Substrate use and survival of fungal plant pathogens on maize residues at winter temperatures around freezing point

Climate scenarios predict increasing temperatures and higher precipitation rates in late autumn to early spring, both of which holding the potential to change the dynamics of plant residue decomposition and overall microbial activity in soil. In company with consequences for nutrient release patterns influences on the survival of fungal plant pathogens and their phytopathogenicity can be expected. Both, litter decomposition and pathogen survival, was analyzed in a 70-day litterbag incubation experiment. Continuous +4 °C was compared to permanent frost (−3 °C) and different freeze-thaw cycles for the decomposition of maize residues and disease potential of soil-borne plant pathogens Fusarium culmorum, Fusarium graminearum, and Rhizoctonia solani. Frost generally reduced maize residue decomposition. On the lower levels of CO2 production in the permanent or occasionally frost treatments pathogen inoculation had large effects on microbial maize use, indicating high saprotrophic activity of pathogens even in cold winter scenarios. Pathogen inoculation led to higher amino sugar contents of maize residue dwelling microbial organisms. At constant 4 °C remarkable high amounts of glucosamine were detected, indicating higher substrate use efficiency without frost. Both, temperature treatments as well as intra- and interspecific competition directed the development of pathogens after inoculation. F. culmorum took large advantage from the non-frost scenario, while no significant increase was found under continuous frost. F. graminearum was also able to increase its abundance at +4 °C. But this was strongly reduced when F. graminearum was in competition to the other two pathogens. In summary, F. culmorum was found to be highly frost tolerant and competitive against F. graminearum, particularly under conditions of freeze-thaw cycles since F. culmorum was able to take a large share of saprotrophic litter residue use under the cold conditions. Biomass of R. solani was strongly decomposed in all treatments. We conclude that constant mild conditions during winter can increase biomass of F. culmorum and F. graminearum in crop residues, causing increased infection pressure in the next season. In contrast to that, frost and freeze-thaw events can lower the build-up of Fusarium biomass and thus diminish the risk of crop infection.