The Role of LIME Application on Reducing Straighthead of RICE.

Straighthead is a physiological disorder of rice (Oryza sativa L.) causing floret sterility, upright panicles because of unfilled grains, distorted lemma and palea in to a parrot-beak shape and leading to reduce grain yield. Lime was used in this study, to investigate the influence of calcium on reducing naturally occurring straighthead and selecting resistant varieties and germplasm under field conditions. Forty-four varieties, including 27 inbred, 6 breeding lines, and 11 sterile were planted on a silt loam soil at University of Arkansas at Pine Bluff (UAPB) farm where the straighthead naturally occurred in the history. The experiment included three treatments in a randomized completely block design with three replications in each treatment. Grounded limestone (CaCO₃) was applied in the soil at a rate of 0 ton /acre, 2 tons/acre and 4 tons/acre in control, Ca-I and Ca-II treatments respectively. Straighthead severity was recorded at physiological maturity by using a 0-9 straighthead rating scale described by Yan et al., 2005.Random sampled rice panicles were harvested and seed set rates were determined and analyzed.  Results indicated that straighthead score for rice susceptible varieties has been significantly reduced with lime application, for example, straighthead score of Cocodrie, one of the most susceptible variety in Arkansas has been reduced from 8 to 3. But, resistant cultivars have not been affected by lime application. Similarly, Seed set rate for susceptible varieties has been drastically increased with lime application. This study demonstrates that Lime application might be a measure to overcome straighthead severity in rice and increase grain yield in the silt loam soil type.