Results
The analysis of variance for larval weight evolution during 26 days
showed that all sources of variation [random (first-order
autoregressive covariance structure of within-subject correlation among
weights recorded on the same lava; σ2 = 0.7539 ±
0.0163) and fixed effects] were significant (p <
0.05) except treatments, but the interaction treatment x genotype was
significant suggesting that maize genotypes would differentially respond
to feeding treatments. At the end of the bioassay, larvae reared on
stems from control susceptible inbred plants weighed less than larvae
fed on the resistant ones (Fig. 1). Resistant plants pre-conditioned by
48 hours of feeding by MCB larvae decreased significantly larval weight
compared to its control, while average weight of larvae fed with
susceptible plants pre-conditioned by 48 hours feeding did not differ
from its corresponding control larval weight (Fig. 1 and 2). On the
other hand, susceptible plants exposed to feeding by larvae for a longer
period (nine days) had opposite effects on larval weight to resistant
plants and long-term attack to the resistant genotype caused stronger
effect on the weight of larvae than short-term attack. In addition,
induced responses by long-term attack made that the mortality of larvae
fed on the resistant plants significantly higher than that of larvae fed
on the susceptible ones although no differences for mortality between
both inbreds were detected at control conditions (Table 1).
Attending to the metabolomics approach, 4362 different features were
detected among the different samples (Supplementary table S1). 194 and
192 ions were selected as important features (based on VIP-score values
of the PLS-DA analysis) in the short and long-term responses,
respectively, of the susceptible inbred line; 108 of them being
important in both responses (Fig. 3). On the other hand, 101 ions out of
the 188 and 227 detected as relevant in the short and long-term
responses of the resistant inbred, respectively, were common in both
responses. Although 194 and 188 ions had important contributions to the
48h responses to S. nonagrioides in the susceptible and resistant
inbreds, respectively, only 57 of them contributed to both responses.
Ninety ions were selected as important features based on VIP-score
values of the PLS-DA analysis for the responses to 9-day stem borer
attack in both inbreds. Finally, 30 ions were involved in the four
responses. Identification and characterization of the metabolites from
which the ions detected could be derived have been done with the ions
with relevant effects on the long term response, either detected across
genotypes or genotype-specific (Table S2).