Somatic hybrids were produced by PEGinduced symmetric and asymmetric protoplast fusions in order to transfer resistance to Alternaria brassicicola, A. brassicae, Phoma lingam, Plasmodiophora brassicae and Turnip mosaic virus (TuMV) into Brassica oleracea var. capitata (cv. 'Toskama') and botrytis (cv. 'Korso'). As resistance donors, ten species belonging to several genera of the family Brassicaceae including wild relatives were used. Of 2,189 plants (somatic hybrids, partially in vitro cloned) tested, 1,616 (73.8%) were resistant against at least one of the pathogens, indicating that, mostly, a successful resistance transfer has taken place. Five hundred and twenty-two hybrids showed multiple resistances to two, three and, in a single case, to four pathogens. Irrespective of the donor parents used in the fusion, a broad variability in symptom manifestation ranging from 0 (without symptoms) to 9 (highly susceptible) could be observed. With regard to the Alternaria pathogens, Sinapis alba, B. nigra and B. juncea were the most effective resistance donors, whereas fusions with Raphanus sativus resulted in the most hybrids with resistance to clubroot and TuMV. As could be shown especially in asymmetric fusions with S. alba, Barbarea vulgaris and Hesperis matronalis, transferred resistance to a pathogen may not correspond with resistance exhibited by the donor parent. Some combinations in which both parents were highly susceptible, e.g. R. sativus (?) B. oleracea var. capitata, yielded hybrids that exhibited strong resistance, e.g. to A. brassicicola, revealing that a new type of resistance might be occurring. With regard to the Alternaria pathogens, resistance expression was very unstable. Many hybrids into which (also variable) resistance of some donors, such as B. vulgaris, S. alba and B. carinata, was transferred became as highly susceptible as those of which the fusion parents did not show any resistance reaction (e.g. R. sativus). For reliable characterization of the resistance response, hybrids should be subjected to several resistance tests during growth period of the host, at least until flowering.
A barley cDNA for the thaumatin-like protein Hv-TLP8 driven by the CaMV 35S promoter was introduced into oilseed rape (Brassica napus) via Agrobacterium-mediated transformation. Some transgenic lines were obtained which exhibited enhanced resistance to the clubroot pathogen (Plasmodiophora brassicae). To increase resistance, double haploid (DH) lines were generated from these transgenic plants. Of these, DH-line 189 showed stable inheritance of the transgenic trait and its associated resistance for at least three generations.
Five asparagus cultivars, three breeding lines and the wild relative Asparagus amarus were tested for natural infection by Asparagus virus 1 (AV-1) in experimental fields at two locations over 3 and 4 years, respectively. In the first year after re-planting the annual crowns in the field, more than 90% of tested plants of cultivars were infected by AV-1. In the third and fourth year, 100% of tested plants of cultivars were AV-1 infected. In comparison, all plants of the wild relative A. amarus were completely free of AV-1, suggesting a high level of resistance. Additionally, 1-year-old glasshouse-cultivated plants of A. officinalis and A. amarus were placed in an AV-1 provocation cabin under field conditions. Seven months later, 100% of the A. officinalis plants showed a high virus concentration in ELISA, whereas no AV-1 was detectable in the A. amarus plants. This result was confirmed by highly sensitive AV-1-specific RT-PCR. To exclude vector resistance, the feeding behaviour of green peach aphid Myzus persicae was tested over 12 h using the electrical penetration graph method. Both asparagus genotypes were accepted by the aphids as potential hosts, but the feeding time was significantly longer on A. amarus. A genetic distance analysis of the various cultivars of Asparagus officinalis and selected wild relatives of the JKI collection was carried out, resulting in a clear discrimination of cultivars and wild relatives, especially A. amarus. The potential breeding value of the putative resistance carrier is discussed. IntroductionVirus infections are an underestimated problem in asparagus production because symptoms are often inconspicuous or plants are symptomless. Currently, ten viruses have been identified in garden asparagus (Asparagus officinalis) worldwide, including three Asparagus viruses (AV-1, AV-2 and AV-3) for which asparagus is the only natural host. While AV-1 and AV-2 occur in many asparagus growing regions of the world, AV-3 has been found only in Japan (Fujisawa 1986;Tomassoli et al. 2012). Furthermore, apart from infecting various other vegetables, Tobacco streak virus (TSV), Cucumber mosaic virus (CMV) and Tobacco mosaic virus (TMV) have also been found infecting asparagus. Another four viruses -Alfalfa mosaic virus (AMV), Arabis mosaic virus (ArMV), Strawberry latent ring spot virus (SLRSV) and Tomato black ring virus (TBRV), that are of minor importance in asparagus have been reviewed by Knaflewski et al. (2008) and Tomassoli et al. (2012).The potyvirus Asparagus virus 1 (AV-1) is distributed worldwide and is transmitted in a non-persistent manner by aphids. Its main vector is the green peach aphid Myzus persicae, but it can be transmitted also by
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