Winter wheat crown and root rot are affected by soil tillage and crop rotation in Latvia

Reduced soil tillage and wheat monoculture have become increasingly widespread technologies in Latvia. The aim of this study was to estimate the development of winter wheat crown and root rot, depending on soil tillage and crop rotation. Two-factor experiments were carried out from 2009 to 2012: (1) crop rotation and (2) soil management. The incidence of the complex of stem-base diseases (root and crown rot) was determined after wheat harvesting. Causal agents were determined microscopically; species of Fusarium were identified by sequencing the Transcription Elongation Factor (TEF) region and subsequent phylogenetic clustering of acquired DNA sequences. The most important factor influencing the progression of crown and root rot was year (p < 0.05). The disease incidence among years fluctuated between 13 and 72%. Crop rotation (p < 0.05) and soil tillage method (p < 0.1) also affected the level of crown and root rot development. Conventional soil tillage slightly decreased disease development. The disease incidence in continuous wheat cropping was 10% higher compared to that in winter wheat fields following oilseed rape. The spectrum of pathogens and other fungi did not differ depending on soil tillage and crop rotation. The most common pathogens were fungi of the Fusarium genus: on average, 36% of isolates were identified as Fusarium spp: F. culmorum and F. avenaceum were the dominant species, but F. sporotrichioides and F. trinctum were also identified. The problem of wheat stem base and root rot is complex; different circumstances and unknown factors influence the spectrum of causal agents and the total disease level. Further investigations are necessary to research changes in disease development during a longer time period, as well as to clarify the occurrence of different pathogens, depending on different factors.