We studied the effect of Silicon (Si) on Casparian band (CB) development, chemical composition of the exodermal CB and Si deposition across the root in the Si accumulators rice and maize and the Si non-accumulator onion. Plants were cultivated in nutrient solution with and without Si supply. The CB development was determined in stained root cross-sections. The outer part of the roots containing the exodermis was isolated after enzymatic treatment. The exodermal suberin was transesterified with MeOH/BF3 and the chemical composition was measured using gas chromatography-mass spectroscopy (GC-MS) and flame ionization detector (GC-FID). Laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) was used to determine the Si deposition across root cross sections. Si promoted CB formation in the roots of Si-accumulator and Si non-accumulator species. The exodermal suberin was decreased in rice and maize due to decreased amounts of aromatic suberin fractions. Si did not affect the concentration of lignin and lignin-like polymers in the outer part of rice, maize and onion roots. The highest Si depositions were found in the tissues containing CB. These data along with literature were used to suggest a mechanism how Si promotes the CB development by forming complexes with phenols.

A direct soil DNA extraction method from soil samples (250 g) was applied for detection of the soilborne sugar-beet-infecting pathogen Rhizoctonia solani anastomosis group (AG) 2-2IIIB using a newly developed real-time polymerase chain reaction assay that showed specificity to AG2-2IIIB when tested against various R. solani AG. The assay showed a good relation between cycle threshold and amount of AG2-2IIIB sclerotia detected in three spiked field soils and was also able to detect the pathogen in naturally infested field soil samples. A field trial was conducted to quantify R. solani AG2-2IIIB soil inoculum potential (IP) before and after growing a susceptible and a resistant sugar beet variety as well as after subsequent growth of an expected nonhost winter rye. Plants of the susceptible sugar beet variety displayed a higher disease severity. A more than sixfold increase of the R. solani AG2-2IIIB soil IP was observed in contrast to the resistant variety that resulted in a constant IP. Growing winter rye significantly reduced soil IP to the initial level at sowing. Further research is required to better understand the interaction between disease occurrence and soil IP as well as the environmental influence on IP development.

No abstract

Der bodenbürtige Pilz Rhizoctonia solani Kühn ist der Erreger der Späten Rübenfäule der Zuckerrübe und kann erhebliche Ertragsverluste verursachen. Krankheitsauftreten und Befallsstärke sind neben dem Zuckerrübengenotyp und der Vorfrucht abhängig von spezifischen bodenstrukturellen Eigenschaften. In den vorgestellten Versuchen wurde die Bodenstruktur durch eine variierte Bodenbearbeitung (Pflug, Grubber, Überrollen und flache Grubberbearbeitung) differenziert. Zwei Zuckerrübengenotypen (anfällig, resistent) wurden nach Mais angebaut. Aufgrund eines insgesamt niedrigen Befallsniveaus mit R. solani an Zuckerrüben konnten keine Zusammenhänge zwischen der Befallsstärke von R. solani und den untersuchten Bodenparametern (Eindringwiderstand, Luftkapazität, Gesamtporenvolumen, Pneumatische Leitfähigkeit) festgestellt werden. Darüber hinaus gab es keine Befallsunterschiede zwischen den Bodenbearbeitungsvarianten. Die Ergebnisse lassen allerdings vermuten, dass reduzierte Bodenbearbeitung zu einem höheren Befall mit R. solani als konventionelle Pflugbearbeitung führen könnte. Kam es zum Befall, war dieser beim anfälligen Genotyp stärker ausgeprägt als beim resistenten Genotyp.