A Collision of Maize Stressors: Drought and Dalbulus maidis, Vector of Corn Stunt Disease

Abstract

Drought, insect pests, and diseases pose serious threats to maize production globally. Risks associated with drought are being addressed through the constant breeding of new drought-tolerant maize cultivars. However, under field conditions, multiple stressors co-exist. Therefore, to be fully prepared for the likelihood of insect stress coinciding with drought, it is crucial to understand the interaction between these stressors. This dissertation focused on investigating the potential outcome of Dalbulus maidis, the corn leafhopper, (vector of corn stunt spiroplasma, Maize bushy stunt phytoplasma, Maize rayado fino virus and Maize striate mosaic virus) converging with drought stress in drought-tolerant maize hybrids. Firstly, an assessment was done to measure the implications of D. maidis on morphological expressions of drought tolerance in maize. The results suggested that that combined drought and D. maidis stress may negatively impact the productivity of drought-tolerant maize. However, seedlings showed consistent drought-tolerant response strategies (reduced growth and complete recovery after periods of stress) with and without D. maidis infestations. Next, I assessed the performance and preference of D. maidis during drought in drought-tolerance maize. Overall, results led to the conclusion that drought in drought-tolerance maize led to an increase in D. maidis body size (mass) but had no effects on oviposition, survival nor nymph development. Additionally, D. maidis showed clear preferences for controlled (no-drought) seedlings compared to drought-stressed seedlings. To further tackle the growing threats caused by insect vectors, a literature review was conducted on biotic stress interactions using the corn stunt pathosystem (D.maidis, Zea mays, and Spiroplasma kunkelii) as a model for identifying the interactions that can be interrupted for control through RNA interference (RNAi). Subsequently, as a proof-of-concept, the functionality of RNAi was assessed in D. maidis and showed that specific genes’ expressions could be regulated to trigger mortality and phenotypic deformities. This dissertation highlighted the importance of testing combined stress impacts in the context of plant breeding; as well as presented a viable solution to tackle insect stress genetically.