High genetic variability of herbivore-induced volatile emission within a broad range of maize inbred lines

Abstract

Maize plants (Zea mays) attacked by caterpillars release a mixture of odorous compounds that attract parasitic wasps, natural enemies of the herbivores. We assessed the genetic variability of these induced volatile emissions among 31 maize inbred lines representing a broad range of genetic diversity used by breeders in Europe and North America. Odors were collected from young plants that had been induced by injecting them with caterpillar regurgitant. Significant variation among lines was found for all 23 volatile compounds included in the analysis: the lines differed enormously in the total amount of volatiles emitted and showed highly variable odor profiles distinctive of each genotype. Principal component analysis performed on the relative quantities of particular compounds within the blend revealed clusters of highly correlated volatiles, which may share common metabolic pathways. European and American lines belonging to established heterotic groups were loosely separated from each other, with the most clear-cut difference in the typical release of (E)-beta-caryophyllene by European lines. There was no correlation between the distances among the lines based on their odor profiles and their respective genetic distances previously assessed by neutral RFLP markers. This most comprehensive study to date on intraspecific variation in induced odor emission by maize plants provides a further example of the remarkably high genetic diversity conserved within this important crop plant. A better understanding of the genetic control of induced odor emissions may help in the development of maize varieties particularly attractive to parasitoids and other biological control agents and perhaps more repellent for herbivores.

Figure 1.

Odor profiles of 31 maize inbred lines and of the hybrid Delprim. The amount of each compound is expressed in percent of the total emission, i.e. the sum of all 23 compounds.

Figure 2.

Factor loadings and factor scores representing the association among the 31 maize inbred lines as revealed by PCA on relative amounts of odors emitted (least square means obtained by ANCOVA; see Table II). The first three axes account for 26.6%, 18.4%, and 10.8% of the total variation, respectively.

Figure 3.

Comparison of genetic distances among the maize inbred lines based on RFLP markers (Rogers distances obtained from Dubreuil et al., 1996) and the corresponding Mahalanobis distances based on the odor profiles (least square means obtained by ANCOVA; see Table II).