Screening of Rice Cultivars for Morpho-Physiological Responses to Early-Season Soil Moisture Stress

The majority of rice(Oryza sativa L.) produced in the southern USA is drill-seeded and grown under upland-like conditions because permanent flooding is established after the four-leaf stage. Therefore, rice during the seedling growth stage will be subjected to variable soil moisture content. A greenhouse experiment was conducted to evaluate the performance of 15 rice cultivars commonly grown in Mississippi of USA under early-season soil moisture stress. Twenty morpho-physiological parameters of rice seedlings subjected to three different levels(100%, 66% and 33% field capacity) of soil moisture, from 10 to 30 d after sowing, were measured. Significant moisture stress × treatment interaction(P < 0.001) was observed for most of the parameters. Further, the total drought response index(TDRI) was developed to score the cultivars for drought tolerance with the variation from 26.88 to 36.21. Accordingly, the cultivars were classified into different groups of tolerance. The cultivars CL152 and CL142-AR were classified as the least and the most tolerant to drought based on TDRI and standard deviation, respectively. Even though both total root(R^2 = 0.98) or shoot(R^2 = 0.76) drought responses indices were positively correlated with TDRI, root traits were important in deriving the indices. Therefore, TDRI could be used to select cultivars for drought tolerance in a given environment and develop rice varieties with early-season drought tolerance. However, further research is needed to identify and characterize tolerance at other stages to assist breeding programs in rice.

Distinct Morpho-Physiological Responses of Maize to Salinity Stress

Most plants demonstrate wide interactive and complex adaptive morphological, biochemical, and physiological responses when subjected to salinity stress. Salt stress negatively impacts agricultural yields more especially cultivated crops throughout the world. Of interest to this study is maize a salt- sensitive crop that is widely grown worldwide, and receiving most attention due to its significant attributes and ability to serve as a great model for stress response studies. We exposed QN701 maize cultivar, to simulated salinity stress and investigated its morphological and physiological responses. Salinity negatively induced various morphological responses such as the reduction in plant height, number of leaves, shoot and root (length and biomass), and leaf width;however, it significantly increased the leaf area. On the physiological aspect, salt stress decreased the number of stomata, stomatal density, and photosynthesis, while it increased the respiration rate. This study expanded our knowledge of the morphological and physiological responses of maize to salinity stress. Additionally, these findings may serve as a recommendation for salinity breeding programs in maize and related cereal crops.

Leaf morpho-physiology and phytochemistry of olive trees as affected by cultivar type and increasing aridity

The olive species(Olea europaea L.)is an ancient traditional crop grown under rainfed conditions in the Mediterranean Basin.In response to the growing national and international demand for olive oil,the olive cultivars are introduced into highly arid new bioclimatic areas.Subsequently,the morpho-physiology and phytochemistry of olive trees are potentially changing among cultivar types and geographical conditions.In the present work,we have undertaken an assessment on the impacts of geographical location and cultivar types on the leaf morpho-physiology and phytochemistry of olive trees.Thus,leaves of the two most cultivated olive tree varieties,Chemlal and Sigoise,were collected from three geographical regions(Setif,Batna,and Eloued)with increasing aridity in Algeria.Leaf samples from the geographical regions were analyzed using the standard physiological experiment,colorimetric method,and a chromatography assay.Leaves of both cultivars exhibited a significant variance in terms of the leaf shape index but not for the leaf tissue density,specific leaf weight,and specific leaf area.Photosynthetic pigment contents were affected by both cultivar type and geographical location,with the lowest pigment content recorded in the Sigoise cultivar from the Setif region.Compared with the Setif and Batna regions,dried leaves of both cultivars from the Eloued region showed the higher levels of the total polyphenol,total flavonoid,and total tannin,as well as a better antioxidant capacity.Liquid chromatography-mass spectrometry analysis of all leaf extracts identified the following phenolic acids as major compounds:oleuropein,naringin,apigenin-7-O-glucoside,kaempferol,quercetin,quercitrin,luteolin-7-O-naringenin,and quinic acid.Lower contents were found for p-Coumaric acid,trans-Ferulic acid,hyperoside,rutin,apigenin,caffeic acid,protocatechuic acid,o-Coumaric acid,and gallic acid.Also,epicatechin and catechin+were not found in the leaf extracts of the Sigoise cultivar.The leaf organic extracts in both cultivars displayed promising anti-cancer activity that was affected by geographical location and organic solvent polarity.Briefly,although increasing aridity and soil organic and mineral deficiency affected the leaf morpho-physiological parameters,both cultivars sustained a chemical richness,a good antioxidant,and an anti-tumoral capacity in leaves.Furthermore,the findings revealed that regardless the olive tree genotype,there was a significant impact of geographical location on the leaf morpho-physiology,bioactivity,and chemical composition,which may consequently modulate the growth and oil production of olive trees.

Physiological Basis of Stagnant Flooding Tolerance in Rice

Stagnant flooding(SF) is an important constraint which prolonges partial submergence damages of rice plants and reduces grain yield. Due to the heterogeneity in flood-prone ecosystem, many different types of traditional rice varieties are being grown by the farmers. The local landraces adapted to extreme in water availability could be the sources of new gene(s) which would be utilized to improve the adaptability of rice to SF with high yield. The main goal of this study is to identify new genetic resources tolerant to SF based on morpho-physiological traits. A total of 16 rice varieties were selected after initial screening from more than 400 rice varieties which were collected from eastern states of India. The increase rate of plant height was higher under SF compared to control, whereas no such trend was observed in the increment rate of aboveground total dry weight and culm dry weight. Area of aerenchyma gas spaces per tiller increased whereas root oxidase activity decreased under SF. The reduction of root oxidase activity, leaf area, and leaf dry weight was higher in susceptible varieties under SF compared to control. Stability index for different grain yield and yield attributes revealed that the impact of SF differed among different varieties. Correlation coefficient studies among different parameters taking stability index showed significant association with the grain yield. Based on the findings, it was concluded that maintenance of equivalent panicle weight and panicle number, plant height and harvest index at the maturity stage, leaf area, leaf and culm dry weights, root oxidase activity and tiller numbers at the flowering stage under SF compared to control help the plant to counteract the adverse effects of SF.

Screening of Rice Accessions for Tolerance to Drought and Salt Stress Using Morphological and Physiological Parameters

Drought and salinity are the most widespread soil problems, posing a big threat to food security in rice growing regions. The present study evaluated the performance of eleven rice genotypes using morphological and physiological parameters, under induced drought and salinity conditions. The seedlings were raised in 5 kg of homogenous soil in plastic bags in the greenhouse. For the drought experiment, each bag was watered with 200 ml of water twice daily until plants reached the five-leaf stage when watering was suspended for 2 weeks for the drought stressed plants but not suspended for the control plants. The experiment was a 2 × 11 factorial and the set up was arranged using the completely randomized design with three replications. Data were taken on Plant height, Number of tillers, leaf length, Number of green leaves, Number of dead leaves, Leaf rolling score (LRS) and Rate of water loss. The salinity experiment was set up in a similar manner except that the plants were irrigated twice a day for 2 weeks with 200 ml of treatment solution containing either 0 mM NaCl or 75 mM and data were collected on plant height, number of tillers, shoot fresh weight, shoot dry weight, Na+ and K+ concentrations, relative water content and chlorophyll content. Data from both experiments were subjected to Analysis of variance test using the GenStat software 10th edition and the means separated using least significant difference test. Individual stress response index (ISRI) was calculated for each parameter and the means used in grouping the varieties. Of the genotypes evaluated, four (FARO 44, NERICA 2, NERICA 8 and NERICA 5) were identified as tolerant, two (NERICA 4 and FARO 57) as moderately tolerant, while the rest were found to be sensitive to drought. Equally, two varieties (FARO 44 and RAM 137) stood out in the salinity screening as tolerant varieties, five were moderately tolerant while four (FARO 64, FARO 52, NERICA 2 and FARO 55) were clearly susceptible. FARO 44 is the only genotype that showed tolerance to both drought and salinity. The identified drought and salinity tolerant rice genotypes from this study can be recommended as genetic sources for future breeding programs for drought and salinity tolerance in rice.

Ecophysiological acclimatization to cyclic water stress in Eucalyptus

Drought is considered the main environmental factor limiting productivity in eucalyptus plantations in Brazil. However, recent studies have reported that exposure to water deficit conditions enables plants to respond to subsequent stresses. Thus, this study investigates the ecophysiological acclimatization of eucalyptus clones submitted to recurrent water deficit cycles. Eucalyptus seedlings were submitted to three recurrent water deficit cycles and anatomical, morphological and physiological changes were analyzed. The results were:(1) Eucalyptus seedlings responded to water deficits by directing carbohydrates to root and stem growth;(2) Size and number of stomata were reduced;(3) Stomatal conductance decreased which allowed the plants to reduce water losses through transpiration,increasing instantaneous water use efficiency;(4) The relationship between gas exchanges and available water contents allowed the seedlings to uptake the retained soil water athigher tensions;and,(5) Physiological recovery from subsequent water deficits became faster. As a result of these changes, the eucalyptus seedlings recovered from the same degree of water stress more rapidly.

Responses of Aquatic Vegetation to Pollution: Preliminary Results on Ecotoxicological Effects and Bioenrichment Factors

This study evaluates, on a preliminary basis, the principal morpho-physiological effects induced by pollution stress in four aquatic vegetation species of great ecological relevance in transitional water ecosystems. Three macroalgae (Chaetomorpha linum, Valonia aegagrophyla, Graciliariopsis longissima) and one phanerogams species (Ruppia cirrhosa) were exposed to different doses of trace elements (Cu, Hg, Zn) and surfactants (dodecylbenzenesulfonic acid sodium salt) in laboratory controlled microcosm conditions and morpho-physiological responses (photosynthetic complex alteration, percentage of died cells, morphological changes) were measured before and after 7 and 14 days of exposure. Levels of pollutants in tissues and BioConcentration Factors (BCF) for each species were calculated after 14 days of exposure. Results suggest that photosynthetic complex alteration can be a useful tool to evaluate early and sub-lethal significant changes due to exposure to pollution stress in all of the considered species. A clear species-specificity was observed concerning trace element levels in tissues after 14 days of exposure, while dose-dependent behavior was observed for BCFs.