Uso do silício na micropropagação visando o manejo da murcha-de-fusário e do moko da bananeira

Abstract

This study evaluated the use of silicon (Si) in micropropagation of banana 'Silk' and 'Pacovan Ken' aiming to reduce the severity of fusarium wilt caused by Fusarium oxysporum f. sp. cubense and moko disease caused by Ralstonia solanacearum race 2. The banana plantlets were produced in vitro by adding calcium silicate and potassium silicate (0, 0.25, 0.5, 0.75 and 1 g L-1) to MS medium in the phases of multiplication and rooting. After in vitro culture, the plants were transferred to plastic tubes containing substrate plus the same sources of Si, and maintained in a greenhouse for 45 days, when they were inoculated with the pathogens. With respect to fusarium wilt in cultivars Silk and Pacovan Ken, the elevation of Si increased the incubation period (IP) and reduced the disease index (DI) and area under the disease progress curve (AUDPC). In cultivar Silk but not in Pacovan Ken calcium silicate was significantly more effective than potassium silicate. In shoots and roots of both cultivars in both sources, before and after acclimatization Si concentration was greater at a dose of 1.0 g L-1 compared to the control without Si. Before acclimatization, calcium silicate provided higher Si concentration in the shoots than potassium silicate. The opposite happened with the Si concentration in the roots. After acclimatization, there was no difference between the calcium silicate and potassium silicate, for both cultivars. In general, for both cultivars and sources of Si there were positive correlations with the concentration of Si and IP, and negative correlations with DI and AUDPC. Before and after acclimatization, the anatomical variable of roots: thickness of the root epidermis, cortex, endodermis and central cylinder of banana 'Silk' and 'Ken Pacovan' were influenced by Si sources. Calcium silicate was more efficient in increasing the thickness of the root epidermis, cortex and central cylinder, while potassium silicate was more efficient in thickening of the endodermis. In general, there were positive correlations among anatomical variable of roots with PI and negative correlations with DI and AUDPC, except for potassium silicate in cultivar Silk. The research conducted with moko disease showed that increase of Si in Silk and Pacovan Ken cultivars caused increase in IP and decreases the DI and AUDPC. At the dosage of 1.0 g L-1 AUCPD was reduced by 27.3%. In cultivar Silk, calcium silicate was more effective than potassium silicate (P≤0.05), while in „Pacovan Ken‟ there was no difference. In both cultivars, plants treated with Si showed, in general, concentrations of chlorophylls a, b and total higher than plants Si- up to six days after inoculation, which may have influenced the disease IP. In general, both the enzymes related to oxidative stress (CAT, SOD and APX), as the plant defense (POX, PPO, CHI and GLU), had increased its activities in plants treated with Si, especially those with calcium silicate, indicating a possible role in reducing the severity of the disease. The supply of Si in micropropagation of banana 'Silk' and 'Pacovan Ken' promoted reduction of Fusarium wilt and moko disease, and therefore can be used as a new technology in the management of these diseases.