Study on fine mapping of QTL for juice yield traits of sweet sorghum (Sorghum dochna)

The stem juice yield is a key factor that influences both the biological and economic production of sweet sorghum [Sorghum dochna (Forssk.) Snowden]. To elucidate upon the genetic basis of the stem juice yield, an F5 population developed from a cross between the low juice yielding Xinliang52 (XL52) and high juice yielding W455 lines, were used in a quantitative trait locus (QTL) analysis. A main effect of the QTL controlling stem juice yield was separated with an SSR marker called Xtxp97, which explained 46.7% of the phenotypic variance. In addition, F5 and F6 populations were constructed with XL52 and W452 as the parents to further verify the QTLs, and a significant correlation was found between the juice yield trait and the Xtxp97 marker. Based on the progeny tests of 29 recombinants, QJy-sbi06 was located in a region of about 21.2 kb on chromosome 6, where a candidate gene encoding an NAC transcription factor (sobic.006G147400) was identified. Combining the different population association analysis and sequencing technology showed that XL52 inserted a 1.8 kb transposon in the NAC to directly interrupt and inactivate the juice yield gene. This study also demonstrated that the colour of the leaf midribs was controlled by a single gene and was significantly positive correlated with juiciness (r = 0.784, P < 0.01). These results could lay the foundation for map-based cloning of QJy-sbi06 and provide genes or QTLs for breeding sorghum lines with a high juice yield and quality.