Browsing by Subject "Radish"

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Genetic diversity in germplasm of cornsalad (Valerianella locusta L.), radish (Raphanus sativus L.), and celeriac (Apium graveolens L. var. rapaceum), investigated with PCR-based molecular markers
(2004) Muminovic, Jasmina; Melchinger, Albrecht E.
During the last couple of decades, production and economic importance of cornsalad (Valerianella locusta L.; fam. Valerianaceae), radish (Raphanus sativus L. var. sativus convar. radicula; fam. Brassicaceae), and celeriac (Apium graveolens L. var. rapaceum; fam. Apiaceae) have been considerably increasing in Europe. Nevertheless, genetic diversity currently utilized for breeding cornsalad, radish, and celeriac is narrow, whereas their germplasm collections in gene banks are relatively poor. Assessment of genetic diversity among breeding materials and genetic resources is an important consideration for the optimal design of further breeding programs. The major objective of this study was to investigate genetic diversity in germplasm of cornsalad, radish, and celeriac, applying amplified fragment length polymorphisms (AFLPs) and inter simple sequence repeats (ISSRs) molecular markers. In particular, the objectives were to (i) analyze relationships among breeding materials of the three vegetable crops (referred to as elite germplasm), as well as among their formerly grown varieties, gene bank and botanical garden accessions (referred to as exotic germplasm), (ii) reveal genetic structure of radish germplasm to establish heterotic pools for hybrid breeding, and (iii) evaluate the usefulness of introducing exotic materials for broadening of the elite germplasm in cornsalad, radish, and celeriac. Average genetic similarity in 34 elite varieties of cornsalad was very high (GS = 0.90), which is comparable with other autogamous crops. The majority of elite varieties clustered closely applying the UPGMA analysis because of a narrow-based germplasm in cornsalad breeding. A substantial level of genetic diversity (GS = 0.47) was detected in 30 cornsalad varieties representing exotic germplasm. Exotic varieties that interspersed the sub-clusters of the elite may serve as a direct genetic resource for broadening the elite cornsalad germplasm base, whereas Valerianella locusta-related species that were distinct from cultivated germplasm can contribute to the introgression of new (resistance) genes. Sixty-eight varieties of cultivated radish (garden and Black radish) created sub-clusters with GS estimates higher than 0.70, thus supporting the assumption that the currently used radish germplasm in Europe relies on a narrow genetic base. Owing to a high degree of heterogeneity and heterozygosity within radish varieties, the detected between-variety diversity was low, but there still was a substantial overall diversity in available radish germplasm. Applying both UPGMA and principal coordinate analyses, Black radish varieties were distinct from garden radish. A further unambiguous division within garden radish germplasm was revealed with the model-based clustering approach. These sub-groups can be employed for establishment of heterotic pools within European modern cultivars of garden radish. In addition, ISSRs can substantially reduce hybrid radish production costs by an early detection of two closely related weed species (R. raphanistrum and R. sativus L. var. sativus convar. sinensis). AFLPs and the evaluation of morphological traits were used to investigate genetic diversity in 34 varieties of elite celeriac germplasm and 35 accessions of exotic germplasm. Only two morphological traits supported the clustering pattern obtained with UPGMA analysis of morphological distance estimates. AFLP-based GS estimates offered a clearer view of diversity present in elite (GS = 0.68-0.95) and exotic germplasm (GS = 0.05-0.95), and clustered the two sets in distinct UPGMA-based sub-clusters. This indicated that only a small fraction of available genetic diversity is exploited for current breeding of celeriac. Exotic celeriac germplasm as well as varieties of celery and leaf celery might substantially improve commercial celeriac breeding. Wild relatives of Apium graveolens are valuable resources for the introgression of resistance genes. Regarding the generally high level of GS in celeriac germplasm conserved in the German gene bank, a broadening of the germplasm collection was suggested. This study demonstrated the capacity of molecular markers to be highly discriminating among varieties of cornsalad, radish, and celeriac. AFLP-based genetic similarity estimates in the three vegetable crops (i) allowed the first insight into the genetic diversity and structure present in the germplasm, (ii) offered suggestions for germplasm broadening, and (iii) proposed a way of rationalization and utilization of available germplasm resources.
Neu auftretende bakterielle Blattfleckenerreger an Radies und Entwicklung eines Resistenztests als Grundlage für die Züchtung resistenter Sorten
(2014) Scholze, Inka S.; Vögele, Ralf
Radish is one of the most important vegetable crops in Rhineland Palatinate. During the last decades, an increase in bacterial leaf spots on radish has been observed. Although the bulb is unaffected, leaf spot symptoms lead to a decline in sales and profits as German consumers prefer marketable red radish bunches including the freshness-indicating foliage. So far, preventive methods for the control of bacterial pathogens on radish were limited to irrigation strategies (for example drip irrigation) or field hygiene. These methods are, however, often difficult to implement and their effect predominantly insufficient. Resistant or tolerant breeds would provide a solution, however, breeding companies have been lacking the necessary information regarding the causative agents and their biology and epidemiology needed for the development of such breeds. Previous examinations of infested plants and seed lots suggest different pseudomonads and Xanthomonas campestris as possible agents. The main objective of this study was therefore to identify the relevant pathogens causing leaf-spot symptoms on radish. Furthermore, another objective was to clarify the infection and growth requirements of bacterial pathogens on hosts for the development of a screening method for resistance to leaf spot pathogens on radish. On account of increasing compensation claims from breeding companies by farmers, the role of seed transmissibility was also to be determined. during a three year observation, bacterial pathogens from plants and seed lots were isolated and characterized. The characterization of unknown bacterial strains was performed by a combination of physiological and molecular methods. Molecular characterization methods such as 16s rDNA sequence analysis and MLST (multilocus sequence typing) were needed to complete the designation of P. syringae pathovars. In addition, virulence assays clarified the importance of single pathovars. Hence bacterial leaf spot pathogens could be determined as P. syringae pv. maculicola, P. viridiflava, P. cannabina pv. alisalensis and X. campestris whereas the former two species were the most abundant in Rhineland Palatinate. Infection trials on radish plants concluded that the different pathogens induced different typical symptom characteristics. To evaluate the influence of environmental factors such as humidity and temperature, it was demonstrated that inoculations with pseudomonads and a leaf spot inducing X. campestris strain caused successful infection and symptom development under a wide temperature range. Humidity was shown to be the most influential factor limiting infestation intensity with P. viridiflava displaying a higher demand for humid conditions than P. syringae pv. maculicola and X. campestris. All three types induced a higher disease infestation on radish plants in high humidity conditions (~94% rH) contrary to a lower infestation in dry conditions (~63% rH). In a first test series, plants inoculated with P. viridiflava were almost symptom free under dry conditions, whereas P. syringae and X. campestris were still able to induce leaf spots. Based on the results of infections assays, it was possible to develop a screening method on radish plants for resistance to the leaf spot inducing bacterial pathogen P. syringae pv. maculicola. The screening method was based on the spray-inoculation of radish leaves fixed in water filled orchid tubes, incubated under high humidity in a climate chamber at 24 °C day/10 °C night. Determination of resistance was performed 7 to 10 days past inoculation by rating disease intensity of infested leaves. Whereas tests could be performed by inoculations with P. viridiflava and P. cannabina as well as P. syringae, the latter proved to be most suitable for the screening method.
Weed suppression with cover crops and undersown crops in modern cropping systems
(2014) Brust, Jochen; Gerhards, Roland
The agronomic situation in Germany is characterized by a reduction of crop diversity within crop rotations, which is mainly a consequence of present economic conditions. This results in rare change between fall and spring seeded crops, combined with increasing weed populations. The integration of cover crops and undersown crops into such cropping systems could be a step to reduce the amount of herbicides during crop cultivation but also within a fallow period. The aim of this study was to determine the influence of cover crop and undersown crop cultivation on arable farming systems from the perspective of weed science. Furthermore it should be clarified in which way it is possible to integrate cover crops and undersown crops in intensive cropping systems. Within the cover crop topic this was done by the search for new cover crop species which are suitable for cultivation in Central Europe to expand the range of available cover crop species for lots of cropping situations and site conditions. Additionally the weed suppression ability of different cover crop species in fall and spring was analyzed to determine if it is possible to avoid a mechanical or chemical weed control prior seeding the next cash crop. Within the undersown crop topic the influence of different management practices on growth of undersown crop as well as growth and yield formation of the main crop was investigated. Furthermore, it was researched if it is possible to achieve a suppression of weeds by undersown crops. The conducted experiments relating the cover crop topic showed that from the new cover crop species especially tartary buckwheat, forage radish and lopsided oat are well suited for cultivation. The shoot and root growth of weeds could be effectively reduced by the successful establishment of a cover crop stand in fall. In plots of competitive cover crops like yellow mustard, oilseed radish, tartary buckwheat and lopsided oat, no further growth of weeds and volunteer cereals occurs after the first measurement in fall four weeks after cover crop planting. The weed-suppressing effect of cover crop cultivation was measurable not only in fall during growth, but also in spring after freezing of cover crops. Especially in plots of late freezing cover crop species like oilseed radish and phacelia only a very reduced plant density or even no living weeds and volunteer grains were observed. The conducted experiments relating the undersown crop topic demonstrate that it is possible to integrate undersown crops in high yielding cereal cropping systems without decreasing growth and yield formation of the main crop. During the four conducted field experiments, a reduction in grain yield was only observed when perennial ryegrass was seeded at the three leaves stage of spring wheat and grew under sufficient nitrogen conditions. The study shows that undersown crops are able to reduce weed density during main crop growth. However, the habitus of weeds was an important factor influencing the weed suppression ability of undersown crops. Undersown crops were able to reduce the density of small growing weed species such as Veronica persica while density of high-growing weeds like Chenopodium album were not affected. The experiments in this study offer that is possible to successfully integrate cover crops and undersown crops into modern agricultural systems without reducing their productivity. Furthermore it was demonstrated that due to the cultivation of cover crops and undersown crops it is possible to control the growth of weeds not only during but also between cash crop vegetation. By these methods, under certain conditions a reduction of the required amount of herbicides is possible, which can be a contribution to a more sustainable food production.