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Influence of Soil Type on Severity of Straighthead in Rice

Straighthead is a physiological disorder of rice (Oryza sativa) that causes symptoms including deformed florets and panicles, floret sterility, and reduced grain yield. Naturally occurring straighthead is very erratic in its expression, hampering efforts to determine its cause and effect. A greenhouse experiment was conducted using soils from four rice fields with variable histories of straighthead occurrence. The experiment included incorporation of zero or 20 t ha–1 of wheat straw and used two rice varieties of varying tolerances to straighthead, Doongara (susceptible) and Jefferson (tolerant). Relationships between straighthead severity and soil and plant nutrients were investigated. There was a large difference between soils in the rate of soil redox potential decline after flooding, rice growth and yield, and the presence and severity of straighthead. Straighthead score was significantly correlated with decreased grain yield and increased floret sterility. The incorporation of 20 t ha–1 straw significantly reduced grain yield and increased floret sterility and straighthead scores in three of the four soils. Plant copper (Cu) and magnesium (Mg) were positively and iron (Fe) and molybdenum (Mo) negatively correlated with straighthead score. There were no consistent relationships among soil properties, plant nutrients at panicle initiation, and straighthead severity. The results indicate that no one soil mineral/nutrient is controlling the severity of straighthead but a combination of soil chemical factors may be involved. It is recommended that only straighthead-tolerant rice varieties be grown on soils that have a history of straighthead and the incorporation of stubble prior to rice growing should be avoided in these fields. Further research needs to be conducted into ranking Australian rice varieties on their tolerance to straighthead so farmers can choose the most suitable variety for their field.