Dorette Müller-Stöver

Granular Pesta formulation of Fusarium oxysporum f. sp. orthoceras for biological control of sunflower broomrape: efficacy and shelf-life

Abstract Formulation of fungal propagules encapsulated in a wheat-gluten matrix (termed ‘Pesta’) has proved to be a suitable technique for the development of Fusarium oxysporum f. sp. orthoceras (FOO) as a bioherbicide for sunflower broomrape (Orobanche cumana). To improve the efficacy of this fungus, 19 Pesta formulations, using two types of fungal spores and 8 adjuvants, used singly or in combinations, were examined for their shelf-life and for efficacy under greenhouse conditions. Amending Pesta with yeast extract reduced the loss of viability of microconidia and chlamydospores during production of the formulations by 40 and 100%, respectively. Sodium alginate and Water Lock also prevented loss of viability of chlamydospores during Pesta production. The longest shelf-life (inoculum viability) was obtained when granules were stored at 3xa0°C. In greenhouse experiments, there were no differences among the 19 Pesta treatments in disease severity (DS). In terms of the number of Orobanche attachments, Orobanche dry matter, and the number of Orobanche shoots that produced seeds, the most effective formulations were Pesta 14 (containing chlamydospores [PC] with yeast extract, glycerol, and sucrose as additives), Pesta 1 (containing microconidia [PM] with yeast extract and sucrose), Pesta 5 (PM with yeast extract, glycerol, and sucrose), Pesta 7 (PM with sodium alginate as an additive), and Pesta 15 (PC with stillage). These formulations produced 99, 98, 98, 97, and 97%, DS, respectively, and caused reduction in Orobanche biomass by 80, 76, 71, 80, and 67%, respectively. These Pesta formulations of FOO increased sunflower seed yield by 5–11 times in comparison with the negative control inoculated with fungus-free Pesta. In general, applications of the formulations of FOO in Pesta did not affect the number of leaves, stem diameter, plant height, or the dry matter of roots of sunflower or the rate of photosynthesis in sunflower plants.

Optimization of storage conditions for adequate shelf-life of ‘pesta’ formulation of Fusarium oxysporum ‘foxy 2’, a potential mycoherbicide for Striga: Effects of temperature, granule size and water activity

An adequate shelf-life of mycoherbicidial products is an essential requirement for their acceptance and commercialization. Therefore, attempts were made to study the effects of temperature, granule size, and water activity (R.H./100) on the viability of the encapsulated propagules of Fusarium oxysporum ‘Foxy 2’ in ‘Pesta’ granules during storage. ‘Pesta’ granules were made with different inocula of Foxy 2, including: microconidia; mixture of mycelia and microconidia; fresh and dried chlamydospore-rich biomass. Two sizes of each granular preparation (0.5–2 and 0.25–0.5 mm) were stored in the refrigerator at 4°C as well as at room temperature (21±3°C) for 1 year. Additional samples were also stored at water activities (aw) of 0.12 and 0.41 at 25°C. Regardless of the type of formulated propagules and the granule size, all samples stored at 4°C maintained a significantly higher viability compared to those kept under room temperature. At 4°C, the ‘Pesta’ preparations with the larger granule size (0.5–2 mm) maintained more viable propagules than those with the smaller one (0.25–0.5 mm) in case of microconidia, mycelia plus microconidia and fresh chlamydospore inoculum after 1 year of storage. Granule size did not affect the viability of the dried chlamydospores. At 25°C, shelf-life of all ‘Pesta’ granules was significantly prolonged when stored at a low water activity of 0.12 compared to the storage at 0.41 aw. The results of the combined effect of water activity and temperature also revealed clearly that all formulated propagules in ‘Pesta’ granules retained a significantly higher viability when stored at 0.62 aw and 4°C than at 0.12 aw and 25°C, indicating the most pronounced effect of storage temperature.

Two granular formulations of Fusarium oxysporum f.sp. orthoceras to mitigate sunflower broomrape Orobanche cumana

Fusarium oxysporum Schlecht. f.sp. orthoceras (Appel & Wollenw.) Bilai, a potential biocontrol agent against Orobanche cumana Wallr.,was formulated into two granular forms, wheatflour kaolin (`Pesta) granules and sodium alginatepellets. The formulations were compared in terms ofeffectiveness for mitigating O. cumanaparasitism in sunflower and shelf-life forstorage. `Pesta granules reduced the emergence of O. cumana shoots by 64% while sodium alginatepellets did not reduce the emergence rate but increased thepercentage of diseased O. cumana plants.Calculated efficacy of the application was better for`Pesta granules. Viability of the formulatedmaterial tested in the laboratory was higher in sodium alginatepellets than in the `Pesta formulation.However, a loss of virulence after six months of storage wasalso observed in sodium alginate pellets in agreenhouse experiment.

Increasing control reliability of Orobanche cumana through integration of a biocontrol agent with a resistance-inducing chemical

AbstractFusarium oxysporum Schlecht. f.sp. orthoceras (Appel & Wollenw.) Bilai is a potential biocontrol agent against the root-parasitic weed Orobanche cumana. In pot experiments with different sunflower cultivars, the application of F. oxysporum was combined with a treatment of BTH (Benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester), a product known to induce resistance against O. cumana in sunflower. The combined treatments resulted in highly reliable control and sometimes in increased control level compared to the Fusarium treatment alone. In laboratory experiments, no enhancing effect of BTH on virulence and growth of the fungus was observed. Future experiments should further investigate the basic mechanisms of the effect achieved by combining the two control strategies as well as the transfer of this innovative control approach into field experiments.n

Chlamydospores of Fusarium Oxysporum Schlecht f.sp. orthoceras (Appel & Wollenw.) Bilai as Inoculum for Wheat-flour—Kaolin Granules to be Used for the Biological Control of Orobanche cumana Wallr.

The formation of chlamydospores of Fusarium oxysporum Schlecht. f.sp. orthoceras (Appel & Wollenw.) Bilai, a potential mycoherbicide for the parasitic weed Orobanche cumana Wallr., was optimised regarding the composition of the liquid growth medium. After 16 days of incubation, highest chlamydospore counts (approximately 2 × 107ml−1) were determined in an aqueous solution amended with 1.5% (w/v) finely ground sorghum stover and 30% (v/v) wheat-based stillage, a liquid by-product of ethanol production. The produced fungal biomass retained viability after being air-dried and stored. Granules made from wheat-flour and kaolin (Pesta) containing microconidia or air-dried chlamydospore-rich biomass were prepared and showed high efficacy in controlling O. cumana in the greenhouse. No differences in efficacy were observed between the different types of inoculum used.

Fungi of Orobanche aegyptiaca in Nepal with Potential as Biological Control Agents

A survey of pathogens of the root-parasitic weed Orobanche aegyptiaca Pers. was carried out in Nepal. More than 70% of the fungal strains isolated from infected plants belonged to the genus Fusarium. Other fungi isolated were Acremonium fusidioides, Alternaria alternata, Cladosporium cladosporioides, Epicoccum nigrum, Mortierella alpina, Papulaspora sp., Phoma spp., Sordaria fimicola , Rhizoctonia sp., Trichoderma spp. and Trichothecium roseum.

Biological Control of Root Parasitic Weeds with Plant Pathogens

Root parasitic weeds are nutrition specialists. Using special organs, the haustoria, they penetrate into the vessels of roots of host plants in order to supply themselves with water and nutrients. They can be either facultative or obligate, obligate parasitic weeds being considered as one of the most serious constraints to food production in many parts of the world. Obligate parasites are either hemi-parasites with chlorophyll, like species of the genus Striga (Scrophulariaceae), witchweeds, or holo-parasites without chlorophyll such as species of the genus Orobanche (Orobanchaceae), broomrapes. Forty Striga species are reported world-wide: 33 in Africa, 7 in Asia and 4 endemic in Australia. Eleven species are parasites on agricultural crops. The genus Orobanche has more than 100 species but only 7 are considered as economically significant parasitic weeds (Parker and Riches, 1993; Raynal-Roques, 1996).

A commercial iron fertilizer increases the survival of Fusarium oxysporum f. sp. orthoceras propagules in a wheat flour-kaolin formulation

Abstract Fusarium oxysporum f.sp. orthoceras, a potential biocontrol agent against the parasitic weed Orobanche cumana Wallr., has proven to be efficacous under greenhouse conditions when formulated as wheat–kaolin granules. To help minimize the loss of viable fungal propagules during the formulation process, the addition of a commercial fertilizer containing the iron chelate of EDDHA to the formulation was investigated. The proportion of surviving propagules was significantly increased after adding the fertilizer. However, growing conidia in fertilizer-amended liquid medium did not reduce losses in viability during formulation. The efficacy of the formulated fungus and the storability at room temperature for the first 3 months was not affected by the iron fertilizer. The protective effect could neither be obtained with the chelator EDDHA alone nor with FeEDTA or FeSO4.

Main effects and interactions among acibenzolar-S-methyl, a biocontrol fungus and sunflower cultivar on control of Orobanche cumana Wallr.

In this paper, combined application of the plant activator acibenzolar-S-methyl (ASM) and the biocontrol fungus Fusarium oxysporum f. sp. orthoceras (Foo) in an integrated system was evaluated with two sunflower cultivars in a three-factor experiment under greenhouse conditions in order to understand their main effects and interactions on Orobanche cumana control and on sunflower production. The main effects of ASM at 5 mg LS–1 (litre soil) thrice as soil drenches significantly reduced O. cumana number by 83% and dry matter by 80% and significantly increased sunflower shoot and head dry matter in average of two sunflower culti-vars. ASM at 250 g L–1 thrice as foliar sprays significantly reduced only O. cumana dry matter by 18%. Foo at 1 g LS–1 significantly reduced O. cumana number by 48% and dry matter by 32% and significantly increased sunflower root and shoot dry matter. Sunflower cv. GO was more susceptible to the parasite than HA89. The interaction between ASM and Foo was highly significantly different on O. cumana number and dry matter and significantly different on sunflower shoot dry matter. In general, the combination of ASM and Foo increased control reliability of O. cumana and improved security of ASM to sunflower. Control of O. cumana in sunflower by ASM was cultivar-dependent. ASM soil drenches combined with Foo were more effective than ASM foliar sprays with Foo.Zusammenfassungp ]In einem Gewächshausversuch mit Sonnenblumen wurde das Pflanzenstärkungsmittel Acibenzolar-S-methyl (ASM) in Kombination mit dem Pilz Fusarium oxysporum f. sp. orthoce-ras (Foo) auf ihre Kontrollwirkung gegenüber dem Wurzelparasiten Orobanche cumana erfasst. Die Wechselwirkung von Sonnenblumen mit O. cumana und ihre Ertragsleistung unter Präparateeinwirkung wurde anhand zweier Sonnenblumensorten (Givat Oz und HA 89) untersucht. ASM in einer Konzentration von 5 mg pro Liter Boden, dreimal auf das Erdreich appliziert, verringerte signifikant die Anzahl an O. cumana um 87% und das Trockengewicht um 80%. Die durchschnittliche Spross- und Korbtrockenmasse der beiden Sonnenblumensorten wurde durch die Behandlung signifikant erhöht. ASM in einer Dosis von 250 g pro Liter, dreimal auf die Blätter der Sonnenblumen appliziert, reduzierte die Trockenmasse von O. cumana um lediglich 18%. Foo in einer Aufwandmenge von 1 g pro Liter Boden reduzierte signifikant die Anzahl von O. cumana um 48% und das Trockengewicht um 32%. Spross- und Wurzeltrockenmasse der Sonnenblume waren signifikant erhöht. Die Sonnenblumensorte GO reagierte auf den Wurzelparasiten empfindlicher als die Sorte HA 89. Die Versuche zeigten, dass ASM und Foo in Kombination ausgebracht, die Verlässlichkeit der Orobanche-Kontrolle steigert und die Behandlungswirkung von ASM auf Sonnenblumen verstärkt. Die Kombination von Foo mit ASM als Gießapplikation auf den Boden war effektiver in der Oroban-chebekämpfung als ASM zusammen mit Foo, appliziert auf die Blätter der Sonnenblume.