| The tetraploid cotton species Gossypium hirsutum and G. barbadense are commercially important fiber crops to the textile industry. G. hirsutum is the predominant type due to its high lint yield while G. barbadense is renowned for superior fiber strength, length, and fineness. Fiber yield and quality, disease resistance, abiotic resistance, and physiological and morphological traits are all trait types selected for in cotton breeding programs. Quantitative trait loci (QTL) are genes or DNA segments on chromosomal regions which contribute cumulatively to a quantitative trait each with differing degrees of phenotypic variance. Numerous QTL studies in cotton have been done on a wide variety of traits with the majority of them being focused on fiber quality and yield related traits. Cotton marker assisted selected (MAS) breeding programs use markers that anchor known QTL in breeding to improve cultivar performance. However, because different QTL studies used different markers on different populations tested in different environments, it is difficult to manually determine common chromosomal regions that have the most QTL of interest in different mapping populations tested in different environments for MAS programs. Furthermore, since QTL are discovered through a statistical marker and trait association, false positive QTL may exist. Identifying QTL which have been identified by multiple studies lends further validation of the QTL's presence in the region. To address these problems, this study conducted a comprehensive meta-analysis in tetraploid cotton first, followed by a comparative meta-analysis between intraspecific G. hirsutum and interspecific G. hirsutum x G. barbadense populations. Using 1,223 QTL published from 42 papers, the comprehensive meta-analysis identified 76 QTL clusters and 51 QTL hotspots in tetraploid cotton. The further comparative meta-analysis using 1,075 QTL in the G. hirsutum population and 1,059 QTL in the G. hirsutum x G. barbadense population from 88 papers identified 58 and 76 QTL clusters and 51 and 46 QTL hotspots, respectively. The results indicated that QTL are not evenly distributed over the Gossypium genome and the distribution of QTL differs significantly between the two types of populations. To share with the cotton community, a cotton QTL database, CottonQTLdb (Release 1) including 2,274 QTL was developed to provide a useful tool for QTL tabulation, visualization and analysis. To remain current with QTL studies, the database has functions to accept submission of new QTL data from the cotton community. The database is accessible from www.cottonqtldb.org. |
