Abstract
Weedy rice infests paddy fields worldwide at an alarmingly increasing rate. There is substantial evidence indicating that many weedy rice forms originated from or are closely related to cultivated rice. There is suspicion that the outbreak of weedy rice in China may be related to widely grown hybrid rice due to its heterosis and the diversity of its progeny, but this notion remains unsupported by direct evidence. We screened weedy rice accessions by both genetic and molecular marker tests for the cytoplasmic male sterility (CMS) genes (Wild abortive, WA, and Boro type, BT) most widely used in the production of indica and japonica three-line hybrid rice as a diagnostic trait of direct parenthood. Sixteen weedy rice accessions of the 358 tested (4.5%) contained the CMS-WA gene; none contained the CMS-BT gene. These 16 accessions represent weedy rices recently evolved from maternal hybrid rice derivatives, given the primarily maternal inheritance of this trait. Our results provide key direct evidence that hybrid rice can be involved in the evolution of some weedy rice accessions, but is not a primary factor in the recent outbreak of weedy rice in China.
Highlights
Phenomena have existed for thousands of years and contribute to the evolutionary history of crops and their wild relatives[14]
It is suspected that weedy rice in some areas of Jiangsu province may have evolved from segregating progeny of indica hybrid rice, which is supported by results from genetic and morphological analyses[12,22]
To test the hypothesis that some weedy rice accessions may have directly originated from hybrid rice, we used the cytoplasmic male sterility (CMS)-wild abortive (WA) and CMS-Boro type (BT) genes as markers to test the lineage of a collection of weedy rice samples
Summary
Phenomena have existed for thousands of years and contribute to the evolutionary history of crops and their wild relatives[14]. If weedy rice directly evolved as progeny of hybrid rice, weedy rice individuals should contain a CMS gene regardless of any involvement of gene flow during the evolution process. A wild abortive (WA) cytoplasmic male sterile line was first developed and became the most widely used to breed indica hybrid rice. To test the hypothesis that some weedy rice accessions may have directly originated from hybrid rice, we used the CMS-WA and CMS-BT genes as markers to test the lineage of a collection of weedy rice samples These genes are largely maternally inherited and are not expected to be transferred to weedy rice through pollen-mediated gene flow
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