Summary: Plant parasitic nematodes cause an estimated $80 billion of annual damage to global agriculture and threaten food security in many regions. The potato cyst nematode (PCN) is a plant parasitic nematode that infects solanaceous species and causes significant damage, primarily to potato crops. In the UK alone, PCN causes more than £31 million in damage annually. Historically, PCN has been managed by using nematicides. However, due to potential environmental concerns, these chemicals have become tightly regulated. Currently there is only one granular nematicide left on the UK market and this has an uncertain future with an upcoming regulation review in 2024. Scotland is a large producer and exporter of seed potatoes. Current regulations state that if PCN has been detected in a field, that field can no longer be used for seed potato production. PCN is spreading in seed growing areas and recent predictions suggest that without improved PCN management tools this industry will collapse by 2050. Chitin is an abundant biomolecule which is found in insects, fungi and shellfish. Chitin is also present in PCN eggshells where it protects the developing juvenile by providing the eggshell with rigidity and tensile strength. Chitinous soil amendments have previously been proposed for control of plant parasitic nematodes. Addition of chitin to soils may help select for chitin-degrading microbial populations, naturally raising the prevalence of these organisms in that environment. The microbes may subsequently use sources of chitin already present in the soil, such as PCN eggshells, as an energy source, allowing the suppression of PCN numbers to a level where they are no longer a threat to the potato crop. We currently do not know if chitinous soil amendments are suitable for Scottish growing conditions or the impact they have on beneficial, chitin-containing, soil organisms. In this work we will investigate whether chitinous soil amendments control PCN in UK soils and how this control is achieved. Soil samples from field plots treated either with or without chitinous soil amendments will be collected. These samples will be used to identify the presence of different fungal, bacterial and free-living nematode populations and to quantify PCN numbers and chitin degrading activity. Comparing treated and untreated samples will allow understanding of changes in PCN populations, which microorganisms are responsible and if there is a negative impact on wider soil biodiversity. Testing in a controlled greenhouse environment will confirm whether the chitin within the soil amendment has a positive effect towards reducing PCN populations through eggshell degradation and will confirm which microorganisms are responsible. The project outcomes will include identifying differences in microbial and nematode populations in field samples treated with or without a chitin-rich soil amendment. Analysis of the increased presence of chitinase, the enzyme responsible for chitin degradation, in soil samples will confirm the pathway utilised to degrade PCN eggshells. Additionally, structural investigation of PCN eggshells will validate whether eggshells are degraded sufficiently to prevent PCN hatching. Populations of potentially beneficial free-living nematodes will be identified in treated and untreated samples to survey for potential wider nematocidal effects of chitin-based soil amendments.

Rhynchosporium leaf blotch of barley, caused by the fungus Rhynchosporium secalis, is of increasing importance in world agriculture. It is the most serious disease on winter and spring barley in the UK, causing substantial losses nationally, despite expenditure of £50M per year on fungicides. The disease is difficult to control with fungicides, as the fungus can exist for a long period in the crop without causing symptoms. A severe epidemic may then emerge without warning. The sources of infection responsible for such epidemics are not well understood. We have recently discovered, for instance, that contaminated seed may be an important primary source of the disease. This project aims to clarify the origin and early dynamics of epidemics using molecular techniques (quantitative PCR) that can detect and quantify the DNA of the pathogen in barley plants before symptoms occur. The same techniques can also detect genetic characteristics of the fungus, such as mating type, virulence, and genes responsible for resistance to fungicides. Each season, epidemics will be monitored on both winter (October-sown) and spring (March-sown) barley. Work will also be done on historical spring barley samples archived at Rothamsted over 150 years, and on samples from current crops from at least 10 sites in England, Scotland and Ireland. We aim to study short-term and long-term changes in the pathogen population. Knowledge from this project will be combined with new information from related projects being funded by BBSRC LINK, Defra, HGCA and SEERAD (at ADAS, and in Scotland, SAC and SCRI) to develop guidelines for crop husbandry and agronomic practices to reduce R. secalis population size and genetic variation to achieve sustainable control of rhynchosporium disease of barley.