Emergence of invasive weedy rice in Southeast Asia. A review

Weedy rice has recently emerged as a serious problem in Southeast Asia, despite the region’s long history of rice culture. Major economic losses have resulted from reduced yield, grain quality deterioration, and increased control cost. This review seeks to describe the complete set of circumstances leading to the sudden invasiveness of weedy rice in Southeast Asia. The paper begins with a timeline of weedy rice records in the region, along with the chronological sequence of the spread of modern rice technology. This is followed by a review of evidence of genetic interaction between cultivated, wild, and weedy rice. The consequence of the introduction of photoperiod insensitivity from modern rice varieties into the local cultivated-wild-weedy rice gene pool is analyzed. The influence of the agronomic practices of modern rice farming on the competitiveness, adaptation, and dispersal of weedy rice is reviewed. Detrimental effects of weedy rice on rice production are evaluated. The main finding is that weedy rice, like its wild ancestor, the common wild rice, is likely endemic to deepwater rice areas in Southeast Asia. Its recent ecological success in the wider region is based primarily on introgression of photoperiod insensitive trait from modern rice varieties. This has resulted in the removal of reproductive control by daylength in weedy rice, which broadens its adaptive capacity and increases hybridization opportunities. The paddy field environment favorable to weedy rice is created by modern crop management practices—from land preparation to direct seeding, combine harvesting, and chemical weed control. The arrival of modern rice technology at the end of the twentieth century has brought economic and social benefits to Southeast Asia, and also an unintended harm to rice production with invasive weedy rice. Weedy rice control should benefit from a comprehensive understanding of the mechanisms driving its sudden invasiveness and spread.