A newly isolated Fusarium oxysporum strain was investigated for its biocontrol potential against the root parasitic weed Orobanche ramosa (branched broomrape). The fungus was found to affect all developmental stages of the parasite. Orobanche seed germination was reduced by 40% in the presence of fungal conidia in vitro. The number of underground tubercles and shoots of the weed was reduced by the fungus by 55% compared with the control and 92% of tubercles were recorded as diseased in root chambers. In pot experiments, soil application of a granular formulation of the fungus resulted in a reduction of number and dry matter of Orobanche shoots by more than 90%. Spraying of a conidial suspension on aboveground Orobanche shoots caused the death of 75% of them within 2 weeks. Data from initial host-range experiments indicate that the isolate is very host-specific, not even attacking shoots of other Orobanche species. Because of these promising results, we conclude that the fungal isolate should be investigated under field conditions and be compared with other Fusarium isolates proposed for biocontrol of O. ramosa.
Summary Under the changing agro‐climatic conditions of western Europe, the parasitic weed Phelipanche ramosa infests host crops such as tomato, hemp, tobacco and oilseed rape at an increasing rate. A Fusarium oxysporum isolate (FOG), that had effectively reduced the parasite’s incidence under controlled environmental conditions, was tested in different granular formulations (pesta granules, alginate pellets) on P. ramosa parasitising tobacco under field‐grown conditions. FOG reduced number and biomass of P. ramosa shoots by between 50% and 70% in three consecutive years (2006–2008). A single pesta application did not show consistent results throughout seasons; 50% reduction of P. ramosa biomass (DM) in the first year could not be repeated in the following years (20–30%). An alginate formulation applied alone performed better. However, a combination of pesta granules with alginate pellets had the highest reliable control efficacy (60–70%) of all treatments in two seasons, compared with the untreated control. Fungal population counts in soil samples did not show a close correlation to biocontrol efficacy. To understand field performance of this biocontrol agent, additional glasshouse and laboratory studies were conducted using soil from the experimental site. The glasshouse study revealed some fungistatic effects of the field soil that partly explain the reduced efficacy (‐40%) in the field compared with results obtained under controlled conditions. Results show the potential of FOG for P. ramosa control. Because formulation affected the biocontrol efficacy, it may be worthwhile to test how the delivery system can be changed in order to achieve increased disease development in the field.
Zusammenfassung als wurzelparasitisches Unkraut besitzt Phelipanche ramosa (verzweigte sommerwurz) neben P. aegyptiaca den breitesten Wirtspflanzenkreis unter den Orobanche und Phelipanche arten. in Westeuropa befällt sie mit zunehmender aggressivität kulturen wie raps, tabak, hanf und tomaten. Die einzigartige biologie der Wurzelparasiten und die enge Verbindung zu ihrer Wirtspflanze reduziert ihre bekämpfung auf ein Minimum. Zu den bekämpfungsmaßnahmen zählen (a) physikalische Verfahren (z. B. Jäten, Solarisation, tiefes Pflügen, Abflammen und Überschwemmen), (b) chemische (z. b. bodenfumigation, einsatz von herbiziden und keimstimulantien und (c) biologische Methoden (z. b. resistente sorten, einsatz von Pilzen und insekten als antagonisten, Feind und Fallenpflanzen). In Deutschland wird im Tabakanbau überwie-gend auf das Herbizid-Verfahren gesetzt. Dafür wird Glyphosphat in sehr niedriger konzentration, wenn sich die ersten tuberkel gebildet haben, ausgebracht. ein pilzlicher antangonist ist zwar gegen das parasitisches Unkraut an tabak in Deutschland gefunden worden, konnte aber bisher nicht bis zum Mykoherbizid entwickelt werden.Nachdem der hanfanbau in Deutschland an bedeutung verloren hatte, ist vor allem Tabak als Hauptwirt für P. ramosa geblieben. in den letzten 10 Jahren scheint sie sich immer weiter auszubreiten und kommt mittlerweile in Gebieten vor, die früher frei von der verzweigten Sommerwurz waren. Durch Wegfall der eU-subventionen in 2009 begannen manche Tabakpflanzer anstatt Tabak Petersilie auf ihren Flächen anzubauen. Dies hatte zur Folge, dass diese nun mit P. ramosa befallen wurde. Noch vor 10 Jahren als Fallenpflanze eingesetzt, hatte die Petersilie eine eher geringe Wirkung auf die verzweigte sommerwurz. Dieses Gefährdungspotential vor allem durch weitere potentielle Wirtspflanzen, wie z. B. Raps, Tomaten und kartoffeln oder ackerunkräuter sollte nicht unterschätzt werden. Durch geeignete phytosanitäre Maßnahmen und einer verbesserten informationspolitik sollte die stetig wachsende Ausbreitung sowie Ausweitung des Wirtspflanzenspektrums der verzweigten sommerwurz in Deutschland eingedämmt werden.Schlüsselwörter Verzweigte sommerwurz · Orobanche · Petersilie · Petroselinum crispum · tabak Spreading of the Parasitic Weed Phelipanche ramosa in German AgricultureAbstract the root parasitic weeds Phelipanche ramosa (branched broomrape) and P. aegyptiaca have the widest host range among Orobanche and Phelipanche species. in Western europe, P. ramosa attacks, with increasing aggressiveness, crops such as oilseed rape, tobacco, hemp, and tomato. the unique biology of root parasites, establishes a closed link with their host plant, thus reducing the possibility to successfully control them. control measures include (a) physical processes (such as weeding, solarization, deep ploughing, burning off, flooding), (b) chemical (like soil fumigation, use of herbicides, germination stimulants) and (c) biological methods (e.g. resistant varieties, use of fungi and insects as antagonists, trap and catch cr...
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