The importance of light on the application of resistance inductor in barley against Bipolaris sorokiniana ; Importância da luz na aplicação de indutor de resistência em plantas de cevada contra Bipolaris sorokiniana

Barley (Hordeum vulgare) has been used not only as food, but in the production of malt for the brewing industry. The most common disease that attacks the plants is the blight caused by Bipolaris sorokiniana with heavy losses for farmers. Fungicides have been used to control the disease although they damage the environment and human health. One of the suggested methods is the employment of resistance inducers to eliminate these drawbacks. Xanthan gum has proved to be a resistance inducer in plants such as wheat, barley and coffee shrubs. Current analysis evaluates the effect of different light wavelengths on barley plants, since total light is not always reflected on plants in the field, beside the occurrence of cloudy days. Fungus conidia were sprayed on groups of plants; another group was treated with xanthan gum and fungus conidia; yet another group was made up only of healthy plants. The percentage of protection was evaluated after 4 days and leaves underwent extraction and analysis for proteins, phenols and chlorophyll. Results demonstrated protection varying from 93 to 99.5%, with increased protein and decrease of phenols in plants treated with GX-conidia. Results revealed a 93 to 99.5% protection, coupled to an increase of protein and a decrease of phenols in GX-conidia-treated plants. When induced protection and total chlorophyll were correlated, xanthan gum demonstrated activity in all light wavelengths. Xanthan gum has an induction activity in any light wavelength. ; A cevada (Hordeum vulgare) tem sido utilizada como alimentos e na produção de malte para indústria cervejeira. A doença mais comum que ataca as plantas no campo tem sido a mancha foliar causada por Bipolaris sorokiniana, causando prejuízos ao agricultor. Para o controle destas doenças, o mais utilizado é o tratamento com fungicidas, podendo provocar riscos para o meio ambiente e para a saúde do homem. Visando eliminar estes inconvenientes, um dos métodos preconizados é o da utilização de indutores de resistência. A goma xantana foi ...