A very promising isolate of Fusarium graminearum is being studied in the UNESP/Campus de Jaboticabal, where it was proven to be effective in the control of Egeria densa and E. najas, the submerged aquatic macrophytes. To study the effect of different concentrations of inoculum in disease severity, experiments have been conducted in Biochemical Oxigen Demand (BOD) incubators with concentrations varying from one-tenth, of 0.1 up to 1.4 g/l in rice colonized with F. graminearum mycelia. To verify the possible effect of the age of the plant on disease severity, plants with at least 35 cm of length, were excised in diverse segments corresponding to the age of growth. The treatments with concentrations of inoculum from 0.5 g/l had presented symptoms. All the treatments inoculated with fungi, in concentrations from 0.5 g/l, presented drastic reduction in the production of fresh biomass. All the segments used as plant-test (0-32 cm length) presented susceptibility to fungus. The top of the leaves of both the species at age 1 had the most severe disease symptoms at the sixth and eighth days after the corresponding inoculation. However, segments to ages 2 and age 3 presented the greatest reduction of fresh biomass at day eight, although symptoms were not severe as in age 1. With relation to the profit of fresh biomass, the control had always presented bigger growth over the respective inoculated treatments, however the corresponding segments to age 4 had presented minor profit of fresh biomass than the other ages.
