Michael J. Mulvaney

Differentiation of Life-History Traits among Palmer Amaranth Populations (Amaranthus palmeri) and Its Relation to Cropping Systems and Glyphosate Sensitivity

Palmer amaranths ability to evolve resistance to different herbicides has been studied extensively, but there is little information about how this weed species might be evolving other life-history traits that could potentially make it more aggressive and difficult to control. We characterized growth and morphological variation among 10 Palmer amaranth populations collected in Florida and Georgia from fields with different cropping histories, ranging from continuous short-statured crops (vegetables and peanut) to tall crops (corn and cotton) and from intensive herbicide use history to organic production. Palmer amaranth populations differed in multiple traits such as fresh and dry weight, days to flowering, plant height, and leaf and canopy shape. Differences between populations for these traits ranged from 36% up to 87%. Although glyphosate-resistant (GR) populations collected from cropping systems including GR crops exhibited higher values of the aforementioned variables than glyphosate-susceptible (GS) populations, variation in traits was not explained by glyphosate resistance or distance between populations. Cropping system components such as crop rotation and crop canopy structure better explained the differences among populations. The higher growth of GR populations compared with GS populations was likely the result of multiple selection forces present in the cropping systems in which they grow rather than a pleiotropic effect of the glyphosate resistance trait. Results suggest that Palmer amaranth can evolve life-history traits increasing its growth and reproduction potential in cropping systems, which explains its rapid spread throughout the United States. Furthermore, our findings highlight the need to consider the evolutionary consequences of crop rotation structure and the use of more competitive crops, which might promote the selection of more aggressive biotypes in weed species with high genetic variability. Nomenclature: glyphosate; Palmer amaranth, Amaranthus palmeri S. Wats.; corn, Zea mays L.; cotton, Gossypium hirsutum L.; peanut, Arachis hypogaea L.

Influence of Planting Depth and Application Timing on S-metolachlor Injury in Sesame (Sesamum indicum L.)

Two experiments were conducted in 2015 at multiple locations in Florida to evaluate the effects of planting depth and application timing on S-metolachlor injury in sesame. In both studies, sesame responded negatively to increases in S-metolachlor rate. Altering sesame planting depth did not provide increased safety to PRE S-metolachlor applications. Sesame establishment declined with increased planting depth, likely because of the physical inability of the small seed to emerge from the 3.8-cm depth. Delaying applications of S-metolachlor by 3 or 6 d after planting (DAP) consistently improved sesame establishment. Applications 3 and 6 DAP resulted in 89 to 92% seedling emergence at 2 wk after planting (WAP), relative to 55 to 63% emergence when S-metolachlor was applied the day of planting (0 DAP) or 3 days before (−3 DAP), respectively. Applications 3 DAP resulted in 21 and 2% plant stunting when evaluated 3 and 6 WAP, respectively, whereas all other timings caused 25 to 51% stunting. Yield was reduced 22 and 33% by the −3 DAP and 0 DAP application timings, respectively, whereas no reduction in yield was observed by the delayed application timings. Therefore, delaying applications of S-metolachlor by 3 to 6 days will likely result in improved sesame seedling establishment and total seed yield. Nomenclature: S-metolachlor; sesame, Sesamum indicum L. ‘S38’.

No-till with high biomass cover crops and invasive legume mulches increased total soil carbon after three years of collard production

ABSTRACT Studies have shown that conversion to conservation tillage from conventional tillage does not increase total soil organic carbon (SOC) significantly in the short term (<5 yrs). While no-till increases total SOC in the medium to long term, it was hypothesized that the inclusion of high biomass cover crops and organic mulches may increase total SOC in the short term. The use of invasive, perennial leguminous species as mulch may sustainably increase SOC during limited-input fall vegetable production. The objective of this study, conducted in Alabama (USA), was to quantify total SOC changes due to organic mulches and forage soybean (Glycine max (L.) Merr. cv. Derry) as a summer cover crop after conversion to no-till during limited-input fall collard (Brassica oleracea L.) production. Forage soybean as a summer cover crop did not increase SOC. No-till without mulch (control treatment) significantly increased SOC at 0–5 cm from 6.3 to 14.0 g kg−1 soil in 3 yrs, whereas inclusion of cut-and-carry mulches increased SOC to ≥22.6 g kg−1 soil. Treatments did not affect collard yield, which averaged 17,863 kg ha−1 yr−1. This represents a novel, limited-input system that may help control on-farm invasive species while sustainably increasing SOC in the short term.

Evolutionary Adaptations of Palmer Amaranth (Amaranthus palmeri ) to Nitrogen Fertilization and Crop Rotation History Affect Morphology and Nutrient-Use Efficiency

Palmer amaranth control has become a major challenge for multiple cropping systems across the southeastern and midwestern United States. Despite extensive research on herbicide-resistance evolution, little research has been done exploring how Palmer amaranth might also be evolving other adaptive traits in response to different selection forces present in agricultural fields and the enrichment of soils with nutrients such as nitrogen. The objective of the present study was to determine whether Palmer amaranth populations have evolved different morphology and growth patterns in response to glyphosate use and fertilization history. Ten Palmer amaranth populations, including glyphosate-resistant (GR) and glyphosate-susceptible (GS) populations, were collected from different cropping systems with histories of high and low nitrogen fertilization in the states of Florida and Georgia. All populations were grown in pots filled with soil fertilized with either 0 or 40 kgNha-1, and their response to nitrogen was compared for morphological, growth, and nutrient-use traits. Populations differed in how they modified their morphology and growth in response to N, with major differences in traits such as foliar area, branch production, leaf shape, and canopy architecture. Populations with high nitrogen-fertilization histories had higher (>43%) nutrient-use efficiency (NUE) than populations with low nitrogen-fertilization histories. Similarly, GR populations have evolved higher NUE (>47%) and changed canopy architecture more than GS populations in response to nitrogen fertilization. The results of the present study highlight the importance of paying more attention to adaptations to cultural practices that might increase weediness and how genetic changes in traits involved in morphology and metabolism might favor compensatory mechanisms increasing the fitness of the population carrying herbicide-resistant traits. Nomenclature: Glyphosate; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA.

Comparative physiological and metabolomics analysis of wheat (Triticum aestivum L.) following post-anthesis heat stress

Genetic improvement for stress tolerance requires a solid understanding of biochemical processes involved with different physiological mechanisms and their relationships with different traits. The objective of this study was to demonstrate genetic variability in altered metabolic levels in a panel of six wheat genotypes in contrasting temperature regimes, and to quantify the correlation between those metabolites with different traits. In a controlled environment experiment, heat stress (35:28 ± 0.08°C) was initiated 10 days after anthesis. Flag leaves were collected 10 days after heat treatment to employ an untargeted metabolomics profiling using LC-HRMS based technique called IROA. High temperature stress produced significant genetic variations for cell and thylakoid membrane damage, and yield related traits. 64 known metabolites accumulated 1.5 fold of higher or lower due to high temperature stress. In general, metabolites that increased the most under heat stress (L-tryptophan, pipecolate) showed negative correlation with different traits. Contrary, the metabolites that decreased the most under heat stress (drummondol, anthranilate) showed positive correlation with the traits. Aminoacyl-tRNA biosysnthesis and plant secondary metabolite biosynthesis pathways were most impacted by high temperature stress. The robustness of metabolic change and their relationship with phenotypes renders those metabolites as potential bio-markers for genetic improvement.

Rotating peanut into established bahiagrass pastures: identifying sustainable tillage operations

ABSTRACT Integrating bahiagrass (Paspalum notatum Flueggé) into peanut (Arachis hypogaea L.) production systems can improve soil structure, and increase peanut yield. A study was conducted in 2012 and 2013 in north Florida to evaluate practices for planting peanut into bahiagrass with three tillage methods i.e.; strip till (ST), ST and high residue cultivation (ST/HRC), and conventional (CT) tillage. Tillage times were 30 d before planting (DATE1) and at planting (DATE2). Peanut grown under CT outyielded ST/HRC (6940, 6580, and 6370 kg ha−1 for CT, ST, and ST/HRC, respectively), but there was no difference in economic return across treatments (adjusted revenue avg. = US

Sesame Tolerance to Preplant Applications of 2,4-D and Dicamba

2478 ha−1). Tillage DATE2 increased total root length compared with DATE1, particularly for CT and ST. The ST/HRC had increased total root length below 30 cm for DATE1. When peanut was planted into bahiagrass, conservation tillage practices maintained adjusted revenue comparable with CT while providing environmental benefits.

Carinata Tolerance to Preemergence and Postemergence Herbicides

Two separate experiments were conducted in 2015 and 2016 in Citra, FL to investigate the effects of preplant application timing of 2,4-D and dicamba on sesame stand and yield. Nonlinear regression analysis was performed to determine the application timing that caused 10% stand or yield reduction (GR10) compared to the nontreated control (NTC) and expressed as d before planting (DBP; longer intervals indicate more injury). Likewise, regression analysis was used to determine sesame stand that resulted in 10% yield reduction (YR10) expressed as plants m-1 row. Stand measured 3 wk after planting (WAP) revealed 2,4-D applied at 0.53 kg ae ha-1 to be the least injurious treatment to sesame stand (GR10 = 6.4 DBP). Conversely, dicamba at 1.12 kg ha-1 produced a GR10 of 15.7 DBP for sesame stand at 3 WAP. 2,4-D applied at 0.53 and 1.06 kg ha-1 and dicamba applied at 0.56 kg ha-1 had the lowest GR10 for yield of 2, 3.7, and 3 DBP, respectively. Dicamba applied at 1.12 kg ha-1 proved to be the most injurious treatment to yield, which produced a GR10 value of 10.3 DBP. To simulate possible stand losses associated with dicamba or 2,4-D and the subsequent effect on yield, a separate experiment was conducted in which sesame was thinned to various plant densities and yield was recorded to determine the relationship between plant stand and seed yield. The regression analysis of these data was then compared to that of the experiment treated with 2,4-D and dicamba to separate any physiological effects of the herbicides that would lead to yield reduction from yield effects due to stand loss only. Rate constants were compared and no statistical differences were detected between herbicide and non-herbicide treatments, suggesting that yield reductions that occur from preplant applications of 2,4-D and dicamba were purely due to stand reductions. Nomenclature: 2,4-D; dicamba; sesame, Sesamum indicum L.

Decomposition, nitrogen and carbon mineralization from food and cover crop residues in the central plateau of Haiti

Carinata is a new biofuel crop that was recently introduced in the southeastern USA as a winter crop. This crop is competitive after canopy closure, but there is a need for weed control options at earlier growth stages. Field experiments were conducted from 2014 to 2016 to determine the safety of several PRE and POST herbicides in carinata. Pendimethalin at 1080 g ai ha-1 applied preplant incorporated (PPI) and PRE caused no carinata injury, or plant density and yield reductions. S-metolachlor was also safe at 694, 1070, 1390, and 2780 g ai ha-1 applied at PRE, 3 d after planting (DAP) and at the 2- to 6-leaf stage. Flumioxazin at 72 g ai ha-1 applied PRE was highly injurious on carinata preventing its establishment. Among the POST herbicides evaluated, clopyralid at 210 g ae ha1 and clethodim at 136 g ai ha-1 caused minor injury to carinata but did not reduce yield compared to the nontreated control. Acifluorfen at 420 g ai ha-1, bentazon at 840 g ai ha-1, and carfentrazone at 18 g ai ha-1 applied POST to carinata caused 75 to 100% injury. Under stressful conditions (i.e. high summer temperatures) all POST herbicides caused more injury than under more favorable conditions for growth in Florida (i.e. winter). The present study identified pendimethalin, S-metolachlor, clopyralid and clethodim as potential herbicides for weed control in carinata, and flumioxazin, acifluorfen, bentazon, and carfentrazone as herbicides that can be used to control volunteer carinata plants in rotational crops. Nomenclature: Acifluorfen; bentazon; carfentrazone; flumioxazin; pendimethalin; S-metolachlor; carinata, Brassica carinata A. Braun.