What influences the composition of fungi in wheat grains?

Wheat grains are inhabited by different fungi, including plant pathogens and fungi – mycotoxin producers. The composition of seed mycobiota can be influenced by different factors, including agronomic practices, but the results are still contradictory. The aim of this study was to evaluate the mycobiota of wheat grains depending on agroecological conditions. Wheat grains were obtained from a two-factorial field trial: A – tillage system (A1 – ploughing at a depth of 22–24 cm; A2 – harrowing at a depth of up to 10 cm); B – crop rotation (B1 – continuous wheat; B2 – oilseed rape and wheat; B3 – crop rotation). The mycobiota of grain were determined by mycological and molecular methods. The most abundant and widespread of the mycobiota were Pyrenophora tritici-repentis, Alternaria spp., Arthrinium spp., and Fusarium avenaceum. Higher amounts of precipitation increased the infection of grains with Fusarium fungi. Seven species of Fusarium were identified in the grain samples: F. avenaceum, F. poae, F. graminearum, F. culmorum, F. acuminatum, F. sporotrichioides, and F. tricinctum. The soil tillage method and crop rotation did not influence the total incidence of Fusarium spp., but the abundance of a particular species differed depending on agronomic practice. The research suggests that continuous wheat sowing under conditions of reduced soil tillage can increase the level of risk of grain infection with F. graminearum and, consequently, the accumulation of mycotoxins

Importance of Agronomic Practice on the Control of Wheat Leaf Diseases

Soil tillage and crop rotation are considered important tools in wheat leaf disease control; however, the results of investigations are inconsistent. The aim of the present study was to determine the effect of the soil tillage system and cropping sequence on the development of winter wheat leaf diseases in 2012–2017. The disease development was assessed in a two-factor experiment: (a) soil tillage system; and (b) crop rotation. Foliar fungicides were used uniformly in all variants. The results showed that tan spot (caused by Pyrenophora tritici-repentis) dominated in 2012, 2013, and 2016, but the level of Septoria tritici blotch (Zymoseptoria tritici) was essentially lower and exceeded the severity of tan spot only in 2015. The agronomic practice used significantly influenced only the development of tan spot. Reduced soil tillage and continuous wheat sowing substantially increased tan spot severity, especially when both practices were used simultaneously. Short crop rotation (only wheat and oilseed rape) provided sufficient control of tan spot in ploughed fields, whereas in non-ploughed fields, the level of this disease did not decrease. The results could be explained by differences in the pathogens’ life cycle: P. tritici-repentis ascospores in wheat debris is the main source of infection; in contrast, Z. tritici spreads by conidia from living plants

DIVERSITY OF FUNGI ASSOCIATED WITH WHEAT STEM BASE DISEASES

Wheat stem base diseases can be caused by different pathogens – previous research has showed complex infections. Also, fungi from other ecological niches can be associated with wheat stem base. Wheat stems with disease symptoms were collected in a field experiment where agronomic practices (different soil tillage systems under various crop rotation schemes) were evaluated from 2012 to 2020. Causal agents and other fungi associated with stem bases were identified by mycological and molecular genetic methods to genera/species level. A high diversity of fungi associated with stem base diseases was determined – fungi from 30 different genera were found. Altogether, 48% of identified fungi belonged to typical causal agents of stem base diseases, 15% were pathogens of wheat leaves and ears, and 37% were saprotrophs or fungi with unclear ecological guilds. Most often, stem base diseases were caused by Oculimacula spp., Fusarium culmorum, and F. avenaceum. Other pathogens (Rhizoctonia spp., Pythium spp., other species of Fusarium, etc.) were found only in some cases. Important pathogens of wheat – Pyrenophora tritici-repentis and Parastagonospora nodorum – were determined frequently. The spectrum of pathogens differed depending on the meteorological conditions of the vegetation period. Further research is required to clarify the relationships between different fungi and their influence on wheat development