Efeito do extrato aquoso de cúrcuma (Curcuma longa L.) em Xanthomonas axonopodis pv. manihotis

Abstract

The cassava bacterial blight caused by Xanthomonas axonopodis pv. manihotis is the most importance disease of the culture and it is distributed in all the places where it is cultivated. Infected stems constitute themselves in the principal way of the bacterium dissemination to new cultivation areas. The chemical control of phytobacteria is difficult due to the products shortage, as well as, the existing ones are used exclusively in plantations of high economic value. By the other hand, the alternative control of the plants diseases is promising, with the discovery of many secondary compounds of medicinal plants that present antimicrobial activity. In this context, the turmeric (Curcuma longa - Zingiberaceae) native plant from the southeast of Asia, presents rhizomes that have compounds with an antimicrobial action that can be used in the control of bacterial diseases in plants. In this way, the objectives of this study were to evaluate the effect of using of aqueous extract of four turmeric genotypes in X. axonopodis pv. manihotis in vitro proceeding from Jaboticabal-SP, Mara Rosa-GO, Maringá-PR and Mercedes-PR, and verify the curative effect through the treatment of the infected stems of cassava with the pathogen and plantation in sterilized soil and in field conditions. In the experiment in vitro aqueous extracts from the four genotypes of curcuma were used in concentrations of 1, 5, 10, 15 and 20%, while in vivo only in the concentrations of 1 and 10% for the genotypes of Maringá and Mercedes. Distilled water and antibiotic (22.5 mg L-1 of oxytetracycline + 225 mg L-1 of streptomycin) were the negative and positive control treatments, respectively. The stems (12 cm long) were treated by partial immersion (1/2 of its length) during 72 hours (± 28ºC) in each solution. Three stems for treatment were used for the plantation in sterile soil with five repetitions and 36 in field with four repetitions. In the in vitro experiment the curcuma extract inhibited completely the bacterium growth in the concentration of 10% for the material proceeding from Mercedes, while for the Jaboticabal curcuma there was a total control at 15% and for Mara Rosa at 20%. Although the chemical treatment with antibiotic has reduced the population, it hasn't completely inhibited the bacterial growth in the used dosage. Though the curcuma proceeding from Maringá presents the control trend, it did not inhibited completely the growth in any of the experiment concentrations. But in the in vivo experiment, as well in sterilized soil as in field, the sproutings were extremely low, due to the stems infection degree. The curcuma raw extract at 10% proceeding from Mercedes, although presented in vitro effect against X. axonopodis pv. manihotis, behaved as harmful to the cassava in field condition, thus there was a stand reduction in relation to the control treatments. Possibly there was a direct toxic action on the plant physiology or susceptibility induction. But in the 1% concentration of the curcuma proceeding from Maringá, there was not statistical difference in relation to witnesses to the plants stand parameter. The used chemical control was not efficient, once it behaved the same as the water witness. In relation to the severity and productivity it was not observed significative differences among the treatments. The results indicate that, while presenting antibacterial activity to X. axonopodis pv. manihotis, the curcuma extracts, in the used concentrations, they do not present curative effects in cassava stems infected with the pathogen