The aim of this study was to evaluate the effect of using silicon (Si) on the control and biochemical aspects of cotton resistance to ramulosis. Cotton plants of BRS Araçá and FM 993 were grown in nutrient solution containing (+Si) or not (-Si) silicon. We evaluated the incubation period (PI), the incidence (I), the area under the curve of index ramulosis (AACIR) and leaf concentration of Si (CESi). The CESi and PI increased by 76% and 19.5% in plants supplied with Si relative to the -Si and the AACIR decreased by 64% and 18%, respectively. The concentration of total soluble phenolics (CFST) and derivatives of lignin-thioglycolic acid (DLATG) in plants of both cultivars supplied with Si increased during the progress of ramulosis, but were lower as compared to plants that did not receive Si. In BRS Araçá supplied with Si, the activity of the enzymes chitinase (QUI) and glucanase (GLI) increased until 10 days after inoculation (dai) compared to - Si plants. The activity of peroxidase (POX) and polyphenol oxidase (PPO) in BRS Araçá supplied with Si increased between 20 and 30 dai with regard to plants -Si, while FM 993 supplied with Si presented increases in the activity of PPO and POX up to 10 dai. In FM 993 supplied with Si there was no increase in the activity of phenylalanine ammonia-lyase (FAL). The supply of Si to cotton plants increased resistance to ramulose by increasing the concentration CFST and DLATG in both cultivars, and the activities of POX, PPO, QUI and GLU in BRS Araçá, and POX and FAL in FM 993.
biochemistry; defense compounds; enzymes; Colletotrichum gossypii var. cephalosporioides; resistance
