Sensitive Crop Species Research Articles

PGPR-based biofertilizer modulates strawberry photosynthetic apparatus tolerance responses by severe drought, soil salinization and short extreme heat event

Drought, soil salinization and the extreme heat events increments associate to climate change will notably impact sensitive crop species, such as strawberry. A greenhouse experiment was arranged to evaluate the potential of a PGPR-based biofertilizer, with multiple PGP properties, including ACC deaminase production highly related to the limitation of ethylene levels under abiotic stress, in modulation of photosynthetic apparatus tolerance responses by severe drought (complete water withholding), salinity in irrigation water (340 mM NaCl) and short extreme heat event (37/28 °C maximum and minimum temperature range). Our results show that all stress factors triggered acute injury effects on strawberry carboxylation capacity and photosystem II energy assimilation efficiency ability; whose intensity varied depending on factor nature. However, bacterial inoculation diminished ∼67 %, 20 % and 18 % the deleterious impact imposed by drought, heat and salinity stress on the net photosynthetic rate (AN). This effect was primarily mediated by counterbalancing the diffusion of CO2 in the stomata and biochemical limitations in response to heat and salinity stress, while the reduction of biochemical damage was more notable in response to drought. Complementarily, inoculation was able to highly buffer the photochemical limitations imposed by all abiotic stress factors tested. Despite these positive effects, the application of PGPR-based biofertilizer was unable to completely reverse the impact of stress factors on strawberry photosynthesis metabolism. However, the signal of these ameliorative effects was significant enough to consider the implementation of PGPR-based biofertilizer application as a complementary tool in the management of strawberry cultivation in increasingly stressful agronomic contexts.

Evaluation of Moisture Regime on Agronomic Traits of Rice Genotypes

Drought stress is a major constraint to the production and yield stability of crops. Rice (Oryza sativa L.) is one of the most important cereals and considered as a drought sensitive crop species. A field experiment was conducted in the vinylhouse of the Department of Agronomy, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh, during March - August 2018 to evaluate the performance of 38 rice genotypes under control and drought conditions. The experiment was laid out in a completely randomized design containing two water regimes with three replications. The water regimes were well-watered and induced moisture stress conditions. Multivariate and principal components analyses revealed that different plant characters, viz. plant height, total tillers hill-1, panicle number hill-1, length of panicle, filled grains panicle-1, 1000-grain weight, grain yield plant-1 and straw weight plant-1 showed a wide range of variation due to variation in moisture level. Correlation study and biplot analysis considering PC1 and PC2 explained that grain yield was positively correlated with filled grain panicle-1, total tiller hill-1, panicle number hill-1 and 1000-grain weight. Based on the grain yield plant-1 (g) and others agronomic characters, the genotypes BU Acc 33 (26.68 g), BU Acc 30 (21.81 g), and BU Acc 21 (20.58 g) were identified as promising genotypes for developing drought tolerant variety (ies). Ann. Bangladesh Agric. (2021) 25 (1) : 89-104

Jasmonate-Dependent Response of the Flower Abscission Zone Cells to Drought in Yellow Lupine.

Lipid membranes, as primary places of the perception of environmental stimuli, are a source of various oxygenated polyunsaturated fatty acids—oxylipins—functioning as modulators of many signal transduction pathways, e.g., phytohormonal. Among exogenous factors acting on plant cells, special attention is given to drought, especially in highly sensitive crop species, such as yellow lupine. Here, we used this species to analyze the contribution of lipid-related enzymes and lipid-derived plant hormones in drought-evoked events taking place in a specialized group of cells—the flower abscission zone (AZ)—which is responsible for organ detachment from the plant body. We revealed that water deficits in the soil causes lipid peroxidation in these cells and the upregulation of phospholipase D, lipoxygenase, and, concomitantly, jasmonic acid (JA) strongly accumulates in AZ tissue. Furthermore, we followed key steps in JA conjugation and signaling under stressful conditions by monitoring the level and tissue localization of enzyme providing JA derivatives (JASMONATE RESISTANT1) and the JA receptor (CORONATINE INSENSITIVE1). Collectively, drought-triggered AZ activation during the process of flower abscission is closely associated with the lipid modifications, leading to the formation of JA, its conjugation, and induction of signaling pathways.

Biomass yield and growth allometry of some crops growing under weed stress

Abstract. Qadir S, Khan A, Salam IU. 2020. Biomass yield and growth allometry of some crops growing under weed stress. Biodiversitas 21: 5621-5629. The conventional approach in crop science generally focuses on nutritional yield of crops. Crop yield is basically ranked by its photosynthetic efficiency. Hence the higher reserves of photosynthetic products are achieved in the form of biomass. Current study explains the gain and loss in biomass of five different crops viz, Zea mays L. (maize), Hordeum vulgare L. (barley), Cicer arietinum L. (chickpea), Pisum sativum L. (pea) and Phaseolus vulgaris L. (French beans) treated by weed manure of Portulaca oleracea L., Euphorbia hirta L. and Amaranthus viridis L. at 5%, 10% and 15% concentration. The inhibitory effects of the given weeds persist with significant (p < 0.5) differences in the biomass of tested crops. Absolute growth rate (AGR), relative growth rate (RGR) and carbon content are highest (29.43 mg day-1, 2.43 mg gm-1day-1 and 15.25% respectively) in Chickpea plants induced by 5% P. oleracea extract. The highest inhibition recorded in Pea plants induced by 15% of A. viridis extract with 8.33 mg day-1, 1.42 mg gm-1day-1 and 4.67% of AGR, RGR and carbon yield respectively. Inhibition rate of weeds on leaf growth indices also exists in the same order i.e., the highest in A. viridis and the lowest in P. oleracea. Therefore, it is concluded that A. viridis has produced the highest level of inhibition among the three weeds while Pea species is the most sensitive crop species among the five tested crops.

Evaluation of Morphological and Biochemical Characteristics of Sorghum [Sorghum bicolor [L.] Moench] Varieties in Response Salinity Stress

Salinity is among the most severe and widespread environmental constrains to global crop production, especially in arid and semi-arid climates and negatively affecting productivity of salt sensitive crop species. Breeding and selection of salt tolerant crop varieties is therefore necessary for sustainable plant productivity. Given that germination and seeding phases are the most critical phase in the plant life cycle, this study aimed to evaluate seed germination potential and associated traits under salt stress conditions as a simple approach to identify salt tolerant sorghum varieties [Gadam, Sc Sila and Serena] which are adaptated to various agroecological regions. Salinity stress was applied by addition of NaCl at three different levels of stress [100, 200 and 300 mM NaCl], while plants irrigated with water were used as control. Evaluation of tolerance was performed on the basis of germination percentage, shoot and seed water absorbance, shoot and root length, leave water content, seedling total chlorophyll content and morphologic abnormality. Our results showed that salinity stress significantly impacts all features associated with germination and early development of seedlings. Our results indicated that salinity stress substantially affects all traits associated with germination and early seedling growth, with the effect of salinity being dependent on the variety used and level of salinity stress applied. Among the tested sorghum varieties, Gadam was established to the most salt tolerant variety, suggesting its potential use for cultivation under salinity stress conditions as well as its suitability for use as germplasm material in future sorghum breeding programmes. For a greater insight into comprehensive mechanisms of salinity tolerance in sorghum, we suggest further research on genomic and molecular analysis.

Physiological and Biochemical Analyses of Sorghum Varieties Reveal Differential Responses to Salinity Stress

ABSTRACT Salinity is among the most severe and widespread environmental constrains to global crop production, especially in arid and semi-arid climates and negatively affecting productivity of salt sensitive crop species. Breeding and selection of salt tolerant crop varieties is therefore necessary for sustainable plant productivity. Given that germination and seeding phases are the most critical phase in the plant life cycle, this study aimed to evaluate seed germination potential and associated traits under salt stress conditions as a simple approach to identify salt tolerant Sorghum varieties. There Sorghum varieties whose adaptation to various agroclimatic conditions is not well elucidated. Salinity stress was applied by addition of NaCl at three different levels of stress (100, 200 and 300 mM NaCl), while plants irrigated with water were used as controls. Evaluation of tolerance was performed on the basis of germination percentage, shoot and seed water absorbance, shoot and root length, leave water content, seedling total chlorophyll content and morphologic abnormality. Our results showed that salinity stress significantly impacts all features associated with germination and early development of seedlings. Our results indicated that that salinity stress substantially affects all traits associated with germination and early seedling growth, with the effect of salinity being dependent on the variety used and level of salinity stress applied. Among the tested Sorghum varieties, Gadam was established to the most salt tolerant variety, suggesting its potential use for cultivation under salinity stress conditions as well as its suitability for use as germplasm material in future Sorghum breeding programmes. For a greater insight into comprehensive mechanisms of salinity tolerance in Sorghum, we suggest further research on genomic and molecular analysis.

Ecological risk assessment of cerium for tropical agroecosystems

Cerium (Ce) is present in high technology materials and in mineral P fertilizers and the use and discharge of such resources may change the natural status of Ce in the soil environment. Brazilian soils in farming areas are significantly exposed to increased levels of unintentionally-added Ce through intensive input of phosphate fertilizers. The aims of this study were to evaluate the ecotoxicological risk to plants growing in tropical soils contaminated with Ce, as well as to create a database to support future legislation regulating the limits of this element in Brazilian and conceivably other tropical soils. Eight crop species (corn, sorghum, rice, wheat, soybeans, sunflower, radish, and beans) were exposed to a Ce concentration gradient in two typical tropical soils (Oxisol and Inceptsol), and an artificial soil. Our findings showed that among the endpoints measured, Ce phytotoxicity was more pronounced on shoot dry matter than on percent germination and germination speed index. Sensitivity of plants is species specific and our data showed that sunflower and radish exposed to Ce were the most sensitive crop species. Soil properties such as pH, cation exchange capacity, and organic carbon may have influenced the severity of Ce phytotoxicity. Because of that, the Oxisol contaminated with this element caused higher phytotoxicity than the other soils tested. Our risk assessment results (hazardous concentration, HC5 = 281.6 mg Ce kg−1) support the idea that unintentional Ce input through P fertilizers does not pose a risk to soils of Brazilian agroecosystems.

Identification of salt-induced transcripts by suppression subtractive hybridization and their expression analysis under the combination of salt and elevated CO2 conditions in Salicornia brachiata

Soil salinity is a major abiotic stress that affects global agricultural productivity. Exploring the mechanisms that halophytes employ to thrive and flourish under saline environments is essential to increase the salt tolerance in sensitive crop species. Of the three halophytes used in this study Salicornia brachiata and Suaeda maritima belong to the same family Chenopodiaceae, while Sesuvium portulacastrum, a mangrove-associated halophyte, belongs to the family Aizoaceae. Assuming that halophytes of same family share similar salt tolerance mechanisms, we generated a suppression subtractive hybridization (SSH1) cDNA library from salt-treated leaf tissues of S. brachiata as tester and that of S. maritima as driver to identify salt-responsive genes unique to S. brachiata. To elucidate the difference in salt-tolerance mechanisms, and to identify salt-tolerance mechanisms amongst different families of halophytes, SSH2 library was generated from salt-treated leaf tissue of S. brachiata as tester and that of S. portulacastrum as driver. Totally, 87 and 49 EST clones representing unique genes were obtained from SSH1 and SSH2 libraries, respectively. Examination of the expression patterns of 17 (SSH1) and 15 (SSH2) differentially expressed genes using semi-quantitative RT-PCR confirmed up-regulation of these genes in shoots in response to salt treatment and elevated CO2 condition, but to a different extent. This study has provided insights into the molecular responses of S. brachiata to salt stress and elevated CO2 conditions.

Involvement of plasma membrane H+‐ATPase in the ammonium‐nutrition response of barley roots

AbstractBarley (Hordeum vulgare L.) is a typical ammonium ()‐sensitive crop species and exhibits a futile‐ efflux from root cells. Plasma membrane (PM) H+‐ATPase is responsible for pumping H+ out of plant cells and providing the driving force for the transport of various substances. We hypothesized that PM H+‐ATPase is involved in this efflux process of barley roots. Barley plants were cultivated in hydroponic solution with 1.0 mM or 1.0 mM nitrate () as the sole nitrogen source. Plasma membrane vesicles were isolated from the root tips for analyses of the activity. Plasma membrane H+‐ATPase was tested by Western Blot. The transcription of PM H+‐ATPase genes was analyzed using qRT‐PCR. Proton and efflux from barley roots was analyzed by scanning ion‐selective electrode technique. The results show that root and shoot growth was repressed by nutrition when compared to nutrition. Plasma membrane H+‐ATPase activity of barley roots under nutrition was significantly higher than that under nutrition. Methyl‐ammonium (MeA), a non‐metabolizable analog of , had no significant effect on PM H+‐ATPase activity. The enhanced PM H+‐ATPase activity by nutrition was consistent with a higher abundance of PM H+‐ATPase protein and higher transcription levels of six PM H+‐ATPase genes. By using the pharmacological agents vanadate and fusicoccin, a close linkage was observed between H+ efflux and efflux from barley roots. Taken together, nutrition stimulates PM H+‐ATPase activity, and this stimulation is possibly triggered by assimilation in barley roots. efflux from barley roots is associated with PM H+‐ATPase activity which could provide the driving force for efflux. Ammonium efflux might be considered as a disposal strategy in barley roots which prevents overloading the root cytoplasm.

Agronomic management of AMF functional diversity to overcome biotic and abiotic stresses - The role of plant sequence and intact extraradical mycelium

Intentional use of arbuscular mycorrhizal fungi (AMF) in cropping systems has been marginal, owing to the high cost and limited biodiversity of commercial inocula, together with the timeliness of colonization to achieve benefits. Additionally, mycorrhiza are considered incompatible with high input cropping systems. Combining results from 4 different experiments resulted in a strategy for the earlier and faster colonization by AMF, through an extensive extraradical mycelium (ERM) acting as a preferential source of inoculum if kept intact by the adoption of appropriate tillage techniques. Selection of host plants on which the ERM develops, provides the tool to manage AMF functional diversity. This strategy resulted in protection of sensitive crop species against biotic and abiotic stresses and can be implemented in low- and high-input cropping systems. Under Mn toxicity arbuscular colonization increased 2.6-fold and shoot dry weight 2.3-fold. In presence of Fusarium, arbuscular colonization increased 2.1-fold and shoot dry weight 1.5-fold.

Role of sodium ion transporters and osmotic adjustments in stress alleviation of Cynodon dactylon under NaCl treatment: a parallel investigation with rice.

Comparative analyses of the responses to NaCl in Cynodon dactylon and a sensitive crop species like rice could effectively unravel the salt tolerance mechanism in the former. C. dactylon, a wild perennial chloridoid grass having a wide range of ecological distribution is generally adaptable to varying degrees of salinity stress. The role of salt exclusion mechanism present exclusively in the wild grass was one of the major factors contributing to its tolerance. Salt exclusion was found to be induced at 4days when the plants were treated with a minimum conc. of 200mM NaCl. The structural peculiarities of the salt exuding glands were elucidated by the SEM and TEM studies, which clearly revealed the presence of a bicellular salt gland actively functioning under NaCl stress to remove the excess amount of Na+ ion from the mesophyll tissues. Moreover, the intracellular effect of NaCl on the photosynthetic apparatus was found to be lower in C. dactylon in comparison to rice; at the same time, the vacuolization process increased in the former. Accumulation of osmolytes like proline and glycine betaine also increased significantly in C. dactylon with a concurrent check on the H2O2 levels, electrolyte leakage and membrane lipid peroxidation. This accounted for the proper functioning of the Na+ ion transporters in the salt glands and also in the vacuoles for the exudation and loading of excess salts, respectively, to maintain the osmotic balance of the protoplasm. In real-time PCR analyses, CdSOS1 expression was found to increase by 2.5- and 5-fold, respectively, and CdNHX expression increased by 1.5- and 2-fold, respectively, in plants subjected to 100 and 200mM NaCl treatment for 72h. Thus, the comparative analyses of the expression pattern of the plasma membrane and tonoplast Na+ ion transporters, SOS1 and NHX in both the plants revealed the significant role of these two ion transporters in conferring salinity tolerance in Cynodon.

Plant responses to environmental stresses-from gene to biotechnology.

Increasing global population, urbanization and industrialization are increasing the rate of conversion of arable land into wasteland. Supplying food to an ever-increasing population is one of the biggest challenges that agriculturalists and plant scientists are currently confronting. Environmental stresses make this situation even graver. Despite the induction of several tolerance mechanisms, sensitive plants often fail to survive under environmental extremes. New technological approaches are imperative. Conventional breeding methods have a limited potential to improve plant genomes against environmental stress. Recently, genetic engineering has contributed enormously to the development of genetically modified varieties of different crops such as cotton, maize, rice, canola and soybean. The identification of stress-responsive genes and their subsequent introgression or overexpression within sensitive crop species are now being widely carried out by plant scientists. Engineering of important tolerance pathways, like antioxidant enzymes, osmolyte accumulation, membrane-localized transporters for efficient compartmentation of deleterious ions and accumulation of essential elements and resistance against pests or pathogens is also an area that has been intensively researched. In this review, the role of biotechnology and its successes, prospects and challenges in developing stress-tolerant crop cultivars are discussed.

Has the sensitivity of soybean cultivars to ozone pollution increased with time? An analysis of published dose-response data.

The rising trend in concentrations of ground-level ozone (O3 ) - a common air pollutant and phytotoxin - currently being experienced in some world regions represents a threat to agricultural yield. Soybean (Glycine max (L.) Merr.) is an O3 -sensitive crop species and is experiencing increasing global demand as a dietary protein source and constituent of livestock feed. In this study, we collate O3 exposure-yield data for 49 soybean cultivars, from 28 experimental studies published between 1982 and 2014, to produce an updated dose-response function for soybean. Different cultivars were seen to vary considerably in their sensitivity to O3 , with estimated yield loss due to O3 ranging from 13.3% for the least sensitive cultivar to 37.9% for the most sensitive, at a 7-h mean O3 concentration (M7) of 55ppb - a level frequently observed in regions of the USA, India and China in recent years. The year of cultivar release, country of data collection and type of O3 exposure used were all important explanatory variables in a multivariate regression model describing soybean yield response to O3 . The data show that the O3 sensitivity of soybean cultivars increased by an average of 32.5% between 1960 and 2000, suggesting that selective breeding strategies targeting high yield and high stomatal conductance may have inadvertently selected for greater O3 sensitivity over time. Higher sensitivity was observed in data from India and China compared to the USA, although it is difficult to determine whether this effect is the result of differential cultivar physiology, or related to local environmental factors such as co-occurring pollutants. Gaining further understanding of the underlying mechanisms that govern the sensitivity of soybean cultivars to O3 will be important in shaping future strategies for breeding O3 -tolerant cultivars.

Effect of Aerobic Environment on Physio-Morphological Traits in Aerobic and Lowland Indica Rice Genotypes

Rice (Oryza sativa L.) is cultivated under flooded lowland conditions and is a single biggest user of fresh water. Overexploitation of groundwater has caused serious problems in many parts of India including Haryana and Punjab. A new development in water saving technologies is the concept of aerobic rice. Rice is considered a drought sensitive crop species, however, aerobic rice withstand water stress. In the present investigation, different morphological and agronomical traits were studied in aerobic (MAS25, MAS26) and lowland (HKR47, PAU201, HBC 19 and PUSA1121) indica rice genotypes, grown under submerged and aerobic conditions in pots. Root length, shoot biomass, root biomass, yield and yield attributes declined in all lowland rice genotypes while, conversely, aerobic rice genotypes showed enhancement under aerobic environment. Better agronomic performance displayed by aerobic varieties may be due to longer, thick and dense root system in these rice genotypes.

Transgenic cucumber lines expressing the chimeric pGT::Dhn24 gene do not show enhanced chilling tolerance in phytotron conditions

AbstractIn cucumber, low temperatures can result in chilling injuries and can lead to significant yield decreases in open field production. The lack of a cold‐tolerant cucumber germplasm has limited classical breeding. Recent progress in understanding plant response to cold stress has allowed to develop transgenic approaches to improving cold tolerance in chilling sensitive crop species. The pGT::Dhn24 gene construct containing an anthocyanidine glucosyltransferase promoter and the DHN24 dehydrin‐encoding gene originating from cold‐acclimated species Solanum sogarandinum was developed, and preliminary study showed that its expression could increase cucumber chilling tolerance. In this study, a set of transgenic cucumber lines was developed and tested for cold tolerance. Expression of pGT::Dhn24 was confirmed in the transgenic cucumber lines at both the transcript and protein level. At the protein level, chilling‐induced pGT::Dhn24 transgene expression was observed in the leaves; however, it was constitutive in the roots. Cold stress‐related physiological parameters, germination ability and severity of chilling injury were measured for the transgenic lines at the phytotron conditions. No evidence for increased cold tolerance of the transgenic cucumber lines was found.

Sensitive crop species and appropriate bioassays for potential use in phytotoxicity assessment of Pb-contaminated soils

The present study aims to determine the phytotoxic effects of lead (Pb) on corn (Zea mays), wheat (Triticum aestivum), cucumber (Cucumis sativus), cabbage (Brassica oleracea) and lettuce (Lactuca sativa) and to identify the sensitive crop species and appropriate bioassays for potential use in phytotoxicity assessment of Pb-contaminated soil. In a laboratory experiment, Pb(NO3)2 was added to the background soil to obtain eight Pb treatments. The results indicate that the seed germination rate of lettuce decreases by 14.44%, 30.00% and 40.00% at 2000, 3000 and 4000 mg Pb kg−1 soil, respectively. However, the germination of corn, wheat, cucumber and cabbage is not significantly influenced by the Pb-contaminated soil treated with all the tested concentrations. Furthermore, the root elongation is more sensitive to Pb than is seed germination. The minimum concentrations of adverse effect of maize, wheat, cucumber, cabbage and lettuce are 2000, 3000, 1300, 800 and 300 mg Pb kg−1 soil, respectively. Moreover, dicotyledon species are more sensitive than monocotyledon species. In the genotoxicity study, the mitotic index (MI) fluctuates with an increasing Pb concentration. The micronuclei (MN) frequencies of cucumber, cabbage and lettuce exhibit a dose-dependent effect at concentrations ranging from 1300 to 4000 mg Pb kg−1 soil. It can be concluded that lettuce is a good candidate for indicating the toxicity of Pb in soil. Root elongation and the micronucleus frequency of dicotyledon are appropriate bioassays for potential use in phytotoxicity assessment of Pb-contaminated soil.

Plant physiological responses to UV-B radiation

During the last few decades, there has been considerable concern over the depletion of stratospheric ozone as a result of anthropogenic pollutants. This has resulted in a concomitant increase in solar ultraviolet-B radiation (280–320 nm). High levels of UV-B radiation are responsible for multiple biologically harmful effects in both plants and animals. Many different plant responses to supplemental UV-B radiation have been observed, mostly injurious but sometimes beneficial. UV-B can influence plant processes either through direct damage or via various regulatory effects. In plants, direct effects include DNA damage, membrane changes and protein denaturation, which often cause heritable mutations affecting various physiological processes, including the photosynthetic apparatus. These could adversely affect plant growth, development and morphology, especially the productivity of sensitive crop species. This paper reviews the current knowledge about the plant physiological responses to UV-B stress. doi: http://dx.doi.org/10.9755/ejfa.v24i6.14669

Growth of soybean at future tropospheric ozone concentrations decreases canopy evapotranspiration and soil water depletion

Tropospheric ozone is increasing in many agricultural regions resulting in decreased stomatal conductance and overall biomass of sensitive crop species. These physiological effects of ozone forecast changes in evapotranspiration and thus in the terrestrial hydrological cycle, particularly in intercontinental interiors. Soybean plots were fumigated with ozone to achieve concentrations above ambient levels over five growing seasons in open-air field conditions. Mean season increases in ozone concentrations ([O 3]) varied between growing seasons from 22 to 37% above background concentrations. The objective of this experiment was to examine the effects of future [O 3] on crop ecosystem energy fluxes and water use. Elevated [O 3] caused decreases in canopy evapotranspiration resulting in decreased water use by as much as 15% in high ozone years and decreased soil water removal. In addition, ozone treatment resulted in increased sensible heat flux in all years indicative of day-time increase in canopy temperature of up to 0.7 °C.

Effects of prolonged UV-B exposure in plants

Over the past few decades, there has been a depletion of the stratospheric ozone layer due to emissions of halogen-containing compounds of anthropogenic origin. This has resulted in a concomitant increase in solar ultraviolet-B radiation. High levels of UV-B radiation are responsible for multiple biologically harmful effects in both plants and animals. In plants, these effects include DNA damage, which often causes heritable mutations affecting various physiological processes, including the photosynthetic apparatus, protein destruction and signal transduction via UV-B photoreceptors. High UV-B levels introduce a number of different lesions, predominantly cyclobutane pyrimidine dimmers (CPDs) and pyrimidine (6-4) pyrimidinone products [(6-4) PPs] in the genome. These could adversely affect plant growth, development and morphology, especially the productivity of sensitive crop species. This paper reviews the genetic effects of long-term UV-B exposure in plants.

Tropospheric Ozone: a Menace for Crops and Natural Vegetation in Greece

Based on instrumental monitoring (AOT40s) and phytodetection (with Bel-W3 and KK6/5 tobacco cultivars) data we evaluated ambient ozone phytotoxicity in Greece. In the greater region of Mesogia-Attica, during the summer of 2000, the year before the new airport Eleftherios Venizelos (March 2001) began operating in this region, the AOT40s (ppb*h) were 16,325 over 110 days at Spata; 18,646 over 113 days at Markopoulo; 8,093 over 22 days at Artemis and 16,679 over 121 days in Athens. The Bel- W3 and KK6/5 plants were extensively injured at all places with the greatest injury occurring at Artemis. During the same summer, ozone was also monitored in three rural areas of Corinth, at the Astronomical Observatory of Krionerion, Bogdani Hill and Kiato; The highest average daily AOT40 (192 ppb*h) was observed in Krionerio, and it was almost equal to that occurred in Athens (193 ppb*h). Bel-W3 and KK6/5 plants placed at 11 rural areas in Corinth showed extended injury. The following year (2001), high injury was observed on other sets of bioindicator plants exposed in a network of 28 locations throughout the greater area of Volos and Pelion Mountain. Symptoms were more severe at Mortias, Xinovrisi, Tsagarada, Makrinitsa and Chania. The AOT40 (May-July) was 11,391 and 10,351 ppb*hours for 2001 and 2002 respectively. Severe ozone-like symptoms have also been observed on field-cultivated grape vines, onion and watermelon plants. Synoptically, our investigations suggest that ozone occurs in the Greek mainland at levels that are potentially phytotoxic for sensitive crop species and for sensitive natural vegetation species including forest trees.