Developmental Change of Vegetative Plant Architecture of Annual-Form-Wild Rice (<i>Oryza rufipogon</i> Griff.) Elevates Competitive Ability during the Late Development under a Dense Condition

Abstract

Annual-form-wild (AFW) rice developmentally changes the vegetative plant architecture from flat to elect shape. The main objective of the present study is to suggest that the change might be related to competitive ability (CA). Recombinant inbred lines (RILs) derived from a cross between an AFW rice and a cultivar were grown under high-density (H) and low-density (L) conditions in a weedy paddy field. At two and three months after transplanting (MATs), we evaluated the two traits associated with utilization of light resource, tiller angle (TA) and actual plant height (APH), and amount of the growing weeds using an index, weed-denseness score (WDS). Then, DC-TA, DC-APH and SC-WDS was defined as the amount of change in TA, APH, and WDS from two to three MATs, respectively. Multiple regression analysis revealed that only DC-TA significantly affected SC-WDS specific under H condition that is relatively similar to habitats of AFW rice. Quantitative trait locus (QTL) analyses identified that one of the two QTLs associated with DC-TA shared a linked molecular marker with a QTL associated with SC-WDS only under H condition. Further, RILs with AFW-rice-derived allele on the QTL associated with DC-TA tended to show drastic changes of TA toward narrow angle as well as large decreases of weed amount. All the QTLs associated with DC-APH were not linked to the QTL associated with SC-WDS under H condition. Therefore, it is suggested that under the crowded conditions during the late plant development, AFW-rice plants might not survive through canopy domination but elevate CA through increases of efficiency of capturing light due to changes from wide to narrow tiller angle. Since flat-plant shape of AFW rice during the early development would have been evolved by trampling pressures, the present finding suggest that different selective pressures in life time might have cooperatively evolved the developmental change.