Minimum Number of Genes Controlling Cotton Fiber Strength in a Backcross Population

34.3, and 22.2%, respectively of the total variance components as indicated in the analysis of 36 yr of high Textile mills in the USA require strong cotton fiber (Gossypium quality cultivar testing (Meredith, 2003). The lack of hirsutum L.) for modern high-speed textile operations. The primary breeding progress for fiber quality has led some (Felker, objective of this study was to determine the inheritance of strength descending from FTA 263-20 (FTA). FTA was developed by introgres2001) to question if modern U.S. cotton breeders were sion into G. hirsutum from G. arboreum L., G. thurberii Todaro, and mindful of their best customers’ fiber needs. G. barbadense L. Five backcrosses (BCs) into ‘Deltapine 16’ (DP 16) Fiber bundle strength (T1) has long been recognized followed by six BCs into DP 90ne were made. In 2001, three sets as being inherited as a quantitative trait (Richmond, of 64 BC6 F2:F3 progenies were evaluated for strength. Significant 1951). It is generally assumed that high fiber strength variability for F2:F3 strength (F 2.79), yield, three yield components, is caused by many genes. Self and Henderson (1954) in and four other fiber traits were detected. From a three replication populations involving high strength AHA 50 and ‘Half test, strength gene number(s) estimates ranged from 1.10 to 1.29 and and Half’ reported Pressley strength was determined by combined over sets was 1.23 genes. Average strength for the three BC5 five genes. Tipton et al. (1964) with F2 plant populations parents was 10.3% greater than DP 90ne and yield was 16.9% less. of ‘Cleveland Short Sympodia’ AHA-6-1-4 and CleveStrength was highly correlated with lint percentage, boll weight, seed weight, and 2.5% span length. Gene numbers for these correlated land Short Sympodia ‘Stardel’ estimated the number traits ranged from 0.02 for micronaire to 1.04 for yield. A separate of genes to be 12 to 13 and 13 to 14, respectively. Both study involving the BC5 parents, ‘Deltapine 90’ (DP 90) and DP 90ne studies used the Castle–Wright formula for estimating was used to determine the major physical components of strength. number of genes. Fineness and individual fiber strength had no effect. Short fiber conMay (1999) concluded in his review that fiber strength tent significantly impacted strength as the three BC5 parents average was quantitatively inherited. Recent genomic studies short fiber was 6.7 versus 8.7% for the DP 90s. The BC5 parents reinforce that many genes are involved in fiber strength average strength was 11% higher, 240 vs. 219 kN m kg 1, and its yield inheritance. Shapley et al. (1998) using RFLP molecular was 9.0% lower than DP 90ne. Probably a single major gene or closely markers, identified six linkage groups associated with linked cluster of genes resulted in increased fiber strength. fiber strength inheritance. Ulloa and Meredith (2000) detected three QTLs associated with fiber strength. In a large G. hirsutum G. barbadense population, PatT U.S. cotton and textile industry has been terson et al. (2003) recorded 21 QTLs while Zhang et al. described as an industry in crisis. Labor, regulatory (2003) detected nine molecular markers linked to two controls, and technology costs are less in competing QTLs for fiber strength. One QTL in their study accountries than in the USA. As a result, many U.S. textile counted for 18.5 to 53.8% of the total phenotypic varioperations closed or moved to other countries. As a reance and they considered this QTL a major gene for sult, U.S. grown cotton used by the U.S. textile industry fiber strength. In Ulloa and Meredith’s (2000) study, has also decreased from about 11 million bales for the one QTL explained 24.6% of the strength variation and 1996 to 1997 and 1997 to 1998 periods to the current esa second explained 10.6%. After a BC study to improve timate of 7.4 million bales (USDA, Foreign Agricultural fiber strength, Meredith (1977) suggested that a relaService, 2003). The remaining U.S. textile industry is tively small number of major genes are conditioning fiber modernizing by shifting to high-speed ring, open end, and strength, perhaps as few as one or two in the genotypes utiair jet spinning (Felker, 2001). Machines that in 1988 lized. Meredith (1992) continued the backcross program required 15.5 min to weave have been replaced with air but changed to another recurrent parent, ‘DPL90ne’. In jet looms that require less than 2.5 min to weave the BC2, he recorded four high strength lines from a small same fabric (Felker, 2001). The new machinery requires population of nectariless (ne1, ne2) progeny that averhigher fiber quality, including fiber strength, than is aged 9% higher strength than its recurrent parent. One currently being used for maximizing both efficiency and of these lines was released as a cultivar ‘MD51ne’ (Mereproduct quality. The USDA-AMS (2003) reports fiber dith, 1993). strength has not been increasing for the last 10 yr. The Some of the components of T1 are fiber length and its most efficient way to increase fiber strength is through distribution, fineness, and individual fiber strength. A genetics and breeding. The genetic, environmental, and previous study using a sample of 24 G. hirsutum culgenetic environmental variance components are 43.5, tivars (Meredith, 1992) reported that the fiber trait most influencing T1 was 50% span length which accounted for USDA-ARS-CG&P, P.O. Box 314, Stoneville, MS 38776. Received 22% of the total variation. The interaction of 50% span 9 Sept. 2003. Crop Breeding, Genetics & Cytology. *Corresponding length, fineness, and individual fiber strength accounted author ([email protected]). for another 23.8%. The major objective of this study was Published in Crop Sci. 45:1114–1119 (2005). doi:10.2135/cropsci2003.0425 Abbreviations: AFIS, Automated Fiber Information System; BC, backcross; DP, Deltapine; FTA, FTA 263-20; HVI, high volume instru© Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA mentation; QTL, quantitative trait loci; T1, fiber bundle strength. 1114 Published online May 6, 2005