Quantitative Trait Loci Mapping for Theobromine and Caffeine Contents in Tea Plant (Camellia sinensis)

Understanding the genetic basis of theobromine and caffeine accumulation in the tea plant is important due to their contribution to tea flavor. Quantitative trait loci (QTL) analyses were carried out to identify genetic variants associated with theobromine and caffeine contents and ratio using a pseudo-testcross population derived from an intervarietal cross between two varieties of Camellia sinensis. A total of 10 QTL controlling caffeine content (CAF), theobromine content (TBR), sum of caffeine and theobromine (SCT), and caffeine-to-theobromine ratio (CTR) were identified over four measurement years. The major QTL controlling CAF, qCAF1, was mapped onto LG01 and validated across years, explaining an average of 20.1% of the phenotypic variance. The other QTL were detected in 1 or 2 years, and of them there were four, two, and three for TBR, SCT, and CTR, respectively. The present results provide valuable information for further fine mapping and cloning functional genes and for genetic improvement in tea plant.