Resistência de algodoeiro a murcha de fusário: métodos de obtenção de plântulas e inoculação ;avaliação de germoplasmas ; indução de resistência e caracterização da atividade enzimática

Abstract

The cotton has been in the human history for ages; it is used to the confection of clothes and its subproducts are an important source of protein to the domestic animals. Because of its wide distribution in the Brazil, the ocurrence of disease has become more frequently. Among the diseases, great importance is given to the fusarium wilt of cotton (Fusarium oxysporum f. sp. vasinfectum) because of its potential to cause severe losses and its hard control. The present work aimed to develop alternatives to be offered to the cotton producers. The first experiment refers to the evaluation of the planting methods of cotton and the reaction of 106 cultivars in relation to the vascular wilt of fusarium. Among the methods of planting, the plastic cups was chosen because in this method the roots of the seedlings can grow more vigorously. In the water restricion method there was no ocurrence of typical simptoms of the vascular wilt. The paper towel method resulted in anormal seedlings or the seedlings were contaminated with parasites. It was possible to determinated a group with a high level of resistance among the cultivars tested. In this group, its important to say that the cultivar SP 2473-A also exhibit resistance to the ramulosis. The second experiment is reffered to the resistance induction with the abiotic inducers (acibenzolar-S-metil, metil jasmonato e fosfato de potássio) in seedlings of the cotton cultivar ‘BRS Cedro’ and the evaluation of the enzymatic activity elicited (in samples of leaves and stem) in seedlings induced (once and twice) and seedlings without the induction, inoculatedand not inoculated with Fusarium oxysporum f. sp. vasinfectum. The infection index was also evaluated in this treatments. The treatment with methyl jasmonate (two inoculations) in the stem showed the minor infection index (45,00). It was possible to correlate this treatment with the minor infection index and the high level of the enzyme superoxide dismutase in the stem.