Development of SCAR Marker Linked to a Major QTL for High Fiber Strength and Its Usage in Molecular-Marker Assisted Selection in Upland Cotton

vide a promising method of streamlining plant breeding programs (Kohel et al., 2001; Lawson et al., 1997; Mohan Cotton fiber is a basic raw material in the textile industry. All et al., 1997). In 1999-2000, we used a G. anomalum the changes in spinning technology require unique and often greater Wawra ex Wawra & Peyritch introgression line 7235, cotton fiber quality, especially strength, for processing. On the basis of genetic analysis and molecular mapping, a major quantitative trait which had been determined to possess good fiber quallocus (QTL) for fiber strength was identified in 7235, an Upland ity, to identify molecular markers linked to fiber cotton (Gossypium hirsutum L.) germplasm line in our institute, strength QTLs. By use of F2 and F2:3 populations derived which possesses super quality fiber properties. Eight molecular markfrom a cross between 7235 and TM-1, a widely used ers, two simple sequence repeat (SSRs) and six random amplified genetic standard of Upland cottons, a major QTL for polymorphic DNA (RAPDs) markers, were linked to the QTL. The fiber strength was identified. Eight molecular markers, objective of this study was to develop rapid and reliable sequence two SSRs and six RAPDs, covering 15.6 centimorgans characterized amplified region (SCAR) markers linked to the QTL (cM) of genetic distance, were linked to this QTL. It for marker-assisted selection (MAS). Two RAPD markers, UBC4311920 could explain more than 30% of the phenotypic variaand UBC7571365, were converted to SCAR markers after sequencing tion. The QTL was detected in different locations, such the two ends of the two polymorphic DNA fragments. Only SCAR4311920 marker detected polymorphism between TM-1 and 7235, as Nanjing and Hainan in China, and College Station, whereas SCAR7571365 showed monomorphism. SCAR4311920 marker TX, in the USA. Therefore, these DNA markers can was explored to determine its stability in (7235 TM-1) F2 with be used in MAS to increase fiber strength of commercial UBC4311920 marker as a control and to screen the major fiber strength cultivars (Zhang et al., 2003). QTL of (7235 Simian 3) BC1F4 population for transferring good RAPD technology has the shortcoming of relatively fiber quality. The result showed that the specific SCAR4311920 marker low reproducibility and reliability, which limits its use could be applied to large-scale screening for the presence or absence in breeding program, whereas molecular markers based of the major fiber strength QTL in breeding populations. on polymerase chain reaction (PCR) technology should be an efficient means of screening large populations, and they are relatively easy analyze, can be screened C fiber is an important raw material for the at with reproducibility, and are economical. Paran and textile industry. As a result of the recent advances Michelmore (1993) described a reliable PCR assay that in the textile industry in spinning technology, greater cotthey called sequence characterized amplified regions ton fiber quality, especially strength, is required (Deus(SCARs) in which the two ends of the polymorphic sen, 1992). Because of the rigors of ginning, opening, DNA fragment are sequenced and two longer primers cleaning, carding, combing, and drafting, an important homologous to each end are then synthesized. Some breeding objective has been to increase fiber strength. SCAR markers have been developed for insect and Fiber strength in Upland cotton grown in the USA has disease resistance and fertility restoration genes (Nair been increased by 0.19 cN tex 1 yr 1 over the 10-yr et al., 1995; Nair et al., 1996; Nagvi and Chatto, 1996; period of 1982 to 1992. The average strength of the Ohmori et al., 1996; Norio, 1997; Liu et al., 1999). These commercial cultivars in 1991 to 1992 was close to 21.7cN SCAR markers increased reliability and specificity for tex 1 (Benedict et al., 1999). There is an urgent need screening large breeding populations by means of the to improve cotton fiber quality further. However, there converted molecular markers for assisting breeding seis no rapid way to do this by current plant breeding lection. The objective of this study was to develop methods and on the basis of current genetic information. SCAR markers for molecular identification of the high In traditional breeding to develop super quality fiber fiber strength QTL that we identified and to use such properties, the quality of the fiber can be determined markers to select the high fiber strength QTL in cotton only after harvesting and testing the fiber. As a result, breeding programs. it is difficult, expensive, and time-consuming to develop cotton cultivars with super quality fiber by these methods. MATERIALS AND METHODS Advances in the use of DNA markers for MAS pro-