Soil and Plant Minerals Affected By Natural and Induced Straighthead in Susceptible and Resistant Rice Varieties.

Soil and Plant Minerals Affected by Natural and Induced Straighthead in Susceptible and Resistant Rice Varieties. S. Tiwari Pokhrel, B. Huang, Y. Li and S. Ntamatungiro*, Department of Agriculture, University of Arkansas at Pine Bluff Straighthead is a physiological disorder in rice which causes grain sterility and due to unfilled grains rice panicles remain upright. Rice yield can be totally lost when a highly susceptible variety is planted. The straighthead-like symptoms can occur naturally in some soils and frequently occur when susceptible rice varieties are grown on soils with a history of use of monosodium methanearsonate (MSMA), which is an arsenic containing herbicides. A rice field located at UAPB Farm where straighthead occurred naturally and a rice field at the National Research Center near Stuttgart where straighthead is induced by applying 6.7 kg MSMA/A were used to study soil, water and plant factors attributable to straighthead. Straighthead susceptible and resistant rice varieties were planted in a randomized complete block design with four replications at each location. Soil, plant and water samples were collected at different rice growth stages. Plant height, straighthead rating and rice panicles were taken at physiological maturity. Rice varieties did not show straighthead symptoms in 2014 at the natural site contrary to the previous four years. Straighhead was severe in susceptible varieties at the site where straighthead was induced by application of MSMA. Analysis of plant samples showed high arsenic (As) concentrations in susceptible rice varieties and high calcium (Ca) concentrations in roots and above-ground plant parts of resistant rice varieties. Analysis of irrigation water and soil before flooding revealed that the concentrations of all the tested elements were neither high enough to cause toxicity or deficiency for the rice plants. These findings are in agreement with previous reports of the erratic occurrence of straighthead in natural conditions. The results will be important in our understanding of the differences in straighthead occurence in natural and induced conditions and in developing straighthead resistant varieties on the UAPB natural site.