Over-expression of <Emphasis Type="Italic">Arabidopsis</Emphasis><Emphasis Type="Italic">FT</Emphasis> gene reduces juvenile phase and induces early flowering in ornamental gentian plants

Ornamental gentian plants are perennial and have a juvenile period of over 1 year before flowering. We transformed gentian plants with a construct comprising the Arabidopsis FLOWERING LOCUS T (FT) gene (encoding a major component protein of the flowering hormone ‘florigen’) under the control of the rolC promoter from Agrobacterium rhizogenes, which is known to induce vascular-specific expression. The resultant rolCpro-FT transgenic gentian plants showed early flowering in vitro and the earliest line formed floral buds within 4 months after transformation. Regeneration experiments from leaf explants of these rolCpro-FT transgenic plants also confirmed the early flowering phenotype. After acclimatization, these transgenic plants showed normal floral development in a closed greenhouse. There is no effective method to induce early flowering by cultivation management in gentian, therefore these lines might be very useful as annual early season cultivars.     

Exploiting the natural variation of <Emphasis Type="Italic">Arabidopsis</Emphasis><Emphasis Type="Italic">thaliana</Emphasis> for the seed-specific production of proteins

The seed-specific expression of recombinant proteins in transgenic plants offers several interesting advantages over other production platforms. The aim of this study was to select accessions of Arabidopsis thaliana with the highest potential as a platform for seed-specific production of recombinant proteins. A. thaliana was chosen because of its flexibility, high seed yield per m2, high natural protein content and its non-food status. Seven characteristics were measured for 96 accessions; days to first flower bud, days to complete senescence, rosette size, number of main bolts, dry biomass of plant, seed yield and protein content of seeds. Three characteristics (length of life cycle, seed yield and protein content) were used to select accessions with a maximal yield. A variation of length of life cycle between 87 ± 11 days (Ler-1) and more than 200 days (several accessions) was registered. Seed yields per accession varied between 18 ± 16 mg (Wa-1) and 274 ± 76 mg (Mr-0). Protein content ranged between 30% (Ws-2) and 38% (Cvi-0). Based on the results of this study, accession Nok-3 is selected as the accession best suited for exploitation as a seed-based platform for the production of recombinant proteins. Nok-3 has a high seed yield (194 ± 66 mg) combined with a moderate protein content of 34.8% and short life cycle of 126 ± 17 days, resulting in a calculated protein yield per year three times higher than reference accession Col-0. In conclusion, this study illustrates the unexploited variability present in the Arabidopsis gene pool that can be used directly for further optimization of Arabidopsis seeds as production platform. In combination with A. thaliana’s rapid life cycle, flexibility, and high fertility, this makes it an attractive platform for the production of specific groups of recombinant proteins, such as high-purity products produced on a relatively small scale.     

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.     

Amenability of castor to an <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated <Emphasis Type="Italic">in planta</Emphasis> transformation strategy using a <Emphasis Type="Italic">cry1AcF</Emphasis> gene for insect tolerance

Agrobacterium tumefaciens mediated in planta transformation protocol was developed for castor, Ricinus communis. Two-day-old seedlings were infected with Agrobacterium strain EHA105/pBinBt8 harboring cry1AcF and established in the greenhouse. Screening the T₁ generation seedlings on 300 mg L⁻¹ kanamycin identified the putative transformants. Molecular and expression analysis confirmed the transgenic nature and identified high-expressing plants. Western blot analysis confirmed the co-integration of the nptII gene in the selected transgenic plants. Bioassay against Spodoptera litura corroborated with high expression and identified five promising effective lines. Analysis of the T₂ generation plants proved the stability of the transgene indicating the feasibility of the method.     

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.     

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.     

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.     

Development of microsatellite markers in cultivated and wild species of sections <Emphasis Type="Italic">Cepa</Emphasis> and <Emphasis Type="Italic">Phyllodolon</Emphasis> in <Emphasis Type="Italic">Allium</Emphasis>

The potential of microsatellite markers for use in genetic studies has been evaluated in Allium cultivated species (Allium cepa, A. fistulosum) and its allied species (A. altaicum, A. galanthum, A. roylei, A. vavilovii). A total of 77 polymerase chain reaction (PCR) primer pairs were employed, 76 of which amplified a single product or several products in either of the species. The 29 AMS primer pairs derived from A. cepa and 46 microsatellites primer pairs from A. fistulosum revealed a lot of polymorphic amplicons between seven Allium species. Some of the microsatellite markers were effective not only for identifying an intraspecific F₁ hybrid between shallot and bulb onion but also for applying to segregation analyses in its F₂ population. All of the microsatellite markers can be used for interspecific taxonomic analyses among two cultivated and four wild species of sections Cepa and Phyllodolon in Allium. Generally, our data support the results obtained from recently performed analyses using molecular and morphological markers. However, the phylogeny of A. roylei, a threatened species with several favorable genes, was still ambiguous due to its different positions in each dendrogram generated from the two primer sets originated from A. cepa and A. fistulosum.     

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.     

Reduction of <Emphasis Type="Italic">Aegilops sharonensis</Emphasis> chromatin associated with resistance genes <Emphasis Type="Italic">Lr56</Emphasis> and <Emphasis Type="Italic">Yr38</Emphasis> in wheat

The Lr56/Yr38 translocation consists primarily of alien-derived chromatin with only the 6AL telomeric region being of wheat origin. To improve its utility in wheat breeding, an attempt was made to exchange excess Ae. sharonensis chromatin for wheat chromatin through homoeologous crossover in the absence of Ph1. Translocation heterozygotes that lacked Ph1 were test-crossed with Chinese Spring nullisomic 6A tetrasomic 6B and nullisomic 6A-tetrasomic 6D plants and the resistant (hemizygous 6A) progeny were analyzed with four microsatellite markers. Genetic mapping suggested general homoeology between wheat chromosome 6A and the translocation chromosomes, and showed that Lr56 was located near the long arm telomere. Thirty of the 53 recombinants had breakpoints between Lr56 and the most distal marker Xgwm427. These were characterized with additional markers. The data suggested that recombinants #39, 157 and 175 were wheat chromosomes 6A with small intercalary inserts of foreign chromatin containing Lr56 and Yr38, located distally on the long arms. These three recombinants are being incorporated into adapted germplasm. Attempts to identify the single shortest translocation and to develop appropriate markers are being continued.     

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.     

Identification of resistant sources against <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> in <Emphasis Type="Italic">Brassica</Emphasis> species with emphasis on <Emphasis Type="Italic">B. oleracea</Emphasis>

Stem rot caused by Sclerotinia sclerotiorum is one of the most devastating diseases of rapeseed (Brassica napus L.) which causes huge loss in rapeseed production. Genetic sources with high level of resistance has not been found in rapeseed. In this study, 68 accessions in six Brassica species, including 47 accessions of B. oleracea, were evaluated for leaf and stem resistance to S. sclerotiorum. Large variation of resistance was found in Brassica, with maximum differences of 5- and 57-folds in leaf and stem resistance respectively. B. oleracea, especially its wild types such as B. rupestris, B. incana, B. insularis, and B. villosa showed high level of resistance. Our data suggest that wild types of B. oleracea possess tremendous potential for improving S. sclerotiorum resistance of rapeseed.     

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

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

Increased resistance to <Emphasis Type="Italic">Ustilago zeae</Emphasis> and <Emphasis Type="Italic">Fusarium verticilliodes</Emphasis> in maize inbred lines bred for <Emphasis Type="Italic">Fusarium graminearum</Emphasis> resistance

Preliminary field observations in our maize breeding nurseries indicated that breeding for improved resistance to gibberella ear rot (Fusarium graminearum) in maize may indirectly select for resistance to another ear disease, common smut (Ustilago zeae). To investigate this, we compared the disease severity ratings obtained on 189 maize inbreds, eight of which included our inbreds developed with selection for gibberella ear rot resistance after field inoculation and breeding for 8–10 years. No correlation was found between disease severities for the 189 inbreds but the eight gibberella-resistant lines were consistently more resistant to smut. To further examine this relationship and to determine if these eight inbreds would be useful for developing inbreds with either common smut or fusarium ear rot (F. verticilliodes) resistance, we conducted a Griffing’s diallel analysis on six inbreds of maize, four with high levels of gibberella ear rot resistance representing all of the pedigree groups in our eight gibberella lines, and two with very low levels. Our most gibberella ear rot resistant inbreds, CO433 and CO441, had the lowest disease ratings for all three diseases, the consistently largest general combining ability effects and several significant specific combining ability effects. It was concluded that some inbreds bred specifically for gibberella ear rot would also be useful in breeding for resistance to common smut and fusarium ear rot.     

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.     

Search in <Emphasis Type="Italic">Solanum</Emphasis> (section <Emphasis Type="Italic">Lycopersicon</Emphasis>) germplasm for sources of broad-spectrum resistance to four <Emphasis Type="Italic">Tospovirus</Emphasis> species

The genus Tospovirus was considered as monotypic with Tomato spotted wilt virus (TSWV) being the only assigned species. However, extensive studies with worldwide isolates revealed that this genus comprises a number of species with distinct virulence profiles. The Neotropical South America is one center of Tospovirus diversity with many endemic species. Groundnut ringspot virus (GRSV), TSWV, Tomato chlorotic spot virus (TCSV), and Chrysanthemum stem necrosis virus (CSNV) are the predominant tomato-infecting species in Brazil. Sources of resistance were found in Solanum (section Lycopersicon) mainly against TSWV isolates from distinct continents, but there is an overall lack of information about resistance to other viral species. One-hundred and five Solanum (section Lycopersicon: Solanaceae) accessions were initially evaluated for their reaction against a GRSV isolate by analysis of symptom expression and systemic virus accumulation using DAS-ELISA. A subgroup comprising the most resistant accessions was re-evaluated in a second assay with TSWV, TCSV, and GRSV isolates and in a third assay with a CSNV isolate. Seven S. peruvianum accessions displayed a broad-spectrum resistance to all viral species with all plants being free of symptoms and systemic infection. Sources of resistance were also found in tomato cultivars with the Sw-5 gene and also in accessions of S. pimpinellifolium, S. chilense, S. arcanum, S. habrochaites, S. corneliomuelleri, and S. lycopersicum. The introgression/incorporation of these genetic factors into cultivated tomato varieties might allow the development of genetic materials with broad-spectrum resistance, as well as with improved levels of phenotypic expression.     

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

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

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.     

Dominant gene for common bean resistance to common bacterial blight caused by <Emphasis Type="Italic">Xanthomonas</Emphasis><Emphasis Type="Italic">axonopodis</Emphasis> pv. <Emphasis Type="Italic">phaseoli</Emphasis>

The common bacterial blight pathogen [Xanthomonas axonopodis pv. phaseoli (Xap)] is a limiting factor for common bean (Phaseolus vulgaris L.) production worldwide and resistance to the pathogen in most commercial cultivars is inadequate. Variability in virulence of the bacterial pathogen has been observed in strains isolated from Puerto Rico and Central America. A few common bean lines show a differential reaction when inoculated with different Xap strains, indicating the presence of pathogenic races. In order to study the inheritance of resistance to common bacterial blight in common bean, a breeding line that showed a differential foliar reaction to Xap strains was selected and was crossed with a susceptible parent. The inheritance of resistance to one of the selected Xap races was determined by analysis of segregation patterns in the F₁, F₂, F₃ and F₄ generations from the cross between the resistant parent PR0313-58 and the susceptible parent ‘Rosada Nativa’. The F₁, F₂ and F₃ generations were tested under greenhouse conditions. Resistant and susceptible F_3:4 sister lines were tested in the field. The statistical analysis of all generations followed the model for a dominant resistance gene. The resistant phenotype was found to co-segregate with the SCAR SAP6 marker, located on LG 10. These results fit the hypothesis that resistance is controlled by a single dominant gene. The symbol proposed for the resistance gene is Xap-1 and for the bacterial race, XapV1.