Suppression of tungro with added dose of nitrogen

The seedlings and at different growth stages of tungro inoculated plants were topdressed with added dose of nitrogenous fertilizers from urea and ammonium sulfate at the rate of 46 kg N/ha at two and three weeks interval in screenhouse and field condition to determine the effect on disease severity and virus amount through ELISA test and on yield and yield components of rice. Added dose of nitrogen fertilizers regardless of the source, whether urea or ammonium sulfate significantly increased plant heights, number of tillers, leaf N content, panicle length, number of spikelets, percent filled grains, 1000-grain weights and grain yields of tungro-infected plants both in screenhouse and field condition. Grain yield increment was 169-263 percent in the field. The number of leaves and leaf area of tungro-plants were not greatly influenced by added N and maturity was prolonged for one to two weeks. Severity ratings in screenhouse reduced disease incidence by 53-65.5 percent at 55 DAT [days after transplanting] and 70.27-83.78 percent at 75 DAT. In the field, disease incidence was reduced by 52.85 percent-61.29 percent at 55 DAT and 46.19-65.23 percent at 75 DAT. Disease rating tended to be more severe in the field and at early growth stage than in screenhouse and at later growth stage. ELISA test in screenhouse reduce bacilliform virus by 29.44-66.66 percent and spherical virus by 65.96-85.5 percent while in the field reduction in bacilliform virus is 11.57-62.39 percent and 63.45-79.52 percent in spherical virus. There was greater reduction of spherical virus than bacilliform both in the screenhouse and field condition. In some samples, both strains tended to disappear in the screenhouse. IR60, initially found positive, was later found negative of the tungro viruses. Economic analysis on yield experiment gave a net return of P16,930.50-P27,792.90 with a benefit cost ratio of 1.46-1.83. Application of added dose of N regardless of the source whether urea or ammonium sulfate therefore can be used as emergency curative measure on tungro plants. Possible mechanism was discussed in the text