LB 1-3 - CANCELLED - Maize intercropping provides associational resistance to herbivores and pathogens

Background/Question/Methods:

Agricultural practices – such as intercropping – provide a more sustainable and diversified alternative to conventional monoculture systems. While intercropping practices have been widely adopted across temperate and tropical biomes, the mechanisms by which they provide ecosystem services remain unknown. The phenomenon where two spatially close plants decrease their susceptibility to herbivore or pathogen attack is known as “associational resistance. The goal of the of this research is to better understand how maize neighborhood to four different intercrop plants modulate resistance to antagonists, thus providing associational resistance. In a glasshouse environment maize plants were grown in diversified systems or monoculture systems. We conducted bioassays to quantify plant resistance to the generalist herbivore Spodoptera frugiperda and measured the leaf area consumed and herbivore weight gained. Choice essays were conducted to measure herbivore feeding preference. To investigate the susceptibility to pathogens, focal maize plants were inoculated with Glomerella graminicola, which causes Anthracnose Leaf Blight. Leave lesions where quantified as a measure of resistance in focal maize plants. Lastly, we sampled across maize leaf tissue, root tissue, and the collected volatile organic compounds to explore the role of plant secondary metabolism in mediating resistance.

Results/Conclusions:

Leaf area consumed decreased in diversified treatments compared to monoculture control. Maize intercropped with Alfalfa had the largest reduction of defoliation by almost 50% percent. While intercropping with Bean decreased 19%, Desmodium decreased 33%, and Red Clover decreased 5%. Herbivores gained on average 0.5 micrograms less weight when feeding on diversified mixtures compared to controls, except when intercropped with Red Clover which increased herbivore performance by 1.44 micrograms. When provided with feeding choice, herbivores preferred feeding on intercropped plants more often than control plants. Especially, herbivores were seven times more likely to choose maize plants that had been intercropped with Red Clover and Bean. In comparison, herbivores were eight times more likely to choose monoculture maize rather than intercropped with Alfalfa. A lower number of lesions were observed in maize intercropped plants, but the reduction was not significant compared to control plants. Intercropped Maize plants induced higher numbers of defensive compounds. Lastly, we propose intercropping as a method of manipulated associational resistance and identify this phenomenon as an important emergent property of diversified cropping systems.