Race Stocks Research Articles

QTL analysis for yield and fibre quality traits using three sets of introgression lines developed from three Gossypium hirsutum race stocks.

Upland cotton (Gossypium hirsutum L.) race stocks may possess desirable traits for the genetic improvement of cotton. Quantitative trait locus (QTL) analysis can assist in uncovering new alleles from unadapted race stocks. In this study, three sets of chromosome segment introgression lines (ILs) were developed from three backcrosses (BC3) between three race stocks, G. hirsutum races latifolium accs. TX-34 and TX-48 and punctatum acc. TX-114, as donor parents and Texas Marker-1 (TM-1) as the recurrent parent. Based on a total of 452 polymorphic simple sequence repeat (SSR) markers in BC3F2 genotyping, 149, 150 and 184 ILs were obtained from TM-1 × TX-34, TM-1 × TX-48 and TM-1 × TX-114, respectively. The average introgressed chromosomal segment length was 12.7cM, and the total genetic distance was 3268cM covering approximately 73.4% of the Upland cotton genome. The BC3F2, BC3F2:3 and BC3F2:4 progeny, which produced the ILs, were evaluated for yield and fibre quality traits. A total of 128 QTLs were detected, each of which explained 1.6-13.0% of the phenotypic variation. Thirty-five common QTLs related to eight traits were detected. Six QTL clusters were found on five chromosomes. Thirty-eight QTLs were previously unreported, and they may be footprints of cotton domestication. Domestication or artificial selection by humans successfully eliminated most unfavourable QTLs (21/38); however, some favourable QTLs (17/38) are not present in modern cultivars, demonstrating the importance of race stocks for improving cotton cultivars. The 26 elite ILs developed could be used to improve the yield and fibre quality components simultaneously. These results provide information on desirable QTLs for cotton improvement.

Genetic Diversity and Population Structure in Elite U.S. and Race Stock Accessions of Upland Cotton (Gossypium hirsutum)

Assessing genetic diversity and population structure is prerequisite to the systematic utilization and conservation of germplasm resources of crop plants. The genetic diversity and population structure in a combined panel of 557 Gossypium hirsutum L. accessions including 375 cultivars and 182 race stocks using 114 pairs of simple sequence repeat primers were evaluated in the current study. Six G. barbadense L. accessions were included as an out-group. Genotyping the diversity panel of 563 accessions with the markers identified a total of 819 alleles and 662 alleles within G. hirsutum. Population structure analysis identified one G. barbadense group and five G. hirsutum groups corresponding to southwestern cultivars, Mexican collections, western cultivars, southeastern and mid-south cultivars, and Guatemalan collections. Average genetic distance of 0.253 indicated a moderate level of genetic diversity in this panel. Analysis of molecular variance revealed a low level of differentiation among cultivated cotton groups compared to landrace accessions. Genetic diversity and population structure analyses suggest landraces of Guatemala could be a potential source of novel genetic variability for U.S. cotton. Further, multiple core sets with different levels of allele richness were identified. The diversity panel and the core sets identified could be a good resource for broadening the genetic base of U.S. cotton and for genetic analysis of agronomic traits.

Resistance to Cotton Fleahopper Feeding in Primitive and Converted Race Stocks of Cotton, Gossypium hirsutum

The cotton fleahopper, Pseudatomoscelis seriatus Reuter, is a widespread and important insect pest of cotton in Texas and Oklahoma. This plant bug feeds on small floral buds, which results in bud abscission, delayed fruiting, and subsequent crop loss. In central and southeastern Texas, two to four insecticide applications are typically applied for cotton fleahopper management. Primitive race stocks of cotton have been identified as an important source of resistance to a wide range of insect pests, but they have not been evaluated for resistance to cotton fleahopper. The objective of this study was to evaluate selected groups of primitive race stocks of Gossypium hirsutum L. for resistance to cotton fleahopper. Resistance was identified by caging cotton fleahoppers on cotton plants in a no-choice feeding trial and comparing the mean number of damaged squares per plant to a standard susceptible genotype. Four primitive race stocks, TX706, TX188, TX1530, and TX1156, were identified as resistant to cotton fleahopper in a collection of 65 primitive race stocks representing 18 genetic groups and collected throughout Mexico and Central America. No resistance was found in a collection of 11 accessions previously identified as resistant to Lygus spp. and no resistance was identified in a collection of 78 primitive accessions converted to day-neutrality. The possibility that some genetic resistance in these race stocks to the cotton fleahopper might have been lost as a result of the conversion to day-neutrality is discussed.

Registration of Four Diverse Random-Mated Cotton Germplasm Populations

Dwarf GP (Reg. No. GP-967; PI 669119), Fiber GP (Reg. No. GP-968; PI 669120), Glandless GP (Reg. No. GP-969; PI 669121), and Race GP (Reg. No. GP-970; PI 669122) are four unique upland cotton (Gossypium hirsutum L.) germplasm populations (GP) released by the USDA–ARS. Dwarf GP is a four-parent, narrow-based population developed to incorporate dwarfing genes into nondwarf genetic backgrounds. The remaining three populations are broad-based, complex populations. Fiber GP (24 parents) was developed to include potential sources of variation that would improve fiber length and strength. At the time these populations were developed, a viable glandless seed industry existed, and Glandless GP (22 parents) incorporated glandless germplasm from public and private breeders. Race GP (42 parents) was developed to obtain new genetic recombination events among a set of primitive race stock parents. These populations were created to recombine the variability from multiple parents into a single source from which selection can be initiated. Glandless GP was formed by random mating for nine cycles using a bulked pollen methodology. Dwarf GP, Fiber GP, and Race GP were formed by random mating for one cycle using a bulked pollen methodology followed by eight cycles using a male sterile. These populations possess trait specific and non-trait specific genetic diversity resulting from multiple generations of recombination and, therefore, present breeders with useful tools for improvement of elite germplasm.

Water‐Use Efficiency Is Negatively Correlated with Leaf Epidermal Conductance in Cotton (Gossypium spp.)

Water‐use efficiency (WUE) may be a useful trait for improving productivity of cotton (Gossypium spp.) under certain water‐limited conditions, but it is difficult to measure in the field or in large controlled‐environment screening studies. Recently, an easily measured trait, the epidermal conductance of dark‐adapted leaves (gdark), was shown to be predictive of whole‐plant WUE in soybean [Glycine max (L.) Merr.]. Here, a greenhouse experiment was conducted using 22 cotton race stocks, converted lines, and commercial varieties to determine if the relationship between WUE and gdark previously observed in soybean also exists in cotton. A secondary objective was to determine if genotypic differences in WUE and gdark in cotton were constitutive in nature, or if they differed between water replete and drought conditions. There was significant genotypic variation for both WUE and gdark, and in both cases the lack of a treatment × genotype interaction indicated that the trait was constitutive. The relationship between WUE and gdark (r = −0.75, P < 0.0001) was very similar to that reported previously for soybean. Understanding the mechanistic link between gdark and WUE may provide further insight into the physiological basis of genotypic differences in WUE.

Germplasm Potential for Trait Improvement in Upland Cotton: Diallel Analysis of Within‐Boll Seed Yield Components

Within-boll seed yield components (seed per boll, motes per boll, ovules per boll, and seed-setting efficiency [SSE]) were evaluated in a diallel analysis of eight upland cotton (Gossypium hirsutum L.) genotypes. Genotypes included four converted race stock (CRS) accessions representing putative extremes for SSE and four commercial types representing Texas, mid-South, and eastern cotton production regions. Parents and their F1 progeny without reciprocals were evaluated in 2000 and 2001 near College Station, TX. General combining ability (GCA) effects and specific combining ability effects (P = 0.05) were found for each trait, indicating potential for improvement of seed yield components in this population. The CRS accession M-9044-0162 had the best mean performance and GCA effects for each trait, suggesting that it would be a good parent for improving within-boll seed yield components in upland cotton.

Gene action and morphological characteristics of pink flower and pink filament mutants in cotton (Gossypium hirsutum L.)

Morphological mutants of cotton are used in studies of plant development and genetic mapping and occasionally have proven to have agronomic value. With few exceptions, the most useful mutants have been those found as spontaneous mutants in breeding populations. In general, they are more vigorous and easier to maintain and to manipulate in experimental conditions than induced mutants. The ability of cotton to tolerate duplication and deficiencies complicates recovery of mutants from high-energy-radiation treatments (Kohel et al. 1970). The majority of cultivated upland (Gossypium hirsutum L.) cottons have petal colour varying over white, cream, light yellow, yellow and pale purple which often becomes pinkish or purplish with age, but lack other petal colours. However, these colours are not uncommon in the so-called primitive cottons or race stocks. Other colours in flower parts, i.e. pink filament, are relatively uncommon in G. hirsutum although pink filament is diagnostic in a few other Gossypium species (Fryxell 1984; Wilson 1987). Inheritance of pink filament in the study of Wilson (1987) was found to be conditioned by two complementary dominant gene pairs, which were designated Pf1 and Pf2. These morphological mutants are therefore additional mutants for genetical research in cotton.

Development of a Screening Method for Drought Tolerance in Cotton Seedlings

The key to an efficient screening method is the ability to screen large amounts of plant material in the shortest time possible. Due to the complexity of drought tolerance, a quick and effective screen for this trait has yet to be established. The research reported herein was designed to evaluate a screening method for drought tolerance in cotton (Gossypium hirsutum L.) seedlings. Twenty‐one converted race stocks (CRS) and two cultivars were evaluated for seedling drought tolerance (SDT) on an individual plant basis. Genotypes were evaluated October–November 2004 and February–March 2005 under greenhouse conditions. Seedlings were subjected to three sequential cycles of drought at 15 d after planting (DAP). Drought cycles consisted of withholding water until the moisture content of indicator ‘Deltapine 491’ (DP 491) plants had an average volumetric water content of 0.07. Plants then were watered to saturation and allowed to drain to field capacity and percent survival recorded after 48 h. Genotypes differed in their percent survival following three consecutive drought cycles. Drought cycles 2 and 3 did not contribute to the separation of genotypes. DP 491 was the most tolerant genotype evaluated. The drought tolerance of the CRS was similar to that of ‘Acala 1517–99’. CRS M‐9044–0165 was the most stable genotype, according to an analysis of the difference in percentage of survival for each genotype across the two experiments.

Shoot and Root Characteristics of Converted Race Stocks Accessions of upland Cotton (Gossypium hirsutum L.) Grown under Salt Stress Conditions

Shoot and Root Characteristics of Converted Race Stocks Accessions of upland Cotton (Gossypium hirsutum L.) Grown under Salt Stress Conditions

Seedling Drought Tolerance in Upland Cotton

Combining root morphological and plant physiological traits associated with drought tolerance should result in improved drought resistance in cotton (Gossypium hirsutum L.). This study was designed to evaluate the response of root growth of selected Converted Race Stocks (CRS), TAM94L‐25, and ‘Lankart 142’ (LK 142) under water stress and nonstressed conditions, and to compare their excised leaf water loss (ELWL). Two putative seedling drought tolerant and two putative nonseedling drought tolerant CRS lines, plus TAM94L‐25 and LK 142, were grown with and without moisture stress in a greenhouse at College Station, TX, in 2002 and 2003. The robust rooting CRS, M‐9044‐0031‐R and M‐8744‐0175‐R, had longer tap root length (RL), higher lateral root number (LRN), greater total root dry weight (TRDW), greater root weight per unit length of tap root (W/L), and greater shoot dry weight (SDW) than the nonrobust CRS M‐9044‐0045‐NR and M‐9044‐0057‐NR, and LK 142 regardless of water regime. Two cycles of seedling drought resulted in an increase in LRN in M‐9044‐0057‐NR, TAM94L‐25, and LK 142. SDW and TRDW were highly correlated and SDW was associated with W/L. The excised leaf water loss (ELWL) tended to be greater in the NR CRS lines when measured at 30‐m intervals for 8 h. Results suggested (i) that root parameters, initial water content (IWC), and ELWL, could be used as a reliable selection criteria for drought tolerance and (ii) that day‐neutral CRS accessions could be used as a source of useful genetic variability for a cotton drought tolerance improvement program.

Root Growth Parameters of Converted Race Stocks of Upland Cotton and Two BC2F2 Populations

Genetic modification of the rooting system may lead to more drought tolerant upland cotton, Gossypium hirsutum L. This experiment was designed to evaluate rooting traits at the seedling stage for 68 Converted Race Stocks (CRS) compared with TAM94L‐25 and ‘Lankart 142’, and to investigate the recoverability of robust rooting traits in two BC2F2 populations derived by crossing a robust (M‐9044‐0031) and a nonrobust (M‐9044‐0057) rooting CRS donor parent with TAM94L‐25. Initial screen of the CRS showed that genetic variation occurred among the 68 accessions for root length (RL), lateral root number (LRN), root fresh weight (RFW), lateral root dry weight (LRDW), and total root dry weight (TRDW). There was a 2.3‐, 2.6‐, 4.6‐, 4.8‐, and 4.4‐fold difference among the 11 most robust and 11 least robust rooting CRS accessions for RL, LRN, RFW, LRDW, and TRDW, respectively. However, no CRS were identified that were superior to the elite germplasm and BC2F2 recurrent parent, TAM94L‐25. The robust rooting population of M‐9044‐0031/3*TAM94L‐25 produced longer RL and more LRN per plant than the nonrobust rooting population of M‐9044‐0057/3*TAM94L‐25. However, no differences were observed between the two BC2F2 populations for root weight parameters. Results suggest that the day‐neutral CRS accessions have useful genetic variability for root growth parameters, that robustness of seedling rooting parameters can be recovered easily, and that seedling rooting robustness can be improved by crossing robust rooting parents.

Simple Sequence Repeat–Based Assessment of Genetic Diversity in Cotton Race Stock Accessions

Effective use of converted day‐neutral Gossypium hirsutum L. race stocks in cotton genetic improvement programs depends on the extent of genetic variation for desirable alleles and the accurate characterization of the variability within and among germplasm accessions in the collection. This study was conducted to survey the molecular variation in the converted race stock collection by using simple sequence repeat (SSR) DNA markers and to determine the genetic distance of each race stock from a typical G. hirsutum cultigen. The molecular marker data will also provide a measure of the degree to which the recurrent photoperiodic parent has been recovered during backcross conversion to day‐neutral stocks. Fifty‐six flourescently labeled SSR primer pairs arranged in multiplex bins were used to genotype 97 day‐neutral BC4F4 race stock accessions. The majority of the accessions had genetic distances <0.25 from the G. hirsutum standard TM1. There was strong evidence that the accessions were heterozygous or heterogeneous, so 10 plants were genotyped within the most diverse nine accessions, those with genetic distance from TM1 >0.25. In some families, the primitive photoperiodic parent was recovered, and in others there was extensive linkage drag from the day‐neutral donor parent. The recovery of the primitive recurrent parent could be improved by marker‐assisted backcrossing with SSR markers reported in this experiment. Careful genotyping with SSR markers prior to introgression into breeding programs is suggested to ensure maximum genetic diversity and integrity of the exotic race‐stock donor germplasm.

Isoenzymatic variation in the germplasm of Brazilian races of maize (Zea mays L.)

There are more than 200 races of maize (Zea mays L.) divided into three groups (ancient commercial races, the recent commercial races, and indigenous races). Although the indigenous races have no commercial value, they have many important characteristics which can be incorporated into maize breeding programs. Most Brazilian indigenous germplasm race stocks were collected at least 40 years ago, and nothing is known of the genetic variability present in this germplasm. The genetic variability was assayed in 15 populations from four indigenous races of maize (Caingang, Entrelaçado, Lenha and Moroti) and five indigenous cultivars, using five isoenzymatic systems encoded by 14 loci. The analysis revealed a low level of variability among the samples studied. Overall, the mean number of alleles/polymorphic locus was three, 64.3% of the loci analyzed being polymorphic and the estimated heterozygosity was 0.352. The mean number of alleles/polymorphic locus per population was 1.6. A mean of 47.5% of the loci were polymorphic. The mean expected heterozygosity was 0.195, the mean genetic identity was 0.821 and the proportion of total genetic diversity partitioned among populations (Gst) was 0.156. A founder effect could explain the low variability detected.

Diversity in cyclic sesquiterpene production by Gossypium hirsutum

Major sesquiterpene components of oil of Texas Race Stock 810 of Gossypium hirsutum were α- and β-selinene. This is the seventh cyclic terpene type found to date in this genus. Both α- and β-selinene, along with aromadendrene, were found but only as minor components of extracts of several domestic cultivars of G. hirsutum.

Boll weevil Anthonomus grandis Boh. oviposition is decreased in cotton Gossypium hirsutum L. lines lower in anther monosaccharides and gossypol.

Several cotton Gossypium hirsutum L. race stocks have been identified that possess resistance to the boll weevil Anthonomus grandis Boh. because oviposition in the bud is decreased. In three tests of 13 boll weevil resistant lines conducted over a 6 year period on average, boll weevil punctures were decreased by 37.2% as compared to two susceptible commercial lines, while anther sugars were decreased 34.3% and anther gossypol was decreased 19.6%. Sugars and gossypol in the petals and ovaries were not different, however. Gas-liquid chromatographic analyses via the alditol acetate procedure revealed that the major free sugars of both the boll weevil suppressant and commercial cotton lines were glucose, fructose, sucrose, and arabinose with lesser amounts of xylose, galactose, and erythritol. Efforts to incorporate genes for oviposition resistance into commercial lines based on their correlation with low anther sugar content may have some promise.

Genetic variation for root-shoot relationships among cotton germplasm

Twenty-five cotton ( Gossypium spp.) genotypes were used to evaluate the genetic variability in partitioning of biomass into roots and shoots when plants were grown under conditions of declining soil water and different atmospheric evaporative demands. The entries ranged from primitive race stocks to modern cultivars and were selected on field observations of growth under water stress conditions in the field. Seeds of each genotype were planted in soil (56 kg) in large containers in the greenhouse. Water was added to the soil to bring the water content to field capacity and the plants were allowed to grow with no additional water until they reached the permanent wilting point. Large fans were utilized in the second experiment to reduce the leaf boundary layer resistance and increase the evaporative demand. When the plants of each entry had reached the permanent wilting point, the plants were harvested, the roots washed free of the soil, and the dry weights of both roots and shoots were determined. Information on total water used and days to permanent wilting were also collected for each genotype. Differences were observed in partitioning of total biomass between roots and shoots between experiments and genotypes. There was no significant interaction, however, between entries and experiments. Root-shoot ratios increased in plants grown in the more stressful environment resulting from a significant increase in root dry weights with little change in shoot dry weights. The distribution for root-shoot ratios coincided in general with the distribution for root weights.among the entries, with a 59% decrease from the highest to lowest value. The exotic strains also in general had higher root-shoot ratios than the commercial varieties, the herbaceum species and the experimental strain (Lubbock dwarf). There was no direct relationship between shoot weights and root weights among the genotypes for either environment. Those plants that grew large tops did not necessarily grow correspondingly large root systems (e.g. T141 has a large root system with a very small shoot compared to the herbaceum species, which has a relative large shoot and a small root system). The lack of a correlation between shoot and root growth along with genotypic differences in changes in root-shoot ratios in response to environmental demand may provide an opportunity to exploit the observed variability to improve production for a wide range of growth conditions by altering the root development and function independent of shoot development.

Genetic variation among cotton germplasm for water-use efficiency

Cotton ( Gossypium spp.) genotypes including three species, five modern cultivars, one strain and 18 primitive race stocks were grown in two greenhouse experiments to determine differences in water-use efficiency (WUE). Water-use efficiency was defined as “the weight of total biomass (shoot and root) produced per unit of water transpired”. Plastic containers were filled with air-dried soil, and water was added until the soil reached field capacity. Plants were then grown (with further watering) until reaching the permanent wilting point. Data on plant biomass (shoot and root), water use, and days to permanent wilting were then collected. Differences occurred between the two experiments in water used prior to permanent wilting. No significant differences between genotypes were observed in the amount of water used, but differences did occur in biomass production and days to permanent wilting. Genotypes did not interact with environments for water used, biomass produced, or WUE. Differences did occur among genotypes between experiments for WUE. Genotypic means showed a 28% range in WUE between the highest vs the lowest entries and a 14% improvement above the best cultivar. G. herbaceum L. and G. barbadense L. fell within the distribution range for G. hirsutum L. Primitive race stocks of G. hirsutum were more efficient as a group in water use than were modern cultivars of the species.

Possible roles of cotton bud sugars and terpenoids in oviposition by the boll weevil

Several cottonGossypium spp. race stocks have been identified that possess resistance to the boll weevilAnthonomus grandis Boh. because oviposition is decreased. In this work, a number of known cotton constituents that influence stimulation of feeding and attractancy for this insect were found to have little or no influence on oviposition. These include gossypol, β-bis-abolol, caryophyllene, some fatty acids and their methyl esters, some wax esters, flavonoids, condensed tannins, and chrysanthemin. Analysis of cotton bud surfaces showed that the content of volatile terpenoids was generally higher in resistant lines, but bioassays did not show decreased oviposition in the presence of the terpenoids. The sugars (glucose, fructose, and sucrose) found in anthers, uniformly stimulated oviposition in the bioassay, and their content was higher in susceptible lines. These results suggest that a major basis of resistance to boll weevils as related to oviposition may be the decreased content of sugars in resistant lines. The analysis of free sugars in the anthers, and perhaps also the analysis of bud surface terpenoids, may provide a basis for selection or genetic production of cotton lines resistant to the boll weevil.

Inheritance of pink filament in cotton

The stamens of a photoperiodic race stock of cotton, Gossyplum hirsutum L., had pink filaments and the petals had a basal wine-colored spot, the latter conditioned by the R2 gene. A cross of this stock to cultivars of upland cotton, which had cream filaments and lacked a petal spot, showed that non-petal spot was epistatic to pink filament. A cross between a line selected for full petal spot and pink filaments and one selected for full petal spot and cream filament showed that pink filament is conditioned by two incompletely dominant gene pairs, tentatively designated Pf1 and Pf2.

Pink Bollworm (Lepidoptera: Gelechiidae): Selecting for Antibiosis in Artificially and Naturally Infested Cotton Plants

Artificial and natural infestation methods were used to separate internal-boll antibiosis from other types of resistance in cotton, Gossypium hirsutum L., to the pink boll worm (PBW), Pectinophora gossypiella (Saunders). Nine cottons, which included seven Texas race stocks (T-) and a susceptible and resistant check, were planted in field plots at Phoenix, Ariz., in 1979. Green bolls, 14 to 21 days old, in one row of each plot were infested weekly with PBW eggs on 1-cm2 slips of paper. Green bolls were harvested from half of the row and seed cotton was harvested from the other half. One race stock, T-53, had significantly fewer entrance holes per boll than the susceptible check, ‘Deltapine 61’ (DPL-61), while T-39, T-40, T-53, and T-167 had significantly fewer insects per boll. T-39 and T-705 caused lower insect survival in the boll—i.e., lower ratios of insects per boll to entrance holes per boll—than did the susceptible check. Seed that was X-rayed showed that T-39, T-167, and T-705 had significantly lower percentages of seed damage than DPL-61. In naturally infested plots, only T-39 and the resistant check, AET-5, had less seed damage than the susceptible check. Subsequent tests suggested that T-39 contained both PBW-resistant and PBW-susceptible component lines. In 1982, in plots infested artificially via a repeating pipette method, only 1 of 10 progenies of selected T-39 sublines had significantly less seed damage, but seven sublines had significantly more, than DPL-61. In 1983, two T-39 sublines, selected for low damage in 1982, had significantly less damage than DPL-61. The one T-39 subline selected for high damage in 1982 did not differ significantly in damage from DPL-61 in 1983. T-167, the other race stock selected from the 1979 test, failed to show resistance in the 1983 test. Five (AET-5 × T-167)F4 hybrids had significantly less seed damage than T-167 but did not differ from AET-5 in the 1983 test.