Resistência de caupi a Fusarium oxysporum f. sp. tracheiphilum: avaliação de germoplasmas, indução de resistência, caracterização de mecanismos bioquímicos, estruturais e análise da capacidade funcional do xilema

Abstract

Cowpea Vigna unguiculata (L.) Walp. is a high economic outcome crop, mainly in North and Northeast regions of Brazil. One of limiting factors of crop is, the occurrence of diseases like Fusarium wilt, caused by Fusarium oxysporum f. sp. tracheiphilum (E.F. Smith) Snyder& Hansen, which demandsthe use of resistant cultivars as the main measure of control. The resistance of 30 cowpea germ plasms of to the ISO-PE isolate F. oxysporum f. sp. tracheiphilum, the effect of the inoculation methods deeping and root cutting on the cultivar BR-17 Gurguéia, and the resistance heritage in a F² population, composed of 386 individuals resulted from L-288004 andBR-17 Gurguéia cross were evaluated. Seven days old plants were inoculated with a conidia suspension, adjusted to concentration of 1 x 10⁶ conidia.mL-¹ in a side of the root system, after wound had been made on the plants. For the deeping method, plants cultivated in vermiculite, were removed and the roots immersed in aconidia suspension for five minutes, then they were planted in a pot containing esterilized soil. Assessment was carried out 25 days after germination, based on grade scale, disease intensity and severity. More over, the effect of the inducers ESM,BABA and Chitosan was verified on IPA-206 and BR-17 Gurguéia, which were applied to the soil five days after germination and inoculated with a 1 x 10⁶ conidia.mL-¹ suspension of ISO-PE isolate, and evaluated through severity and disease control, 25 days after germination, by the grade scaleand disease intensity. In adition, the effect of these inducers was compared through ẞ-1,3-glucanase peroxidase and phenilalanina ammonium liase enzime activity, at five and 10 days after inoculation of the pathogen. By tissue analysis from root cuttings of BR-17 Gurgueia and IPA-206, induced and inoculated with the pathogen, following the methodology above,it was observed the effect of these inducers on lignification of the xylem as resistance structural mechanism and capacity of water conduction by the plant xylem,assessedat 17 and25 daysafter germination.Halfofthe30 evaluated germ plasms showed resistance to the pathogen, mainly L-288004 and L-190004 lines. Inoculation methods, deeping and wounds on roots, led to the same symptoms, although deeping method provided sooner symptoms. In the analysis of resistance heritage et was found frequency of 13 resistant to 3 susceptible plants, what pointed out a segregation of two independent genes,a recessive and a dominante one. Among the inducers, ESM provided 68,90%and 71,59% disease control for BR-17 Gurguéia and IPA-106, respectively. The enzyme activity, ESM revealed better results for ẞ-1,3-glucanase, peroxidase and PAL on IPA-206 cultivar, at five and 10 days.BABA and chitosan differed from the control, for the PAL and ẞ-1,3-glucanase, respectively, on IPA-206. For the structural aspect, chitosan provided deposition of lignin inside xylem of both cultivars, at 17 and 25 days after germination. ESM applied to BR-17 Gurguéia induced higher water conduction when compared to the control, suggesting that the inducer did not interfer onmetabolism ofthe induced plants.