Validazione di Piani di Disaster Recovery mediante Simulatore

Contribution published online at: http://www.mimos.it/nuovo/contenuto_view.asp?check=10

Phytotoxicity of metabolites produced by 'Pyrenophora semeniperda' in liquid culture

'Pyrenophora semeniperda' was shown to produce heat stable, biologically active metabolites under agitated liquid culture conditions. Using a seedling bioassay it was shown that filtrates harvested from 'P. semeniperda' cultures had a significant impact on coleoptile length of both wheat and Bromus diandrus, but had no effect on seed germination. The relative toxicity of filtrates derived from several isolates of 'P. semeniperda' and infiltrated into wheat leaves was highly correlated with the virulence of these isolates. A comparison of metabolites harvested from 'P. semeniperda' and Pyrenophora teres grown under the same cultural conditions revealed that 'P. teres' did not affect wheat coleoptile growth, but affected the coleoptile elongation of 'B. diandrus', although less than filtrates produced by 'P. semeniperda'. Culture filtrates harvested after 6 days were toxic to wheat and 'B. diandrus' and toxicity was maximal in filtrates derived from cultures that were 12 days old. Culture filtrates diluted to 1 in 20 produced symptoms in wheat seedlings, but only undiluted or 5 × concentrated filtrates produced symptoms on 'B. diandrus' seedling leaves. Plants older than first node stage (Z 31) were significantly less sensitive to filtrate than younger plants. A degree of host selectivity to the metabolites was observed since leaves of 'Gossypium hirsutum', 'Helianthus annuus', 'Lablab purpureus' and 'Xanthium occidentale' were unaffected by infiltrates

Optimizing conditions for growth and sporulation of 'Pyrenophora semeniperda'

The effects of photo period, light quality, wounding and sealing of culture plates on in vitro growth and sporulation of 'Pyrenophora semeniperda' were examined to define conditions conducive to the abundant and rapid production of conidia. For maximum growth and sporulation, the leaf-spotting and seedborne plant pathogen required an alternating light/dark sequence. Fewer conidia were produced under conditions of constant illumination or constant darkness. Growth was enhanced by light of wavelengths longer than 500 nm, while sporulation was enhanced by light of wavelengths shorter than 500 nm. Sporulation was enhanced under conditions of alternating temperature with a diurnal photo period and by mycelial wounding. Sealing of Petri plates had an inhibitory effect on sporulation. Significantly more conidia of higher quality formed when unsealed cultures, wounded after 7 days, were exposed to 23°C during the light phase and 19°C during darkness. Under these optimal conditions, conidial numbers were increased by 800% or more compared with unwounded cultures grown at constant 25°C in 12 h alternating cool-white ligh

Burial depth and cultivation influence emergence and persistence of Phalaris paradoxa seed in an Australian sub-tropical environment

Emergence and persistence characteristics of Phalaris paradoxa seeds in no- and minimum-till situations and at different burial depths were studied in a sub-tropical environment. Three experiments were carried out using naturally shed seeds. In the first experiment, seedlings emerged from May through to September each year, although the majority of seedlings emerged in July. In the second experiment with greater seed density, cultivation in March of each year stimulated seedling emergence, altered the periodicity of emergence and accelerated the decline of seeds in the seedbank compared with plots that received no cultivation. The majority of seedlings in the cultivated plots emerged in May whereas the majority of seedlings in the undisturbed plots emerged in July. Emergence accounted for only 4-19% of the seedbank in both experiments over 2 years. Seed persistence was short in both field experiments, with less than 1% remaining 2 years after seed shed. In the third experiment, burial depth and soil disturbance significantly influenced seedling emergence and persistence of seed. Seedlings emerged most from seed mixed in the top 10 cm when subjected to annual soil disturbance, and from seed buried at 2.5 and 5.0 cm depths in undisturbed soil. Emergence was least from seed on the soil surface, and buried at 10 and 15 cm depths in undisturbed soil. Seeds persisted longest when shed onto the soil surface and persisted least when the soil was tilled. These results suggest that strategic cultivation may be a useful management tool, as it will alter the periodicity of emergence allowing use of more effective control options and will deplete the soil seedbank more rapidly