Weedy (red) rice: an emerging constraint to global rice production

Ongoing increases in the human population necessitate that rice will continue to be an essential aspect of food security for the 21st century. While production must increase in the coming decades to meet demand, such increases will be accompanied by diminished natural resources and rising production costs that will alter how rice is grown and managed. Such resource constraints are the impetus for the current transition from traditional flooding and transplanting to direct-seeded rice (DSR). However, such a transition can result in an increase in pest pressures, especially weeds. Rice production, can be particularly vulnerable to weed competition, with significant yield losses (i.e. >50%) occurring. Among pernicious weeds, weedy (red) rice (Oryza sativa L.) is increasingly recognized as a major constraint in achieving maximum yields in DSR. This is due, in part, to its phenotypic similarity to cultivated rice lines, and its ability to negatively influence qualitative and quantitative aspects of production. As rice will continue to serve as a cornerstone for future food security, a comprehensive assessment of weedy rice impacts associated with increasing adoption of DSR is both timely and critical. In this review, we examine the biological basis for the competitive ability of weedy rice, including its evolution, ecophysiology and genetics; quantify spatial-temporal shifts in its distribution and spread; and emphasize and outline a number of regional and global management strategies for its detection and control. Lastly, we suggest a number of critical research areas that deserve additional scrutiny with respect to weedy rice management.