Ryan P. Viator

Reproductive abnormalities in glyphosate-resistant cotton caused by lower CP4-EPSPS levels in the male reproductive tissue

Abstract Glyphosate treatments to glyphosate-resistant (GR) cotton have been associated with poor pollination and increased boll abortion. Anatomical studies were conducted to characterize the effect of glyphosate treatments on the development of male and female reproductive organs of cotton flowers at anthesis. In comparison with nontreated plants, glyphosate applied at both the four-leaf stage postemergence (POST) and at the eight-leaf stage POST directed inhibited the elongation of the staminal column and filament, which increased the distance from the anthers to the receptive stigma tip by 4.9 to 5.7 mm during the first week of flowering. The increased distance from the anthers to the stigma resulted in 42% less pollen deposited on stigmas of glyphosate-treated plants than in nontreated plants. Moreover, pollen from glyphosate-treated plants showed numerous morphological abnormalities. Transmission electron microscopy showed the presence of large vacuoles, numerous starch grains, and less organized pockets of the endoplasmic reticulum containing fewer ribosomes in pollen from glyphosate-treated plants than from nontreated plants. Pollen development in glyphosate-treated plants is likely inhibited or aborted at the vacuolate microspore and vacuolate microgamete stages of microgametogenesis, resulting in immature pollen at anthesis. Although stigmas from glyphosate-treated plants were 1.2 to 1.4 mm longer than those from nontreated plants, no other anatomical differences in stigmas were visibly evident. The presence of the GR 5-enolpyruvylshikimate-3-phosphate synthase (CP4-EPSPS) enzyme from Agrobacterium sp. strain CP4 was quantified in reproductive and vegetative tissues using enzyme-linked immunosorbent assay. The content of CP4-EPSPS in the stigma, anther, preanthesis floral bud (square), and flower petals was significantly less than that in the vegetative leaf tissue. Glyphosate effects on the male reproductive development resulting in poor pollen deposition on the stigma, as well as production of aborted pollen with reduced viability, provide a likely explanation for reports of increased boll abortion and pollination problems in glyphosate-treated GR cotton. Nomenclature: Glyphosate; cotton, Gossypium hirsutum L. ‘Delta Pine & Land 5415RR’, ‘Delta Pine & Land 50’, ‘Delta Pine & Land 90’, ‘SureGrow 125RR’.

Effects of Glyphosate Application Timing and Rate on Sicklepod (Senna obtusifolia) Fecundity1

Greenhouse experiments were conducted to examine the effect of glyphosate on reproductive development in sicklepod. Glyphosate was applied postemergence over the top at 112 and 280 g ai/ha to sicklepod at 4-leaf stage (L), 8-L, 4-L followed by 8-L, and 12-L. A nontreated control was included. Immediately after the 12-L application, number of flowers was recorded for all treatments twice per week for 8 wk. Pollen viability was measured on 1 open flower/plant/sampling time using Alexander stain. The number of pods, pod length, seeds per plant, 50-seed weight, total seed weight, seed germination, seed viability, and dry weight of aboveground biomass were also recorded. No significant differences among the treatments were found for average pod length, 50-seed weight, seed germination, seed viability, and aboveground biomass. The nontreated had 18 flowers counted over 8 wk. Glyphosate applied at 12-L and sequentially at 4-L and 8-L, averaged over glyphosate rates, reduced cumulative flower production after 8 wk by 65 and 54%, respectively, compared with the nontreated. Similarly, glyphosate at 280 g/ha, averaged over treatment timings, reduced flower production by 58% compared with the nontreated. Because the number of flowers produced was limited by glyphosate treatment due to flower abscission, pollen viability measurements could not be analyzed because of large numbers of missing data points. The number of pods, seeds, and total seed weight were reduced by 79, 80, and 81%, respectively, with 280 g/ha of glyphosate compared with the nontreated. Nomenclature: Glyphosate; sicklepod, Senna obtusifolia (L.) Irwin and Barneby #3 CASOB. Additional index words: Alexander stain, pollen viability, tetrazolium chloride. Abbreviations: fb, followed by; IAA, indoleacetic acid; L, leaf stage.

Effect of glyphosate application timings and methods on glyphosate-resistant cotton

Abstract Under certain conditions, application of glyphosate to glyphosate-resistant (GR) cotton can lead to fruit shedding and yield reductions. Field studies were conducted at the Texas Agricultural Experiment Station using GR cotton, cv. ‘DeltaPine 5690RR’, to determine if application method and timing affect cotton fruit retention. Glyphosate at 1.12 kg ai ha−1 was precisely postdirected (PD), postdirected with 25% foliage coverage (PDFC), or applied over the top (OT) at the 8- or 18-leaf stage after an initial topical application of 1.12 kg ha−1 glyphosate at the four-leaf stage. In one of the years of this study, 8 PD, 18 PDFC, and 18 OT reduced yield. In 1999 and 2000, 8 PDFC and 8 OT applications of glyphosate caused yield loss, mainly due to lower mean boll weight. Glyphosate applied topically at the eight-leaf stage also affected the Position 1 boll retention throughout the plant in both years. Glyphosate contact with leaves and stems should be avoided when applying glyphosate after the four-leaf stage to prevent possible yield loss. Nomenclature: Glyphosate; cotton, Gossypium hirsutum L. ‘DeltaPine 5690RR’.

Boll Abscission Responses of Glyphosate-Resistant Cotton (Gossypium hirsutum) to Glyphosate1

Response of glyphosate-resistant cotton to various rates of topically applied glyphosate was investigated in growth chamber experiments to determine the relationship between glyphosate rate and boll abscission. Glyphosate at 0, 0.56, 1.12, or 2.24 kg ai/ha was applied to all exposed foliage at the 12-leaf growth stage. Immediately after this treatment, 14C-glyphosate was applied to the three uppermost fully expanded leaves at 0, 37, 74, or 148 kBq per leaf for the 0, 0.56, 1.12, or 2.24 kg/ha treatment, respectively. After glyphosate application, glyphosate accumulated in reproductive tissue, and bolls were abscised. Abscission increased as the amount of glyphosate translocated to fruiting sites increased. Nomenclature: Glyphosate; cotton, Gossypium hirsutum L., ‘Delta & Pine Land 5690RR’. Additional index words: Boll abscission; transgenic crops. Abbreviations: EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase (EC 2.5.1.19); GR, glyphosate resistant; WAT, weeks after treatment.

Sugarcane Chopper Harvester Extractor Fan and Ground Speed Effects on Yield and Quality

Operational settings on chopper harvesters are extremely important in green-cane harvesting since one is relying solely on the harvester to remove extraneous matter instead of the traditional pre-harvest burn method. The objective of this research was to determine the combined effect of selected ground and fan speeds on sugar yield, cane quality, and field losses using a commercial chopper harvester. In both 2003 and 2004, a split-plot experiment was performed at harvest with the main plots having ground speeds of 4.0, 4.8, and 5.6 km h-1 and subplots having primary extractor fan speeds of 650, 850, and 1050 rpm of the 1.5-m diameter fan. Under the optimal conditions (low leaf and soil moisture), the 1050 rpm fan speed increased theoretical recoverable sugar (TRS) by 10% but decreased cane yield by 15% compared to the two lower fan speeds resulting in similar sugar yields for all fan settings. Under poor conditions (high leaf and soil moisture), the 1050-rpm fan speed decreased cane yield by 13% without an increase in TRS, resulting in lower sugar yields than the low or medium fan settings. Ground speed, under both conditions, did not affect cane yield or quality. The chopper harvester performed well under ideal conditions with a primary fan speed of 1050 rpm but had decreasing performance under poor conditions regardless of fan speed.

Microsatellite DNA marker-assisted selection ofSaccharum spontaneum cytoplasm-derived germplasm

New lines of Saccharum hybrids with an array of S. spontaneum cytoplasm backgrounds are reported. To expand the genetic base of sugarcane, we made eleven bi-parental crosses between ten S. spontaneum (S) and six commercial-type sugarcane (C) clones during the 2001 crossing season. Prior to crossing, all the maternal S. spontaneum inflorescences were emasculated by immersion in a 50°C circulating water bath for 5 minutes. Analysis of microsatellite fingerprints between parents and progeny allowed us to classify 1,952 progeny grown out from these crosses into four genotypic classes. Class H progeny inherited microsatellite alleles from both the S. spontaneum and the commercial-type parents and were, therefore, considered being F1 hybrids. Class S and Class C progeny inherited microsatellite alleles only from one parent and were considered to be either selfs of either parent or F1 hybrids that only inherited allele(s) from one parent. Class X progeny inherited non-parental microsatellite allele(s) in addition to the allele(s) from the maternal S. spontaneum parent and were considered to be contaminants. With the exception of one cross, eight to ten Class H progeny were pre-selected from each cross while still in seedling greenhouse and were backcrossed with commercial-type sugarcane clones. The remaining progeny were transplanted into a breeding nursery for phenotypic evaluation that concurred with the molecular classification. Pearson Correlation Coefficients between molecular and phenotypic classifications were inconsistent that justified the need of molecular markers in the selection process. This study demonstrated that the molecular approach of fingerprinting progeny to confirm parentage prior to field planting even with only one microsatellite marker might substantially increase selection efficiency.

Glufosinate does not affect floral morphology and pollen viability in glufosinate-resistant cotton

Studies were conducted to determine whether glufosinate treatments to glufosinate-resistant cotton caused changes in floral morphology, pollen viability, and seed set. Four glufosinate treatments were included: (1) glufosinate applied postemergence over the top (POST) at the four-leaf stage, (2) glufosinate applied POST at the eight-leaf stage, (3) the first two treatments sequentially, and (4) a POST application at the four-leaf stage followed by (fb) a postemergence-directed stem application (PDS) at the eight-leaf stage. Glufosinate was consistently applied at 0.49 kg ai/ha. A nontreated control was included. Glufosinate treatments did not affect stigma height, length of the staminal column, or pollen viability. However, the distance from the top anther to the tip of the stigma was less in plants treated with an eight-leaf POST treatment than in nontreated plants, although this difference is not likely to influence pollen deposition because in both cases anthers reached above the stigma tip. Plants receiving four-leaf POST fb eight-leaf PDS treatment with glufosinate had eight seeds per boll less than nontreated plants; however, the more rigorous four-leaf POST fb eight-leaf POST treatment did not differ from the nontreated in seeds per boll. Nomenclature: Glufosinate; cotton, Gossypium hirsutum L. Additional index words: Glyphosate, herbicide-resistant crops, transgenic crops. Abbreviations: fb, followed by; PDS, postemergence-directed stem application; POST, postemergence over the top.

Stem and Root Carbohydrate Dynamics in Modern vs. Obsolete Cotton Cultivars

Abstract Starch reserves in the lower stem and root are important sources of photoassimilates for completion of reproductive development in cotton. The objective of this research was to determine if carbohydrate levels in the lower stem and roots have been altered because of more than 100 years of breeding efforts. In 2001 and 2002, 33 cultivars released from 1900 to 2000 were evaluated. In addition, two elite lines were included in 2002. Plants were sampled at first bloom and cutout. Tissues were analyzed for starch content and concentration by using a colorimetric technique. Analysis of variance by year revealed cultivar differences for starch concentration at both sample times, but starch content was only significant at first bloom in 2002. These differences, though, did not show a strong relationship with release date, indicating that a century of breeding efforts had not altered stem and root starch dynamics. Orthogonal contrast did reveal differences in starch content and concentration between obsolete, modern, and elite lines. However, these differences were not consistent across experimental years. At first bloom in 2001, modern cultivars had lower root and stem starch concentrations, 69.8 and 63.6 mg g−1, compared to 94.5 and 84.8 mg g−1 for the obsolete lines. Modern cultivars also had lower root starch content, 537.5 mg, compared to 784.4 mg for the obsolete lines. At cutout in 2001, modern cultivars had lower root and stem starch concentrations, 20.6 and 20.9 mg g−1, compared 39.7 and 32.4 mg g−1 for the obsolete lines. Modern cultivars also had lower stem starch content, 349.0 mg, compared to 518.4 mg for the obsolete lines. These same trends were not seen in 2002. In 2002, modern cultivars did not differ from obsolete cultivars for all parameters. Elite lines, though, had higher stem starch concentrations at cutout, 56.9 mg g−1 compared to 39.5 and 46.6 mg g−1 for the obsolete and modern lines, respectively. Elite lines also had higher stem starch contents at cutout, 318.6 mg compared to 181.7 and 195.7 mg for the obsolete and modern lines, respectively. This higher stem starch concentration and content for elite lines may indicate higher photosynthetic rates. Environmental conditions seem to affect starch dynamics more than genetics when one considers the high significance of year on most data in this study.

Estimating Broad Sense Heritability and Investigating the Mechanism of Genetic Transmission of Cold Tolerance Using Mannitol as a Measure of Post-freeze Juice Degradation in Sugarcane and Energycane (Saccharum spp.)

In approximately 25% of the sugarcane-producing countries worldwide, conventional sugarcane (Saccharum spp. hybrids) is exposed to damaging freezes. A study was conducted during the 2009 and 2010 harvest seasons to compare late-season freeze tolerance among three groups: commercial Louisiana sugarcane genotypes, early generation genotypes selected for cold tolerance in the U.S. Department of Agriculture sugarcane breeding programs at Houma, LA, and Canal Point, FL, and potential energycane genotypes selected for high total biomass per acre. Mannitol concentrations in cane juice following freezing temperatures were determined to evaluate levels of cold tolerance. Genotypes selected for cold tolerance in Houma, LA, had significantly more late-season freeze tolerance than commercial sugarcane genotypes and genotypes selected in Canal Point, FL. Genotypes showing the most cold tolerance were Ho02-146 and Ho02-152, and those that were most highly susceptible were US87-1006 and US87-1003 (early-generation breeding genotypes) and L99-233 (commercial genotype). Broad-sense heritability for late-season cold tolerance in the two-year study was estimated at g(2) = 0.78. The enzymatic mannitol analysis successfully differentiated high-fiber energycane genotypes from those from other sources.

Integrated Management of Bermudagrass (Cynodon dactylon) in Sugarcane

Abstract Bermudagrass is a difficult perennial weed to manage in Louisiana sugarcane. Research was conducted to compare interrow tillage practice, postharvest residue management, and herbicide placement on bermudagrass proliferation and sugarcane yield. Tillage frequencies included conventional (four tillage operations per season), reduced (two tillage operations), and no-till. Residue management practices included removal by burning, sweeping from row top into the wheel furrow, and not removed. Spring herbicide placement treatments included broadcast, banded, or no herbicide application. With conventional tillage, broadcast and banded herbicide applications resulted in similar bermudagrass cover in the first and second ratoon crops, but bermudagrass cover was greater when using banded applications (22%) compared with broadcast application (15%) in the third-ratoon crop. Bermudagrass cover was greatest with no-till. When herbicides were banded, bermudagrass cover was greater in reduced tillage than conventional tillage in all three ratoon crops. Postharvest residue management did not affect bermudagrass ground cover. In plant cane, sugarcane yields were lowest when herbicide was not applied. In ratoon crops, sugarcane and sugar yield were reduced when herbicide was not applied regardless of tillage practice. Cane and sugar yield were generally equal when comparing reduced and conventional tillage. Total sugarcane yield (4 crop yr) for the no-till program was reduced 11, 15, and 25%, respectively, when herbicides were broadcast, banded, and when herbicide was not applied, compared with conventional tillage. Failure to remove residue reduced sugarcane yield by 5, 7, and 10% in first, second, and third ratoons, respectively, compared with burning. Eliminating unnecessary tillage practices can increase profitability of sugarcane through reduced costs, but it will be imperative that herbicide programs be included to provide adequate bermudagrass control and that postharvest residue is removed to promote maximum sugarpostane yield. Nomenclature: Metribuzin; pendimethalin; bermudagrass, Cynodon dactylon (L.) Pers.; sugarcane, Saccharum interspecific hybrid.