Update:
Objectives 1 is ongoing in this project and we continue to sample symptomatic soybean plants in all states, when disease is observed. In 2017 stem canker was spotty in some locations (Iowa and Wisconsin). However, several Diaporthe isolates were obtained and will be sent to Co-PI Mathew for further speciation. In South Dakota, more stem canker was observed with additional isolates being collected. These will be speciated. Additionally, all isolates collected in Wisconsin over the term of this project are currently being prepared to be sent to Co-PI Mathew for speciation and additional aggressiveness evaluation.
Progress has been made on a project to assess the aggressiveness of the various species of Diaporthe collected on soybean. Several inoculation techniques to assess soybean variety resistance have been developed. However, these have not been compared with newer isolates of Diaporthe. Thus, an experiment to assess the performance of inoculation techniques and begin to measure isolate aggressiveness was performed. Preliminary data suggest that species of Diaporthe respond differently based on inoculation technique. However, depending on technique, isolates do vary in aggressiveness within and among species. Work will continue to establish the most consistent technique for inoculation so that variety resistance can be assessed in future studies.
Progress on objective 2 continues. Crop Protection Network materials related to stem canker and pod and stem blight are being promoted at field events and local meetings. PI Smith also made several field visits in Wisconsin in 2017 and connected farmers with fact sheets and online Crop Protection Network materials after these site visits.
Much progress has been made on objective 3 by Co-PI Mathew. A graduate research assistant funded on this project recently completed his thesis research. The title of this work was Diaporthe, soybean cyst nematode, and soybean aphid: An evaluation of potential interactions occurring among pests on soybean in South Dakota. Results of this work suggest that SCN reproduction is reduced by 90% when Diaporthe species precede SCN infection. When SCN preceded D. longicolla a 76% increase in stem lesion length was recorded as a result of infection by the fungus. When SCN preceded D. caulivora a decrease in lesion length of 35% was recorded. Additionally, D. longicolla and soybean aphid did not interact on soybean. However, a potential compensatory effect was observed on soybean plants in the concomitant infestation of both D. longicolla and soybean aphid, where aphid counts were reduced by 47% when both pests were introduced together. Interactions among pests is relatively understudied, more studies will be needed in the future to determine if new management strategies are needed for soybean pest and disease complexes.
To address objective 4, in-furrow and seed treatment studies were established by all cooperators in the 2017 field season. Stem canker and pod and stem blight were both evaluated in these trials. Disease data are currently being analyzed. Also, yield data are still being recorded in many of the locations. However, results will be quantifiable in several of the sites. Additionally, quantitative PCR is being performed on some samples from these trials to quantify Diaporthe species in soybeans under various treatments. Results of this work will be delivered to farmers in the respective states during winter and spring extension meetings. Progress on objective 5 will be dependent on results from these field studies. Once yield data have been obtained we can begin to develop return on investment calculations that can be delivered for farmer use.