D. T. Bowman

Genetic Uniformity of the U.S. Upland Cotton Crop since the Introduction of Transgenic Cottons

cotton producing regions of the USA between 1970 and 1995, but increases in rf because of the planting of genetiField genetic uniformity is the probability that any two plants cally related cultivars was buffered by availability of selected at random within a region carry alleles that are identical by descent. Genetic uniformity of field crops can occur through breeding new cultivars. with genetically related backgrounds and grower choice of a few Cotton cultivar development for certain U.S. producrelated cultivars among other factors. Transgenic cotton cultivars curtion regions rested on a narrow genetic base in the early rently dominate the U.S. cottonseed market, comprising approxi1990s (May et al., 1995). Since 1995, the U.S. cotton mately 72% of the Year 2000 cotton hectares. All transgenic cotton crop has experienced a nearly complete turnover in cultivars were derived through backcross breeding with popular nonmajor cultivars, primarily because transgenic cultivars transgenic cultivars. The objective of this study was to apply pedigree possessing pest management traits have become very analysis to estimate field genetic uniformity since transgenic cultivars popular (USDA-AMS, 1996, 2000). Transgenic cultivars were introduced into the U.S. cottonseed market in 1996. Coefficients comprised 72% of U.S. hectarage in 2000. Cotton proof parentage and proportion of hectares planted to transgenic cultivars were employed to estimate field genetic uniformity for the southeastduction has been simplified through the incorporation ern, south-central, southwestern, and western production regions. of a gene from Bacillus thuringiensis (Bt or Bollgard) Compared with field genetic uniformity estimated in the Year 1995 imparting resistance to lepidopteran insect pests (Jenpreceding introduction of transgenic cultivars, field genetic uniformity kins et al., 1997) and genes (Johnson, 1996) conferring did change (0.18 vs. 0.13). The number of cultivars planted on the resistance to application of the broad spectrum nonselargest hectarage has not changed, but the percentage of the crop lective herbicide glyphosate [N-(phosphonomethyl)planted to a few cultivars has declined. The proportion of the hectarage glycine Roundup Ready, Monsanto Corp., St. Louis, planted to the most popular cultivar also has declined. Both of these MO, or RR], or the less broad spectrum herbicide brofactors affected field genetic uniformity resulting in a 28% reduction moxynil (3,5-dibromo-4-hydroxybenzonitrile BXN). in uniformity across the USA. Many cultivars planted on significant hectarage since 1996 have either the herbicide tolerance gene alone or glyphosate with the Bt gene, and less frequently the F genetic uniformity is the probability that any Bt gene without an accompanying herbicide resistance two plants selected at random within a region carry gene. Cultivars containing the glyphosate resistance alleles that are identical by descent. Genetic uniformity gene alone or in combination with a Bt gene comprised predisposes crops produced over large hectarage to over 54% of the U.S. cottonseed market in 2000 losses from biotic and abiotic stresses, an occurrence (USDA-AMS, 2000). observed with the near failure of the southern corn Genetic uniformity of the U.S. cotton crop has not (Zea mays L.) crop in 1970 (Ullstrup, 1972). Genetic been determined since the deployment of transgenic uniformity of a crop can be enumerated by considering cultivars. Backcross introgression (an average of three relationships among cultivars available for planting backcrosses) of pest management transgenes has been through molecular approaches or pedigree analysis. the most common method of cultivar development in Pedigree analysis remains an attractive approach in cotrecent years. All transgenic cultivars available to U.S. ton (Gossypium hirsutum L.) because of simplicity and growers were derived through backcross breeding with the fact that most molecular markers exhibit low polygenetically related recurrent parent cultivars widely morphism within G. hirsutum (Paterson and Smith, grown in 1995. Genetic gains in lint yield may have 1999). Bowman et al. (1996) employed coefficients of suffered as a consequence. Genetic uniformity is further parentage (rp) to assess breadth of the cotton genetic imposed through incorporation of the same transgenes base and found it to be relatively expansive, but that only a fraction of the available genetic base has been into different genetic backgrounds because the DNA exploited in cultivar development. Van Esbroeck et al. insert containing the transgene and its regulatory ele(1998) calculated field uniformity (rf) through 1995 conments also is accompanied by DNA surrounding the sidering cultivar genetic relationships adjusted for the site of insertion into the donor parent (Falconer, 1989), hectarage planted to each cultivar. They found rf to be typically the cv. Coker 312. This nontarget DNA is not relatively high (average rf 0.30) among the major entirely eliminated during the introgression and selection phases of transgenic cultivar development. The objective of this study was to determine the impact of D.T. Bowman, Dep. of Crop Science, North Carolina State Univ., Box 8604, Raleigh, NC 27695-8604; O.L. May, Dep. of Crop & Soil breeding transgenic cultivars on field genetic uniformity. Science, Univ. of Georgia, P.O. Box 748, Tifton, GA 31793; J.B. Creech, Delta Res. & Ext. Ctr., P.O. Box 197, Stoneville, MS 38776. Received 15 April 2002. *Corresponding author (daryl_bowman@ MATERIALS AND METHODS ncsu.edu). Methods used in this study are identical to those published by Van Esbroeck et al. (1998). Data on hectarage planted for Published in Crop Sci. 43:515–518 (2003).

Status of the USA cotton germplasm collection and crop vulnerability.

The National Plant Germplasm System (NPGS) is a cooperative effort among State, Federal and Private organizations aimed at preserving one of agriculture’s greatest assets: plant genetic diversity. The NPGS serves the scientific community by collecting, storing, and distributing germplasm as well as maintaining a searchable database of trait descriptors. Serving the NPGS, a Crop Germplasm Committee (CGC) is elected for each crop and is comprised of a group of scientists concerned with development, maintenance, characterization, and utilization of germplasm collections. Each CGC serves in an advisory role and provides a status report every seven years to determine scientific efforts, adequacy of germplasm base representation, and progress in breeding through utilization of germplasm. In addition, each committee can call attention to areas of concerns regarding facilities and staffing associated with the maintenance, collection, and taxonomic activities for a specific crop within the system. The following report was developed by the CGC for cotton and provides a record of collections, activities, concerns, crop vulnerabilities, and recommendations associated with the cotton collection for the period 1997–2005. Information provided within this document is a much expanded and detailed description of a report provided to the NPGS and includes the most exhaustive citation of germplasm depositions and research activity descriptions available anywhere in the USA for this time period. This documentation will be a valuable resource to breeders, geneticists, and taxonomists with an interest in this important food and fiber crop.

Effects of Rate and Time of Application of Poultry Litter on Hoplolaimus columbus on Cotton

Field experiments were conducted to evaluate the effect of soil-incorporated poultry litter on the population dynamics of Hoplolaimus columbus and cotton lint yield. Rates of poultry litter applied varied from 0.0 to 27.0 t/ha and were applied in December, February, or March. Time of application did not influence population densities of this nematode or cotton yield. The rate of poultry litter applied was negatively related to the population density of H. columbus at midseason, but not at other sampling dates. The lower midseason levels of this nematode corresponded with increases in cotton lint yield in all experiments. Cotton yield increases generally were linear with respect to the rate of litter applied, although the highest rates of litter applied did not always result in the greatest cotton yield. Poultry litter can be used effectively to supply nutrients to the crop and suppress damaging levels of H. columbus. Optimal rates of litter application were from 6.0 to 13.4 t/ha. Application of poultry litter at these rates, however, may exceed nutrient levels required for best management practices.

Modifications to a LATE MERISTEM IDENTITY1 gene are responsible for the major leaf shapes of Upland cotton (Gossypium hirsutum L.)

Significance Leaves are the primary source of photoassimilate in crop plants. A precise understanding of the genetic architecture underlying leaf morphology is critical to engineering climate-resilient crop varieties. An ideal cotton cultivar would produce a lower canopy of broad, normal leaves before transitioning to an upper canopy of highly lobed, okra leaves. Here we show that the major leaf shapes of cotton are controlled by the okra locus, which encodes an HD-Zip transcription factor Gossypium hirsutum LATE MERISTEM IDENTITY1-D1b (GhLMI1-D1b). Using gene silencing, we temporarily induced normal leaf formation in okra, thus validating the candidate gene and creating the leaf shape ideotype in cotton. This study, identifying a single locus responsible for cotton leaf shape, expands the genetic toolbox for breeders to produce superior cotton varieties. Leaf shape varies spectacularly among plants. Leaves are the primary source of photoassimilate in crop plants, and understanding the genetic basis of variation in leaf morphology is critical to improving agricultural productivity. Leaf shape played a unique role in cotton improvement, as breeders have selected for entire and lobed leaf morphs resulting from a single locus, okra (l-D1), which is responsible for the major leaf shapes in cotton. The l-D1 locus is not only of agricultural importance in cotton, but through pioneering chimeric and morphometric studies, it has contributed to fundamental knowledge about leaf development. Here we show that an HD-Zip transcription factor homologous to the LATE MERISTEM IDENTITY1 (LMI1) gene of Arabidopsis is the causal gene underlying the l-D1 locus. The classical okra leaf shape allele has a 133-bp tandem duplication in the promoter, correlated with elevated expression, whereas an 8-bp deletion in the third exon of the presumed wild-type normal allele causes a frame-shifted and truncated coding sequence. Our results indicate that subokra is the ancestral leaf shape of tetraploid cotton that gave rise to the okra allele and that normal is a derived mutant allele that came to predominate and define the leaf shape of cultivated cotton. Virus-induced gene silencing (VIGS) of the LMI1-like gene in an okra variety was sufficient to induce normal leaf formation. The developmental changes in leaves conferred by this gene are associated with a photosynthetic transcriptomic signature, substantiating its use by breeders to produce a superior cotton ideotype.

Cotton Tolerance to Hoplolaimus columbus and Impact on Population Densities

Glyphosate-tolerant transgenic-cotton cultivars were evaluated for tolerance to Hoplolaimus columbus in field experiments conducted from 2001 to 2003. The studies were arranged in a split-plot design that included treatment with 1,3-dichloropropene at 42 liter/ha to establish fumigated versus nonfumigated subplots with cultivars as whole plots. Cotton cultivars were divided by relative maturity into two separate but adjacent experiments in order to facilitate cotton defoliation, with 10 early-maturity and 5 late-maturity cultivars. Fumigation was effective in suppressing H. columbus population densities and increased cotton lint yield. The cultivar-fumigation interaction was significant for early-season cotton cultivars but not for late-season cultivars. A tolerance index ([yield of nontreated/yield of treated] × 100) was used to compare cultivar differences. Both groups of cultivars expressed significant levels of tolerance to H. columbus, but late-season cultivars tended to yield more than early-season cultivars in infested fields.

Field Cotamination of Sorghum with Zeralenone and Deoxynivalenol in North Carolina: Density Segregation to Remove Mycotoxins

Studies by Hagler et al. (1987) from 1981-1985 revealed that much of the grain sorghum grown in North Carolina was, except in 1983, contaminated at - harvest with zearalenone (ZE), deoxynivalenol (DON), and toalesser degree, aflatoxins (AF) B1 and B2. These studies defined some factors controlling occurrence of these mycotoxins in grain sorghum. Rainfall during flowering and early maturation was associated with the Increased incidence and concentration of ZE and DON. In 1983, there was a drought during this critical period which apparently prevented ZE and DON contamination (Bowman et al. , 1986; Hagler et al. , 1987). Zearalenone had been reported in grain sorghum previously (Schroeder and Hein, 1975; Bennett and Shot well, 1979; Shotwell et al. , 1980; M c Millian et al. , 1983). Deoxynivalenol, which frequently occurs with ZE in corn ( Thiel et al. , 1982), had not been previously reported as a contaminant of sorghum until 1981 (Hagler et al. , 1987).

Screening Germplasm and Quantification of Components Contributing to Thrips Resistance in Cotton

Abstract Three hundred and ninety-one Gossypium hirsutum and 34 Gossypium barbadense accessions were screened for thrips resistance under field conditions at the Upper Coastal Plain Research Station in Rocky Mount, North Carolina in years 2014 and 2015. Visual damage ratings, thrips counts, and seedling dry weights were recorded at 2.5, 3.5, and 4.5 wk after planting, respectively. Population density and thrips arrival times varied between years. Data from the three separate damage scoring dates provided a better estimate of resistance or susceptibility to thrips than ratings from the individual dates over the season. Tobacco thrips [Frankliniella fusca (Hinds) (Thysanoptera: Thripidae)], followed by western flower thrips [Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)], were the dominant thrips species observed in the study. Five resistant G. barbadense accessions and five moderately resistant upland cotton accessions were identified from field evaluations. Greenhouse experiments were conducted in Fall 2015 and Spring 2016 to determine if plant height, growth rate, leaf pubescence, and leaf area were significantly different in resistant and susceptible groups of G. hirsutum and G. barbadense accessions identified from the field screenings. Leaf pubescence and relative growth rate were significantly higher in resistant accessions compared with susceptible accessions in absence of thrips. There was no difference for plant height and leaf area between resistant and susceptible groups. Results suggest thrips-resistant plants have a possible competitive advantage through faster growth and higher trichome density, which limits thrips movement.