Broad spectrum insect resistance and metabolites in close relatives of the cultivated tomato

Wild relatives of tomato possess effective means to deal with several pests, among which are a variety of insects. Here we studied the presence of resistance components against Trialeurodes vaporariorum, Myzus persicae, Frankliniella occidentalis, and Spodoptera exigua in the Lycopersicon group of Solanum section Lycopersicon by means of bioassays and comprehensive metabolite profiling. Broad spectrum resistance was found in Solanum galapagense and a few accessions of S. pimpinellifolium. Resistance to the sap sucking insects may be based on the same mechanism, but different from the caterpillar resistance. Large and highly significant differences in the leaf metabolomes were found between S. galapagense, containing type IV trichomes, and its closest relative S. cheesmaniae, which lacks type IV trichomes. The most evident differences were the relatively high levels of different methylated forms of the flavonoid myricetin and many acyl sucrose structures in S. galapagense. Possible candidate genes regulating the production of these compounds were identified in the Wf-1 QTL region of S. galapagense, which was previously shown to confer resistance to the whitefly B. tabaci. The broad spectrum insect resistance identified in S. galapagense will be very useful to increase resistance in cultivated tomato.     

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

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

Resistance to <Emphasis Type="Italic">Bemisia tabaci</Emphasis> in tomato wild relatives

Bemisia tabaci is one of the most threatening pests in agriculture, particularly in Solanaceous crops such as tomato and pepper that are cultivated in the open field. Pesticide application is often not effective and hazardous to humans and environment. The exploitation of plant natural defenses that are present in wild relatives of tomato, may offer a solution. To evaluate resistance parameters and to identify plant material with high levels of resistance, we screened a number of accessions of tomato wild relatives using three methods; a free-choice test in a screenhouse in Indonesia, a no-choice test with clip-on cages in a greenhouse and a leaf disc test in a climate-room in the Netherlands. Antibiosis resulting in low adult survival was the major component for resistance in tomato. However, other resistance component(s) may play a role as well. In some accessions there was a change in the resistance level over time. Several resistance parameters used in the different tests were well correlated. The best resistance source was an accession of Solanum galapagense, which had not been identified as being resistant in the past. This is of particular interest as this species is closely related to the cultivated tomato, which may facilitate introgression of the resistance component(s). Whitefly non-preference and resistance were associated with the presence of type IV trichomes. Other mechanisms might be involved since some accessions without type IV trichomes showed low nymphal density. The leaf disc test is a good in vitro alternative for the clip-on cage whitefly resistance screening, as shown by the high correlation between the results obtained with this test and the clip-on cage test. This offers breeders the possibility to carry out tests more efficiently.     

Antixenosis and antibiosis mechanisms of resistance to pod borer, <Emphasis Type="Italic">Helicoverpa armigera</Emphasis> in wild relatives of chickpea, <Emphasis Type="Italic">Cicer arietinum</Emphasis>

The noctuid pod borer, Helicoverpa armigera is one of the most damaging pests of chickpea, Cicer arietinum. The levels of resistance to H. armigera in the cultivated chickpea are low to moderate, but the wild relatives of chickpea have exhibited high levels of resistance to this pest. To develop insect-resistant cultivars with durable resistance, it is important to understand the contribution of different components of resistance, and therefore, we studied antixenosis and antibiosis mechanisms of resistance to H. armigera in a diverse array of wild relatives of chickpea. The genotypes IG 70012, PI 599046, IG 70022, PI 599066, IG 70006, IG 70018 (C. bijugum), ICC 506EB, ICCL 86111 (cultivated chickpea), IG 72933, IG 72953 (C. reticulatum), IG 69979 (C. cuneatum) and IG 599076 (C. chrossanicum) exhibited non preference for oviposition by the females of H. armigera under multi-choice, dual-choice and no-choice cage conditions. Based on detached leaf assay, the genotypes IG 70012, IG 70022, IG 70018, IG 70006, PI 599046, PI 599066 (C. bijugum), IG 69979 (C. cuneatum), PI 568217, PI 599077 (C. judaicum) and ICCW 17148 (C. microphyllum) suffered significantly lower leaf damage, and lower larval weights indicating high levels of antibiosis than on the cultivated chickpea. Glandular and non-glandular trichomes showed negative correlation with oviposition, while the glandular trichomes showed a significant and negative correlation with leaf damage rating. Density of non-glandular trichomes was negatively correlated with larval survival. High performance liquid chromatography (HPLC) fingerprints of leaf surface exudates showed a negative correlation of oxalic acid with oviposition, but positive correlation with malic acid. Both oxalic acid and malic acid showed a significant negative correlation with larval survival. The wild relatives exhibiting low preference for oviposition and high levels of antibiosis can be used as sources of resistance to increase the levels and diversify the basis of resistance to H. armigera in cultivated chickpea.     

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.     

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.     

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.     

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.     

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.     

Creating cold resistant strawberry via interploidy hybridization between octoploid and dodecaploid

Strawberry cultivars showed limited cold resistance in the Northeast of China, while we obtained a synthetic dodecaploid strawberry hybrid ‘YH15-10’ (2n = 12x = 84) which showed sufficient cold resistance in this area. The reciprocal crosses between F. × ananassa cv. ‘Allstar’ (2n = 8x = 56) and ‘YH15-10’ (2n = 12x = 84) were carried out to select cold resistant strawberry in this study. The 134 seedlings were obtained from the cross of Allstar × YH15-10, while failed in its reciprocal cross. The 30 randomly selected seedlings were examined in terms of morphological characters, chromosome numbers and cold resistance. Most morphological characters were widely separated among F1 progeny with a high broad-sense heritability, which showed that these variations mainly resulted from genetic effect. Some hybrids exhibited heterosis, especially in growth vigor and runner production. Among the 30 tested hybrids, 28 decaploids (2n = 10x = 70), one octoploid (2n = 8x = 56) and one enneaploid (2n = 9x = 63) were observed. The 63.3% hybrids demonstrated higher cold resistance than that of ‘Allstar’ at P < 0.05. These high polyploidy strawberries have potential values in commercial production and modern cultivar improvement.     

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

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

Development of high-density interspecific genetic maps for the identification of QTLs conferring resistance to <Emphasis Type="Italic">Valsa ceratosperma</Emphasis> in apple

Valsa canker (Valsa ceratosperma (Tode ex Fr.) Maire) is one of the most destructive fungal diseases of apple, especially in Eastern Asia. In this study, the first high density genetic linkage map of Malus asiatica × Malus domestica was constructed by 640 simple sequence repeats (SSRs) and 490 single nucleotide polymorphisms (SNPs), which spanned 1497.5 cM with an average marker interval of 1.33 cM per marker. Quantitative trait loci (QTLs) for apple’s resistance to V. ceratosperma isolates 03-8 and xc56 were identified using the linkage map. Lesion lengths were used as the phenotypic data for the QTL analysis, which were measured on 1-year-old shoots inoculated with conidia of the two isolates. One QTL for resistance to isolate 03-8 was mapped on LG 16, and one QTL for resistance to isolate xc56 was detected on LG 9. Our research not only promoted the further understanding of the genetic basis of apple’s resistance to Valsa canker but also provided two molecular markers that might be used in future marker-assisted selection for resistance in apple breeding programs.     

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.     

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.     

Evaluating the contribution of Yr genes to stripe rust resistance breeding through marker-assisted detection in wheat

Numerous stripe rust resistance genes have been identified from wheat, and new virulent races of Puccinia striiformis f. sp. tritici have also emerged in recent years. Deployment of diverse combinations of resistance genes is an efficient way to combat virulent evolution of strip rust pathogen. In this study, publically available molecular markers were used to identify the distribution of 36 Yr genes in 672 wheat accessions. The effectiveness of Yr genes individually and in combinations was also evaluated in field conditions. The result showed effective resistance of some recently applied genes, such as Yr15 and Yr65. It also showed the lost efficacy of some once widely used genes, such as Yr9 and Yr10. Moreover, significant additive effects were observed in some gene combinations, such as Yr9 + Yr18 and Yr30 + Yr46. Proper deploying of Yr genes and utilizing the positive interactions will be helpful for durable resistance breeding in wheat.     

Effective selection of soybean cultivars to wildfire disease pathogen Pseudomonas amygdali pv. tabaci

Wildfire, caused by Pseudomonas amygdali pv. tabaci is one of the most destructive bacterial diseases and was recognized as a disease of soybean in 1943. Wildfire has been seen a steady increase in the incidence and prevalence on some cultivars of soybean in Korea by climatic changes but there is little information on effective control measures for wildfire or soybean varieties showing complete resistance to the disease. In this study, the efficient and reliable screening method to evaluate soybean genotype for resistance to P. amygdali pv. tabaci in field had been developed. In order to determine the host resistance of the soybean cultivar against P. amygdali pv. tabaci, development of symptom by infiltration inoculation was evaluated. Significant differences between susceptible plants and resistant plants were observed through these assays. Based on these results, ‘Shinpaldal2’, ‘Daepung’ are resistant to wildfire compared to ‘Hwangeum’, ‘Taekwang’. The optimum temperature of this pathogen was between 20-25°C and when the pathogen was in the optimum temperature, the responses of susceptible or resistant cultivar were dramatically different. Prior to initiation of resistance breeding of soybean wildfire, it is imperative to set uniform resistance screening techniques. The obtained results can be effectively used to enhance the selection of wildfire resistance as well as directly applied in resistant soybean development. Resistant lines identified through this assay could be directly used in soybean breeding programs for wildfire resistance.     

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

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

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

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

Selection of pea genotypes with partial resistance to <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> across a wide range of temperatures and periods of high relative humidity

Partial resistance to Sclerotinia sclerotiorum based on stem lesion advancement was assessed for nine wild pea genotypes from five geographic origins and two cultivated genotypes, when peas were inoculated and incubated at all combinations of five temperatures (15.6, 18.3, 21.1, 23.9, 29.4°C) and four period(s) of high relative humidity (PHRH; 12, 24, 48, 72 h). PHRH of 12 and 24 h should not be used when screening plants for resistance to S. sclerotiorum regardless of the incubation temperature, since stem lesions are rarely (2.7%) visible at 12 h and there were no significant differences (P ≤ 0.05) in lesion lengths among and within genotypes at all temperatures assessed after 24 h. However, PHRH of 48 and 72 h are recommended for use to assess partial resistance since significant differences in stem lesion length among the genotypes were observed and characterized for these periods. Genotypes with cool (15.6 and 18.3°C) versus warm (23.9 and 29.4°C) temperature partial resistance to S. sclerotiorum were identified, and genotypes PI 240515 and PI 169603 appear to have the best cool and warm temperature partial resistance, respectively, among the genotypes assessed. A temperature of 21.1°C was the optimal temperature favouring lesion advancement for the majority of the genotypes evaluated. PI 169603 demonstrated the best partial resistance to S. sclerotiorum across the widest temperature and PHRH ranges and is recommended to plant breeders as the best single genotype to develop future cultivars with improved partial resistance to S. sclerotiorum based on stem lesion advancement.     

A SNP mutation affects rhizomania-virus content of sugar beets grown on resistance-breaking soils

Rhizomania is one of the most devastating biotic stresses affecting sugar beet (Beta vulgaris L.). It is caused by Beet necrotic yellow vein virus (BNYVV) vectored by the plasmodiophorid Polymyxa betae K. The only means available to control the disease is the use of genetically resistant varieties. “Rizor” or “Holly” (Rz1) and WB42 (Rz2) have been the most widely used resistance sources in the commercial varieties. Recently, naturally occurring resistance-breaking (RB) rhizomania strains have been identified causing major concerns. The aim of this study was to identify SNP mutations that show associations with resistance to rhizomania in sugar beet plants grown under resistance-breaking (RB)-BNYVV soils. Rhizomania virus content was evaluated by indirect triple-antibody sandwich-ELISA within two F ₂ segregating populations respectively grown on an AYPR and IV-BNYVV strain infected soils. Bulked segregant analysis (BSA) was performed. The resistant and susceptible plants were genotyped with a 384-SNPs panel. Of the 384 SNPs, SNP249 was found to associate with the resistance both to the AYPR strain (R ² = 0.37; P = 0.0004) and to the IV-BNYVV (R ² = 0.09; P = 0.0074). Our results suggested that the SNP249 could be readily applicable for marker-assisted breeding of resistance to AYPR strain of rhizomania.