Ethylenediurea (EDU) effects on hybrid larch saplings exposed to ambient or elevated ozone over three growing seasons

Ground-level ozone (O3) pollution is a persistent environmental issue that can lead to adverse effects on trees and wood production, thus indicating a need for forestry interventions to mediate O3 effects. We treated hybrid larch (Larix gmelinii var. japonica × L. kaempferi) saplings grown in nutrient-poor soils with 0 or 400 mg L−1 water solutions of the antiozonant ethylenediurea (EDU0, EDU400) and exposed them to ambient O3 (AOZ; 08:00 − 18:00 ≈ 30 nmol mol−1) or elevated O3 (EOZ; 08:00 − 18:00 ≈ 60 nmol mol−1) over three growing seasons. We found that EDU400 protected saplings against most effects of EOZ, which included extensive visible foliar injury, premature senescence, decreased photosynthetic pigment contents and altered balance between pigments, suppressed gas exchange and biomass production, and impaired leaf litter decay. While EOZ had limited effects on plant growth (suppressed stem diameter), it decreased the total number of buds per plant, an effect that was not observed in the first growing season. These results indicate that responses to EOZ might have implications to plant competitiveness, in the long term, as a result of decreased potential for vegetative growth. However, when buds were standardized per unit of branches biomass, EOZ significantly increased the number of buds per unit of biomass, suggesting a potentially increased investment to bud development, in an effort to enhance growth potential and competitiveness in the next growing season. EDU400 minimized most of these effects of EOZ, significantly enhancing plant health under O3-induced stress. The effect of EDU was attributed mainly to a biochemical mode of action. Therefore, hybrid larch, which is superior to its parents, can be significantly improved by EDU under long-term elevated O3 exposure, providing a perspective for enhancing afforestation practices.

Safety and efficacy of linuron with or without an adjuvant or S-metolachlor for POST control of Palmer amaranth (Amaranthus palmeri) in sweetpotato

Field studies were conducted to evaluate linuron for POST control of Palmer amaranth in sweetpotato to minimize reliance on protoporphyrinogen oxidase (PPO)-inhibiting herbicides. Treatments were arranged in a two by four factorial where the first factor consisted of two rates of linuron (420 and 700 g ai ha−1), and the second factor consisted of linuron applied alone or in combinations of linuron plus a nonionic surfactant (NIS) (0.5% v/v), linuron plus S-metolachlor (800 g ai ha−1), or linuron plus NIS plus S-metolachlor. In addition, S-metolachlor alone and nontreated weedy and weed-free checks were included for comparison. Treatments were applied to ‘Covington’ sweetpotato 8 d after transplanting (DAP). S-metolachlor alone provided poor Palmer amaranth control because emergence had occurred at applications. All treatments that included linuron resulted in at least 98 and 91% Palmer amaranth control 1 and 2 wk after treatment (WAT), respectively. Including NIS with linuron did not increase Palmer amaranth control compared to linuron alone, but increased sweetpotato injury and subsequently decreased total sweetpotato yield by 25%. Including S-metolachlor with linuron resulted in the greatest Palmer amaranth control 4 WAT, but increased crop foliar injury to 36% 1 WAT compared to 17% foliar injury from linuron alone. Marketable and total sweetpotato yield was similar between linuron alone and linuron plus S-metolachlor or S-metolachlor plus NIS treatments, though all treatments resulted in at least 39% less total yield than the weed-free check resulting from herbicide injury and/or Palmer amaranth competition. Because of the excellent POST Palmer amaranth control from linuron 1 WAT, a system including linuron applied 7 DAP followed by S-metolachlor applied 14 DAP could help to extend residual Palmer amaranth control further into the critical period of weed control while minimizing sweetpotato injury.

Rice Response to Sub-lethal Rates of Paraquat, Metribuzin, Fomesafen, and Cloransulam-methyl at Different Application Timings

Paraquat mixtures with residual herbicides before planting is a common treatment in Mississippi, and rice in proximity is susceptible to off-target movement of these applications. Four concurrent studies were conducted in Stoneville, MS, to characterize rice performance following exposure to a sub-lethal rate of paraquat, metribuzin, fomesafen, and cloransulam-methyl at different application timings. Applications were made to rice at spiking to one-leaf (VEPOST), two- to three-leaf (EPOST), three- to four-leaf (MPOST), 7 d postflood (PFLD), and panicle differentiation (PD) growth stages. Regardless of application timing, rice injury following exposure to paraquat was ≥ 45%. Delays in maturity were increased by 0.3 d d-1 following paraquat from emergence through PD. Dry weight, rough rice yield, panicle density, and germination were reduced 18.7 g, 131.5 kg ha-1, 5.6 m-2, and 0.3%, respectively, d-1 from paraquat at emergence through PD. By 28 d after treatment (DAT), metribuzin injured rice 3 to 6%, and that injury did not translate into a yield reduction. Regardless of application timing, rice injury following fomesafen ranged from 2 to 5% 28 DAT. Rice exposed to cloransulam-methyl EPOST exhibited greatest root and foliar injury 21 and 28 DAT, respectively. Additionally, yield was reduced to 6,540 kg ha-1 compared with 7,850 kg ha-1 in the nontreated when rice was exposed to cloransulam-methyl EPOST. Rice yield was negatively affected following paraquat applied any time after rice emergence. However, applications of paraquat to rice in early reproductive growth reduced rough rice yield and seed germination the greatest. Application timing is crucial in determining severity of rice injury. Early-season injury to rice following paraquat had less effect on yield compared with injury at later stages. Additionally, fields devoted to seed rice production are at risk for reduced seed germination if exposed to paraquat during early reproductive growth stages.

Ozone Stress Responsive Gene Database (OSRGD ver. 1.1): a literature curated database for crop improvement

Ozone (O3) is a major abiotic stress which severely affects the growth and development of plants. In order to cope up with ozone stress, plants exhibit a plethora of morphological, physiological and molecular changes. Various molecular studies have been performed and a variety of genes exhibiting expression in response to ozone stress have been identified. However, no existing database has been designed yet to present information on ozone stress responsive genes differentially expressed across different plant species. The lack of a curated database limits the research potential in the area and therefore a cohesive database should be designed as a data repository of the ozone responsive genes. OSRGD ver. 1.1 is a user friendly web interface to explore ozone stress specific transcriptome dataset of different plant species. It allows users to retrieve the ozone stress responsive gene data by keyword based search. Each entry upon keyword query contains detailed information about the specific species, its foliar injury symptoms, pattern of gene expression, and platform used for gene expression analysis with reference literature. This comprehensive biocuration will offer researchers a better biological insight into plants response to ozone stress which will focus on development of climate smart crops through crop breeding.

No evidence for flooding stress memory in saplings of eight hardwood floodplain forest species

Alluvial floodplain forests became rare in many parts of Europe, due to anthropogenic changes. Therefore, restoration of floodplain forests is important, but a difficult task because of the complex environmental conditions. The zonation of woody species in floodplains is mainly determined by hydrological conditions, not only within one year but also during the previous years. Tolerance to flooding can be regarded as a key factor for the successful establishment. We examined whether a previous flooding showed an increased flooding tolerance of saplings from eight woody floodplain forest species after a recurrent flooding under controlled common garden conditions at the research station Gießen-Leihgestern (Germany). This would indicate a stress memory towards flooding stress. The individuals of the experiment already experienced a partial flooding of three different durations (three, six or nine weeks) or no flooding in the previous year. After nine months of recovery, these fourteen-month-old saplings were again either exposed to a partial flooding of nine weeks or no flooding. We assessed foliar injury and growth in terms of plant height, number of leaves and stem diameter three weeks (short-term recovery) and nine months (medium-term recovery) after flooding. The saplings showed no increased tolerance to a recurrent flooding irrespective of the previous experienced flooding duration. Therefore, no immediate stress memory towards flooding stress could be observed. To recover after flooding seems to be the better option compared to forming a stress memory, which explained that most species showed a decreased foliar injury after medium-term compared to short-term recovery period.

Response of Sensitive and Resistant Snap Bean Genotypes to Nighttime Ozone Concentration

Effects of nighttime (2000 to 0700 hr) O3 on the pod mass of sensitive (S156) and resistant (R123) snap bean (Phaseolus vulgaris) genotypes were assessed using continuous stirred tank reactors located within a greenhouse. Two concentration-response relationship trials were designed to evaluate yield response to nighttime O3 exposure (10 to 265 ppb) in combination with daytime exposure at background levels (44 and 62 ppb). Three replicated trials tested the impact of nighttime O3 treatment at means of 145, 144, and 145 ppb on yields. In addition, stomatal conductance (gS) measurements documented diurnal variations and assessed the effects of genotype and leaf age. During the concentration-response experiments, pod mass had a significant linear relationship with the nighttime O3 concentration across genotypes. Yield losses of 15% and 50% occurred at nighttime exposure levels of ≈45 and 145 ppb, respectively, for S156, whereas R123 yields decreased by 15% at ≈150 ppb. At low nighttime O3 levels of ≈100 ppb, R123 yields initially increased up to 116% of the treatment that received no added nighttime O3, suggesting a potential hormesis effect for R123, but not for S156. Results from replicated trials revealed significant yield losses in both genotypes following combined day and night exposure, whereas night-only exposure caused significant decreases only for S156. The gS rates ranged from less than 100 mmol·m−2·s−1 in the evening to midday levels more than 1000 mmol·m−2·s−1. At sunrise and sunset, S156 had significantly higher gS rates than R123, suggesting a greater potential O3 flux into leaves. Across genotypes, younger rapidly growing leaves had higher gS rates than mature fully expanded leaves when evaluated at four different times during the day. Although these were long-term trials, gS measurements and observations of foliar injury development suggest that acute injury, occurring at approximately the time of sunrise, also may have contributed to yield losses. To our knowledge, these are the first results to confirm that the relative O3 sensitivity of the S156/R123 genotypes is valid for nighttime exposure.

Peanut and Weed Response to Postemergence Herbicide Tank-Mixtures Including Paraquat and Inorganic Liquid Nutrients

ABSTRACT Weed control is an integral part of peanut (Arachis hypogaea L.) production systems. Paraquat is a staple postemergence (POST) herbicide used in peanut production in the Southeast US. Inorganic liquid nutrient (ILN) concentrates are liquid fertilizers that are recommended for use by producers in tank-mixtures with paraquat by some distributors. Irrigated and non-irrigated field trials were conducted to quantify the safening effect of ILN in various herbicide tank-mixtures on peanut and determine the suitability as tank-mix replacements for bentazon. Field studies indicated similar POST herbicide responses for peanut injury. Greenhouse experiments evaluated POST paraquat tank-mixtures with ILN for weed control and biomass reduction. Paraquat plus S-metolachlor caused significant leaf burn and stunting. Greatest peanut foliar injury occurred 3 d after treatment (DAT) but was transient. For the irrigated field trial, paraquat plus S-metolachlor plus ILN had similar injury levels as compared to paraquat plus S-metolachlor plus acifluorfen plus bentazon at 22 to 25%. For the non-irrigated field study, the application of paraquat plus ILN had 10% injury compared to paraquat at 22%. While injury was the greatest directly following application, peanut was able to recover with no yield or grade loss for both the irrigated and non-irrigated studies. In the greenhouse study, the effect of ILN varied by weed species and reduced leaf injury on several broadleaf weeds. While the addition of ILN to the various paraquat tank-mixtures initially reduced injury, it did not correspond to increases in yield or grade. The variability in weed control, transient injury mitigation, and no yield increase indicates that Georgia peanut growers will receive no benefit for including ILN in their paraquat tank-mixtures but if needed to improve crop nutrition, ILN will not reduce weed control.

Evidence of Ozone-Induced Visible Foliar Injury in Hong Kong Using Phaseolus Vulgaris as a Bioindicator

(1) Background: Hong Kong is one of the most densely populated cities in the world, with millions of people exposed to severe air pollution. Surface ozone, mostly produced photochemically from anthropogenic precursor gases, is harmful to both humans and vegetation. The phytotoxicity of ozone has been shown to damage plant photosynthesis, induce early leaf death, and retard growth. (2) Methods: We use genotypes of bush bean Phaseolus vulgaris with various degrees of sensitivity to ozone to investigate the impacts of ambient ozone on the morphology and development of the beans. We use ozone-induced foliar injury index and measure the flowering and fruit production to quantify the ozone stress on the plants. (3) Results: We expected that the ozone-sensitive genotype would suffer from a reduction of yield. Results, however, show that the ozone-sensitive genotype suffers higher ozone-induced foliar damage as expected but produces more pods and beans and heavier beans than the ozone-resistant genotype. (4) Conclusions: It is postulated that the high ozone sensitivity of the sensitive genotype causes stress-induced flowering, and therefore results in higher bean yield. A higher than ambient concentration of ozone is needed to negatively impact the yield production of the ozone-sensitive genotype. Meanwhile, ozone-induced foliar damage shows a graduated scale of damage pattern that can be useful for indicating ozone levels. This study demonstrates the usefulness of bioindicators to monitor the phytotoxic effects of ozone pollution in a subtropical city such as Hong Kong.

Evidence of Ozone-induced Visible Foliar Injury in Hong Kong using Phaseolus Vulgaris as an Ozone Bioindicator

Hong Kong is one of the most densely populated cities in the world, with millions of people exposed to severe air pollution. (1) Background: Surface ozone, mostly produced photochemically from anthropogenic precursor gases is harmful to both human and vegetation. The phytotoxicity of ozone has been shown to damage plant photosynthesis, induce early leaf death and retard growth. (2) Methods: We use genotypes of bush bean Phaseolus vulgaris with various degrees of sensitivity to ozone to investigate the impacts of ambient ozone on the morphology and development of the bean. We use ozone-induced foliar injury index and measure the flowerings and fruit production to quantify the ozone stress on the plants. (3) Results: We expected that the ozone-sensitive genotype would suffer from a reduction of yield. Results however show that the ozone-sensitive genotype suffers higher ozone-induced foliar damage as expected but produces more pods and beans and heavier beans than the ozone-resistant genotype. (4) Conclusions: It is postulated that the high ozone sensitivity of the sensitive genotype causes stress-induced flowering and therefore results in higher bean yield. A higher-than-ambient concentration of ozone is needed to negatively impact the yield production of the ozone-sensitive genotype. This study demonstrate the usefulness of bioindicators to monitor the phytotoxic effects of ozone pollution in a subtropical city such as Hong Kong.

Chromosome Location Contributing to Ozone Tolerance in Wheat

Breeding wheat for higher grain yield can contribute to global food security and sustainable production on less land. Tropospheric ozone can injure wheat plants and subsequently reduce grain yield. Identification of ozone tolerance in the wheat genome can assist plant breeders in developing new sources of tolerant germplasm. Our objective was to use the ‘Chinese Spring’ monosomic lines to screen for ozone response and identify the chromosomic locations contributing to ozone tolerance based on foliar injury. Two methodologies, Continuous Stirred Tank Reactors and Outdoor Plant Environment Chambers, were used to expose wheat monosomic lines to varying concentrations and durations of ozone. Each wheat monosomic line in ‘Chinese Spring’ has a missing chromosome in each of the wheat subgenomes (A, B, and D). In both methodologies, we found significant and repeatable data to identify chromosome 7A as a major contributor to tolerance to ozone injury in ‘Chinese Spring’. In every experiment, the absence of chromosome 7A resulted in significant injury to wheat due to ozone. This was not the case when any other chromosome was missing.