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.     

Role of <Emphasis Type="Italic">Berberis</Emphasis> spp. as alternate hosts in generating new races of <Emphasis Type="Italic">Puccinia graminis</Emphasis> and <Emphasis Type="Italic">P. striiformis</Emphasis>

The common barberry and several other Berberis spp. serve as the alternate hosts to two important rust pathogens of small grains and grasses, Puccinia graminis and P. striiformis. Barberry eradication has been practiced for centuries as a means to control stem rust. Diverse virulence variations have been observed in populations of P. graminis f. sp. tritici that were associated with susceptible barberries in North America. Barberry likely has played a role in generating new races of P. striiformis f. sp. tritici in some regions in the world. Several North American stem rust races, namely races 56, 15B and QCC, initially originated from barberry, were subsequently responsible for generating large-scale epidemics. Thus, sexual cycles on Berberis spp. may generate virulence combinations that could have serious consequences to cereal crop production.     

Measurement of the field response of <Emphasis Type="Italic">Musa</Emphasis> genotypes to <Emphasis Type="Italic">Radopholus Similis</Emphasis> and <Emphasis Type="Italic">Helicotylenchus Multicinctus</Emphasis> and the implications for nematode resistance breeding

Crop growth and damage parameters (plant growth and yield, root damage and nematode population densities), believed to be associated with resistance of Musa genotypes to nematodes under field conditions, were evaluated in a field trial of 24 Musa genotypes inoculated at planting with a combination of Radopholus similis and Helicotylenchus multicinctus with the objective to identify parameters with strong association with nematode resistance and high heritability. Correlation and path analysis of the association between plant growth, yield, root damage and nematode population densities showed a strong negative association between percentage dead roots, percentage root necrosis, R. similis and H. multicinctus population densities and yield. The strongest negative association was observed between percentage dead roots and yield. Broad-sense genotype heritability estimates demonstrated that heritability estimates for percentage dead roots, number of large lesions and nematode population density were most affected by inoculation with nematodes. These results indicate therefore that effective selection for nematode resistance under field conditions could be obtained by using an index, that includes percentage dead roots, the number of large lesions, and nematode population density.     

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.     

Broadening the genetic base of <Emphasis Type="Italic">Brassica napus</Emphasis> canola by interspecific crosses with different variants of <Emphasis Type="Italic">B. oleracea</Emphasis>

Broadening the genetic base of the C genome of Brassica napus canola by use of B. oleracea is important. In this study, the prospect of developing B. napus canola lines from B. napus?×?B. oleracea var. alboglabra, botrytis, italica and capitata crosses and the effect of backcrossing the F₁’s to B. napus were investigated. The efficiency of the production of the F₁’s varied depending on the B. oleracea variant used in the cross. Fertility of the F₁ plants was low—produced, on average, about 0.7 F₂ seeds per self-pollination and similar number of BC₁ seeds on backcrossing to B. napus. The F₃ population showed greater fertility than the BC₁F₂; however, this difference diminished with the advancement of generation. The advanced generation populations, whether derived from F₂ or BC₁, showed similar fertility and produced similar size silique with similar number of seeds per silique. Progeny of all F₁’s and BC₁’s stabilized into B. napus, although B. oleracea plant was expected, especially in the progeny of F₁ (ACC) owing to elimination of the A chromosomes during meiosis. Segregation distortion for erucic acid alleles occurred in both F₂ and BC₁ resulting significantly fewer zero-erucic plants than expected; however, plants with?≤?15% erucic acid frequently yielded zero-erucic progeny. No consistent correlation between parent and progeny generation was found for seed glucosinolate content; however, selection for this trait was effective and B. napus canola lines were obtained from all crosses. Silique length showed positive correlation with seed set; the advanced generation populations, whether derived from F₂ or BC₁, were similar for these traits. SSR marker analysis showed that genetically diverse canola lines can be developed by using different variants of B. oleracea in B. napus?×?B. oleracea interspecific crosses.     

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.     

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.     

<Emphasis Type="Italic">Nicotiana debneyi</Emphasis> has a single dominant gene causing hybrid lethality in crosses with <Emphasis Type="Italic">N. tabacum</Emphasis>

To elucidate the genetic mechanism of hybrid lethality observed in hybrids between cultivated tobacco, Nicotiana tabacum, and wild tobacco species in the section Suaveolentes, genetic analyses were conducted through the triple cross of the hybrids of wild species, including N. benthamiana and N. fragrans, and N. tabacum. N. benthamiana and N. fragrans produced only viable hybrids after crossing with N. tabacum. Subsequently, N. benthamiana and N. fragrans were crossed with N. africana, N. debneyi, and/or N. suaveolens, which produced inviable hybrids after crossing with N. tabacum. Hybrids of the wild species were obtained from four of the six cross combinations. Only when hybrid plants of N. debneyi × N. fragrans, whose hybridity was confirmed by morphological characteristics, random amplified polymorphic DNA analysis, and chromosome observation, were crossed with N. tabacum, triple hybrids were obtained and segregated 1:1 (lethal:viable). Based on these results, a single dominant gene, designated Hybrid Lethality A1 (HLA1), in N. debneyi was found to control hybrid lethality by the interaction with gene(s) on the Q chromosome in N. tabacum. This represents the first report to identify a causal gene for hybrid lethality in the genus Nicotiana.     

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.     

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.     

Wild <Emphasis Type="Italic">Coffea arabica</Emphasis> resistant to <Emphasis Type="Italic">Meloidogyne paranaensis</Emphasis> and genetic parameters for resistance

Arabica coffee production is based on highly productive cultivars; however, these cultivars are susceptible to infestation by several biotic agents, including root-knot nematodes. Collections of wild Coffea arabica germplasm represent an important source of genetic variability for resistant cultivar development. In this study, 1046 plants derived from 71 wild coffee trees were evaluated with respect to Meloidogyne paranaensis resistance. In addition to information on plants reactions, we also evaluated the genetic parameters related to resistance. Progenies from the five most promising plants were also evaluated regarding resistance to M. incognita and M. exigua. The yield potential of selected plants was estimated through analysis of data for fruits harvested in 4 different years. Forty-seven plants were considered resistant based on reproduction factor values. The estimated heritability was high for all analyzed variables leading to substantial selection gain, mainly at the progeny mean level. On the basis of heritabilities and genetic correlations, we conclude that selection could be performed based on values of the gall and egg mass index. However, higher genetic gain could be obtained based on nematode count variables. A second experiment confirmed the reactions of the selected five plants to M. paranaensis, and multiple resistance was detected in three of them. The resistant accessions also have yield potential.     

Reaction of <Emphasis Type="Italic">Phaseolus</Emphasis> spp. genotypes to ashy stem blight caused by <Emphasis Type="Italic">Macrophomina phaseolina</Emphasis>

Ashy stem blight (ASB) caused by Macrophomina phaseolina (Tassi) Goidanich (Mp) is a devastating seed-transmitted disease in common bean in the tropics. The identification of resistant cultivars throughout the cropping season contributes to disease management. Resistance is found in the primary and tertiary gene pools. Our objectives were to determine (1) the reaction of Phaseolus spp. genotypes to two Mp isolates at vegetative and reproductive stages, (2) the area under disease progress curve (AUDPC), and (3) resistant plants per genotype at harvest. Twenty-three genotypes from different origins were planted in the greenhouse in 2016 and 2017. One less-aggressive Mp (PRJD16) and one more-aggressive (PRI16) isolate were inoculated one and three times, respectively, by the cut-stem method. ‘Beníquez’, ‘Othello’, and ‘Verano’ were highly susceptible (mean scores >8.0, and AUDPC values from 264.6 to 300.8) to both isolates. BAT 477 and NY6020-4 were intermediate (5.6 and 6.2; AUDPC: 161.6 and 187.1) to PRJD16 and susceptible (7.4 and 8.2; AUDPC: 209.4 and 235.1) to PRI16. Resistant genotypes (mean scores ≤3) were not identified in this study. However, A 195, ‘Badillo’, and ‘PC 50’ possessed lower mean scores (4.3–5.4) and AUDPC values (126.4–150.9) to both isolates. Furthermore, A 195 had the highest percentage of resistant plants (55.6%) followed by PC 50, I9365-31, and PI 321637 (27.8%) to PRJD16 at harvest. Thus, the identification of resistant parents across Phaseolus species is necessary to increase the levels of ASB resistance in common bean cultivars throughout the entire cropping season.     

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.     

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.     

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.     

Transgressive segregations for yield criteria in reciprocal interspecific crosses between <Emphasis Type="Italic">Cicer arietinum</Emphasis> L. and <Emphasis Type="Italic">C. reticulatum</Emphasis> Ladiz.

Wild Cicer species are considered to be more resistant for biotic and abiotic stresses than that of the cultivated chickpea (Cicer arietinum L.). Alien genes conferring resistance for biotic and abiotic stresses can be transferred from wild Cicer species to the cultivated chickpea but success in interspecific hybridizations has already been achieved with only two wild Cicer species. The current study was undertaken to compare fruitful heterosis in F₂ and F₃ for yield and yield criteria and to identify transgressive segregation in F₂ and F₃ in reciprocal interspecific crosses between C. arietinum and C. reticulatum Ladiz. We define fruitful heterosis as a useful parameter that can be used instead of residual heterosis. Considerable fruitful heterosis in F₂ and F₃ was found for number of seeds, pods per plant, biological yield, and seed yield. Maximum values of most of the characteristics in F₂ and F₃ were higher than that of the best parent indicating that superior progeny could be selected for yield from transgressive segregation. Progeny selection should be based on number of seeds, pods per plant, and biological yield since these characteristics had the highest direct effect on seed yield. The narrow sense heritability was found to be the highest for 100-seed weight. It was suggested that the cultivated chickpea could be used as female parent in interspecific hybridization to increase yield and yield criteria since progeny in F₂ and F₃ had better performance when it was used as female. In conclusion, interspecific hybridization of wild and cultivated chickpea can be used to improve yield and yield components and resistance to biotic and abiotic stresses as well.     

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.     

Genetic effects and genetic relationships among <Emphasis Type="Italic">shrunken</Emphasis> (<Emphasis Type="Italic">sh2</Emphasis>) sweet corn lines and F1 hybrids

The objectives of this study were to quantify the components of genetic variance and the genetic effects, and to examine the genetic relationship of inbred lines extracted from various shrunken2 (sh2) breeding populations. Ten diverse inbred lines developed from sh2 genetic background, were crossed in half diallel. Parents and their F1 hybrids were evaluated at three environments. The parents were genotyped using 20 polymorphic simple sequence repeats (SSR). Agronomic and quality traits were analysed by a mixed linear model according to additive-dominance genetic model. Genetic effects were estimated using an adjusted unbiased prediction method. Additive variance was more important than dominance variance in the expression of traits related to ear aspects (husk ratio and percentage of ear filled) and eating quality (flavour and total soluble solids). For agronomic traits, however, dominance variance was more important than additive variance. The additive genetic correlation between flavour and tenderness was strong (r = 0.84, P < 0.01). Flavour, tenderness and kernel colour additive genetic effects were not correlated with yield related traits. Genetic distance (GD), estimated from SSR profiles on the basis of Jaccard’s similarity coefficient varied from 0.10 to 0.77 with an average of 0.56. Cluster analysis classified parents according to their pedigree relationships. In most studied traits, F1 performance was not associated with GD.     

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.