Submitted to: Journal of Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/25/2011
Publication Date: 1/31/2011
Publication URL: hdl.handle.net/10113/50280
Citation: Piesik, D., Lemnczyk, G., Skoczek, A., Lamparski, R., Bocianowksi, J., Kotwica, K., Delaney, K.J. 2011. Fusarium infection in maize: Volatile induction of infected and neighboring uninfected plants has the potential to attract a pest cereal leaf beetle, Oulema melanopus. Journal of Plant Physiology. 168:1534-1542. Interpretive Summary: Fusarium spp. infection of maize (corn- Zea mays) leaves and/or roots through the soil can stimulate the emission of volatile organic compounds. These emitted compounds have been shown in other contexts to attract natural enemies of herbivores to an injured plant, attract herbivores to an injured plant, or induce greater levels of defense responses and/or volatile organic compound emission in nearby undamaged plants. Here, we sought to study how concentrations of emitted maize volatile organic compounds was influenced: by source of initial infection (via soil vs. directly on leaves), at different leaf post-infection durations (3 vs. 7 days), of levels uninjured plants at different distances (1 vs. 3 meters) from an infected plant, and whether the cereal leaf beetle (O. melanopus) males and females were attracted or repelled to 4 different doses of 4 individual volatile organic compounds in lab trials. Maize emitted higher levels of 14 compounds as degree of fungal infection increased (leaf 7d > leaf 3d > via soil infection > control plant), and higher levels in infected plants than uninfected plants that further decreased with distance from an infected plant (infected plant > uninfected plant 1m away > uninfected plant 3m away > control plant). The cereal leaf beetles were attracted to all four tested compounds induced by a fungal pathogen on maize at different ng concentrations, so beetles had different sensitivity to the 4 tested compounds. Our results indicate that maize infection by Fusarium influences volatile organic compound levels of the infected plant and nearby uninfected maize plants that could increase the attractiveness compound inducing plants to a cereal crop pest. Thus, as one enemy (fungal pathogen) influences uninjured plants and may attract herbivores to the plants; it would be interesting to examine whether natural enemies of herbivores are also attracted to these induced maize compounds. Our results highlight the complexity of studying interactions between injured and uninjured plants, plant pathogens, and herbivores; future studies could reveal that this picture is even more complicated if enemies of herbivores are attracted to induced compounds in this crop system involving maize, fungal pathogens, and an beetle pest of cereals.
Technical Abstract: Fusarium infection of maize leaves and/or roots through the soil can stimulate the emission of volatile organic compounds (VOCs). It is also well known that VOC emission from maize plants can repel or attract pests. In our experiments, we studied VOC induction responses of Zea mays L. ssp. mays cv. ‘Prosna’ having Fusarium infection (mix of four species) in leaves or roots, then tested for VOC induction of uninfected neighboring plants, and finally examined wind-tunnel behavioral responses of the adult cereal leaf beetle, Oulema melanopus L. (Chrysomelidae: Coleoptera) behavior to four induced VOCs. In the first part of our experiment, we confirmed that several green leaf volatiles (GLVs; (Z)-3-hexenal, (E)-2-hexenal, (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, (Z)-3-hexen-1-yl acetate, 1-hexyl acetate), terpenes (ß-pinene, ß-myrcene, Z-ocimene, linalool, ß-caryophyllene), and shikimic acid pathway derivatives (benzyl acetate, methyl salicylate, indole) were positively induced from maize plants infected by Fusarium spp. The quantities of induced VOCs were higher at 7d than 3d post-infection and greater when plants were infected with Fusarium on leaves rather than through soil. In the second part of our experiment, uninfected maize plants also had significantly positive induction of several VOCs when neighboring an infected plant where the degree of induction was negatively related to the distance from the infected plant. In the third part of our experiment, a Y-tube bioassay was used to evaluate upwind orientation of adult cereal leaf beetles to four individual VOCs. Female and male O. melanopus were significantly attracted to the GLVs (Z)-3-hexenal and (Z)-3-hexenyl acetate, and the terpenes linalool and ß-caryophyllene. Our results indicate that a pathogen can induce several VOCs in maize plants that also induce VOCs in neighboring uninfected plants, though VOC induction could increase the range at which an insect pest species is attracted to VOC inducing plants.