Genetic Distance among Selected Cotton Genotypes and Its Relationship with F2 Performance

are tandem repetitive DNA sequences. The availability and abundance of SSR markers throughout the cotton Knowledge of genetic diversity and relationships among breeding genome, their polymorphic nature, codominance, and materials has a significant impact on crop improvement. Association between parental divergence and progeny performance has not been polymerase chain reaction (PCR)-based assay make SSRs well documented in cotton (Gossypium hirsutum L.). The objectives useful in detecting genetic diversity (Reddy et al., 2001). of this study were to estimate genetic diversity among selected cotton The usefulness of GD as a predictor of hybrid perforgenotypes on the basis of simple sequence repeat (SSR) markers, and mance has been studied in several crops. In maize (Zea to investigate the relationship between genetic diversity and F2-bulk mays L.) and sunflower (Helianthus annuus L.), signifipopulation performance. Five U.S. and four Australian cultivars, and cant correlations between GD and hybrid performance two day-neutral converted lines of G. hirsutum were genotyped by were observed by Lee et al. (1989), Smith et al. (1990), means of 90 SSR primer pairs providing 69 polymorphic marker loci. Lanza et al. (1997), and Cheres et al. (2000). In contrast, Genetic distance (GD) between genotypes ranged from 0.06 to 0.34 Godshalk et al. (1990) and Dudley et al. (1991) observed for the 11 parental genotypes. The highest GD (0.34) was observed weak correlations between marker genotype and hybrid between ST474 and the day-neutral converted line B1388. The lowest GD (0.06) was detected between cultivars FM832 and FM975. The performance in maize. Furthermore, Martin et al. (1995) GD between day-neutral converted lines and cultivars ranged from working with wheat (Triticum aestivum L.) found no 0.26 to 0.34. Among the Australian cultivars, GD ranged from 0.06 association between measures of diversity and hybrid to 0.19 while GD among U.S. cultivars varied from 0.10 to 0.22, performance. Meredith and Brown (1998) using restricindicating a narrow genetic base. Significant correlations between tion fragment length polymorphic (RFLP) markers reagronomic and fiber traits of F2-bulk populations and GD ranged ported that in cotton the correlations between yield of from negative to positive depending on the traits, genetic background, F2 hybrids, heterosis, and GD were very low (r 0.07). and environment. On the basis of SSR markers, GD revealed a lack The utilization of heterosis for lint yield and fiber of genetic diversity among all genotypes and it was a poor predictor quality in F2 hybrids has eluded most researchers beof overall F2 performance. However, when genotypes with maximum cause of inconsistent expression of heterosis and lack range of GD were present, it was a better predictor for some traits. of economically effective means of delivering F2 seeds to growers. Nonetheless, it has been demonstrated that F2 hybrids can exhibit superior performance for agroI about the degree and distribution of genomic and fiber traits when compared with their parennetic diversity and relationships among breeding matal lines. Meredith (1990) reported that F2 hybrids terials has a significant effect on crop improvement. yielded 8% higher than their parents and no differences Selection of suitable parents is one of the most imporin adaptation were detected; however, the F2 hybrids tant criteria used to allocate resources to the most promhad significantly shorter fiber. Moreover, Tang et al. ising crosses and increase the efficiency of breeding (1992, 1993a,b) observed that almost all F2 hybrids deprograms. Molecular markers increasingly play an imveloped from crosses between selected pest-resistant portant role in crop improvement programs. They have germplasms and cultivars were equal to their highest been used to predict genetic variance among inbred parent for most fiber traits. Perhaps the greatest motivalines (Manjarrez-Sandoval et al., 1997), estimate genetic tion to investigate prediction of F2 performance is to diversity in crops (Wendel et al., 1992; Tatineni et al., spur cotton improvement. Presently, F2-bulk population 1996), protect plant cultivar rights (Smith and Smith, performance is used in about 24% of commercial cotton 1992), classify heterotic groups (Dudley et al., 1991; breeding programs in the USA for early generation Senior et al., 1998), study phylogenetic relationships testing and identification of populations upon which to among crops and their wild relatives (Li et al., 2000), focus selection (Bowman, 2000). analyze pedigrees (Smith et al., 1997), and select desired The objectives of this study were to estimate GD on traits (Young, 1999). the basis of SSR markers among selected cotton genoSimple sequence repeats, also called microsatellites, types, and to investigate the association between GD and fiber and agronomic characteristics of F2-bulk popuO.A. Gutiérrez, S. Saha, J.N. Jenkins, and J.C. McCarty, Jr., USDAlations. ARS, Crop Science Res. Lab., Genetics and Precision Agriculture Research Unit, Mississippi State, MS 39762; S. Basu, Dep. of Plant and Soil Sciences, Mississippi State Univ., Mississippi State, MS 39762; MATERIALS AND METHODS C.L. Cheatham, USDA-ARS, Small Fruit Res. Stn., Poplarville, MS 39470; D.B. Shoemaker, Delta and Pine Land Company, Scott, MS Plant Materials and Field Experiments 38772. Contribution of the USDA-ARS in cooperation with the Mississippi Agric. and Forestry Exp. Stn. Journal paper No. J 9891. ReEleven cotton genotypes, five U.S. cultivars, four cultivars ceived 9 July 2001. *Corresponding author ([email protected]. developed by the CSIRO cotton breeding program in Austrausda.gov). Abbreviations: GD, genetic distance; SSR, simple sequence repeats. Published in Crop Sci. 42:1841–1847 (2002).