Using nanotechnology to enhance plant growth

<p>Efficient and effective delivery of fertilisers, herbicides, pesticides and growth regulating compounds to plants is the subject of much ongoing research. The objective of this research was to develop nano-formulations for delivery of compounds to plants. Two formulations were developed: the first was solution-based focused on encapsulation of the active ingredient in a nanoemulsion. Nanoemulsions should be ideal for facilitating transfer of compounds to plant leaves as their size correlates well with the nanoscale surface features of leaves, achieving significantly greater total contact area between the oil droplets and the leaves. The second nano-formulation was solid-state based, focused on locating the active ingredient within the tubules of a nanotube clay. For proof-of-concept two synthetic plant hormones, N-phenyl-N‘-(2-chloro-4-pyridyl)urea (CPPU) or forchlorfenuron, a synthetic cytokinin, and 2,4-dichlorophenoxyacetic acid (2,4-D), a synthetic auxin, were chosen for encapsulation. CPPU is a phenylurea derivative that shows strikingly strong cytokinin-like activity in plants, including delaying senescence. It is highly water insoluble, but soluble in organic solvents. It is widely used in a variety of crops, particularly kiwifruit and table grapes. Delivery of CPPU safely, efficiently and at the appropriate dosage is a priority as overdosing or incorrect timing of application causes detrimental effects on fruit firmness and other quality attributes. Auxins are also a group of plant hormone. 2,4-D is a synthetic auxin which has been widely used at high concentrations as a herbicide, at medium concentrations for fruit thinning, and at low concentrations promotes root initiation, but at even lower concentrations promote root elongation. Consequently, careful control of dosage is required to obtain the desired effect. The nanoemulsion system developed was water/polysorbate 80/glycerol/soybean oil. The active ingredient, CPPU, was incorporated into the nanoemulsion via the oil phase in a pre-concentrate which was then crash diluted to yield the final nanoemulsion. Nanoemulsions are created only when the concentrate is located in the bicontinuous or oil-in-water microemulsion regions of the phase diagram. The droplet size of the nanoemulsions was measured using dynamic light scattering with droplets ranging in size from 30 – 100 nm. The CPPU-loaded nanoemulsions were stable for more than three days. To determine if the nanoemulsion was an effective delivery system, a leaf senescence bioassay was conducted to test the senescence-delaying effect of the CPPU-loaded nanoemulsions when applied to explants. The nanoemulsions were applied directly to the leaves of dwarf bean explants. Chlorophyll was extracted from the leaves and measured spectrophotometrically before and several days following treatment. The CPPU-loaded nanoemulsions enhanced the effectiveness of CPPU in delaying leaf senescence compared with the control experiments, including direct application of CPPU. A >10-fold reduction in CPPU concentration was achieved. The second delivery method was a solid-state preparation, using halloysite clay nanotubes loaded with 2,4-D. A rooting bioassay using mung bean explants was used for proof of concept. Application of 2,4-D nanotubes to the cut end of a young stem, without roots, stimulated root formation compared to controls after 10 days and at a lower applied concentration. The retardation of root elongation, relative to controls after 13 days, potentially indicated continued slow release of the active ingredient from the nanotubes. Results obtained from this research indicate that nano-formulations have the potential to deliver biologically active compounds to plants in the horticultural and agricultural sectors at effective concentrations lower than in current usage.</p>

Using nanotechnology to enhance plant growth

<p>Efficient and effective delivery of fertilisers, herbicides, pesticides and growth regulating compounds to plants is the subject of much ongoing research. The objective of this research was to develop nano-formulations for delivery of compounds to plants. Two formulations were developed: the first was solution-based focused on encapsulation of the active ingredient in a nanoemulsion. Nanoemulsions should be ideal for facilitating transfer of compounds to plant leaves as their size correlates well with the nanoscale surface features of leaves, achieving significantly greater total contact area between the oil droplets and the leaves. The second nano-formulation was solid-state based, focused on locating the active ingredient within the tubules of a nanotube clay. For proof-of-concept two synthetic plant hormones, N-phenyl-N‘-(2-chloro-4-pyridyl)urea (CPPU) or forchlorfenuron, a synthetic cytokinin, and 2,4-dichlorophenoxyacetic acid (2,4-D), a synthetic auxin, were chosen for encapsulation. CPPU is a phenylurea derivative that shows strikingly strong cytokinin-like activity in plants, including delaying senescence. It is highly water insoluble, but soluble in organic solvents. It is widely used in a variety of crops, particularly kiwifruit and table grapes. Delivery of CPPU safely, efficiently and at the appropriate dosage is a priority as overdosing or incorrect timing of application causes detrimental effects on fruit firmness and other quality attributes. Auxins are also a group of plant hormone. 2,4-D is a synthetic auxin which has been widely used at high concentrations as a herbicide, at medium concentrations for fruit thinning, and at low concentrations promotes root initiation, but at even lower concentrations promote root elongation. Consequently, careful control of dosage is required to obtain the desired effect. The nanoemulsion system developed was water/polysorbate 80/glycerol/soybean oil. The active ingredient, CPPU, was incorporated into the nanoemulsion via the oil phase in a pre-concentrate which was then crash diluted to yield the final nanoemulsion. Nanoemulsions are created only when the concentrate is located in the bicontinuous or oil-in-water microemulsion regions of the phase diagram. The droplet size of the nanoemulsions was measured using dynamic light scattering with droplets ranging in size from 30 – 100 nm. The CPPU-loaded nanoemulsions were stable for more than three days. To determine if the nanoemulsion was an effective delivery system, a leaf senescence bioassay was conducted to test the senescence-delaying effect of the CPPU-loaded nanoemulsions when applied to explants. The nanoemulsions were applied directly to the leaves of dwarf bean explants. Chlorophyll was extracted from the leaves and measured spectrophotometrically before and several days following treatment. The CPPU-loaded nanoemulsions enhanced the effectiveness of CPPU in delaying leaf senescence compared with the control experiments, including direct application of CPPU. A >10-fold reduction in CPPU concentration was achieved. The second delivery method was a solid-state preparation, using halloysite clay nanotubes loaded with 2,4-D. A rooting bioassay using mung bean explants was used for proof of concept. Application of 2,4-D nanotubes to the cut end of a young stem, without roots, stimulated root formation compared to controls after 10 days and at a lower applied concentration. The retardation of root elongation, relative to controls after 13 days, potentially indicated continued slow release of the active ingredient from the nanotubes. Results obtained from this research indicate that nano-formulations have the potential to deliver biologically active compounds to plants in the horticultural and agricultural sectors at effective concentrations lower than in current usage.</p>

Using nanotechnology to enhance plant growth

<p>Efficient and effective delivery of fertilisers, herbicides, pesticides and growth regulating compounds to plants is the subject of much ongoing research. The objective of this research was to develop nano-formulations for delivery of compounds to plants. Two formulations were developed: the first was solution-based focused on encapsulation of the active ingredient in a nanoemulsion. Nanoemulsions should be ideal for facilitating transfer of compounds to plant leaves as their size correlates well with the nanoscale surface features of leaves, achieving significantly greater total contact area between the oil droplets and the leaves. The second nano-formulation was solid-state based, focused on locating the active ingredient within the tubules of a nanotube clay. For proof-of-concept two synthetic plant hormones, N-phenyl-N‘-(2-chloro-4-pyridyl)urea (CPPU) or forchlorfenuron, a synthetic cytokinin, and 2,4-dichlorophenoxyacetic acid (2,4-D), a synthetic auxin, were chosen for encapsulation. CPPU is a phenylurea derivative that shows strikingly strong cytokinin-like activity in plants, including delaying senescence. It is highly water insoluble, but soluble in organic solvents. It is widely used in a variety of crops, particularly kiwifruit and table grapes. Delivery of CPPU safely, efficiently and at the appropriate dosage is a priority as overdosing or incorrect timing of application causes detrimental effects on fruit firmness and other quality attributes. Auxins are also a group of plant hormone. 2,4-D is a synthetic auxin which has been widely used at high concentrations as a herbicide, at medium concentrations for fruit thinning, and at low concentrations promotes root initiation, but at even lower concentrations promote root elongation. Consequently, careful control of dosage is required to obtain the desired effect. The nanoemulsion system developed was water/polysorbate 80/glycerol/soybean oil. The active ingredient, CPPU, was incorporated into the nanoemulsion via the oil phase in a pre-concentrate which was then crash diluted to yield the final nanoemulsion. Nanoemulsions are created only when the concentrate is located in the bicontinuous or oil-in-water microemulsion regions of the phase diagram. The droplet size of the nanoemulsions was measured using dynamic light scattering with droplets ranging in size from 30 – 100 nm. The CPPU-loaded nanoemulsions were stable for more than three days. To determine if the nanoemulsion was an effective delivery system, a leaf senescence bioassay was conducted to test the senescence-delaying effect of the CPPU-loaded nanoemulsions when applied to explants. The nanoemulsions were applied directly to the leaves of dwarf bean explants. Chlorophyll was extracted from the leaves and measured spectrophotometrically before and several days following treatment. The CPPU-loaded nanoemulsions enhanced the effectiveness of CPPU in delaying leaf senescence compared with the control experiments, including direct application of CPPU. A >10-fold reduction in CPPU concentration was achieved. The second delivery method was a solid-state preparation, using halloysite clay nanotubes loaded with 2,4-D. A rooting bioassay using mung bean explants was used for proof of concept. Application of 2,4-D nanotubes to the cut end of a young stem, without roots, stimulated root formation compared to controls after 10 days and at a lower applied concentration. The retardation of root elongation, relative to controls after 13 days, potentially indicated continued slow release of the active ingredient from the nanotubes. Results obtained from this research indicate that nano-formulations have the potential to deliver biologically active compounds to plants in the horticultural and agricultural sectors at effective concentrations lower than in current usage.</p>

Using nanotechnology to enhance plant growth

<p>Efficient and effective delivery of fertilisers, herbicides, pesticides and growth regulating compounds to plants is the subject of much ongoing research. The objective of this research was to develop nano-formulations for delivery of compounds to plants. Two formulations were developed: the first was solution-based focused on encapsulation of the active ingredient in a nanoemulsion. Nanoemulsions should be ideal for facilitating transfer of compounds to plant leaves as their size correlates well with the nanoscale surface features of leaves, achieving significantly greater total contact area between the oil droplets and the leaves. The second nano-formulation was solid-state based, focused on locating the active ingredient within the tubules of a nanotube clay. For proof-of-concept two synthetic plant hormones, N-phenyl-N‘-(2-chloro-4-pyridyl)urea (CPPU) or forchlorfenuron, a synthetic cytokinin, and 2,4-dichlorophenoxyacetic acid (2,4-D), a synthetic auxin, were chosen for encapsulation. CPPU is a phenylurea derivative that shows strikingly strong cytokinin-like activity in plants, including delaying senescence. It is highly water insoluble, but soluble in organic solvents. It is widely used in a variety of crops, particularly kiwifruit and table grapes. Delivery of CPPU safely, efficiently and at the appropriate dosage is a priority as overdosing or incorrect timing of application causes detrimental effects on fruit firmness and other quality attributes. Auxins are also a group of plant hormone. 2,4-D is a synthetic auxin which has been widely used at high concentrations as a herbicide, at medium concentrations for fruit thinning, and at low concentrations promotes root initiation, but at even lower concentrations promote root elongation. Consequently, careful control of dosage is required to obtain the desired effect. The nanoemulsion system developed was water/polysorbate 80/glycerol/soybean oil. The active ingredient, CPPU, was incorporated into the nanoemulsion via the oil phase in a pre-concentrate which was then crash diluted to yield the final nanoemulsion. Nanoemulsions are created only when the concentrate is located in the bicontinuous or oil-in-water microemulsion regions of the phase diagram. The droplet size of the nanoemulsions was measured using dynamic light scattering with droplets ranging in size from 30 – 100 nm. The CPPU-loaded nanoemulsions were stable for more than three days. To determine if the nanoemulsion was an effective delivery system, a leaf senescence bioassay was conducted to test the senescence-delaying effect of the CPPU-loaded nanoemulsions when applied to explants. The nanoemulsions were applied directly to the leaves of dwarf bean explants. Chlorophyll was extracted from the leaves and measured spectrophotometrically before and several days following treatment. The CPPU-loaded nanoemulsions enhanced the effectiveness of CPPU in delaying leaf senescence compared with the control experiments, including direct application of CPPU. A >10-fold reduction in CPPU concentration was achieved. The second delivery method was a solid-state preparation, using halloysite clay nanotubes loaded with 2,4-D. A rooting bioassay using mung bean explants was used for proof of concept. Application of 2,4-D nanotubes to the cut end of a young stem, without roots, stimulated root formation compared to controls after 10 days and at a lower applied concentration. The retardation of root elongation, relative to controls after 13 days, potentially indicated continued slow release of the active ingredient from the nanotubes. Results obtained from this research indicate that nano-formulations have the potential to deliver biologically active compounds to plants in the horticultural and agricultural sectors at effective concentrations lower than in current usage.</p>

Evaluating the Spectral Response and Yield of Soybean Following Exposure to Sublethal Rates of 2,4-D and Dicamba at Vegetative and Reproductive Growth Stages

The commercialization of synthetic auxin-resistant crops and the commensurate increase in post-emergent auxin-mimic herbicide applications has resulted in millions of hectares of injury to sensitive soybeans in the United States since 2016. Visual yield loss estimations following auxin injury can be difficult. The goal of this research was to determine if spectral variations following auxin injury to soybean allow for more precise yield loss estimations. Identical field experiments were performed in 2018, 2019, and 2020 in Columbia, Missouri to compare the ability of established vegetative indices to differentiate between exposure levels of 2,4-D and dicamba in soybean and predict yield loss. Soybeans were planted at three timings for growth stage separation and were exposed to sublethal rates of 2,4-D and dicamba at the R2, R1, and V3 growth stages. A UAV-mounted multispectral sensor was flown over the trial 14 days after the herbicide treatments. The results of this research found that vegetative indices incorporating the red-edge wavelength were more consistent in estimating yield loss than indices comprised of only visible or NIR wavelengths. Yield loss estimations became difficult when soybean injury occurred during later reproductive stages when soybean biomass was increased. This research also determined that when injury occurs to soybean in vegetative growth stages late in the growing season there is a greater likelihood for yield loss to occur due to decreased time for recovery. The results of this research could provide direction for more objective and accurate evaluations of yield loss following synthetic auxin injury than what is currently available.

Resistance in Smallflower Umbrella Sedge (Cyperus difformis L.) to Acetolactate Synthase-Inhibiting Herbicides in Rice - First Case in India

Smallflower umbrella sedge is one of the problematic weeds in direct-seeded rice in India. Bispyribac-sodium (acetolactate synthase-inhibiting herbicide) is a commonly used in rice, but recently growers have reported lack of smallflower umbrella sedge control with this herbicide. An extensive survey was carried out in two rice growing states, Chhattisgarh and Kerala, where 53 putative bispyribac-sodium resistant (BR) biotypes were collected. Studies were conducted to confirm resistance to bispyribac-sodium and to test the efficacy of newly developed synthetic auxin herbicide florpyrauxifen-benzyl on putative BR biotypes. Whole-plant bioassay revealed that bispyribac-sodium is no longer effective. Of 53 putative BR biotypes, 17 biotypes survived recommended label rate of 25 g ai ha−1. Effective bispyribac-sodium rate required to control 50% of the plants in most of the BR biotypes (ED50) ranged from 19 to 96 g ha−1 whereas it was 10 g ha−1 in susceptible biotype. In two highly resistant biotypes, ED50 was beyond the maximum tested rate, 200 g ha−1. This suggests 2 to >20-fold resistance in BR biotypes. Acetolactate synthase (ALS) enzyme activity assay suggests altered target site as mechanism of resistance to bispyribac-sodium. This study confirms the first case of evolved resistance in smallflower umbrella sedge for bispyribac-sodium in India. However, the newly developed synthetic auxin, florpyrauxifen-benzyl effectively controlled all BR biotypes at the field use rate 31.25 g ae ha−1.

Herbicide diagnostics reveal multiple patterns of synthetic auxin resistance in kochia (Bassia scoparia)

Herbicide-resistant (HR) kochia is a growing problem in the Great Plains region of Canada and the United States (U.S.). Resistance to up to four herbicide sites of action, including photosystem II inhibitors, acetolactate synthase inhibitors, synthetic auxins, and the 5-enolpyruvylshikimate-3-phosphate synthase inhibitor glyphosate have been reported in many areas of this region. Despite being present in the U.S. since 1993/1994, auxinic-HR kochia is a recent and growing phenomenon in Canada. This study was designed to characterize (a) the level of resistance and (b) patterns of cross-resistance to dicamba and fluroxypyr in 12 putative auxinic-HR kochia populations from western Canada. The incidence of dicamba-resistant individuals ranged among populations from 0% to 85%, while fluroxypyr-resistant individuals ranged from 0% to 45%. In whole-plant dose-response bioassays, the populations exhibited up to 6.5-fold resistance to dicamba and up to 51.5-fold resistance to fluroxypyr based on visible injury 28 days after application. Based on plant survival estimates, the populations exhibited up to 3.7-fold resistance to dicamba and up to 72.5-fold resistance to fluroxypyr. Multiple patterns of synthetic auxin resistance were observed, where one population from Cypress County, Alberta was resistant to dicamba but not fluroxypyr, while another from Rocky View County, Alberta was resistant to fluroxypyr but not dicamba based on single-dose population screening and dose-response bioassays. These results suggest that multiple mechanisms may confer resistance to dicamba and/or fluroxypyr in Canadian kochia populations. Further research is warranted to determine these mechanisms. Farmers are urged to adopt proactive non-chemical weed management tools in an effort to preserve efficacy of the remaining herbicide options available for control of HR kochia.

Elicitation of solid callus cultures of Salvia miltiorrhiza Bunge with salicylic acid and a synthetic auxin (1-naphthaleneacetic acid)

The presented study analyses the influence of salicylic acid (SA) and the synthetic auxin 1-naphthaleneacetic acid (NAA) on total tanshinone level and on dihydrotanshinone (DHT), cryptotanshinone (CT), tanshinine I (TI) and tanshinone IIA (TIIA) level in Salvia miltiorrhiza callus cultures growing on solid Murashige and Skoog (MS) medium. The influence of SA and NAA was evaluated at 10-day intervals throughout a 80-day treatment period. SA was applied at 0.1, 0.2 and 0.4 mM, and NAA at 2.69, 13.43, 26.85 and 40.28 μM. DHT, CT, TI and TIIA concentrations were measured using HPLC. NAA did not increase the concentration of any tanshinone. SA increased content in a concentration- and time-dependent manner; however, the yields were relatively low, possibly due to the metabolic specificity of S. miltiorrhiza cultivars in Poland. Total tanshinone concentration reached 226.38 ± 37.33 μg g−1 DW after 50 days of 0.4 mM SA elicitation. After 50 days of SA elicitation, the following maximum tanshinone concentrations were observed for 0.4 mM SA: DHT (71.58 ± 12.72 μg g−1 DW), CT (108.54 ± 18.29 μg g−1 DW), TI (29.50 ± 4.13 μg g−1 DW) and TIIA (16.75 ± 2.74 μg g−1 DW). To account for these observed differences in tanshinone biosynthesis, the distribution of SA and auxin responsive cis-active motif in the proximal promoters of the mevalonic acid, methylerythritol-4-phosphate and tanshinone-precursor biosynthesis pathway genes was evaluated in A. thaliana and S. miltiorrhiza. Our findings indicate that the SA-responsive cis-active elements have a much broader distribution than those recognized by auxin-responsive transcription factors.

Antitranspirantsc Partially Mitigate Auxin Herbicide Injury on Tomato Plants

The use of dicamba and 2,4-D products on herbicide-tolerant crops has resulted in numerous cases of off-target movement and injury to sensitive plants, including tomato (Solanum lycopersicon L.). Two greenhouse studies were conducted to determine whether ‘Big Beef’ (‘BB’) or ‘Florida 91’ (‘FL’) tomato plants pretreated with an antitranspirant, including Moisture-Loc (ML) at 100 mL·L−1, TransFilm (TF) at 50 g·L−1, or Wilt-Pruf (WP) at 100 mL·L−1, mitigated injury from synthetic auxin herbicides. Dicamba or 2,4-D was applied at a rate corresponding to 1/200 of the manufacturer’s labeled rate of 0.56 kg ae/ha or 1.06 kg ae/ha, respectively. At 2 weeks after treatment (WAT), plants treated with ML or WP before either herbicide exhibited injury symptoms, but they were always less severe than those treated with the herbicide alone for both cultivars. However, shoot length measurements indicated that none of the antitranspirants consistently provided protection against herbicide injury at 2 WAT. By 12 WAT, ML or WP used before either herbicide increased the number of live reproductive organs compared with dicamba or 2,4-D alone for both cultivars. Floral abortion on tomato plants was also reduced when ML or WP was applied before an herbicide treatment by 12 WAT. Although WP and ML did not provide complete protection against synthetic auxin herbicide injury, the concept of using film-forming barriers may be useful in mitigating some of the short-term effects of drift on plants.