing sucrose at different concentrations in vitro. In L. longiflorum × L. lophophorum var. linearifolium, only 1.17% of ovules excised at 10 DAP developed into seedlings, and in L. longiflorum ‘Gelria’ × L. longiflorum, only 0.99% of ovules excised at 25 DAP developed into seedlings; none of the ovules excised at other different DAP in the two cross combinations produced any seedlings. The results showed that interspecific hybridization had a more serious post-fertilization barrier than the intraspecific hybridization, and that a lower concentration (3%) of sucrose led to better embryo development and higher percentage of seedlings in ovule cultures. All hybrid seedlings obtained were successfully transplanted to soil and grew normally. The progenies investigated were identified as true hybrids based on inter-simple sequence repeat (ISSR) analysis.     

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.     

Genetic analysis of <Emphasis Type="Italic">Jatropha</Emphasis> species and interspecific hybrids of <Emphasis Type="Italic">Jatropha curcas</Emphasis> using nuclear and organelle specific markers

The present study aims at characterization of Jatropha species occurring in India using nuclear and organelle specific primers for supporting interspecific gene transfer. DNA from 34 accessions comprising eight agronomically important species (Jatropha curcas, J. gossypifolia, J. glandulifera, J. integerrima, J. podagrica, J. multifida, J. villosa, J. villosa. var. ramnadensis, J. maheshwarii) and a natural hybrid, J. tanjorensis were subjected to molecular analysis using 200 RAPD, 100 ISSR and 50 organelle specific microsatellite primers from other angiosperms. The nuclear marker systems revealed high interspecific genetic variation (98.5% polymorphism) corroborating with the morphological differentiation of the species used in the study. Ten organelle specific microsatellite primers resulted in single, discrete bands of which three were functional disclosing polymorphism among Jatropha species. The PCR products obtained with organelle specific primers were subjected to sequence analysis. PCR products from two consensus chloroplast microsatellite primer pairs (ccmp6 and 10) revealed variable number of T and A residues in the intergenic regions of ORF 77–ORF 82 and rp12–rps19 regions, respectively in Jatropha. Artificial hybrids were produced between J. curcas and all Jatropha species used in the study with the exception of J. podagrica. Characterization of F₁ hybrids using polymorphic primers specific to the respective parental species confirmed the hybridity of the interspecific hybrids. Characterization of both natural and artificially produced hybrids using chloroplast specific markers revealed maternal inheritance of the markers. While the RAPD and ISSR markers confirmed J. tanjorensis as a natural hybrid between J. gossypifolia and J. curcas, the ccmp primers (ccmp6 and 10) unequivocally established J. gossypifolia as the maternal parent. Evaluation of backcross interspecific derivatives of cross involving J. curcas and J. integerrima indicate scope for prebreeding and genetic enhancement of Jatropha curcas through interspecific hybridization.     

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.     

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.     

Morphological,cytological and reproductive characterization of tri-species hybrids (GOS) between <Emphasis Type="Italic">Pennisetum glaucum</Emphasis>, <Emphasis Type="Italic">P. orientale</Emphasis> and <Emphasis Type="Italic">P. squamulatum</Emphasis>

New tri-species hybrids (GOS) in the genus Pennisetum involving the cultivated species pearl millet (P. glaucum L.) and two wild species, viz. P. squamulatum Fresen and P. orientale L. C. Rich, are reported. Six hybrid plants were recovered after crossing a backcross hybrid (2n = 3x = 23, GGO) between P. glaucum (2n = 2x = 14, GG) and P. orientale (2n = 2x = 18, OO) with F₁s (2n = 6x = 42, GGSSSS) between P. glaucum (2n = 4x = 28, GGGG) and P. squamulatum (2n = 8x = 56, SSSSSSSS). The hybrids were perennial, morphologically intermediate to their parents, and represented characters from the three contributing species. The hybrids contained 2n = 44 chromosomes (GGGSSO) representing 21, 14 and nine chromosomes from P. glaucum, P. squamulatum and P. orientale, respectively. Meiotic and flow-cytometric analysis suggested origin of these hybrids from unreduced female and reduced male gametes. Average chromosome configuration (8.42_I + 14.32_II + 1.62_III + 0.52_IV) at Meiosis showed limited inter-genomic pairing indicating absence of significant homology between the three genomes. The hybrids were male sterile (except one) and highly aposporous. P. orientale was identified to induce apospory in hybrid background with P. glaucum at diploid and above levels, though it was quantitatively affected by genomic doses from sexual parent. A case of inducible and recurrent apospory is presented whereby a transition from Polygonum-type sexual embryo-sacs to Panicum-type aposporous embryo-sacs was observed in diploid interspecific hybrids. Results supported independent origin and partitioning of the three apomixis-components (apomeiosis, parthenogenesis, and functional endosperm development), reported for the first time in Pennisetum. Potential utilization of GOS hybrids in understanding genome interactions involved in complex traits, such as perenniality and apomixis, is discussed.     

Overcoming obstacles to interspecific hybridization between <Emphasis Type="Italic">Gossypium hirsutum</Emphasis> and <Emphasis Type="Italic">G. turneri</Emphasis>

Gossypium turneri, a wild cotton species (2n = 2X = 26, D₁₀D₁₀) originating from Mexico, possesses invaluable characteristics unavailable in the cultivated tetraploid cotton gene pool, such as caducous involucels at anthesis, resistance to insects and tolerance to abiotic stresses. However, transferring desired characteristics from wild species into cultivated cotton is often fraught with diverse obstacles. Here, Gossypium hirsutum (as the maternal parent) and G. turneri were crossed in the Hainan Province of China, and the obtained hybrid seeds (2n = 3X = 39, ADD₁₀) were treated with 0.075% colchicine solution for 48 h to double the chromosome complement in order to overcome triploid F₁ sterility and to generate a fertile hexaploid. Chromosome doubling was successful in four individuals. However, the new synthetic hexaploids derived from these individuals were still highly sterile, and no seeds were generated by selfing or crossing. Therefore, an embryo rescue technique was employed in an attempt to produce progenies from the new synthetic hexaploids. Consequently, a total of six large embryos were obtained on MSB2K medium supplemented with 0.5 mg l^?1 KIN and 250 mg l^?1 CH using ovules from backcrossing that were 3 days post-anthesis. Four grafted surviving seedlings were confirmed to be the progenies (pentaploids) of the new synthetic hexaploids using cytological observations and molecular markers. Eight putative fertile individuals derived from backcrossing the above pentaploids were confirmed using SSR markers and generated an abundance of normal seeds. This research lays a foundation for transferring desirable characteristics from G. turneri into upland cotton.     

Production and characterization of amphihaploid hybrids between <Emphasis Type="Italic">Nicotiana wuttkei</Emphasis> Clarkson et Symon and <Emphasis Type="Italic">N. tabacum</Emphasis> L

Nicotiana wuttkei Clarkson and Symon discovered in the 1990s in Australia may be of potential interest to breeders as it carries resistance to Peronospora hyoscyami de Bary. The crossability between N. wuttkei (2n = 4x = 32) and three N. tabacum (2n = 4x = 48) cultivars (‘Puławski 66’, ‘Wiślica’ and ‘TN 90’) and the morphology and cytology of their amphihaploid hybrids (2n = 4x = 40) were studied. Seeds were produced only when N. wuttkei was used as the maternal parent, but under normal germination all seedlings died. Viable F₁ hybrids of N. wuttkei × N. tabacum cv. ‘Puławski’ and N. wuttkei × N. tabacum cv. ‘Wiślica’ were obtained only by in vitro cotyledon culture. The amphihaploid plants were intermediate between the parents for most morphological traits. In 46.4% of the PMC’s, only univalents were present. The remainder of the cells had 1–5 bivalents and 1–2 trivalents. In spite of a detectable frequency of monads (2.6%), dyads (2.6%) and triads (4.5%), the hybrids were self and cross sterile.     

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.     

Expression of <Emphasis Type="Italic">Bruguiera gymnorhiza</Emphasis><Emphasis Type="Italic">BgARP1</Emphasis> enhances salt tolerance in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis> plants

We have previously reported that expression of salt-responsive genes, including Bruguiera gymnorhiza ankyrin repeat protein 1 (BgARP1), enhances salt tolerance in both Agrobacterium tumefaciens and Arabidopsis. In this report, we further characterized BgARP1-expressing Arabidopsis to elucidate the role of BgARP1 in salt tolerance. BgARP1-expressing plants exhibited more vigorous growth than wild-type plants on MS plates containing 125–175 mM NaCl. Real-time PCR analysis showed enhanced induction of osmotin34 in the 2-week-old transformants under 125 mM NaCl. It was also showed that induction of typical salt-responsive genes, including RD29A, RD29B, and RD22, was blunted and delayed in the 4-week-old transformants during 24 h after 200 mM NaCl treatment. Ion content analysis showed that transgenic plants contained more K⁺, Ca²⁺, and NO₃ ⁻, and less NH₄ ⁺, than wild-type plants grown in 200 mM NaCl. Our results suggest that BgARP1-expressing plants may reduce salt stress by up-regulating osmotin34 gene expression and maintaining K⁺ homeostasis and regulating Ca²⁺ content. These results indicate that BgARP1 is functional on a heterogeneous background.     

Molecular mapping of <Emphasis Type="Italic">Pc68</Emphasis>, a crown rust resistance gene in <Emphasis Type="Italic">Avena</Emphasis><Emphasis Type="Italic">sativa</Emphasis>

Crown rust, which is caused by Puccinia coronata f. sp. avenae, P. Syd. & Syd., is the most destructive disease of cultivated oats (Avena sativa L.) throughout the world. Resistance to the disease that is based on a single gene is often short-lived because of the extremely great genetic diversity of P. coronata, which suggests that there is a need to develop oat cultivars with several resistance genes. This study aimed to identify amplified fragment length polymorphism AFLP markers that are linked to the major resistance gene, Pc68, and to amplify the F₆ genetic map from Pc68/5*Starter × UFRGS8. Seventy-eight markers with normal segregation were discovered and distributed in 12 linkage groups. The map covered 409.4 cM of the Avena sativa genome. Two AFLP markers were linked in repulsion to Pc68: U8PM22 and U8PM25, which flank the gene at 18.60 and 18.83 centiMorgans (cM), respectively. The marker U8PM25 is located in the linkage group 4_12 in the Kanota × Ogle reference oat population. These markers should be useful for transferring Pc68 to genotypes with good agronomic characteristics and for pyramiding crown rust resistance genes.     

Allelic variation for the rust resistance gene <Emphasis Type="Italic">Lr34</Emphasis>/<Emphasis Type="Italic">Yr18</Emphasis> in Canadian wheat cultivars

The wheat (Triticum aestivum L.) gene Lr34/Yr18 conditions resistance to leaf rust, stripe rust, and stem rust, along with other diseases such as powdery mildew. This makes it one of the most important genes in wheat. In Canada, Lr34 has provided effective leaf rust resistance since it was first incorporated into the cultivar Glenlea, registered in 1972. Recently, molecular markers were discovered that are either closely linked to this locus, or contained within the gene. Canadian wheat cultivars released from 1900 to 2007, breeding lines and related parental lines, were tested for sequence based markers caSNP12, caIND11, caIND10, caSNP4, microsatellite markers wms1220, cam11, csLVMS1, swm10, csLV34, and insertion site based polymorphism marker caISBP1. Thirty different molecular marker haplotypes were found among the 375 lines tested; 5 haplotypes had the resistance allele for Lr34, and 25 haplotypes had a susceptibility allele at this locus. The numbers of lines in each haplotype group varied from 1 to 140. The largest group was represented by the leaf rust susceptible cultivar “Thatcher” and many lines derived from “Thatcher”. The 5 haplotypes that had the resistance allele for Lr34 were identical for the markers tested within the coding region of the gene but differed in the linked markers wms1220, caISBP1, cam11, and csLV34. The presence of the resistance or susceptibility allele at the Lr34 locus was tracked through the ancestries of the Canadian wheat classes, revealing that the resistance allele was present in many cultivars released since the 1970s, but not generally in the older cultivars.     

Resistance screening of <Emphasis Type="Italic">Coffea</Emphasis> spp. accessions for <Emphasis Type="Italic">Pratylenchus coffeae</Emphasis> and <Emphasis Type="Italic">Radopholus arabocoffeae</Emphasis> in Vietnam

Coffee varieties with resistance for the plant-parasitic nematodes Pratylenchus coffeae and Radopholus arabocoffeae are limited in Vietnam. A selection of imported varieties and high yield varieties of Arabica coffee in Vietnam were evaluated for resistance to both plant-parasitic nematode species in Northern Vietnam. The same experiments were carried out with hybrid arabica coffee, three selected clones of Coffea canephora and one clone of Coffea excelsa in the Western Highland of Vietnam. The screened coffee accessions from Ethiopia (KH1, KH13, KH20, KH21, KH29, and KH31) were susceptible and good host for P. coffeae. Also accessions 90P4 (Portugal) and Oro azteca (Mexico) had a reproduction factor Rf > 1. Pluma Hidalgo (Mexico), 90/6 (Vietnam), 90P3 (Portugal), 90P2 (Vietnam), Variedad (Mexico), 90T (Portugal), and Garnica (Mexico) were poor hosts (Rf < 1) but not tolerant to P. coffeae, expressed by a reduction of root weight compared to untreated control plants. Most of the coffee accessions tested in Northern Vietnam were intolerant to R. arabocoffeae, except 90T which showed no reduction of root weight, even at high initial nematode densities (4,000/pot). Good hosts for R. arabocoffeae were Variedad, KH1, KH21, KH29, KH20, KH31, and KH13 with Rf > 1. Pluma Hidalgo, 90/6, 90P3, 90P2, 90T, Oro azteca, and Garnica were poor hosts (Rf < 1). In the Western Highland experiment, all arabica coffee accessions were susceptible for P. coffeae with Rf ranging from 1.41 to 1.59. Tolerance to P. coffeae was found in C. liberica var. Dewevrei, Hong34 and Nhuantren. Coffea excelsa, Hong34, Nhuantren, and H1C19 were tolerant to R. arabocoffeae at the highest inoculation density (4,000 nematodes/pot). The most susceptible accessions were Nhuantren and K55. Resistance (Rf < 1) to R. arabocoffeae was found in C. liberica var. Dewevrei and Hong34. This article reports on the first screening for resistance and tolerance to P. coffeae and R. arabocoffeae in coffee accessions in Vietnam and shows promising results for enhanced coffee-breeding.     

Successful induction of trigenomic hexaploid <Emphasis Type="Italic">Brassica</Emphasis> from a triploid hybrid of <Emphasis Type="Italic">B.</Emphasis><Emphasis Type="Italic">napus</Emphasis> L. and <Emphasis Type="Italic">B. nigra</Emphasis> (L.) Koch

A triploid hybrid with an ABC genome constitution, produced from an interspecific cross between Brassica napus (AACC genome) and B. nigra (BB genome), was used as source material for chromosome doubling. Two approaches were undertaken for the production of hexaploids: firstly, by self-pollination and open-pollination of the triploid hybrid; and secondly, by application of colchicine to axillary meristems of triploid plants. Sixteen seeds were harvested from triploid plants and two seedlings were confirmed to be hexaploids with 54 chromosomes. Pollen viability increased from 13% in triploids to a maximum of 49% in hexaploids. Petal length increased from 1.3 cm (triploid) to 1.9 cm and 1.8 cm in the two hexaploids and longest stamen length increased from 0.9 cm (triploid) to 1.1 cm in the hexaploids. Pollen grains were longer in hexaploids (43.7 and 46.3 μm) compared to the triploid (25.4 μm). A few aneuploid offsprings were also observed, with chromosome number ranging from 34 to 48. This study shows that trigenomic hexaploids can be produced in Brassica through interspecific hybridisation of B. napus and B. nigra followed by colchicine treatment.     

Confirmation and characterization of interspecific hybrids of <Emphasis Type="Italic">Passiflora</Emphasis> L. (Passifloraceae) for ornamental use

Three new varieties of Passiflora hybrids were developed from crosses between P. sublanceolata J. M. MacDougal (ex P. palmeri var. sublanceolata Killip) versus P. foetida var. foetida L. Twenty putative hybrids were analyzed. Hybridizations were confirmed by RAPD and SSR markers. The RAPD primer UBC11 (5′-CCGGCCTTAC-3′) generated informative bands. The SSR primer A08FP1 amplified species-specific fragments and heterozygote status was observed with the two parent bands 240 and 280 bp. The molecular markers generated by primers were analyzed in terms of the presence or absence of specific informative bands. The morphological characterization of the hybrids enabled their differentiation into three groups, identified as: (1) Passiflora ‘Alva’, composed of five hybrid plants with white flowers, large corona, light purple filaments at base, white and purple/white banding to apex; (2) P. ‘Aninha’, composed of six hybrid plants with pale pink flowers, corona filaments reddish/purple at base, white, purple/white banding to apex; (3) P. ‘Priscilla’, composed of nine hybrid plants with white flowers, small corona, filaments dark purple at base, white and purple to apex. The genomic homology of parent plants was verified by cytogenetic analysis. Both parents were 2n = 22. Meiosis was regular in genitors and hybrids. Aneuploidy was observed at hybrid groups P. ‘Alva’ and P. ‘Priscilla’ (2n = 20). Other authors had already observed the same number of chromosomes for some P. foetida genotypes. Obtaining valuable interspecific hybrids opens up new perspectives to offer opportunities in agribusiness for producers and to arouse the interest of consumers into using passion flowers in the Brazilian ornamental plant market.     

Characterization of genes <Emphasis Type="Italic">Rpp2</Emphasis>, <Emphasis Type="Italic">Rpp4</Emphasis>, and <Emphasis Type="Italic">Rpp5</Emphasis> for resistance to soybean rust

Asian rust, caused by the fungus Phakopsora pachyrhizi, is the most severe disease currently threatening soybean crops in Brazil. The development of resistant cultivars is a top priority. Genetic characterization of resistance genes is important for estimating the improvement when these genes are introduced into soybean plants and for planning breeding strategies against this disease. Here, we infected an F₂ population of 140 plants derived from a cross between ‘An-76’, a line carrying two resistance genes (Rpp2 and Rpp4), and ‘Kinoshita’, a cultivar carrying Rpp5, with a Brazilian rust population. We scored six characters of rust resistance (lesion color [LC], frequency of lesions having uredinia [%LU], number of uredinia per lesion [NoU], frequency of open uredinia [%OU], sporulation level [SL], and incubation period [IP]) to identify the genetic contributions of the three genes to these characters. Furthermore, we selected genotypes carrying these three loci in homozygosis by marker-assisted selection and evaluated their genetic effect in comparison with their ancestors, An-76, PI230970, PI459025, Kinoshita and BRS184. All three genes contributed to the phenotypes of these characters in F₂ population and when pyramided, they significantly contributed to increase the resistance in comparison to their ancestors. Rpp2, previously reported as being defeated by the same rust population, showed a large contribution to resistance, and its resistance allele seemed to be recessive. Rpp5 had the largest contribution among the three genes, especially to SL and NoU. Only Rpp5 showed a significant contribution to LC. No QTLs for IP were detected in the regions of the three genes. We consider that these genes could contribute differently to resistance to soybean rust, and that genetic background plays an important role in Rpp2 activity. All three loci together worked additively to increase resistance when they were pyramided in a single genotype indicating that the pyramiding strategy is one good breeding strategy to increase soybean rust resistance.