Soilborne pathogens of oilseed rape (PhD)

Abstract

With a rising global population it has become ever more important to improve agricultural output in order to meet our societies demand for food, fuel and fibre. Whilst many carbohydrate staples such as wheat, rice and maize are rightly the focus of this effort, other groups such as oilseeds are also important as sources of essential proteins, fats and oils, along with secondary uses such as biofuels and break crops. As an island nation, it is essential that crop yields are maximised in order to meet these increasing demands, as coercing more land area into production is not possible. During the latter half of the 20^th century this was achievable as yields rose steadily due to improved breeding, management and technological advances. However, with the dawn of the 21^st century this trend has plateaued. Many studies attributed this to market pressures and a grower’s need to maximise profitability, resulting in simplified and often shortened arable rotations between wheat and OSR, which as a consequence has led to a build-up of soil-borne pathogens causing an ‘unseen’ erosion of yield, or a yield decline.

This project aimed to elucidate the relationship between soil-borne pathogens and yield decline in oilseed rape crops, focusing on finding candidate pathogens within commercial crops and examining their occurrence and abundance in relation to agronomic factors such as rotational frequency. Using cutting edge molecular techniques, we were able to examine the fungal microbiome of commercial crops across 50 field sites. A wide range of fungal species were found including many generalists and saprophytes, whilst Rhizoctonia solani was the only pathogenic species frequently observed. Real-time PCR was used to quantify its commonality to many field sites irrespective of agronomic or geographical factors, suggesting that factors such as shortened rotations may not be influencing this pathogen. Similarly, through the use of anastomosis group specific primers we were able to demonstrate that AG 2-1 was the most common group occurring in root samples, similar to the findings of other surveys in Canada, Australia and USA. Here we hypothesise that the low influence of agronomic factors is likely due to the survival structures and wide range of host species, particularly wheat, the principal UK arable crop. In glasshouse experiments R. solani was found to be an effective and highly virulent pathogen of brassica seedlings. Yield loss appeared to be caused by a reduction in germination and plant stands, resulting from relatively low amounts of inoculum. Although, variability in inoculum production meant the true clinical threshold for disease was not reached, with this similarly demonstrating the limitations of studying this pathogen where artificial inoculation techniques are difficult to standardise.