Gaylon D. Morgan

Spatial and Temporal Variation in Fungal Endophyte Communities Isolated from Cultivated Cotton (Gossypium hirsutum)

Studies of fungi in upland cotton (Gossypium hirsutum) cultivated in the United States have largely focused on monitoring and controlling plant pathogens. Given increasing interest in asymptomatic fungal endophytes as potential biological control agents, surveys are needed to better characterize their diversity, distribution patterns and possible applications in integrated pest management. We sampled multiple varieties of cotton in Texas, USA and tested for temporal and spatial variation in fungal endophyte diversity and community composition, as well as for differences associated with organic and conventional farming practices. Fungal isolates were identified by morphological and DNA identification methods. We found members of the genera Alternaria, Colletotrichum and Phomopsis, previously isolated as endophytes from other plant species. Other recovered species such as Drechslerella dactyloides (formerly Arthrobotrys dactyloides) and Exserohilum rostratum have not, to our knowledge, been previously reported as endophytes in cotton. We also isolated many latent pathogens, but some species such as Alternaria tennuissima, Epicoccum nigrum, Acremonium alternatum, Cladosporium cladosporioides, Chaetomium globosum and Paecilomyces sp., are known to be antagonists against plant pathogens, insects and nematode pests. We found no differences in endophyte species richness or diversity among different cotton varieties, but did detect differences over time and in different plant tissues. No consistent patterns of community similarity associated with variety, region, farming practice, time of the season or tissue type were observed regardless of the ecological community similarity measurements used. Results indicated that local fungal endophyte communities may be affected by both time of the year and plant tissue, but the specific community composition varies across sites. In addition to providing insights into fungal endophyte community structure, our survey provides candidates for further evaluation as potential management tools against a variety of pests and diseases when present as endophytes in cotton and other plants.

Comparison of Spatial Variables Over Subregions Using a Block Bootstrap

In environmental and agricultural studies, it is often of interestto compare spatial variables across different regions. Traditional statistical tools that assume independent samples are inadequate because of potential spatial correlations. In this article, spatial dependence is accounted for by a random field model, and a non parametric test is developed to compare the overall distributions of variables in two neighboring regions. Sampling distribution of the test statistic is estimated by a spatial block bootstrap. For illustration, the procedure is applied to study root-lesion nematode populations on a production farm in Wisconsin. Choices of the bootstrap block size are investigated via a simulation study and results of the test are compared to traditional approaches.

Identification, distribution, and control of italian ryegrass (Lolium multiflorum) ecotypes with varying levels of sensitivity to triasulfuron in texas

Texas wheat producers have observed reduced efficacy and failure to control Italian ryegrass with registered rates of sulfonylurea herbicides that were previously effective. Growth chamber studies were conducted to quantify the sensitivity and distribution of Italian ryegrass ecotypes in Texas to triasulfuron and to determine alternative herbicide management options. Italian ryegrass seed samples were collected from over 40 wheat fields in 13 central and north Texas counties where declining Italian ryegrass control was reported by farmers following sulfonylurea herbicide application(s). Two-leaf Italian ryegrass was screened with an application of 150 g ai/ha triasulfuron, a rate five times the registered herbicide use rate. Sensitivity was determined by the response of an ecotype to that of a known susceptible population. Of the 48 Italian ryegrass ecotypes sampled, nine were comparable to susceptible standard, while the remaining 39 ecotypes were less sensitive to triasulfuron. Four of the least sensitive ecotypes to triasulfuron plus the susceptible standard were selected for a subsequent study. Diclofop, clodinafop, and metribuzin reduced fresh weights by at least 69, 71, and 62% across all ecotypes. No imazamox or triasulfuron treatment reduced fresh weights more than 60%. Nomenclature: Clodinafop; diclofop; imazamox; metribuzin; triasulfuron; Italian ryegrass, Lolium multiflorum L. #3 LOLMU; wheat, Triticum aestivum L. Additional index words: ALS inhibitor, cross-resistance, herbicide resistance, imidazolinone, resistance survey, sulfonylurea. Abbreviations: ALS, acetolactate synthase; ACCase, acetyl-CoA carboxylase; DAT, days after treatment; LTSE, low triasulfuron-sensitivity ecotypes.

A nonparametric procedure for analyzing repeated measures of spatially correlated data

Many agricultural, biological, and environmental studies involve detecting temporal changes of a response variable, based on data observed at sampling sites in a spatial region and repeatedly over several time points. That is, data are repeated measures over time and are potentially correlated across space. The traditional repeated-measures analysis allows for time dependence but assumes that the observations at different sampling sites are mutually independent, which may not be suitable for field data that are correlated across space. In this paper, a nonparametric large-sample inference procedure is developed to assess the time effects while accounting for the spatial dependence using a block bootstrap. For illustration, the methodology is applied to describe the population changes of root-lesion nematodes over time in a production field in Wisconsin.

Site-Specific Weed Management in Corn (Zea mays)1

Site-specific weed management can increase crop production efficiency by minimizing herbicide input costs without compromising crop yields. A reduction in herbicide inputs resulting from site-specific weed management may also decrease the probability level of nonpoint pollution compared with conventional herbicide applications. A 4.5-ha field was selected to compare site-specific and conventional weed management techniques in 1997 and 1998 at Knoxville, TN. Variable rate applications (VRAs) of atrazine preemergence (PRE) followed by dicamba postemergence (POST) were investigated for the reduction of herbicide inputs and their resulting impact on weed control and corn yield. VRAs of atrazine were on the basis of weed density data collected in 1996. VRAs of dicamba were according to common cocklebur density evaluations within the field. Compared with conventional applications, atrazine usage was decreased by 43 and 32% in the site-specific application treatments in 1997 and 1998, respectively. VRAs of dicamba reduced herbicide inputs by greater than 45% for 1997 and 1998. Corn yields were similar for the conventional and site-specific treatments in both years. On the basis of these data, site-specific herbicide applications have the greatest potential and least risk for managing weeds when POST or PRE + POST variable rate herbicide applications are used. Nomenclature: Atrazine; dicamba; common cocklebur, Xanthium strumarium L. #3 XANST; corn, Zea mays L. ‘Dekalb 689’. Additional index words: Brachiaria platyphylla (Griseb.) Nash, broadleaf signalgrass, geographical information systems, global positioning systems, variable rate application. Abbreviations: DGPS, differential global positioning system; GIS, geographic information system; OM, organic matter; POST, postemergence; PRE, preemergence; VRA, variable rate application.

Association of Flax Seed Yield and Its Components in Southeast Texas Using Path Coefficient and Biplot Analyses

In addition to numerous health and industrial uses, flax (Linum usitatissimum L.) has been evaluated throughout the United States as a potential biodiesel crop. One approach for improving flax yields was to identify the physiological characteristics contributing the most to flax yield. Two locations in southern Texas were selected to evaluate the association between tiller number, number of pods per tiller, number of seeds per pod, seed weight, and overall yields. Tiller number was the most significant positive contributing trait (P < 0.05) to seed yield of flax at both locations. However, the effect of tiller number was almost equally negated by that of pods per tiller (compensatory) at both locations. Seed per pod and seed weight were not significant (P > 0.05) components of seed yield in flax in this study. Selection for higher tiller number would increase grain yield of flax in southern Texas and should be the focus of plant breeders to further enhance seed yield for this area.

Cotton Stage of Growth Determines Sensitivity to 2,4-D

The anticipated release of EnlistTM cotton, corn, and soybean cultivars likely will increase the use of 2,4-D, raising concerns over potential injury to susceptible cotton. An experiment was conducted at 12 locations over 2013 and 2014 to determine the impact of 2,4-D at rates simulating drift (2 g ae ha−1) and tank contamination (40 g ae ha−1) on cotton during six different growth stages. Growth stages at application included four leaf (4-lf), nine leaf (9-lf), first bloom (FB), FB + 2 wk, FB + 4 wk, and FB + 6 wk. Locations were grouped according to percent yield loss compared to the nontreated check (NTC), with group I having the least yield loss and group III having the most. Epinasty from 2,4-D was more pronounced with applications during vegetative growth stages. Importantly, yield loss did not correlate with visual symptomology, but more closely followed effects on boll number. The contamination rate at 9-lf, FB, or FB + 2 wk had the greatest effect across locations, reducing the number of bolls per plant when compared to the NTC, with no effect when applied at FB + 4 wk or later. A reduction of boll number was not detectable with the drift rate except in group III when applied at the FB stage. Yield was influenced by 2,4-D rate and stage of cotton growth. Over all locations, loss in yield of greater than 20% occurred at 5 of 12 locations when the drift rate was applied between 4-lf and FB + 2 wk (highest impact at FB). For the contamination rate, yield loss was observed at all 12 locations; averaged over these locations yield loss ranged from 7 to 66% across all growth stages. Results suggest the greatest yield impact from 2,4-D occurs between 9-lf and FB + 2 wk, and the level of impact is influenced by 2,4-D rate, crop growth stage, and environmental conditions. Nomenclature: 2,4-D; cotton, Gossypium hirsutum L. La anticipada liberación de cultivares Enlist™ de algodón, maíz, y soja probablemente incrementará el uso de 2,4-D, aumentando así la preocupación del daño potencial en algodón susceptible. Se realizó un experimento en 12 localidades durante 2013 y 2014 para determinar el impacto de 2,4-D a dosis de deriva simulada (2 g ae ha−1) y de contaminación en tanque (40 g ae ha−1) sobre algodón durante seis estadios de crecimiento diferente. Los estadios de crecimiento al momento de aplicación incluyeron cuatro hojas (4-lf), nueve hojas (9-lf), primer brote florar (FB), FB + 2 semanas (wk), FB + 4 wk, y FB + 6 wk. Las localidades fueron agrupadas según el porcentaje de pérdida de rendimiento al compararse con el testigo sin tratamiento (NTC), teniendo el grupo I la menor pérdida de rendimiento y el grupo III la mayor. La epinastia producto de 2,4-D fue más pronunciada con aplicaciones durante los estadios de crecimiento vegetativo. Importantemente, la pérdida en el rendimiento no correlacionó con la sintomatología visual, pero siguió de cerca los efectos en el número de frutos. La dosis de contaminación a 9-lf, FB, o FB + 2 wk tuvo el mayor efecto en todas las localidades, reduciendo el número de frutos por planta cuando se comparó con el NTC, pero sin tener efecto cuando se aplicó en FB + 4 wk o después. La reducción en el número de frutos no fue detectable con la dosis de deriva excepto en el grupo III cuando se aplicó en el estadio FB. El rendimiento fue influenciado por la dosis de 2,4-D y el estadio de crecimiento del algodón. Considerando todas las localidades, las pérdidas de rendimiento mayor a 20% ocurrieron en 5 de 12 localidades cuando se aplicó la dosis de deriva entre 4-lf y FB + 2 wk (mayor impacto a FB). Para la dosis de contaminación, la pérdida en rendimiento fue observada en todas las 12 localidades. Al promediar todas las localidades, la pérdida de rendimiento varió entre 7 y 66% entre todos los estadios de crecimiento. Los resultados sugieren que el mayor impacto en el rendimiento causado por 2,4-D ocurre entre 9-lf y FB + 2 wk, y el nivel de impacto es influenciado por la dosis de 2,4-D, el estadio de crecimiento, y las condiciones ambientales.