Title : Synergism of the false root-knot nematode Nacobbus aberrans and Phytophthora capsici manifested by alteration of phenylpropanoid metabolism in Capsicum annuum
Abstract:
The significant role of plant parasitic nematodes in the development of diseases caused by soilborne pathogens has been demonstrated in many cultivated crops throughout the world. In most cases, such interactions involve root-knot nematodes like Meloidogyne spp. and the false root-knot nematode Nacobbus aberrans. Our research group has been using with the interactions among Nacobbus aberrans and pepper (Capsicum annuum L) CM334 resistant to Phytophthora capsici Leoninan, to determine what biochemical and molecular changes are induced by the nematode, which in turn could affecting the host resistence. Resistance in the genotype of chilli pepper CM334 against the three major species of root-knot nematodes and the oomycete Phytophthora capsici has been associated with the phenylpropanoid pathway of secondary metabolism. Therefore, L-phenylalanine ammonia-lyase (PAL) activity and the content of total soluble phenols (TSP) were determined in CM334 plants inoculated with N. aberrans, P. capsici or both pathogens. Besides, the phenylpropanoid profile was analyzed by HPLC-ESI/MS and the in vitro effect of phenylpropanoid compounds on second-stage juveniles (J2s) of N. aberrans and Meloidogyne incognita was also tested. The highest values of PAL activity and content of TSP were registered in plants inoculated only with P. capsici, while those plants inoculated with N. aberrans alone or in combination with P. capsici showed the lowest level (P<0.05). Phenolic acids (p-HBA, gallic, caffeic, syringic, sinapic, ferulic, vanillic, p-coumaric and chlorogenic) and flavonoids (rutin, apigenin and luteolin) were found CM334 plants. Chlorogenic acid and luteolin were the phenylpropanoid compounds in highest quantity in CM334. Concentration of p-hidroxy benzoic and chlorogenic acids and flavonoids was lower in plants inoculated with N. aberrans than in the control (P<0.05) at any sampling date. On the other hand, the flavonoid rutin has a differential particular toxic effect in each of nematodes used in this work. This flavonoid had a nematocidal effect as shown in the experiment carried out on with J2s of N. aberrans, whereas it only had a nemastatic effect on J2s of M. incognita. These results indicate that N. aberrans alters the phenylpropanoid metabolism during the infection of chilli pepper, possibly to create a favorable environment that allowed it to complete their life cycle.
