Effect of Zinc on the Development of Brown Spot in Rice

Brown spot, caused by the fungus B ipolaris oryzae , is one of the most destructive diseases of rice. This study investigated the effect of zinc rates on the development of brown spot in rice. Rice plants (cv. ‘ M etica‐1′) were grown in hydroponic culture amended with Zn rates (applied as Z n SO 4 . 7 H 2 O ) of 0, 0.5, 1, 2 and 4  μ m and inoculated with B . oryzae . The foliar concentration of Z n was determined. Leaf samples were assessed for disease severity, and then, area under brown spot progress curve ( AUBSPC ) was calculated. The relationship between Z n concentrations on leaf tissues and the rates of this micronutrient was best described by a positive linear regression model, while the relationship between the Z n rates and the AUBSPC was best described with a positive quadratic regression model. The correlation between Z n concentrations on leaf tissues and AUBSPC was positive and significant ( r  = 0.68, P < 0.05). The results from this study showed that high foliar concentration of Z n was associated with increasing rice susceptibility to brown spot.