Temporal variation in the coral reefs of the east coast of the inner gulf of Thailand

A series of permanent line transects established on fourteen reefs on the eastern seaboard of the Gulf of Thailand were monitored through a three-year period (1995- 1998) using a video transect method. Hierarchical cluster analysis shows three distinctive reef community types dominated by 1) Porites, 2) Acropora and 3) zoantharians. The reefs are developed under naturally turbid conditions and relatively low salinity due to the proximity of four major river outlets located in the uppermost area of the gulf. The number of Acroporid species on the reefs is positively correlated with distance from the major flver outlets. Eighty-seven species of scleractinian coral were found on the transects. Over the three-year period, the comparison of 1995-97-98 matched stations using Repeated Measures ANOV A reveals no significant time-dependent change in percent area cover of reef components except for an overall significant reduction in the faviid coral component. In the 1997-98 matched station comparison, statistical tests reveal significant increases in both Acropora and Porites components that translated into an overall increase in total living coral cover. These findings indicate that the overall environmental conditions have been favorable for coral growth. Outcompetition of massive corals by faster growing corals on several reefs also indicates conditions favorable for reef expansion. Growth of newlyformed Porites colonies over primary rock substrate and dead coral skeleton was presumably responsible for its rapid increase. Although these reefs are in an area of rapid industrialization and population growth, resultant anthropogenic effects have not yet stopped active coral accretion.

Erwinia amylovora bacteriophage resistance

It has been proposed that phages can be used commercially as a biopesticide for the control of fire blight caused by the phytopathogen Erwinia amylovora. The aim of these studies was to investigate two common bacterial resistance mechanisms, lysogeny and exopolysaccharide production and their influence on phage pathogenesis. A multiplex real-time PCR protocol was designed to monitor and quantify Podoviridae and Myoviridae phages. This protocol is compatible with known E. amylovora and Pantoea agglomerans rtPCR primers/probes which allowed simultaneous study of both phage and bacterial targets. Using in vitro positive phage selection, bacteriophage insensitive derivatives were isolated within sensitive populations of E. amylovora. Prophage screening with real-time PCR and mitomycin C induction determined that the insensitive derivatives harboured the temperate Podoviridae phage ΦEaTlOO. Lysogenic conversion resulted in resistance to secondary homologous phage infections. Prophage screening of environmental samples of E. amylovora and P. agglomerans collected from various locations in Canada, United States and Europe did not demonstrate lysogeny. Therefore, lysogeny is rare or absent while these bacterial species reside on the plant. Recombineering was used to construct exopolysaccharide deficient E. amylovora mutants. The EPS amylovoran mutants became resistant to Podoviridae and certain Siphoviridae phages. Increasing amylovoran production increased phage population growth, presumably by increasing the total number of bacterial cell surface receptors which promoted increased phage infections. In contrast, amylovoran did not playa role in Myoviridae infections, nor did production of the EPS levan for any phage pathogenesis.

Feeding and oviposition preferences of the diamondback moth Plutella xylostella (Lepidoptera: Plutellidae) on six Brassicaceae host plant species

Plutella xylostella (diamondback moth, DBM) is a globally distributed Lepidopteran that feeds and oviposits almost exclusively on plants in the Brassicaceae family. DBM disperses from the southern United States and Mexico into Canada in the spring and summer. Establishment of DBM in Ontario is partially dependent upon the quantity and quality of host plants available and the preference of DBM for different hosts. Host plants include many crops such as broccoli, canola and cabbage, as well as landscape ornamentals and wild plants. It has previously been established that DBM are attracted to host plants by chemicals, specifically glucosinolates. I examined the preference of DBM among crop, wild and ornamental host plant species and how preference varies with insect life stage (3rd and 4th instar larvae and adults). Experiments included exposing DBM larvae from five populations coming from different locations in Canada to six Brassicaceae species and evaluating the preferences and weight gain over one hour. Then adult females were exposed to these same plant species and their oviposition preferences were examined. Populations from Alberta, Saskatchewan and Ontario were compared to assess differences in preference associated with geographic region or species of host plant. The ultimate goal of my study was to understand the potential of various Brassicaceae species to act as reservoirs to sustain and promote population growth of DBM, as well as sinks that may decrease DBM abundance. Results showed that garden cress (Lepidium sativum) was highly preferred over other species (wintercress, black mustard, aubretia, broccoli and ornamental kale) for both food and oviposition sources. Previous studies report that garden cress contains saponins, chemicals shown to be toxic to developing DBM larvae, however no studies have yet shown a preference for garden cress. These results provide information on a novel host plant with the potential to control DBM population growth. No difference in preferences was found among populations of DBM from various sources in Canada.