Cotton is often negatively impacted by drought periods; thus, plant traits that alleviate the impacts of drought on cotton are highly desirable. The limited‐transpiration rate (TRlim) trait under high vapour pressure deficit (VPD) can conserve soil water and prolong crop physiological activity as water deficit progresses. The current research objective was to compare the expression of TRlim in cotton cultivars under variable VPD and temperatures by whole‐plant transpiration in controlled environments and by leaf‐level gas exchange measurements in the field. All cultivars expressed the TRlim trait in a controlled environment with high VPD at 32°C; however, at 38°C, only 5 out of 7 commercial and 2 out of 4 conventional cultivars expressed TRlim. Field trials during 2017 and 2018 showed all 4 commercial cultivars that expressed TRlim in a controlled environment at 38°C expressed TRlim, but shifts in VPD breakpoints were observed. Among conventional cultivars, 2 out of 4 expressed TRlim trait. Cultivars that expressed TRlim also delayed wilting under rainfed environments when soil water deficits developed and resulted in greater lint yields. Three commercial and two conventional cultivars that expressed the TRlim trait in field trials also resulted in greater predawn leaf water potential (LWP). Cultivars that expressed the TRlim trait had significantly higher lint yields only during 2017. This study indicates that the impact of TRlim trait on yield is relatively small in years with adequate rainfall.
The integration of cover crops into cotton (Gossypium hirsutum, L.) production remains challenging. One potential negative impact of cover crops on cotton is allelopathy. Proper selection of cover crop species and termination timing could potentially reduce the impacts of allelopathy on cotton seedlings. Two studies were conducted to determine cotton germination and growth sensitivity to cover crop leachate, which were measured using (I) five cover crops species, including: oats (Avena sativa L.), hairy vetch (Vicia Villosa), winter pea (Lathyrus hirsutus), winter wheat (Triticum aestivum), and annual rye (Lolium multiflorum), and (II) a blend of cover crops at four termination timings, including: at planting, three weeks prior to planting, six weeks prior to planting, and a split termination, where a 25 cm band in the top of the bed was terminated six weeks prior to planting, and the remaining cover crop was terminated at planting (referred to as strip 6-wk). Samples for Experiment I were collected on May 24th and for Experiment II on March 22nd (Strip/6-wk and 6-wk), April 30th (3-wk), and May 11th (at planting) in 2018. The effect of 0 (deionized water), 25, and 50 (v/v) cover crop leachate extract on cotton seed germination was evaluated in a series of controlled environmental studies. All cover crop species’ leachates negatively impacted cotton germination and seedling growth (p < 0.05). Germination inhibition rates declined numerically by species, with winter pea ≥ hairy vetch ≥ oats ≥ annual rye ≥ winter wheat at the 50 v/v concentrations. Winter pea germination inhibition on cotton equaled 47.0% and cotton radicle length was decreased by 62.8%. Termination at planting suppressed cotton germination more than the other termination timings, with the 50 v/v treatment resulting in a germination inhibition of 60.0%. Proper selection of cover crop species and termination timing prior to planting cotton will be critical in maximizing the benefits and minimizing the risks of a cover crop.
In recent years, application of engineered nanomaterials, in particular carbon-based nanostructures, has been initiated in agriculture. To better understand the effects of nanomaterials on plants, four concentrations of graphene oxide (0, 0.01, 0.05, 0.1%) in soil was studied on growth and biochemical traits of Milk thistle under four saline stress (0, 4, 8,12 dS/m) conditions in greenhouse. A completely randomized block design with a factorial treatment arrangement was employed with three replications. The result showed under both saline and control (non-saline) conditions, the maximum plant height (3.7% and 20% in control and saline conditions, respectively), total biomass (17% and 8.2% in control and saline conditions, respectively), and chlorophyll content (8% and 5% in control and saline conditions, respectively), were achieved for plants with graphene oxide (GO) application. By increasing the salinity level, plants treated with 0.01% concentration of graphene oxide produced the highest total biomass (518 mg) under 12 dS/m salinity levels. Also, maximum quantum efficiency of PSII, performance index, and membrane stability index decreased due to salinity stress. Proline and soluble carbohydrates noticeably increased by saline water treatments. Graphene oxide alleviated salt stress-induced damage through increasing plant growth, plant height, chlorophyll content, photosystem efficiency, performance index, membrane stability index, proline and soluble carbohydrate content. Also graphene oxide increased cell water potential through enhancing the net concentration of solutes in plant cells. Graphene nanomaterials could ameliorate the salt stress in Milk thistle plant. Graphene oxide application could be commercially and economically beneficial for Milk thistle production under control and saline conditions.
Identifying environmental factors, plant characteristics, and agronomic activities plays an essential role in medicinal plant production. Milk thistle (Silybum marianum L.) is a well-known medicinal plant with extensive use in diverse liver diseases and is economically a significant crop. This research was conducted to evaluate the effect of the sole and integrated applications of graphene oxide (GO), zeolite, and chitosan as modifying materials on gas exchange and the secondary metabolites of milk thistle under severe salinity stress. Seven sole and integrated combinations of nano-materials comprised of T1, T2, T3, T4, T5, T6, T7, and control (T8, no nano-materials application) and two levels of saline water (12 ds/m) and tap water (control, 0.8 ds/m) were applied to the soil of experimental plots based on a factorial design with three replications. The results showed that the highest photosynthesis rate was obtained with T7 treatment for both water treatments. The highest plant silymarin concentration was obtained from the T6 treatment under both saline and tap water conditions. This treatment increased the silymarin concentration by 15.9% compared to the T8. The highest plant silymarin yield (180 mg per plant) was recorded for the T7 under tap water (control) condition, and 130.3 mg/plant for T6 under salinity stress, respectively. The Transmission Electron Microscope technology indicated that GO at low concentration (0.01%) could be safely used to enhance milk thistle germination and growth under severe salinity stress conditions
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