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

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

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

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

Genetic effect of <Emphasis Type="Italic">Striga</Emphasis> resistance in sorghum genotypes

Striga is an important parasitic weed causing substantial economic losses in cereal and legume crop production in sub-Saharan Africa. Integrated Striga management approaches such as a combined use of Striga resistant varieties and Fusarium oxysporum f.sp. strigae (FOS), a biocontrol agent of Striga, are an option to control the parasite and to boost sorghum productivity. Understanding host gene action influencing Striga resistance, with or without FOS treatment, is key to developing improved sorghum varieties with durable resistance and high yield. The objective of this study was to determine the gene action and inheritance of Striga resistance using genetically diverse populations of sorghum involving FOS treatment. Twelve sorghum parents selected for Striga resistance, FOS compatibility or superior agronomic performances were crossed using a bi-parental mating scheme. The selected male and female parents and their F₁ progenies, backcross derivatives and the F₂ segregants were field evaluated at three locations in Tanzania known for their severe Striga infestations using a lattice experimental design with two replications. The following data were collected and subjected to generation mean analysis (GMA): days-to-50% flowering (DFL), seed yield per plant (SYP) and number of Striga per plant (SN). GMA showed the preponderance of additive genetic action contributing to the total genetic variation in the evaluated sorghum populations. The additive genetic effect for DFL, SYP and SN, with and without FOS treatments, ranged from 72.02 to 86.65% and 41.49 to 95.44%, 75.62 to 91.42% and 71.83 to 91.89%, and 77.35 to 93.56% and 72.86 to 95.84%, in that order. The contribution of non-additive genetic effects was minimal and varied among generations. FOS application reduced DFL and SN and improved SYP in most of the tested sorghum populations. DFL of sorghum populations was reduced by a mean of 8 days under FOS treatment compared to the untreated control in families such as 675 × 654, AS435 × AS426 and 1563 × AS436. FOS treatment improved SYP with a mean of 6.44 g plant^?1 in 3424 × 3993 and 3984 × 672. The numbers of Striga plants were reduced with a mean of 16 plants due to FOS treatment in the crosses of 675 × 654, 1563 × AS436, 4567 × AS424, and 3984 × 672. The study demonstrated that additive genes were predominantly responsible for the inheritance of Striga resistance in sorghum. Pure line cultivar development targeting reduced DFL, SN and high SYP in the selected populations may provide enhanced response to selection for integrated Striga management (ISM) programme.     

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.     

Effects of <Emphasis Type="Italic">Solanum demissum</Emphasis> chromosomes on crossability in the backcross progeny to <Emphasis Type="Italic">Solanum tuberosum</Emphasis>

A balance of maternal and paternal genetic factors, conceptually named the endosperm balance number (EBN), is required for normal endosperm development in interspecific crosses in potato. We previously found that Solanum demissum (D), a hexaploid wild species widely used in potato breeding, has a slightly lower EBN than S. tuberosum (T). To explore the genetic nature of the EBN, the berry-setting rate, seed number/berry, and seed weight were evaluated in BC₁ [(D?×?T)?×?T] plants, each possessing different portions of the S. demissum chromosomes, by reciprocal crosses with D and T, and a quantitative trait locus (QTL) analysis was performed. At least 99 S. demissum-derived QTLs were detected, of which 29 were associated with differential responses to D and T. Three QTLs were possibly co-localized on chromosomes 7A and 10D1, while the remaining 23 QTLs were independently located. The QTLs in the three S. demissum homoeologous chromosomes exhibited three types of interaction: (1) positive, (2) negative, and (3) one positive and one negative effect on the same trait. We found that several major genes, one of which was localized in the S. demissum chromosome 9A, and many minor genes controlled the crossability of BC₁ plants. The QTLs responsible for the differential responses to D and T were different between the BC₁ plants used as male and female parents, indicating that different genes control the male and female EBNs. Consequently, we conclude that the EBN is represented by the sum of various genetic effects controlled by a large number of genes.     

Determining resistance to <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> and fumonisin accumulation in African maize inbred lines resistant to <Emphasis Type="Italic">Aspergillus flavus</Emphasis> and aflatoxins

Fusarium verticillioides and Aspergillus flavus cause Fusarium ear rot (FER) and Aspergillus ear rot (AER) of maize, respectively. Both pathogens are of concern to producers as they reduce grain yield and affect quality. F. verticillioides and A. flavus also contaminate maize grain with the mycotoxins fumonisins and aflatoxins, respectively, which has been associated with mycotoxicosis in humans and animals. The occurrence of common resistance mechanisms to FER and AER has been reported. Hence, ten Kenyan inbred lines resistant to AER and aflatoxin accumulation were evaluated for resistance to FER, F. verticillioides colonisation and fumonisin accumulation; and compared to nine South African lines resistant to FER and fumonisin accumulation. Field trials were conducted at three localities in South Africa and two localities in Kenya. FER severity was determined by visual assessment, while F. verticillioides colonisation and fumonisin content were quantified by real-time PCR and liquid chromatography tandem mass spectrometry, respectively. Significant genotype x environment interactions was determined at each location (P ≤ 0.05). Kenyan inbred CML495 was most resistant to FER and F. verticillioides colonisation, and accumulated the lowest concentration of fumonisins across localities. It was, however, not significantly more resistant than Kenyan lines CML264 and CKL05015, and the South African line RO549 W, which also exhibited low FER severity (≤5%), fungal target DNA (≤0.025 ng μL^?1) and fumonisin levels (≤2.5 mg kg^?1). Inbred lines resistant to AER and aflatoxin accumulation appear to be promising sources of resistance to F. verticillioides and fumonisin contamination.     

Identifying apomixis in matroclinal progeny from an interspecific crossing between <Emphasis Type="Italic">Iris domestica</Emphasis> and three different colors of <Emphasis Type="Italic">Iris dichotoma</Emphasis>

In a previous investigation on the reciprocal difference of interspecific hybridization between three different flower colors of Iris dichotoma and Iris domestica in the F₁ offspring from crosses where I. domestica was a maternal parent were similar in morphological and cytological characters to their maternal parent. This could be evidence of apomixis; however, matroclinal progeny with complete morphological similarity to the maternal parent could be attributed to the heterozygosity for these characters in the pollen parent. The F₁ plants were investigated in order to identify apomixis in I. domestica. Four matroclinal plants were randomly selected from each F₁ population produced from Iris domestica × Iris dichotoma that had three different colors of flowers and were allowed to self-pollinate to establish an F₂ population. All of the F₂ plants had no segregation to I. domestica in their morphological characters. In addition, 13 reciprocal F₁ plants were detected by 25,719 single nucleotide polymorphism (SNP) markers. When I. dichotoma plants with three different flower colors were used as maternal parents, all the progenies were genuine hybrids. When I. domestica were used as maternal parents, all the F₁ plants were apomictic progenies. Apomixis of I. domestica was successfully identified and SNP markers identified F₁ hybrids derived from six interspecific crosses between I. dichotoma and I. domestica, which provides a reference for authenticating offspring identity during Iris cross breeding in the future.     

Fine mapping of <Emphasis Type="Italic">Ren3</Emphasis> reveals two loci mediating hypersensitive response against <Emphasis Type="Italic">Erysiphe necator</Emphasis> in grapevine

Grapevine (Vitis vinifera L.) is economically very important for the production of wine, table grapes and raisins. However, grapevine is threatened by a brought range of pathogens. A destructive disease worldwide is powdery mildew caused by the ascomycete Erysiphe necator. In the grapevine cultivar `Regent’ a resistance locus against E. necator, Ren3, was previously reported. It spans an interval of approximately seven Mb on chromosome 15. We attempted to delimit this interval to facilitate its further molecular analysis. New simple sequence repeat markers targeted to the Ren3 region were designed. They were applied for fine mapping in the cross populations of ‘Regent’ × ‘Lemberger’ and ‘Regent’ × ‘Cabernet Sauvignon’ that segregate for E. necator resistance. Complementarily we scored E. necator infection levels of ‘Regent’ × ‘Lemberger’ progeny at different time points over the course of the vegetation period in 2015 and 2016. Subsequent QTL analysis revealed a maximum LOD value that shifted during the season from marker GF15-10 located at 2.2 Mb to marker GF15-53 located at 3.5 Mb and to marker ScORA7* located at 9.4 Mb on chromosome 15 (positions according to the grapevine reference genome of PN40024). To investigate the Ren3-encoded resistance mechanism we performed detached leaf infection assays for microscopic studies. These revealed that Ren3 carrying individuals react with a hypersensitive response. Results of detached leaf assays on recombinants in the Ren3 locus indicate that not only one, but two distinct genetic regions on chromosome 15 mediate hypersensitive response against E. necator.     

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.     

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.     

Pollination and in vitro germination of seeds for interspecific hybridization of <Emphasis Type="Italic">Psidium guajava</Emphasis> and <Emphasis Type="Italic">Psidium cattleianum</Emphasis>

The genus Psidium includes important fruit crops. However, there are very few studies focusing on its reproductive biology, which limits the establishment of breeding programs. The present work investigated the reproductive biology of Psidium guajava and Psidium cattleianum in terms of compatibility of crossings between these two species aiming at interspecific hybridization because the latter species is an important source of resistance against the nematode Meloidogyne enterolobii. Several types of crosses were performed to understand the reproductive biology of these species, including the compatibility of intra- and interspecific crossings, using assisted in vivo germination of pollen grains on the stigma. In addition, the in vitro germination of both Psidium species was studied at different stages of fruit development to rescue young seeds to improve the chances of obtaining the hybrids. No fruits of 270 pollinations were obtained on guava buds at the pre-anthesis stage, regardless of the source of the pollen grain and the cultivar used as female genotype. Microscopic analyzes demonstrated the germination of pollen grains and pollen tube growth at crosses between guava cv. ‘Pedro Sato’ (P. guajava) and Psidium cattleianum. High germination percentages of Psidium cattleianum seeds were obtained in MS medium without sucrose or containing 15 g/L of this carbohydrate.     

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

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

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

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

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

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

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

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

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

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

Breeding opportunities for early,free-threshing and semi-dwarf <Emphasis Type="Italic">Triticum monococcum</Emphasis> L.

Einkorn wheat, Triticum monococcum L. (2n = 2x = 14, A^mA^m genome), is a primitive, cultivated form of diploid wheat. The shortcoming of einkorn is that it lacks the free-threshing habit. Early heading and semi-dwarf traits are also required to fit modern agricultural practice. In the present study we developed T. monococcum pre-breeding germplasm having early, free threshing traits by utilizing an early heading source, two sources of soft glume (spike) and three sources of semi-dwarfism to combine their phenotypes into pre-breeding materials. We found two different genes determined free threshing of einkorn wheat. One of them was the sog (soft glume) gene from Triticum sinskajae Filat. et Kurkiev (2n = 2x = 14, A^mA^m genome) and another was the sos (soft spike) gene, which was completely linked or pleiotropic with the gene for semi-dwarfism. The genes sos, spd (short peduncle) and sd17654 (semi-dwarf CItr 17654) were utilized to develop semi-dwarf T. monococcum lines. Field performance of 6 early and free-threshing pre-breeding materials with sos and spd genes were tested over three crop seasons. Five semi-dwarf pre-breeding materials (PBMs) were obtained. However, these materials had slightly less grain yield than #252 (tall and hulled check) and PBM-1 (tall free-threshing check). Harvest index of the pre-breeding materials was improved due to the presence of sos and spd genes. If optimized cultivation practice is performed, these pre-breeding materials can be utilized as sources of early, free-threshing and semi-dwarf traits to produce modern T. monococcum varieties.     

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

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

Interspecific hybridization in <Emphasis Type="Italic">Sarcococca</Emphasis> supported by analysis of ploidy level,genome size and genetic relationships

Knowledge of ploidy level differences, genome size and genetic relationships between species facilitates interspecific hybridization in ornamentals. For Sarcococca (Buxaceae) only limited (cyto)genetic information is available. The aim of this study was to determine the genome size and chromosome number and to unravel the genetic relationships of a breeder’s collection using AFLP marker analysis. Based on these results, interspecific crosses were made and the efficiency and hybrid status was verified. Two groups of diploid plants (2n = 2x = 24) were observed, with either a genome size of 4.11–4.20 or 7.25–9.63 pg/2C. All the tetraploid genotypes (2n = 4x = 48) had genome sizes ranging from 7.91 to 8.18 pg/2C. In crosses between parents with equal ploidy level and genome size a higher crossing efficiency (on average 58% of the hybridizations resulting in fruits) and more true hybrids (on average 96% of the offspring) were obtained compared to crosses between plants with different genome size and ploidy level (on average 23% fruits and 24% hybrids, respectively). In none of the cross combinations, the ploidy level or genome size was found to be a complete hybridization barrier, although unilateral incongruity was found in some cross combinations. Distant genetic relationships did not hamper the hybridization within Sarcococca genotypes. Our findings will contribute to a more efficient breeding program and a faster achievement of hybrids with an added value.     

Development and trait evaluation of chromosome single-segment substitution lines of <Emphasis Type="Italic">O. meridionalis</Emphasis> in the background of <Emphasis Type="Italic">O. sativa</Emphasis>

O. meridionalis is a wild species belonging to AA genome in the Oryza genus, which has a lot of beneficial genes for improvement of cultivated rice. In the present study, 99 chromosome single-segment substitution lines (SSSLs) were developed carrying donor segments of O. meridionalis in the genetic background of an indica cultivar, Huajingxian 74 (HJX74). The total lengths of the 99 substituted segments in the SSSLs were 1580.16 cM, with an average length of 15.11 cM per substituted segment, covering 873.94 cM and 54.98% of O.meridionalis genome. Phenotypic investigations of the SSSLs showed that three SSSLs had red pericarp, awn and showed seed shattering, respectively, indicating that these genes of O. meridionalis responsible for these traits have been transferred to the SSSLs. And wide variations were observed in seven quantitative traits including heading date and yield-related traits in 82 SSSLs.At P ≤ 0.001, 77 SSSLs showed significant differences compared with HJX74 in at least one trait either in the fall of 2014 or spring of 2015, and a total of 28 stable QTLs were detected in 24 SSSLs in both seasons. These results suggest that the SSSLs library of O. meridionalis developed in this study offers a good germplasm platform for the identification and transformation of beneficial genes of O. meridionalis, and facilitates the conservation of gene resources of O. meridionalis in vivo for long periods.