Comparison of Biological and Genetic Characteristics between Two Most Common Broad-Leaved Weeds in Paddy Fields: Ammannia arenaria and A. multiflora (Lythraceae)

SIMPLE SUMMARY: Ammannia arenaria and A. multifloras, the most common broad-leaved weeds in rice paddy fields in China, are morphologically similar at the seedling stage. However, their degree of damage to rice may vary. Furthermore, the sensitivity of two species to the constantly emerging new herbicides is also unknown. This study conducted field investigations, indoor biological experiments, and chloroplast genome construction and analysis to clarify the differences in biological characteristics, herbicide sensitivity, and chloroplast genetics between A. arenaria and A. multifloras. Our research results may provide theoretical basis for weed occurrence prediction, selection of herbicides, and Ammannia classification and distinction. Furthermore, the results provided valuable biological information on cp genomes of Ammannia that will be useful to identify and classify Ammannia, and study their phylogenetic relationships and evolution. ABSTRACT: Ammannia arenaria and A. multifloras, morphologically similar at the seedling stage, are the most common broad-leaved weeds in paddy fields. Our study showed that A. arenaria occupied more space than A. multifloras when competing with rice. However, A. multifloras germination has lower temperature adaptability. No difference in sensitivity to common herbicides between two Ammannia species was observed. Chloroplast (cp) genomes could be conducive to clarify their genetic relationship. The complete cp genome sequences of A. arenaria (158,401 bp) and A. multiflora (157,900 bp) were assembled for the first time. In A. arenaria, there were 91 simple sequence repeats, 115 long repeats, and 86 protein-encoding genes, one, sixteen, and thirty more than those in A. multiflora. Inverted repeats regions expansion and contraction and the phylogenetic tree based on cp genomes demonstrated the closely relationship between the two species. However, in A. arenaria, 20 single nucleotide polymorphisms in the CDS region were detected compared to A. multiflora, which can be used to distinguish the two species. Moreover, there was one unique gene, infA, only in A. arenaria. This study provides reliable molecular resources for future research focusing on the infrageneric taxa identification, phylogenetic resolution, population structure, and biodiversity of Ammannia species.