Developing Sustainable Genetic and Agronomic Recommendations for Winter Wheat under Irish Conditions

Ireland’s mild, temperate climate is suitable for producing high-yielding crops of winter wheat with yields closely related to crop nitrogen (N) uptake largely supplied by chemical fertiliser. To obtain high yields in the Irish climate, it is critical to protect crops from disease with plant protection products (PPPs). However, the European Union's (EU) Farm to Fork strategy is driving significant changes in food production systems with Ireland consequently devising Food Vision 2030 to align with EU objectives. The Farm to Fork strategy mandates a 20% reduction in fertiliser use and a 50% reduction in PPP use in every EU member state by 2030. Despite these targets, the strong demand for native grain from livestock sectors necessitates maintaining or increasing current grain production levels. The research conducted investigated how European producers could achieve this dual objective. This thesis comprises the results of two experiments evaluating the effects of key crop management practices including cultivar choice, N application rate and biostimulant use on plant establishment, grain yield, yield components, disease resistance, grain quality and crop phenology of winter wheat grown in county Dublin in 2024. Twenty diverse cultivars of winter wheat were evaluated at four application rates of N fertiliser (0, 60, 140, 240 kg N/ha). Increasing N application rate significantly increased grain number per unit area leading to corresponding increases in grain yield. Cultivar resistance to the fungal pathogen Zymoseptoria tritici varied widely later in the growing season with infection levels increasing with N rate increases up to 140 kg N/ha. Several cultivars had strong resistance to Puccinia striiformis however susceptible cultivars showed increased infection with increasing N rate. N rate increased grain protein content linearly and significant cultivar-specific effects were also observed. While N rate had no effect on crop phenology, significant effects of cultivar choice on phenology were attributed to the diverse genotypes of the panel of wheat cultivars. The effects of combinations of biostimulant seed dressings and foliar sprays were compared to N fertiliser treatments of 60 kg N/ha and 140 kg N/ha to determine their potential to contribute towards the reduction of N fertiliser application rate. The 140 kg N/ha treatment significantly increased grain number per m2 (GN/m2) and subsequently the grain yield compared to all biostimulant treatments indicating that the current biostimulant products available cannot replace large applications of N fertiliser. Similarly, the selected biostimulants were unable to replace large applications of N fertiliser for increasing grain protein content. However, this trial demonstrated potential for biostimulants in crop production systems to partially offset fertiliser requirements as significant effects of a Methylobacterium symbionticum based product on grain yield were observed.