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Chromosome segment substitution lines (CSSLs) are useful tools for precise mapping of quantitative trait loci (QTLs) and evaluation of gene actions or interactions in theoretical studies. To facilitate the genetic analysis of complex traits and use of marker-assisted breeding in Brassica rapa, we developed a set of CSSLs using the extremely early-flowering inbred line RcBr as the recipient and extremely late-bolting Chinese cabbage variety 08A061 as the donor parent. The CSSL population consisted of 120 lines containing a total of 275 substituted segments, of which 47 lines contained only one substituted segment. The total length of the substituted segments spanned 2489.75 cM with an average length of 9.05 cM, representing 91.0% of the B. rapa genome and each line consisting of an average 98.1% of the recurrent parent genome. A total of 15 putative additive QTLs and 10 pairwised epistatic QTLs for three bolting indices were subsequently detected by QTL IciMapping 3.2 under two growth environments. Phenotypic variation explained by the additive QTLs, with the total variation ranging from 3.31 to 31.29% and 10.04 to 75.83%, respectively. Overall, the epistatic QTLs explained only a small amount of the phenotypic variation. The CSSLs and analyses presented here will help enhance our understanding of the genetics of bolting in B. rapa, thereby facilitating future molecular breeding programs. [ABSTRACT FROM AUTHOR]

The hindgut of horses is an anaerobic fermentative chamber for a complex and dynamic microbial population, which plays a critical role in health and energy requirements. Research on the gut microbiota of Mongolian horses has not been reported until now as far as we know. Mongolian horse is a major local breed in China. We performed high-throughput sequencing of the 16S rRNA genes V4 hypervariable regions from gut fecal material to characterize the gut microbiota of Mongolian horses and compare them to the microbiota in Thoroughbred horses. Fourteen Mongolian and 19 Thoroughbred horses were used in the study. A total of 593,678 sequence reads were obtained from 33 samples analyzed, which were found to belong to 16 phyla and 75 genera. The bacterial community compositions were similar for the two breeds. Firmicutes (56% in Mongolian horses and 53% in Thoroughbred horses) and Bacteroidetes (33% and 32% respectively) were the most abundant and predominant phyla followed by Spirochaete, Verrucomicrobia, Proteobacteria, and Fibrobacteres. Of these 16 phyla, five (Synergistetes, Planctomycetes, Proteobacteria, TM7, and Chloroflexi) were significantly different (p<0.05) between the two breeds. At the genus level, Treponema was the most abundant genus (43% in Mongolian horses vs 29% in Thoroughbred horses), followed by Ruminococcus, Roseburia, Pseudobutyrivibrio, and Anaeroplasma, which were detected in higher distribution proportion in Mongolian horses than in Thoroughbred horses. In contrast, Oscillibacter, Fibrobacter, Methanocorpusculum, and Succinivibrio levels were lower in Mongolian horses. Among 75 genera, 30 genera were significantly different (p<0.05) between the two breeds. We found that the environment was one of very important factors that influenced horse gut microbiota. These findings provide novel information about the gut microbiota of Mongolian horses and a foundation for future investigations of gut bacterial factors that may influence the development and progression of gastrointestinal disease in horses.