Letteratura scientifica selezionata sul tema "Fusarium tumidum"

Fusarium tumidum spores formulated in water and three invert emulsions were tested under field conditions as a potential bioherbicide against gorse (Ulex europaeus) and broom (Cytisus scoparius) Inundation with F tumidum spores failed to induce severe disease epidemics The invert emulsion formulants demonstrated some phytotoxicity towards gorse and Pinus radiata Plant species and age spore concentration and application rate all influenced the performance of the bioherbicide formulations It will be necessary to develop further formulations that will better enhance the activity of F tumidum in the field

The effect of Fusarium tumidum a potential mycoherbicide on gorse seedling emergence and growth was examined in three experiments In Experiment 1 F tumiduminoculated wheat grains (one two or three) were placed close to pregerminated gorse seeds at sowing Shoot and root dry weights of inoculated seedlings were lower than the control treatment at all three inoculum densities but there was no significant difference in percentage emergence In Experiments 2 and 3 two inoculated wheat grains were placed in contact with the seedlings at sowing Less than 50 of inoculated seedlings emerged compared with 97 in the control treatments from both experiments Soon after emergence about onethird of the inoculated seedlings that had emerged died from dampingoff disease caused by F tumidum Shoot and root dry weights of inoculated seedlings were significantly lower than the control treatment The results suggest that F tumidum can suppress gorse seedling emergence and growth

Scotch broom (Cytisus scoparius [L.] Link.) is an exotic perennial, leguminous, deciduous shrub, which during the past century has greatly expanded its range along the Pacific and Atlantic coasts of North America, and in Australia, New Zealand, South Africa, Chile, Iran, and India. This shrub rapidly invades disturbed areas, forming dense thickets, which can suppress and inhibit native vegetation, including economically important conifer seedlings. The developmental characteristics whereby Scotch broom invades new sites include specialized stem photosynthesis, prolific seed production, longevity of seeds in the soil, and nitrogen fixation. Human activities such as planting along highways for beautification and prevention of soil erosion have accelerated the problem of rapid geographical dispersal. Various methods of control (chemical, manual, and biological) together with habitat, morphology, reproductive biology, growth and development are discussed. Key words: Cytisus scoparius, Ulex europaeus, Scotch broom, invasive weeds, bioherbicides, Fusarium tumidu

Light sand and heavier sandy loam wheat-growing soils at Wongan Hills, W.A. were fumigated (2: 1 mixture of chloropicrin and methyl bromide) to study its effect on the soil microflora. In fumigated soil, numbers of bacteria and fungi, after an initial reduction, remained high and low, respectively, in comparison to untreated soil, throughout the period of study. In the fumigated soil Trichoderma species rapidly recolonized the soil, becoming the dominant fungus by 15 days and remaining so to the end of the experiment (145 days after fumigation). There was no difference in the total numbers of bacteria, actinomycetes or fungi in the rhizosphere of wheat grown in fumigated and non-fumigated soils. The numbers of some fungal species were lower in the rhizosphere of wheat grown in the fumigated soil, these included Aspergillus glaucus, A. fumigatus, Beauveria bassiana, Cladosporium cladosporoides, Embellisia tumida, Fusarium oxysporum, Penicillium patulum, P. tardum, Phialophora mutabilis and Trichoderma saturnisporurn. The only fungi found to be significantly higher in the rhizosphere of plants in fumigated soil were F. merismoides, T. koningii and T. viride.

Abstract A description is provided for Fusarium tumidum. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Leguminosae. DISEASE: Infects pods and is associated with circular stem lesions and tip dieback. GEOGRAPHICAL DISTRIBUTION: Germany, New Zealand. Possibly more widespread in temperate regions, but not reported. TRANSMISSION: Conidia are dispersed locally by water flow and splash droplets.

The overall objective of this study was to test the hypothesis that insects can vector F. tumidum conidia to infect gorse plants with the aim of developing an alternative approach to mycoherbicide delivery to control weeds. Four potential insect species (Apion ulicis, Cydia ulicetana, Epiphyas postvittana and Sericothrips staphylinus) were assessed for their ability to vector F. tumidum conidia. To achieve this, the external microflora (bacteria and fungi) and the size and location of fungal spores on the cuticle of these insect species were determined. In addition, the ability of the insects to pick up and deposit F. tumidum conidia on agar was studied. Based on the results from these experiments, E. postvittana was selected for more detailed experiments to determine transmission of F. tumidum to infect potted gorse plants. The factors promoting pathogenicity of F. tumidum against gorse and the pathogen loading required to infect and kill the weed were also determined. The external microflora of the four insect species were recovered by washing and plating techniques and identified by morphology and polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) and sequencing of internally transcribed spacer (ITS) and 16S rDNA. A culture-independent technique (direct PCR) was also used to assess fungal diversity by direct amplification of ITS sequences from the washings of the insects. All insect species carried Alternaria, Cladosporium, Nectria, Penicillium, Phoma, Pseudozyma spp. and entomopathogens. Ninety four per cent of the 178 cloned amplicons had ITS sequences similarity to Nectria mauritiicola. E. postvittana carried the largest fungal spores (mean surface area of 125.9 ìm2) and the most fungal CFU/insect. About 70% of the fungi isolated from the insects were also present on the host plant (gorse) and the understorey grass. The mean size of fungal spores recovered from the insect species correlated strongly with their body length (R² = 85%). Methylobacterium aquaticum and Pseudomonas lutea were common on all four insect species. Pseudomonas fluorescens was the most abundant bacterial species. In the pathogenicity trials, the effectiveness of F. tumidum in reducing root and shoot biomass of 16 and 8 wk old gorse plants was significantly increased with wounding of the plants. Older plants (32 wk old) which were wounded and inoculated were significantly shorter, more infected and developed more tip dieback (80%) than plants which were not wounded (32%). This indicates that damage caused by phytophagous insect species present on gorse through feeding and oviposition may enhance infection by F. tumidum. Wounding may release nutrients (e.g. Mg and Zn) essential for conidia germination and germ tube elongation and also provide easier access for germ tube penetration. Conidial germination and germ tube length were increased by 50 and 877%, respectively when incubated in 0.2% of gorse extract solution for 24 h compared with incubation in water. Inoculum suspensions amended with 0.2% of gorse extract caused more infection and significantly reduced biomass production of 24 wk old gorse plants than suspensions without gorse extract. A minimum number of about 900 viable conidia/infection site of F. tumidum were required to infect gorse leaves. However, incorporation of amendments (which can injure the leaf cuticle) or provision of nutrients (i.e. gorse extract or glucose) in the formulation might decrease the number of conidia required for lesion formation. Scanning electron micrographs showed that germ tube penetration of gorse tissue was limited to open stomata which partly explain the large number of conidia required for infection. The flowers and leaves were more susceptible to F. tumidum infection than the spines, stems and pods. An experiment to determine the number of infection sites required to cause plant mortality showed that the entire plant needs to be inoculated in order for the pathogen to kill 10 wk old plants as F. tumidum is a non systemic pathogen. The number of infection sites correlated strongly with disease severity (R² = 99.3%). At least 50% of the plant was required to be inoculated to cause a significant reduction in shoot dry weight. F. tumidum, applied as soil inoculant using inoculated wheat grains in three separate experiments, significantly suppressed gorse seedling emergence and biomass production. In experiments to determine the loading capacity of the insect species, E. postvittana, the largest insect species studied, carried significantly more (68) and deposited significantly more (29) F. tumidum conidia than the other species. Each E. postvittana, loaded with 5,000 conidia of F. tumidum, transmitted approximately 310 conidia onto gorse plants but this did not cause any infection or affect plant growth as determined by shoot fresh weight and shoot height. E. postvittana on its own did not cause any significant damage to gorse and did not enhance F. tumidum infection. It also failed to spread the pathogen from infected plants to the healthy ones. There was no evidence of synergism between the two agents and damage caused by the combination of both E. postvittana and F. tumidum was equivalent to that caused by F. tumidum alone. This study has shown that E. postvittana has the greatest capacity to vector F. tumidum since it naturally carried the largest and the most fungal spores (429 CFU/insect). Moreover, it naturally carried Fusarium spp. such as F. lateritium, F. tricinctum and Gibberella pulicaris (anamorph Fusarium sambucinum) and was capable of carrying and depositing most F. tumidum conidia on agar. Coupled with the availability of pheromone for attracting the male insects, E. postvittana may be a suitable insect vector for delivering F. tumidum conidia on gorse using this novel biocontrol strategy. Although it is a polyphagous insect, and may visit non-target plants, F. tumidum is a very specific pathogen of gorse, broom and a few closely related plant species. Hence, using this insect species to vector F. tumidum in a biological control programme, should not pose a significant threat to plants of economic importance. However, successful control of gorse using this "lure-load-infect" concept would depend, to a large extent on the virulence of the pathogen as insects, due to the large size of F. tumidum macroconidia, can carry only a small number of it.