Controle de mofo-cinzento (Amphobotrys ricini) da mamoneira (Ricinus communis L.) por métodos químico, biológico e com óleos essenciais

Abstract

The castor bean (Ricinus communis L.) is a tropical oily species, and the oil extracted of its seeds is one of most versatile of the nature, with many industrial applications. Even being a rustic species, it still subjects to several diseases, between them the gray mold, caused by the fungus Amphobotrys ricini. The genetic breeding would be the best alternative for the disease control, but spend time to get a resistant cultivar. In this way, the use of methods of control based on chemical, alternative or biological methods shows viable in short time. The aim of this work was to study the efficiency of the control of gray mold, on castor bean crop, using chemical, alternative and biological methods. Therefore, they had been verified, in vitro, the efficiency of different culture medium in the pathogen sporulation and the antagonist C. rosea. The sclerotia production in the culture medium can be also verified. About the efficiency of the methods, in vitro, the inhibition of the mycelial growth and germination of conidia was verified. After to develop and to validate a diagrammatic scale of evaluation of severity of the disease in racemes of castor bean, the efficiency of application of the antagonist C. rosea in inoculated fruits detached of castor bean with the pathogen was verified. In plants submitted to greenhouse and field conditions, the efficiency of the methods in the control of the disease caused by A. ricini was verified About the sporulation, the optimum culture medium for the pathogen was V8-20%, getting 5,7 x 10 6 conidia/mL. For the antagonist C. rosea, the optimum culture medium was TJ-5% (Tomato juice), producing 4.41 x 10 6 conidia/mL. The only one culture medium that propitiated abundant sclerotia production of A. ricini was oats-agar. About the inhibition of the mycelial growth of the pathogen, the best treatments with essential oils were that based on C. martini e C. zeylanicum in the five tested concentrations. In both oils, the average diameter of the colonies was 0,7 cm against the average of 4,79 cm of check treatment. With the fungicides, in the four tested concentrations, most efficient active ingredients were methylic tiofanato , carbendazim, tebuconazole and iprodione. The ED 50 of these fungicides were < 1uL/L, certifying 100% of inhibition of the mycelial growth in all concentrations. About the inhibition of the conidia germination of A. ricini, the fungicides tebuconazole and clorotalonil were best in all the tested concentrations, being the average of the conidia germinated of these fungicides were 0,0 and 0,15%, respectively, against 100% of the check treatment. Already the best essential oils were that based on C. martini e C. zeylanicum in all the tested concentrations, being the average of the conidia germinated of both oils of 0,00% against 100% of the check treatment. The developed diagrammatic scale was validated, therefore the visual estimates of severity (R 2 ) between the appraisers with aid of the scale were of 92 to 97%, with average of 94%, against the average of 80% without the use of the scale. The best application of the antagonist C. rosea in fruits detached of castor bean, of AL-Guarany cultivar and the hybrid Lyra, independently having or not wounds, was in preventive way. As much in the greenhouse applications as at field, the treatment with the fungicide iprodione was optimum on the disease control when compared with biological and alternative treatments. In greenhouse, the average percentage of the sick leaves in the treatment with iprodione was of 0,0% against 50,47% of the inoculated check treatment. In field conditions, the average severity of the disease in the treatment with iprodione was 15,76% against 95,81% of the inoculated check treatment.