Fungi and Diseases Associated with Cultivated Switchgrass in Iowa

Switchgrass (Panicum virgatum L.) is a native perennial prairie grass that is now cultivated as a forage crop and a biomass crop for renewable energy. Biomass yields of switchgrass in southern Iowa have recently dropped significantly in some fields and the reduction has been attributed to disease. A disease survey was conducted in 1999 to assess the prevalence of major diseases in Chariton Valley switchgrass production. There were disease symptoms present on switchgrass plants in each field and thirteen fungal species were identified from leaf, stem, and root samples. Two pathogenic fungi, Tilletia maclaganii and Colletotrichum graminicola, were present in 88% and 100% of fields, respectively. Severity (% diseased leaf area) of C. graminicola was low in each field. However, Tilletia maclaganii was at high incidence (\u3e70%) in some fields and apparently is causing significant reductions in biomass and seed production. Nine of the other fungi identified in the survey have not been reported previously from switchgrass in Iowa

A Comparison of Maize Stalk Rot Occurrence in Bt and Non-Bt Hybrids

Stalk rots, caused by a complex of fungal species, are among the most widespread and destructive diseases of maize. Larvae of the European corn borer (ECB) (Ostrinia nubilalis) promote stalk rot development by creating entry points for fungi, serving as vectors of pathogens, and causing physiological stress that may predispose plants to stalk decay. Field experiments were conducted in 1998, 1999, and 2000 to determine whether the use of transgenic Bt hybrids expressing insecticidal proteins would influence stalk rot symptoms (pith disintegration, pith discoloration, and lodging). Five hybrids representing different Bt types (or “Bt events”) (176, BT11, MON810, DBT418, and CBH351) were paired with their near-isogenic, non-Bt counterparts and subjected to treatments of manual and natural infestation with ECB larvae. Manual infestation resulted in significantly more ECB tunneling than natural infestation in 1998 and 1999 and significantly more lodging in 1998. There were significant linear correlations between ECB injury and stalk rot symptoms in non-Bt hybrids in 1998 and 1999, but not in 2000. A standard foliar insecticide treatment for ECB did not significantly affect stalk rot symptoms. In 1998, Bt hybrids had significantly less ECB tunneling, stalk discoloration, pith disintegration, and lodging compared with non-Bt hybrids, but these effects depended upon the Bt event and the infestation treatment. Similar but less pronounced effects of Bt events were observed in 1999. The 2000 results were more variable; the amount of pith disintegration was significantly lower but discoloration was significantly higher in the BT11 hybrid compared with its non-Bt counterpart, and the amount of lodging was significantly higher in the event 176 hybrid compared with its non-Bt counterpart. The ratio of stalk strength to grain weight did not consistently differ between Bt and non-Bt hybrids. These results indicate that, although specific Bt events in some years may cause reductions in stalk rot, the overall effect of Bt transformation on stalk rot occurrence is highly variable

Fungal Colonization of Alfalfa Stubble Following Harvest

Two-year-old stands of alfalfa cultivars Saranac and Vernal, planted in Central Iowa, were sampled 0, 15, and 30 days after the first harvest in 1995 to identify fungi colonizing the stubble left after harvest and evaluate the role of harvest-induced wounds as infection sites for potential crown-rotting fungi. Analysis of variance was conducted to determine if sampling date and cultivar significantly affected incidence of the fungi. All stems were infected with at least one fungal species at every sampling dare. The fungal genera most frequently isolated were Alternaria, Colletotrichum, Fusarium, Phoma, and Rhizoctonia. Fusarium acuminatum was the most frequently isolated Fusarium species. Other species included F. sambucinum and F. sporotrichioides, but not F. oxysporum or F. solani. Incidence of Colletotrichum decreased significantly over time, while the incidence of Alternaria increased significantly. Cultivar had a significant effect on Colletotrichum incidence, but not on incidence of other fungi. Potential crown rot pathogens were present on the stems at harvest, and their incidence generally did not increase significantly over time. These results do not provide evidence that wounds made by harvest equipment were important infection sites. Potential crown-rotting fungi were present in the stems at harvest; senescence of stem tissue after harvest may be important in the movement of fungi into the crowns

Climate change impacts on mycotoxin risks in US maize

To ensure future food security, it is crucial to understand how potential climate change scenarios will affect agriculture. One key area of interest is how climatic factors, both in the near- and the long-term future, could affect fungal infection of crops and mycotoxin production by these fungi. The objective of this paper is to review the potential impact of climate change on three important mycotoxins that contaminate maize in the United States, and to highlight key research questions and approaches for understanding this impact. Recent climate change analyses that pertain to agriculture and in particular to mycotoxigenic fungi are discussed, with respect to the climatic factors – temperature and relative humidity – at which they thrive and cause severe damage. Additionally, we discuss how climate change will likely alter the life cycles and geographic distribution of insects that are known to facilitate fungal infection of crops

Mycotoxins that Affect the North American Agri-Food Sector: State of the Art and Directions for the Future

This paper summarises workshop discussions at the 5th international MYCORED meeting in Ottawa, Canada (June 2012) with over 200 participants representing academics, government and industry scientists, government officials and farming organisations (present in roughly equal proportions) from 27 countries. Workshops centred on how mycotoxins in food and feed affect value chains and trade in the region covered by the North American Free Trade Agreement. Crops are contaminated by one or more of five important mycotoxins in parts of Canada and the United States every year, and when contaminated food and feed are consumed in amounts above tolerable limits, human and animal health are at risk. Economic loss from such contamination includes reduced crop yield, grain quality, animal productivity and loss of domestic and export markets. A systematic effort by grain producers, primary, transfer, and terminal elevators, millers and food and feed processers is required to manage these contaminants along the value chain. Workshops discussed lessons learned from investments in plant genetics, fungal genomics, toxicology, analytical and sampling science, management strategies along the food and feed value chains and methods to ameliorate the effects of toxins in grain on animal production and on reducing the impact of mycotoxins on population health in developing countries. These discussions were used to develop a set of priorities and recommendations