Author
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MILLER, HELEN |
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BEATY, BRYAN |
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Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/25/2007 Publication Date: 11/1/2007 Citation: Miller, H.B., Beaty, B. 2007. Distribution of arsenic and other minerals in rice plants affected by natural straighthead. Agronomy Journal. 99:1675-1681. Interpretive Summary: Straighthead is a disorder of rice causing sterility. The seed panicles remain upright because of the light weight of the unfilled kernels, hence the name. The empty seed hulls are also distorted into a crescent or parrot-beak. Straighthead-like symptoms can be induced with arsenic-containing herbicides such as monosodium methanearsenate (MSMA). Natural (non-chemically-induced) straighthead is unpredictable in occurrence making it difficult to study. In 2006, an outbreak of naturally-occurring straighthead occurred in some rice yield tests in Stuttgart, Arkansas. This straighthead occurrence provided a rare opportunity to examine the role of minerals in the disorder. One of the affected yield test sites included three nitrogen rates. The straighthead symptoms were most severe at the lowest nitrogen rate. As several minerals, including arsenic, have been associated with straighthead, samples of the soil and plants from three cultivars were tested for the levels of a number of minerals, including arsenic. The straighthead-affected and non-straighthead-affected plants of each cultivar were separated into roots, stems, leaves, and seeds. Each plant part was analyzed for its level of macro- and micro-nutrients plus arsenic. Seeds were further subdivided into hulls and brown rice and stems were further subdivided into nodes and internodes. Of the minerals found in low levels in straighthead soil, magnesium was the most promising for having a role in straighthead as it was consistently lower in all three three cultivars for stems, internodes, leaves, seeds, and hulls, though not in the brown rice or roots. Technical Abstract: In 2006, an outbreak of naturally-occurring (non-chemically-induced) straighthead occurred in some rice (Oryza sativa L.) yield tests in Stuttgart, Arkansas. This straighthead occurrence provided an opportunity to examine the role of minerals in the disorder. Arsenical herbicides are often used to study the disorder largely because of the inconsistency and unpredictability of naturally-occurring straighthead. One of the affected yield test sites included three nitrogen rates for which symptoms were most severe at the lowest rate. As several minerals, including arsenic, have been associated with straighthead, samples of the soil and plants from three cultivars were tested for the levels of a number of minerals, including arsenic. The straighthead-affected and non-straighthead-affected plants of each cultivar were separated into roots, stems, leaves, and seeds. Each plant part was analyzed for its level of macro- and micro-nutrients plus arsenic, from which a relative (straighthead/non-straighthead) nutrient amount for each cultivar was calculated. In the root, only phosphorous and copper were consistently greater in the straighthead plants of all three cultivars. In the leaves, only sodium and magnesium showed a consistent ratio, in this case, less than one. Seven minerals, including arsenic, were found in greater amounts in the straighthead seeds relative to non-straighthead seeds. However, the higher levels seen in whole straighthead seeds did not extend to seeds subdivided into hulls and brown rice. And, the same relative nutrient levels observed in the stem were not present in the subdivided nodes and internodes. Of the minerals found in low levels in straighthead soil, magnesium was the most promising for having a role in straighthead as its relative concentrations were consistent across the three cultivars for stems, internodes, leaves, seeds, and hulls, though not in the brown rice or roots. |
