Morphological characteristics of homozygous wild rice phytoliths and their significance in the study of rice origins

The analysis of wild rice cell structures, tissues, organs, and other morphological characteristics and the development of identification markers for wild rice are the basis for identifying the origins and evolution of prehistorical rice agriculture. However, contemporary wild rice strains are often subject to gene introgression from domesticated rice cultivated by humans during the evolutionary process, which may affect the accuracy of wild rice identification markers. This means that how to eliminate the effects of gene introgression from domesticated rice and other plants on the identification of origin markers, and the purification of the morphological characteristics of wild rice have become critical in research to identify the origin of rice. In this study, we compared and analysed the phytolith morphologies of three common wild rice species ( Oryza rufipogon Griff .) from various habitats and one species of ectopically preserved homozygous common wild rice after six consecutive generations of self-crossing. We found that the morphology of the bulliform phytolith in the homozygous wild rice with reduced domestication gene introgression had three significant differences compared with native wild rice: (1) an overall reduction in size (body length decreased from 41.9  μm in VLnative to 38.6 μm in VLhomozygous); (2) an increase in the proportion of the long-stalked phenotype, with the ratio of B/A decreasing from 1.22±0.47 in B/Anative to 0.92±0.30 in B/Ahomozygous; and (3) a decrease in the number of fish-scale decorations, with the proportion of bulliform phytoliths with ≥9 fish-scale decorations reduced from 53.4% in native wild rice to 37.2% in homozygous wild rice. Thus, this study provides a reliable reference for the identification of rice origins using rice phytolith morphology.