Effect of alcoholic extract of guaco (Mikania glomerata) on the control of dark rot (Xanthomonas campestris pv. campestris) in cauliflower/ Avaliação da eficácia da tintura etanólica de guaco (Mikania glomerata) no controle da podridão negra (Xanthomonas campestris pv. campestris) em couve-flor

With the use of irrigation and new hybrids of cauliflower, it is possible to get production during all the year with hight yield. However, the crop has been affected by diseases, as the dark rot caused by X. campestris pv. campestris. The objective of this research work was to study the potential of Mikania glomerata for the control of this disease. Alcoholic extract 50 ºGL of M. glomerata was evaluated regarding to: in vitro antimicrobial activity through bacterial growth in 100, 250, 500 and 1000 mg L-1 of the alcoholic extract; induction of local or systemic resistance in 25 days old cauliflower, with spray of alcoholic extract concomitantly and three days before the inoculation with the pathogen (water and bordeau mixture were used as control); peroxidases activity in leaves of cauliflower treated and not treated, and harvested concomitantly, 24, 48 and 72 hours after spraying the alcoholic extract and also after inoculation. The alcoholic extract of M. glomerata showed inhibition of the bacterial growth in vitro at the concentrations of 250, 500 and 1000 mg L-1. The concentrations of 500 mg L-1 and 1000 mg L-1 inhibited 24% and 38% of the bacterial growth. This inhibition could be due to antibacterial compounds in the alcoholic extract. An inhibition of the disease in vivo occurred only in the leaves treated with 100 and 500 mg L-1 of alcoholic extract when applied concomitantly with the bacteria. This result was similar to bordeau mixture, indicating a control by direct antimicrobial activity. There was no systemic resistence induction for all treatments. The peroxidases induction was due to infectious pathogen process and not to the treatments with alcoholic extract. The results indicate the potential of M. glomerata alcoholic extract for the preventive control of cauliflower dark rot disease.Com a prática da irrigação e novos híbridos de couve-flor, é possível produzir durante todo o ano e com alta produtividade. Mas, a cultura tem sido afetada por doenças a exemplo da podridão negra causada por Xanthomonas campestris pv. campestris, fomentando novas pesquisas para seu controle. Com o objetivo de verificar o potencial de Mikania glomerata no controle dessa doença, a tintura etanólica 50 oGL dessa planta medicinal foi avaliada quanto: atividade ntimicrobiana in vitro através do crescimento bacteriano em tubos de ensaio contendo 100, 250, 500 e 1000 mg L-1 da tintura; indução de resistência local ou sistêmica em plantas de couve-flor aos 25 dias de i