The response of glyphosate-resistant and glyphosate-susceptible biotypes of Echinochloa colona to carbon dioxide, soil moisture and glyphosate

Genetics Matters: Voyaging from the Past into the Future of Humanity and Sustainability

The understanding of how genetic information may be inherited through generations was established by Gregor Mendel in the 1860s when he developed the fundamental principles of inheritance. The science of genetics, however, began to flourish only during the mid-1940s when DNA was identified as the carrier of genetic information. The world has since then witnessed rapid development of genetic technologies, with the latest being genome-editing tools, which have revolutionized fields from medicine to agriculture. This review walks through the historical timeline of genetics research and deliberates how this discipline might furnish a sustainable future for humanity.

Glyphosate hormesis attenuates water deficit stress in safflower (Carthamus tinctorius L.) by modulating physiological and biochemical mediators

Changes in photosynthetic machinery can induce physiological and biochemical damage in plants. Low doses of glyphosate have been shown to exert a positive effect in mitigating the deleterious effects of water deficit in plants. Here, the physiological and biochemical mechanisms of safflower plants (Carthamus tinctorius L.) were studied under conditions of water deficit mediated by the attenuating effect of low-dose glyphosate. The plants were divided into two groups of water regimes in soil, without water deficit (-10 kPa) and with water deficit (-70 kPa), and were exposed to different concentrations of glyphosate (0, 1.8, 3.6, 7.2, 18, 36, 72, 180, 360, and 720 g a.e. ha-1). Evident protective responses at the physiological and biochemical levels were obtained after applying low doses of glyphosate to plants under water deficit, with a limiting dose for the occurrence of hormesis (LDS) = 72 g a.e. ha-1. The water deficit in plants resulted in hydrogen peroxide (H2O2) accumulation and consequently lipid peroxidation (LPO) associated with the accumulation of shikimic acid and glyphosate in plants, which triggered an increase in the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) that act by dismuting the levels of reactive oxygen species (ROS), maintaining, and/or increasing the maximum quantum efficiency of photosystem II (Fv/Fm), effective quantum yield of photosystem II (ΦPSII), electron transport rate (ETR), photochemical extinction coefficient (qP), and non-photochemical extinction coefficient (NPQ). APX appears to be the main enzyme involved in eliminating H2O2. Low doses of glyphosate act as water deficit ameliorators, allowing the plant to maintain/increase metabolism at physiological and biochemical levels by activating antioxidant enzymes in the dismutation of ROS in safflower plants.

Differential germination characteristics of glyphosate-resistant and glyphosate-susceptible Chloris virgata populations under different temperature and moisture stress regimes

Thorough knowledge of the germination behavior of weed species could aid in the development of effective weed control practices, especially when glyphosate resistance is involved. A study was conducted using two glyphosate-resistant (GR) (SGW2 and CP2) and two glyphosate-susceptible (GS) (Ch and SGM2) populations of Chloris virgata, an emerging and troublesome weed species of Australian farming systems, to evaluate their germination response to different alternating temperature (15/5, 25/15 and 35/25°C with 12 h/12 h light/dark photoperiod) and moisture stress regimes (0, -0.1, -0.2, -0.4, -0.8 and -1.6 MPa). These temperature regimes represent temperatures occurring throughout the year in the eastern grain region of Australia. Seeds germinated in all the temperature regimes with no clear indication of optimum thermal conditions for the GR and GS populations. All populations exhibited considerable germination at the lowest alternating temperature regime 15/5°C (61%, 87%, 49%, and 47% for Ch, SGM2, SGW2, and CP2, respectively), demonstrating the ability of C. virgata to germinate in winter months despite being a summer annual. Seed germination of all populations was inhibited at -0.8 and -1.6 MPa osmotic potential at two alternating temperature regimes (15/5 and 35/25°C); however, some seeds germinated at 25/15°C at -0.8 MPa osmotic potential, indicating the ability of C. virgata to germinate in arid regions and drought conditions. Three biological parameters (T10: incubation period required to reach 10% germination; T50: incubation period required to reach 50% germination; and T90: incubation period required to reach 90% germination) suggested late water imbibition with increasing moisture stress levels. The GR population SGW2 exhibited a distinctive pattern in T10, T50, and T90, possessing delayed germination behaviour and thus demonstrating an escape mechanism against pre-plating weed management practices. Knowledge gained from this study will help in developing site-specific and multi-tactic weed control protocols.

Glyphosate hormesis mitigates the effect of water deficit in safflower (Carthamus tinctorius L.)

BACKGROUND

The current climate change scenario may affect water availability in the soil, impacting the agricultural sector. Planting of safflower (Carthamus tinctorius L.) has increased because of its potential for cultivation under drought conditions during the off-season in Brazil and its high potential for use in biofuel production. There are several reports about the potential of low doses of glyphosate to promote plant growth and development (hormesis). Despite the concept of glyphosate hormesis being well established, little is known about any mitigating effect on plants under water deficit conditions. The hypothesis raised is that low doses of glyphosate promote water stress tolerance during the growth and reproductive phases of C. tinctorius exposed to different water regimes.

RESULTS

In regimes with and without water deficiency, growth of plants treated with low doses of glyphosate increased, reaching a maximum stimulus amplitude of ~ 131% of control. However, plants under water deficit required lower doses to achieve maximum growth and development. They maintained photosynthetic rates at the level of well-watered plants because they had reduced stomatal conductance and transpiration. Gains in plant height and leaf area were the same as for controls.

CONCLUSIONS

Low doses of glyphosate can act as mitigators of water deficit in C. tinctorius, allowing plants to maintain their metabolism, reaching levels close to those of plants without water stress, as observed for plant height and leaf area. Our findings indicate that there are even greater implications for understanding glyphosate hormesis in plants under drought conditions, given the current climate change scenario. © 2020 Society of Chemical Industry.

Response of glyphosate-resistant and susceptible biotypes of Echinochloa colona to low doses of glyphosate in different soil moisture conditions

To evaluate the hormetic effect of glyphosate on Echinochloa colona, two pot studies were done in the screenhouse at the Gatton Campus, the University of Queensland, Australia. Glyphosate was sprayed at the 3-4 leaf stage using different doses [(0, 5, 10, 20, 40, 80 and 800 g a.e. ha-1) and (0, 2.5, 5, 10, 20 and 800 g a.e. ha-1)] in the first and second study, respectively. In the second study, two soil moistures (adequately-watered and water-stressed), and two E. colona biotypes, glyphosate-resistant and glyphosate-susceptible, were included. In both studies, plants that were treated with glyphosate at 2.5-40 g ha-1 grew taller and produced more leaves, tillers, inflorescences and seeds than the control treatment. In the first study, 5 g ha-1 glyphosate resulted in the maximum aboveground biomass (increase of 34% to 118%) compared with the control treatment. In the second study, the adequately-watered and glyphosate low dose treatments caused an increase in all the measured growth parameters for both biotypes. For example, total dry biomass was increased by 64% and 54% at 5 g ha-1 in the adequately-watered treatments for the resistant and susceptible biotypes, respectively, compared with the control treatment. All measured traits tended to decrease with increasing water stress and the stimulative growth of low doses of glyphosate could not compensate for the water stress effect. The results of both studies showed a hormetic effect of low doses of glyphosate on E. colona biotypes and such growth stimulation was significant in the range of 5 to 10 g ha-1 glyphosate. Water availability was found to be effective in modulating the stimulatory outcomes of glyphosate-induced hormesis. No significant difference was observed between the resistant and susceptible biotypes for hormesis phenomenon. The study showed the importance of precise herbicide application for suppressing weed growth and herbicide resistance evolution.