Submitted to: Plant Growth Regulation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/21/2011
Publication Date: 1/8/2012
Citation: Miller, H.B. 2012. Specific panicle responses resulting from MSMA-induced straighthead sterility in rice. Plant Growth Regulation. 66:255-264. Interpretive Summary: Straighthead is a damaging and costly disorder of rice named for the distinctive upright nature of unfilled (light-weight) seed heads. This study was conducted to determine if a greenhouse method could be developed that would induce straighthead symptoms common to what is observed in the field. Monosodium acid methanearsonate (MSMA) was used to induce straighthead-like sterility symptoms in rice in this study. Rating scales were developed in order to better describe the variety of specific MSMA-induced straighthead symptoms such as degree of emergence of the seed head, curvature of seed head structures, and distortion of the grain shape. We found that MSMA increased the length of time for the flowering period in rice and that early flowering seed heads were less affected than later flowering ones. Exposing rice to MSMA at the 4-leaf stage or reducing the root temperature tended to reduce the severity of plant symptoms. These studies demonstrated that MSMA can be a useful tool to induce particular sterility symptoms in rice in controlled environments, and thus, might be applicable to study of the mechanisms of straighthead development or other seed sterility phenomena.
Technical Abstract: Straighthead is a physiological disorder of rice causing sterility. A particular characteristic of straighthead is panicles that remain upright because of the light weight of the unfilled grains and hulls which may be distorted into a crescent or parrot-beak shape. Monosodium acid methanearsonate (MSMA) was used in this greenhouse study, to induce straighthead-like sterility symptoms in rice. Rating scales were developed to quantify the specific symptoms of straighthead (grain distortion, rachis curvature, panicle exsertion, and panicle weight), which were used to examine MSMA-induced straighthead in a greenhouse setting. Different rice cultivars were surveyed for their specific responses to MSMA, to identify targets for focus in rice breeding that differ in their responses. MSMA altered the pattern of anthesis so that flowering continued for a longer period of time although the initial flowering time and total panicle number were not affected. Early flowering panicles were less affected by MSMA than later flowering panicles. While all previous studies of MSMA-induced straighthead used MSMA applied at or before planting, a time course of MSMA application showed a time point for application at about the V4 (4-leaf) stage when the sterility symptoms were reduced and then an interval of time from about V6 to V8 when applications resulted in symptoms more severe than application at planting. A greenhouse temperature study demonstrated that lowering the temperature of the roots reduced the severity of the responses. MSMA is valuable as a trigger to induce sterility symptoms so that the underlying physiological, biochemical, and genetic causes can be studied, and which may have implications for other sterility conditions.