Effect of Nitrogen Fertilization and Inoculation of Durum Wheat with Fusarium pseudograminearum on Yield, Technological Quality and Gluten Protein Composition

In Australia, adoption of reduced tillage and stubble retention cropping systems by growers to conserve soil moisture has seen an increase in the prevalence of the disease Fusarium crown rot (FCR) caused by the stubble-borne fungal pathogen Fusarium pseudograminearum. Durum wheat is particularly susceptible to FCR, exhibiting significant yield and quality losses in the presence of infection. Increasing rates of nitrogen (N) application at sowing exacerbates FCR. However, to achieve the desired grain protein and quality suited to pasta manufacturing, N application is necessary, and this creates a dilemma for growers. The purpose of this study was to investigate the effects of FCR infection in the presence of different N fertiliser application rates in durum wheat varieties on the yield and technological quality. Two durum varieties were evaluated at the same location over two seasons (2020 and 2021). These seasons were characterised by being wetter than normal and showed different responses to FCR and N application. Three rates of FCR inoculation and five rates of N fertilizer were applied (varying according to season) at sowing. In general, the 2021 season showed better responses to applied N regarding the yield and technological properties, with no impact from FCR. The FCR inoculation, while resulting in significant infections in 2020 (15-36-fold increase) and in 2021 (similar to 45-fold increase), had no impacts on the yield or grain quality in 2021, while in 2020, the yield was reduced (24.9%), with variable effects on the technological properties. The 2021 season showed much more responses to applied N (grain protein increased by similar to 24%). Jandaroi was found to maintain its kernel vitreosity at all protein levels (mean of 88.5%), obtaining the premium grade, while DBA Lillaroi did not (mean vitreosity of 76.6%) and could be downgraded if N application was insufficient. However, higher N application rates needed to achieve more than 12% protein lead to a reduction in dough strength, with Jandaroi maintaining its dough strength much better (2.7% reduction in the gluten index) than DBA Lillaroi (18.2% reduction in the gluten index). This was related to the lower glutenin/gliadin (Gli/Glu) ratio in response to applied N at sowing in Jandaroi, which helped retain kernels with a high vitreousness. This suggests genetics plays an important role in a genotype's response to N fertilisation and should be considered when selecting a genotype where higher premium grades are desirable.