Diaporthe, Soybean Cyst Nematode, and Soybean Aphid: An Evaluation of Potential Interactions Occurring Among Pests on Soybean in South Dakota

<p>Soybean <em>Glycine max</em> (L.) Merr., is an important crop grown in South Dakota, with an estimated production of $2.33 billion in 2015. However, soybean production in South Dakota is compromised by four pests, the fungal pathogens <em>Diaporthe longicolla</em> (Hobbs) Santos, Vrandecic, and Phillips and <em>Diaporthe caulivora</em> (Athow and Caldwell) Santos, Vrandecic, and Phillips, the soybean cyst nematode <em>Heterodera glycines</em> Ichinohe (SCN), and the soybean aphid, <em>Aphis glycines</em> Matsumura (Hemiptera: Aphididae). Additionally, these pest can co-occur in fields within South Dakota and the implications associated with interactions among these pests are unknown. We hypothesized that both <em>Diaporthe</em> species would interact with <em>H. glycines</em>, and that<em> D. longicolla</em> would not interact with<em> A. glycines</em>. To test our hypotheses, both studies were set up as a completely randomized design in the greenhouse. For the <em>Diaporthe</em>-SCN interaction, five treatments were designed <em>(Diaporthe</em> alone, SCN alone, co-inoculation of SCN and <em>Diaporthe</em>, and <em>Diaporthe</em> inoculated either 15 days before or after SCN). For the <em>D. longicolla</em>- A. glycines interaction, eight treatments were designed that consisted of two infestation times (Inducer: V1; response: seven days later). Plants were infested with either five <em>A. glycines</em>, 2000 eggs of SCN, and a four mm plug infested with<em> Diaporthe</em> depending on the treatment and experiment. We assessed stem length, lesion length, and SCN reproduction for the <em>Diaporthe</em>-SCN interaction and lesion length and aphid counts for the D. longicolla- A. glycines interaction. Our results showed that SCN reproduction was reduced by 90% when either fungus preceded SCN. Additionally, when SCN preceded <em>D. longicolla</em>, we see an increase in lesion length of 76% or greater on soybean stem. When SCN preceded <em>D. caulivora</em> for experiment one, we see a decrease in lesion length of 35%. Additionally, <em>D. longicolla</em> and<em> A. glycines</em> did not interact on soybean. However, we observed a potential compensatory effect from soybean plants in the concomitant infestation of both <em>D. longicolla</em> and <em>A. glycines</em>, where aphid counts were reduced by 47% when both pests were introduced together. Interactions among pests is relatively understudied, such studies may lead to new management strategies for soybean pest and disease complexes.</p>

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Thesis - Open Access

Discipline thesis:degree_discipline

Agronomy, Horticulture, and Plant Science

Year dc:date.available

2017

Author dc:creator

• Posch, John Philip

Contributors dc:contributor

• Febina Mathew
• Adam Varenhorst

• Plant Sciences

Licence

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language

en

Repository record dc:identifier

https://openprairie.sdstate.edu/etd/1190

OAI identifier oai:identifier

oai:openprairie.sdstate.edu:etd-2184