Fortificación de la pared celular del maíz (Zea mays, L.) como respuesta inducida al ataque del taladro mediterráneo (Sesamia nonagrioides, Lef.)

Sesamia nonagrioides Lefebvre is the main pest of maize (Zea mays L.) in the Mediterranean area causing significant yield losses. However, several mechanisms of resistance to stem borers have been described in the literature as the structure and composition of the cell wall (CW), the most outstanding are those related to the bonds between cell wall polymers by ester bridge links of diferulic acids (DFA), which can act as defense mechanisms. Thus a high concentration of DFA could be used as an indirect method for improving resistance to corn borer. A divergent selection program was carried out for varying the concentration of total esterified DFA to CW in the stalk pith (main feeding tissue of corn borer larvae) developing three cycles of selection for high and low concentrations of totals DFA (AC3 and BC3 respectively). We already know that we can vary the concentration of totals DFAs by selection and that high concentrations of totals DFAs produce greater resistance to stalk corn borer. Moreover there is previous evidence that the inbred line PB130 drives up totals DFA in the stalk a response to the S. nonagriodes attacks. The F2 resulting by crossing PB130 and CO125 was chosen as starting material of selection program. However, in order to be able to use the totals DFA concentration as an indirect criterion of selection to improve resistance to Sesamia nonagrioides is necessary 1) to study the existence of induced response in the pith of the starting material of selection, 2) to check what has occurred with the induced response after the selection program. For this, we have carried out an evaluation of the lines and third cycles of selection in the greenhouse and the F2 was evaluated in the field, In both cases the plants were evaluated in protected conditions and under artificial infestation with eggs of S. nonagrioides. The damages caused by the larvae have been estimated and analysis of concentrations of totals DFA estherified to the pith of CW were carried out by HPLC, for both treatments: infested with S. nonagrioides and not infested. Analysis of variance for the lines, the F2 and the cycles were performed corresponding to a completely randomized design and means were compared using the least significant difference protected by Fisher (LSD), we used the GLM procedure of SAS, and we have studied the distribution (median, kurt The attack of the larvae of S. nonagrioides on maize genotype has resulted in an overall response wich is a decrease of p-cumaric acid, and specific responses were observed after long-term in increasing of ferulic acid and totals DFA for some inbred line as PB130. In the F2 the increase of totals DFA as an induced response to the S. nonagrioides attacks occurs only when concentrations of totals DFA are low. The induced response following the S. nonagrioides attacks has been lost with the selection, for at least not present in the third cycle. The process of incorporation of hydroxycinnamic acids on the cell wall has been altered after the attack, which can result in its turn into effects on lignification witch will be evaluated in futures studies. The selection program has been effective in increasing and decreasing the levels of totals DFA after three cycles of divergent selection and the induced response seems not to be preserved, therefore if we want the plant shows high DFA only when the attack occurs, in such way that the plant invests the least in its defence, one might select for high induced totals DFA. For that each genotype should be evaluated under infestation with S. nonagrioides (it manifest the constitutive and induced totals DFA) and in protected conditions (constitutive totals DFA).We would select those individuals wich have higher concentrations of induced totals DFA (Induced totals DFA = Total DFA - Constitutive totals DFA). On the other hand if we intend to increase or decrease the constitutive totals DFA, the selection should be carried out under protected conditions. Finally if we are interested in high concentrations of DFAT regardless if they occur in a constitutive or induced way the selection under conditions of infestation seems to be most adequate. osis, quartiles, skewness) of the lines, the F2 and cycles for both treatments using the SAS univariate procedure and compared the distributions of both treatments using the SAS NPAR1WAY procedure.