Distribution of arsenic and other minerals in rice plants affected by natural straighthead
Because of the inconsistency and unpredictability of naturally occurring straighthead, arsenical herbicides are sometimes used to induce straighthead-like symptoms to study this sterility disorder. In 2005, an outbreak of naturally occurring (nonchemically induced) straighthead in rice (Oryza sativa L.) study fields in Stuttgart, AR provided an opportunity to examine the role of minerals in this generally unpredictable disorder. The outbreak affected areas of yield and N rate tests thus permitting examination of the effect of N levels on straighthead. It was found that at the higher N levels, straighthead symptoms were reduced. Since several minerals, including As, have been associated with straighthead, samples of the soil and plants from three of the affected cultivars were analyzed for their levels of several minerals. Straighthead-affected and nonstraighthead-affected plants of each cultivar were separated into roots, stems, leaves, and seeds. Each plant part was analyzed for its level of macro- and micronutrients plus As, from which a relative (straighthead/nonstraighthead) mineral level for each cultivar was calculated. Relative levels of As did not show a consistent pattern among the plant parts. Magnesium may play a role in natural straighthead; only its relative concentrations were consistent across the three cultivars in the soil, stems (and its subsection, stem internodes), leaves, seeds (and its subsection, seed hulls); though not in the roots, brown rice, or stem nodes. The data provide a description of nutrient levels in the rice plant from a rare occurrence and so may provide comparisons for other studies of natural and induced straighthead.