Crj80284 1311..1317

Genetic variation available for the improvement of fiber properties is restricted in commercial upland cotton (Gossypium hirsutum L.). Resources for fiber improvement exist in G. barbadense L., but introgression of traits has been a limited success. The objectives of this study were to investigate the genetic variation and heritability of agronomic and fiber traits within a diverse recombinant inbred line (RIL) population created with a stable introgressed parent. The population (n 5 98 lines) had as its parents NM24016, a stable G. hirsutum line with significant introgression from G. barbadense, and TM1, the G. hirsutum genetic standard. Yield, plant height, boll size, lint percentage, and fiber length, strength, micronaire, and elongation were measured in randomized, complete block tests at Las Cruces, NM, and Maricopa, AZ, in 2001 and 2002. Genotype coefficients of variation (CV) were highest for plant height and boll size. Among fiber traits, fiber length and micronaire produced the highest genotype CVs. Most traits (fiber elongation excepted) exhibited high broadsense heritability, ranging from 0.69 for lint yield to 0.92 for 2.5% span length. Transgressive segregants were identified for most traits. Fiber strength and 2.5% span length were favorably correlated (r 5 0.59, P 5 0.001) as were 2.5% span length and micronaire (r 5 20.47, P 5 0.001). The NM24016/TM1 RIL population presents valuable genetic variation for fiber quality improvement efforts in G. hirsutum. H four species of Gossypium have been cultivated for fiber (Brubaker et al., 1999). Of these species, the tetraploid G. hirsutum and G. barbadense currently dominate commercial cotton production, with G. hirsutum accounting for over 90% of the production. Gossypium hirsutum and G. barbadense differ significantly in their agronomic and fiber attributes and their commercial end uses. The higher yield potential and broader environmental adaptability evident in G. hirsutum have been increased through breeding and genetic manipulation. Similarly, the superior fiber attributes of the G. barbadense species have been emphasized in the development of commercial cultivars in that species. Production of G. barbadense has been limited not only by the specialty nature of its high quality fiber but also by its lower yield potential, greater heat sensitivity, and longer growing period. Although G. hirsutum dominates fiber production, modern spinning techniques and end uses have created demands for improved fiber quality in that species (McCreight, 1992; Felkner, 2001). Traits that have been identified as desirable include greater fiber strength, greater length, increased uniformity of length, and finer fiber at maturity (McCreight, 1992; Deussen, 1992). Of the above, commercial G. barbadense possesses greater fiber lengths, strengths, and fineness (micronaire) than currently available in G. hirsutum. In recent years, there has been a growing recognition of the limited genetic diversity of elite commercial germplasm of both species and a growing concern about genetic vulnerability (Bowman et al., 1996). This genetic impoverishment may have resulted from numerous sources and activities. In both species, the process of domestication is thought to have dramatically narrowed the germplasm base (Brubaker et al., 1999). Early and modern improvement efforts further narrowed this base. May (2000) reported that intensive selection imposed to maximize yield and adaptation, along with selection for early maturity, has eliminated substantial variation from elite G. hirsutum germplasm pools. In G. barbadense, only a very small portion of the primitive and obsolete germplasm exhibits the highly desirable fiber characteristics that are common to modern commercial cultivars (Percival, 1987). This genetic resource has been further narrowed by the transfer of a subset of the high fiber quality Sea Island cottons to Egypt for the development of the modern Giza cultivars and the subsequent transfer of a subset of Egyptian cultivars to the USA for the development of modern Pima cultivars (Smith et al., 1999). The genetic narrowness of the commercial germplasm has been cited as a contributing factor for the perceived plateau in yield and fiber improvement in recent years. As a result of concerns regarding genetic vulnerability and improvement plateaus, there has been renewed interest in interspecific introgression and use of related species as sources of genetic variation in improvement efforts (May et al., 1995). Recognition of the complementary attributes of G. hirsutum and G. barbadense has led to interspecific hybridization and introgression efforts in these species that predate the current concerns regarding genetic vulnerability and yield plateaus. Despite past interspecific hybridization efforts, modern cultivars display few traits that can be attributed to introgression. Efforts to improve G. hirsutum or G. barbadense through introgression have been hindered by genetic breakdown in segregating interspecific breeding populations (Stephens, 1949). Infertility and distorted preferential segregation have been prevalent. Rhyne (1958) reported that the number of recombinants occurring in an interspecific backcross program were greatly inferior to the expected number. Reinisch et al. (1994) reported strongly distorted segregation of molecular markers in early generations, and Jiang et al. (2000) reported skewed R. Percy, U.S. Arid-Land Agricultural Research Center, USDA-ARS, 21881 N. Cardon Lane, Maricopa, AZ 85239; R.G. Cantrell, Cotton Incorporated, 6399 Weston Parkway, Cary, NC 27513; J. Zhang, Department of Agronomy and Horticulture, Skeen Hall, New Mexico State University, Las Cruces, NM 88003. Received 29 Aug. 2005. *Corresponding author ([email protected]). Published in Crop Sci. 46:1311–1317 (2006). Crop Breeding & Genetics doi:10.2135/cropsci2005.08-0284 a Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 1311 Published online April 25, 2006