Assessing the factors affecting dispersal and colonisation of fungal plant pathogens across multiple ecological scales

The spread of agricultural plant pathogens is a global problem; 20-40% of crop yield globally are lost to animals, weeds and pathogens, with ~12% of total crop production lost to plant diseases. To date, the most widely used form of control is chemical biocides, however with concern regarding sustainability and toxicity, there is a pressing need to shift to more holistic approaches. To address this need, this thesis begins the essential task of understanding the influence of biotic and abiotic factors on the movement of fungal pathogens and pathogen suppression. Specifically, this thesis investigated the role of soil microbial communities in suppressing the spread of plant pathogens using Fusarium as a model plant pathogen. Using a combination of laboratory experiments, a greenhouse survey (case study) and landscape surveys, this thesis spans multiple scales to provide a comprehensive assessment of the fungal pathogen Fusarium; its dispersal, spread and methods of mitigation. This thesis provided the first empirical data on fungal spillover and highlights the importance of landscape habitats in plant-pathogen dispersal; with woodland soils presenting a hard-edge boundary for fungal plant-pathogen presence/abundance. Moreover, this thesis experimentally demonstrates the importance of both the soil type (parental material) and resident microbial community on fungal suppression; specifically, although woodland soils allow for faster movement and greater dispersal (distance) of Fusarium, the resident microbial community acts as a barrier. This surrounding community also plays a key role in Fusarium dynamics alongside mitigation methods; sterilization methods used to kill pathogens also kill the resident community and ultimately, this allows for the re-emergence of Fusarium. With these results, this thesis opens avenues of study that focus on utilising woodland soil, and its corresponding community, as a mitigation tool in both mid (enclosed/protected e.g. greenhouses) and large scales (agricultural landscape). Firstly, results suggest that woodland soils can be utilized alongside sterilised methods by seeding sterile soil with woodland communities to provide a biotic competitive barrier, and subsequently hindering pathogen growth. Secondly, results suggest the use of woodlands border around patches of agricultural fields could act as a method of isolating plant pathogens within patches and subsequently reducing disease spread. Harnessing woodland soils’ natural inhibitory properties has the potential to provide sustainable, holistic and viable alternatives to current methods.Open Acces

Is coconut coir dust an efficient biofertilizer carrier for promoting coffee seedling growth and nutrient uptake?

Background As a method for sustainable agriculture, biofertilizers containing plant growth-promoting bacteria (PGPB) have been recommended as an alternative to chemical fertilizers. However, the short shelf-life of inoculants remains a limiting factor in the development of biofertilizer technology. The present study aimed to (i) evaluate the effectiveness of four different carriers (perlite, vermiculite, diatomite and coconut coir dust) on the shelf-life of S2-4a1 and R2-3b1 isolates over 60 days after inoculation and (ii) evaluate isolated bacteria as growth-promoting agents for coffee seedlings. Methods The rhizosphere soil-isolated S2-4a1 and plant-tissue-isolated R2-3b1 were chosen based on their P and K-solubilizing capacities and their ability to produce IAA. To evaluate the alternative carriers, two selected isolates were inoculated with the four different carriers and incubated at 25 °C for 60 days. The bacterial survival, pH, and EC in each carrier were investigated. In addition, coconut coir dust inoculated with the selected isolates was applied to the soil in pots planted with coffee (Coffea arabica). At 90 days following application, variables such as biomass and total N, P, K, Ca, and Mg uptakes of coffee seedlings were examined. Results The results showed that after 60 days of inoculation at 25 °C, the population of S2-4a1 and R2-3b1 in coconut coir dust carriers was 1.3 and 2.15 × 108 CFU g−1, respectively. However, there were no significant differences among carriers (P > 0.05). The results of the present study suggested that coconut coir dust can be used as an alternative carrier for S2-4a1 and R2-3b1 isolates. The significant differences in pH and EC were observed by different carriers (P < 0.01) after inoculation with both bacterial isolates. However, pH and EC declined significantly only with coconut coir dust during the incubation period. In addition, coconut coir dust-based bioformulations of both S2-4a1 and R2-3b1 enhanced plant growth and nutrient uptake (P, K, Ca, Mg), providing evidence that isolated bacteria possess additional growth-promoting properties

Bacterial Communities Associated with Crude Oil Bioremediation through Composting Approaches with Indigenous Bacterial Isolate

In this study, we aim to investigate the efficiency of crude oil bioremediation through composting and culture-assisted composting. First, forty-eight bacteria were isolated from a crude oil-contaminated soil, and the isolate with the highest crude oil degradation activity, identified as Pseudomonas aeruginosa, was selected. The bioremediation was then investigated and compared between crude oil-contaminated soil (S), the contaminated soil composted with fruit-based waste (SW), and the contaminated soil composted with the same waste with the addition of the selected bacterium (SWB). Both compost-based methods showed high efficiencies of crude oil bioremediation (78.1% and 83.84% for SW and SWB, respectively). However, only a slight difference between the treatments without and with the addition of P. aeruginosa was observed. To make a clear understanding of this point, bacterial communities throughout the 4-week bioremediation period were analyzed. It was found that the community dynamics between both composted treatments were similar, which corresponds with their similar bioremediation efficiencies. Interestingly, Pseudomonas disappeared from the system after one week, which suggests that this genus was not the key degrader or only involved in the early stage of the process. Altogether, our results elaborate that fruit-based composting is an effective approach for crude oil bioremediation