Some intracellular symbionts of insects confer host protection from a variety of bacterial, fungal and viral pathogens as well as from predators and parasitoids. Within the cryptic species complex of whiteflies known collectively as Bemisia tabaci is a cosmopolitan invasive agricultural pest, which is commonly infected with the symbiont Rickettsia sp. nr. bellii. Rickettsia swept rapidly through southwestern USA whitefly populations of the MEAM1 species and has been associated in a genotype-dependent manner with increased whitefly fitness and female biased sex ratios. Here we sought to determine whether Rickettsia in MEAM1 might have a defensive role against the general entomopathogenic fungus, Beauvaria bassiana. Nymphs from two lines of whitefly, each with Rickettsia positive (R+) and negative (R-) sublines were exposed to different doses of B. bassiana. The results provided evidence of protection by Rickettsia in one genetic line (MAC1) but not in the other (MAC2). In a third experiment, females of the four sublines were each outcrossed for two generations with males from an outbred whitefly culture, derived from the field within the year, and F2 nymphs from these four new sublines were exposed to the fungus. In this experiment, Rickettsia was protective in both MAC1-O and MAC2-O lines. Taken together, our results suggest the symbiont Rickettsia can confer protection against a generalist entomopathogenic fungus, B. bassiana, and that this protection is conditional on host genotype. To our knowledge, this is the first record of an insect symbiont conferring protection against a generalized and commercially available biological control agent. Bemisia tabaci MEAM1 is a global pest of warm temperate and tropical agriculture, and the prevalence of Rickettsia in many populations of this species could limit the predictability or efficacy of fungal pathogens as a potential management tool.

Presently, most bacterial diseases of eel (Anguilla japonica) are controlled by antibiotics. However, antibiotics not only kill the bacterial pathogens but also kill those bacteria which might be beneficial to eels. In the meantime, application of antibiotics may result in spreading and accumulation of the resistance genes which may in turn lower the efficacy the antibiotics in the future and may threat public health. The recent trend to such problems is to screen non-pathogenic bacteria which are competitive to the pathogenic bacteria in the same environments. The eel pathogen, Edwardsiella tarda, was chosen as the target in this study. Bacterial strains were isolated from different eel ponds and tested for the ability to inhibit the growth of E. tarda. Of 2,412 strains tested, eight of them showed the inhibition capability. The molecular weights of the bioactive ingredients are all smaller than 12,000 daltons indicating they are not protein in nature. One of the strains is Bacillus cereus, four of the strains are Bacillus sphaericus, two of the strains are Bacillus laterosporus, and one of the strains of identified as Pseudomonas areuginosa competed extremely well with E. tarda. These antagonistic bacteria may have the potential of becoming as bio-control agents.Tiger shrimp (Penaeus monodon) is an important agricultural product in Taiwan. The over all production peaked in 1988, since then the outbreak of viral infection has caused the shrimp aquaculture a heavy damage. The current production is merely 1/10 of the peak. Many solutions were proposed to solve the problem, such as: increase the immunity of the shrimp, study pumping of the underground water has caused serious land subsidence in the coastal areas. Therefore, conservation of water is the trend of current aquaculture. In this study, culturable bacteria were isolated from a closed tiger shrimp pond. The taxonomy of the bacteria was based on 16S rDNA sequence phylogeny. Roughly 8 groups (genera) of bacteria were identified, including: Vibrio, Pseudoalteromonas, Porphyrobacter, Flavobacterium, Rhodthermus and three uncertain genera.

Rhizoctonia solani causes damping-off, and root and crown rot of sugar beet (Beta vulgaris L.) and overwinters as sclerotia and mycelia. Research was conducted to determine how best to produce large quantities of sclerotia and mycelia in vitro, and compare their pathogenicity with traditionally used colonized barley grains to sugar beet in vitro and in vivo. The greatest number of sclerotia was produced on amended clarified V8 medium and sclerotia caused more disease compared to barley inoculum in the greenhouse. The bio-control potential of Penicillium pinophilum on R. solani AG2-2 on sugar beet was evaluated in vitro and in vivo. Results showed that the presence of P.pinophilum with R.solani reduced damping-off by 75% and thus have the potential to be developed as a bio-control agent for this pathogen.

Com a crescente preocupação por práticas agrícolas mais sustentáveis, o uso de rizobactérias promotoras de crescimento de plantas (PGPR) tem recebido cada vez mais atenção por sua capacidade em melhorar a performance das plantas assim como aumentar sua resistência contra insetos e patógenos. Neste trabalho foi demonstrado que a inoculação de plantas de trigo com a rizobacteria Azospirillum brasilense reduziu alguns sintomas característicos de plantas infectadas pelo vírus do nanismo amarelo da cevada (BYDV), bem como a população do afídeo vetor, Rhopalosiphum padi, nessas plantas. A redução de alguns sintomas relacionados a doença foi associada à resistência sistêmica induzida, desencadeada pelo aumento nos níveis de ácido jasmônico, fitohormônio amplamente conhecido na indução de resistência por bactérias benéficas contra patógenos. Entretanto, não foi possível elucidar as vias de defesa que auxiliaram na diminuição da população do vetor. Adicionalmente, verificou- se que a inoculação bacteriana alterou os padrões de preferência hospedeira por ápteros não- virulíferos e virulíferos e alados de R. padi. Os dados apresentados nessa tese sugerem o grande potencial que a inoculação com A. brasilense pode ter no manejo do BYDV, influenciando não apenas o vírus, mas todo seu patossistema, uma vez que o crescimento populacional e o comportamento de seu vetor, R. padi, foram afetados pela interação BYDV-trigo-PGPR. / With the increasing concern for agricultural practices more sustainable, the use of plant growth promoting rhizobacteria (PGPR) has been received increasing attention for its ability to improve plant performance and increase plant resistance against insects and pathogens. In this work, it was demonstrated that the inoculation of wheat plants with the rhizobacteria Azospirillum brasilense, reduced some characteristic symptoms of plants infected by the barley yellow dwarf virus (BYDV), as well as the performance of its aphid vector, Rhopalosiphum padi. The reduction in disease severity was related to induced systemic resistance, triggered by the increase in the levels of jasmonic acid, phytohormone widely known to induce resistance by beneficial bacteria against pathogens. However, it was not possible to elucidate the pathways of defense involved in decrease the vector population. In addition, bacterial inoculation was found to affect the host preference of R. padi aptera non-viruliferous and viruliferous and alates. The data presented here suggest the great potential that the inoculation with A. brasilense can be in the management of BYDV, influencing not only the virus but all its pathosystem, considering that the population growth and the behaviour of its vector, R. padi, were affected by BYDV-wheat-PGPR interaction.

Fusarium oxysporum Schl. var. vanillae (Tucker) Gondon is known to cause root rot in Vanilla planifolia Andrews in most regions where it is grown, including the major plantations in Xishuangbanna, Yunnan Province of China. This is of serious economic concern to the Province since the vanilla flavouring extractable from the beans of the plant is a valuable food product and an important export commodity. There are no fungicides registered for the control of Fusarium root rot and the only available chemical control methods are ineffective and cause serious contamination of the soil. Breeding for resistance is difficult when no dominant gene is known or where little information is available on fungal pathogenicity. Biocontrol is the main alternative for disease control in this crop, an attractive approach because of increasing concerns for environmental protection. The investigation considers two biocontrol strategies: first the introduction of virulent, antagonistic, non-pathogenic strains, closely-related to the pathogen, to overcome pathogenic populations in infected soils; second the use of essential oils with antimicrobial properties when applied to infected soils. Pathogenicity tests have been done on 81 out of 87 F. oxysporum isolates collected in Yunnan Province. Among these, 32 isolates were non-pathogenic and 49 were pathogenic. The pathogenicity results showed the complexity of F. oxysporum in Yunnan. Seventeen isolates were recovered from the Daluo plantation, of which 14 were pathogenic isolates and 3 non-pathogenic isolates; 26 from the Menglun plantation, in which 12 were pathogenic and 14 were non-pathogenic; 18 isolates from the Manjingdai plantation, in which 12 isolates were pathogenic, whilst the other 6 were non-pathogenic and 20 were obtained from the plantation in Hekou i County, of which 11 were pathogenic isolates and 9 were non-pathogenic. Genetic diversity within this population of F. oxysporum has been investigated with respect to vegetative compatibility and to determine the relationship between VCGs and virulence. The VCG results showed that the 87 strains of Fusarium oxysporum f.sp vanillae isolated from Yunnan Province were complex. They could be distributed into 12 different VCGs and that a direct relationship between VCGs group and virulence could not be drawn. Two non-pathogenic strains, ML-5-2 and HK-5b-4-1, have been screened from 87 strains as candidate biocontrol agents by pathogenicity and VCG, which are self-incompatible and closely related to the pathogens. These two strains were effective in vanilla root rot control in controlled environments, but their effects in field experiments were less conclusive. Seven essential oils, which have long been regarded as having inhibitory effects on pathogens in nature, have also been investigated as biocontrol agents. Three oils, cinnamon oil, thyme oil and clove oil, were effective in inhibiting the growth of pathogen in vitro. These oils may develop into useful components of different management strategies with non-pathogenic strains. For the future, consideration will need to be given to the mechanism(s) of the interaction of the antagonistic components with the soil microbe population and host plant and also to appropriate formulation, to take account of soil type, crop status, cultural practices, environmental and economic factors. Biocontrol methods have considerable potential but must be acceptable to farmers as part of an overall crop management programme.

Bromus tectorum and other annual brome grasses have invaded many ecosystems of the western United States, and because of an annual-grass influenced alteration of the natural fire cycle on arid western range lands near monocultures are created and conditions in which the native vegetation cannot compete are established. Each year thousands of hectares become near monocultures of annual brome grasses. Pyrenophora semeniperda, a generalist seed pathogen of annual grasses, shows major potential as a possible mycoherbicide that could help in reducing the monocultures created by annual grasses. The purpose of this research was to identify the requirements for isolating cultures of P. semeniperda, search for a hypervirulent strain, and evaluate its effect in the field. The techniques for isolating the fungus have evolved and become more efficient. The first two years of working with P. semeniperda resulted in 11 isolates. During the third year of this study, we developed a single spore isolation technique that resulted in 480 additional isolates. Virulence screening resulted in detection of a range of isolate ability to kill non-dormant B. tectorum seeds. Ninety-two isolates represented a range of virulence from 0-44%. The variation in virulence was expressed mostly within populations rather than between populations. Similarly, virulence varied significantly within Internal Transcribed Spacer (ITS) genotypes and habitats but not between them. When conidial inoculum was applied in the field there was no observed difference in disease incidence between different levels of inoculum. This is thought to have been due to applying the inoculum under conditions in which most in situ seeds were infected and killed by already high field inoculum loads. While additional field trials are needed to optimize the inoculum effectiveness, the overall results of this research provide a good foundation for using P. semeniperda as a biological control for seed banks of annual brome grasses.

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