Identification of Resistance of Guangxi Oryza Rufipogon to Sogatella Furcifera with Stem Evaluation Method

White-backed planthopper (WBPH) is a devastating pest of rice, which significantly reduces production and causes millions of dollars in losses worldwide annually. Screening of germplasm resources with resistance to white-backed planthopper plays a crucial role in crop insect resistance breeding. In the present research, a total of 1080 accessions of Guangxi common wild rice(Oryza rufipogon) was screened for WBPH resistance through stem evaluation method (SEM). After preliminary screening, 49 resistance resources were identified, accounting for 4.54% of the total. After verified identification at the adult stage, 15 resistance resources with stable resistance to white-backed planthopper were finally obtained as resistant resources. The regional distribution analysis showed that the highest frequency of WBPH resistance resources appeared in Fusui county located in the upper reaches of Xijiang river(6.80%). Meanwhile, the highest frequency of the high resistance (HR and R) resources appeared in Pingnan located in lower reaches(2.79%). The 49 resistant accessions were genotyped for 43 SSR markers evenly distributed on the 12 chromosomes. The genetic diversity analysis showed a high polymorphism level of common wild rice populations. Fusui county possesses higher level of genetic diversity than the Yongning district and Pingnan county populations. The results from this study are essential to analyze resistance genes, cultivate insect-resistant varieties, and provide regional guidance for the exploration of resistance resources in the future.

Development and verification of SSR markers from drought stress-responsive miRNAs in common wild rice

PREMISE: Dongxiang wild rice (Oryza rufipogon Griff., DXWR) is the northernmost common wild rice found in the world, which possesses abundant elite genetic resources. We developed a set of drought stress-responsive microRNA (miRNA)-based single sequence repeat (SSR) markers for DXWR, which will help breed drought stress-resistant rice varieties. METHODS AND RESULTS: Ninety-nine SSR markers were developed from the drought stress-responsive miRNAs of DXWR. The SSR loci were distributed in all 12 rice chromosomes and most were in chromosomes 2 and 6, with di- and trinucleotides being the most abundant repeat motifs. Nine out of ten synthesized SSR markers were displayed high levels of genetic diversity in the genomes of DXWR and 41 modern rice varieties worldwide. The number of alleles per locus ranged from 2 to 6, and the observed and expected heterozygosity ranged from 0.000 to 0.024 and 0.461 to 0.738, respectively. CONCLUSIONS: These SSR markers developed from drought stress-responsive miRNAs in DXWR could be additional tools for elite genes mapping and useful for drought stress-resistant rice breeding.

Identification and Fine-mapping of a New Bacterial Blight Resistance Gene, Xa47(t), in G252, an Introgression Line of Yuanjiang Common Wild Rice (Oryza rufipogon)

Bacterial blight (BB) disease caused by Xanthomonas oryzae pv. oryzae (Xoo) is a common, widespread, and highly devastating disease that affects rice yield. Breeding resistant cultivars is considered the most effective measure for controlling this disease. The introgression line G252 derived from Yuanjiang common wild rice (Oryza rufipogon) was highly resistant to all tested Xoo strains, including C5, C9, PXO99, PB, T7147Y8, Hzhj19, YM1, YM187, YJdp-2, and YJws-2. To identify the BB resistance gene(s) of G252, we developed an F2 population from the cross between G252 and 02428. A linkage analysis was carried out between the phenotype and genotype in the population. A segregation ratio of 3:1 was observed between the resistant and susceptible individuals in F2 progeny, indicating a dominant resistance gene, Xa47(t), in G252. The resistance gene was mapped within an approximately 26.24 kb physical region on chromosome 11 between two InDel markers, R13I14 and 13rbq-71; and moreover, one InDel marker, Hxjy-1, co-segregated with Xa47(t). Three genes were predicted within the target region, including a promising candidate gene encoding a nucleotide-binding domain and leucine-rich repeat (NLR) protein (LOC_Os11g46200) by combining the structure and expression analysis. Physical mapping data suggested that Xa47(t) was a new broad-spectrum BB resistance gene.

QTL Mapping Integrated with BSA-Seq Analysis Identifies a Novel Gene Conferring Resistance to Brown Planthopper from Common Wild Rice (Oryza rufipogon Griff.)

The brown planthopper (Nilaparvata lugens Stål, BPH) is one of the most destructive rice pests worldwide. GXU202 is a germplasm of common wild rice (Oryza rufipogon Griff. ) with high resistance to the BPH. In this study, the genetic analysis indicated that the BPH resistant phenotype of GXU202 is controlled by a major gene. Through the combination and comparison of QTL linkage and BSA-seq analyses, a novel gene locus BPH41 conferring BPH resistance was identified, which has been finely mapped to a 114-kb region delimited by D01031 and W1 on chromosome 4. The markers D01031 and D01045 showed high accuracy in predicting resistant phenotypes to BPH, suggesting their reliability for marker-assisted selection of BPH41 in breeding for BPH resistant rice varieties. The present identification of BPH41 will establish a foundation for further map-based cloning and functional characterization of the gene.

Identification of microRNAs responding to cold stress in Dongxiang common wild rice

Low temperature is a vital effector of rice at different growth stages. MicroRNAs (miRNAs) play important roles in responding to abiotic and biotic stresses. Here, we confirmed the cold tolerance of Dongxiang common wild rice and explored the miRNAs differentially expressed under cold stress using genome-wide small RNA sequencing. In total, 16 miRNAs, nine upregulated and seven downregulated by cold stress, were characterized in Dongxiang common wild rice, and their target genes were predicted. Additionally, an AgriGO analysis of the target genes revealed that they were enriched in several terms related to cold-stress tolerance, suggesting a complex response mechanism, involving miRNAs, to cold stress in Dongxiang common wild rice.