Intensidade do mofo-cinzento (Amphobotrys ricini (Buchw.) Hernnebert) em linhagens de mamoneira (Ricinus communis L.) cultivadas no estado de Alagoas e influência da adubação fosfatada na intensidade da doença nas cultivares Nordestina e Paraguaçu

Abstract

The castor bean (Ricinus communis) execute important social paper in the Brazilian Northeast, whose main extracted product of your seeds is an oil of excellent quality and of several industrial application, included as biodiesel. The main cultivars used in the area Northeast are the Nortdestina and Paraguaçu, being the performance of these you cultivars dependent of factors as the availability of mineral elements and the occurrence of diseases. Among the diseases that contribute to the low yield of this culture highlight the gray-mold (Amphobotrys ricini), that causes the deterioration of the blossoms, fruits and seeds, reducing thus the oil production. The control of this disease is based essentially on preventive measures, being the use of resistant cultivars associated to a balanced mineral nutrition the tactics more effective and desirable of management. This work had as objectives evaluate the intensity of the gray-mold in castor bean lines cultivated in experimental area and the influence of the fertilization phosphated in the intensity of the gray-mold in the cultivars of castor bean Nordestina and Paraguaçu. The 20 castor bean lines were cultivated in two experimental area, being 10 cultivars in each area. Design used was randomized blocks, with 10 treatments and five replications, where in all the plants of the experimental plots, the total number of bunches and the number of bunches with disease of the symptoms were quantified. The influence of the fertilization phosphated in the development of the gray-mold was led in an experimental area, using the randomized blocks design, with four repetitions, being the treatments formed by five phosphorous doses (0, 20, 20, 60 and 80 kg/ha) and two cultivars of castor bean (Nordestina and Paraguaçu). Evaluations of the gray-mold incidence were realized (INCID), percentage of diseases bunches (POCAD) and percentage of diseases fruits in the main bunch (POFRUD) were accomplished in all the useful plants of the experimental plot. The data of INCID, POCAD and POFRUD were submitted to analysis of lines and no-lines regression. The fertilization phosphated influenced significantly (P0,05) in the disease intensity in the two cultivars of assessed castor bean and that effect varied according to with cultivar assessed. The models y = a+bx2+cx2,5+dx3 and lny = (a+cx)/(1+bx+dx2) provided good fittings the curves for the data of INCID and POCAD (R2 from 0,95 to 0,99) and POFRUD (R2 of 0,99 and 0,96). In agreement with the parameter a of the models for group of assessed variables, the disease of the intensity was smaller in Paraguaçu. The maximum phosphoforus doses determined to obtain the low disease of intensity considering the variable POFRUD, were of 68,48 and 64,39 kg/ha for the cultivars Nordestina and Paraguaçu, respectively. The lines cultivated in Rio Largo presented smaller disease of the intensity that those cultivated in Igaci, standing out as promising resistance sources the lines CSRN 393 and CNPAM 219, respectively. However, there is the need of more detailed studies to confirm the genetic potential of those lines as resistance sources to A. ricini.