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Chinese sprangletop (Leptochloa chinensis), belonging to the grass subfamily Chloridoideae, is one of the most notorious weeds in rice ecosystems. Here, we report a chromosome-scale reference genome assembly and a genomic variation map of the tetraploid L. chinensis. The L. chinensis genome is derived from two diploid progenitors that diverged ∼10.9 million years ago, and its two subgenomes display neither fractionation bias nor overall gene expression dominance. Comparative genomic analyses reveal substantial genome rearrangements in L. chinensis after its divergence from the common ancestor of Chloridoideae and, together with transcriptome profiling, demonstrate the important contribution of tetraploidization to the gene sources for the herbicide resistance of L. chinensis. Population genomic analyses of 89 accessions from China reveal that L. chinensis accessions collected from southern/southwestern provinces have substantially higher nucleotide diversity than those from the middle and lower reaches of the Yangtze River, suggesting that L. chinensis spread in China from the southern/southwestern provinces to the middle and lower reaches of the Yangtze River. During this spread, L. chinensis developed significantly increased herbicide resistance, accompanied by the selection of numerous genes involved in herbicide resistance. Taken together, our study generated valuable genomic resources for future fundamental research and agricultural management of L. chinensis, and provides significant new insights into the herbicide resistance as well as the origin and adaptive evolution of L. chinensis.

Background: The growth of weed is common problem in rice cropping, leading to the application of herbicidal substances to suppress weed growth. Weed biocontrol through novel bioorganic fertilizer (BIO) has been established in rice cultivation, however, its main herbicidal components and influence on soil bacterial community are unknown.Results: We identified three herbicidal components, hexadecanoic, isovaleric, and 2-methylbutyric acids, in BIO extract. We conducted 16S rRNA sequencing to identify changes in soil bacterial community in response to BIO treatments and performed a RDA analysis with soil chemical properties and weed-control effect. The OTU, Chao1 and Shannon indices did not differ substantially among the BIO treatments, and the bacterial diversity was not significantly affected by BIO. As result from PCA analysis, we discovered that soil bacterial community was not significantly influenced by BIO. We identified six dominant phyla (Proteobacteria, Acidobacteria, Chloroflexi, Nitrospirae, and Verrucomicrobia) in BIO-treated paddies. The five most abundant genera were Anaeromyxobacter, Candidatus Nitrosotalea, Clostridum sensustricto1, Haliangium and Candidatus Nitrotoga. From the RDA analysis, the highest correlations were obtained for soil pH, total K, and Pseudomonas. The weed-control effect mostly correlated with the abundance of Candidatus Koribacter, Clostridium sebsustricto 9, and Nonomuraea. Rice yield had a distinct relationship with Nonomuraea, Nitrospira, and Candidatus Koribacter.Conclusions: With the changes in soil pH and total K, BIO could impact bacterial communities and weed control, and in turn affect rice yield. This foundation can be helpful that application BIO is a “not harmful” and feasibility weed biocontrol strategy.

Additional file 3: Fig. S1. PCR-based genotyping for the 28-bp deletion in indica accessions (partially). M: DL2000 DNA marker; lane 1–24: IR64, Nipponbare, Bing 1A, Digu, Yuetai A, 9311, Zhenxian 97A, Fengyuan A, Mianhui 725, II-32A, Tianfeng A, Fenghuazan, Yuanhui 2 hao, Yuetai B, IR36, Gui 99, Fengyuan A, Shuhui 498, Miyang 46, IR64, D62A, G46A, CDR22, Wufeng A. Fig. S2. Pfam motifs of HIS1 and amino acid variation of haplotypes. The shaded parts are predicted amino acids due to the 28-bp deletion in H5. Fig. S3. Protein sequence alignment of 2OGDs. (A) Protein sequence alignment and conserved site analysis of 91 experimentally characterized 2OGDs in plants. (B) Protein sequence alignment and conserved site analysis of 114 putative 2OGDs in rice. Fig. S4. RNA expression of HIS1 in some accessions harboring H1, H2, H3, and H5. The qRT-PCR results were normalized with the actin reference gene. Error bars represent the standard error of the mean (SEM) of three replicates. Fig. S5. The T1510G mutation is completely co-segregated with the susceptibility to BBC (partially). Rice accessions Nongxiang42 and Xianhui207 carry HIS1 haplotypes H2 and H3, respectively. The upper electrophoretic band represents the PCR products of HIS1, and the lower band shows the PCR products treated with the restriction enzyme Dde1. Fig. S6. BBC is effective when the seeds are mixed. (A). BBC can effectively kill hybrid sterile lines (MingS) without harming hybrids (Mingliangyou143). The red arrow indicates the sterile line that was killed. (B). Random selection of 10 normal and severely affected seedlings. Through the detection of 28-bp deletion primers, it was found that the normal materials were all in a heterozygous state, and the sterile line materials lacking 28-bp were killed.

Background Benzobicyclon (BBC) is a β-triketone herbicide (bTH) used in rice paddy fields. It has the advantages of high efficiency, low toxicity, high crop safety, and good environmental compatibility, and shows efficacy against paddy weeds resistant to other types of herbicides. However, as some important indica rice varieties are susceptible to BBC, BBC is currently only registered and applied in japonica rice cultivation areas. Results By analyzing haplotypes of the bTHs broad-spectrum resistance gene HIS1 and phenotypes for BBC in 493 major indica rice accessions in China, we identified a novel non-functional allelic variant of HIS1 in addition to the previously reported 28-bp deletion. Through detection with markers specific to the two non-functional mutations, it was clear that 25.4% of indica conventional varieties, 59.9% of fertility restorers, and 15.9% of sterile lines were susceptible to BBC. In addition, due to natural allelic variations of the HIS1 gene in the sterile and restorer lines, some two-line hybrid sterile lines were sensitive to bTHs, and the corresponding restorers were resistant. We showed the potential effectiveness of using bTHs to address the issue of two-line hybrid rice seed purity stemming from the self-crossing of sterile lines during hybrid rice seed production. Finally, allelic variations of the HIS1 gene may also play an important role in the mechanized seed production of hybrid rice. Conclusions Our findings offer guidance for the application of BBC in indica rice areas and provide a non-transgenic approach to address the seed purity issue of two-line hybrid rice.