Carbon Dioxide Assimilation Rate Research Articles

Physiological and Biochemical Responses Induced by Plum Pox Virus and Plum Bark Necrosis Steam Pitting Associated Virus in Tuscany Autochthonous Plum cv. Coscia di Monaca.

The present study focused on trees of Tuscany autochthonous plum cv. Coscia di Monaca in order to evaluate the presence of viruses and elucidate the physiological and biochemical responses to virus infections under real field conditions. Among the several investigated viruses, plums tested positive only to plum pox virus (PPV) and plum bark necrosis steam pitting associated virus (PBNSPaV), occurring as both singular and co-infections. This is the first report of PBNSPaV in a Tuscany orchard. Furthermore, the present study not only confirmed the detrimental effects of PPV on the carbon dioxide assimilation rate due to both stomatal limitations and mesophyll impairments, but also showed that although PBNSPaV did not induce such photosynthetic impairments when occurring as singular infection, it enhanced this damaging effect when present as a co-infection with PPV, as confirmed by a severe decrease in the chlorophyll content. Infection-specific responses in terms of accessory pigments (i.e., carotenoids and xanthophylls), as well as sugars and organic acids, were also reported, these being likely related to photoprotective mechanisms and osmotic regulations under virus-induced oxidative stress. Overall, the results here presented represent an important step to fill knowledge gaps about the interaction of plant viruses and autochthonous Prunus cultivars.

Seasonal photosynthesis and respiration dynamics of Pinus sibirica latitudinal ecotypes: ex situ study

Photosynthesis and respiration are temperature dependent processes. Therefore, it is important to understand how the physiological processes of photosynthesis and respiration will respond to climate change in the future. Seasonal carbon dioxide gas exchange of vegetative scion Siberian stone pine ecotypes (Pinus sibirica Du Tour) of latitudinal transect grown in the scientific station “Kedr” in the south of the Tomsk region were studied. The latitudinal transect was represented by two ecotypes: the southern ecotype (Tomsk) and the northern ecotype (Urengoy). The age of the grafted trees was 26 years. Apparent uptake of CO2 of the southern ecotype began a week earlier than the one of the southern ecotype, when the needle length reached 35 and 40 % of the final length of the southern and southern ecotypes, respectively. Photosynthesis reaches its maximum values when the needle length was 45-52 % of the final length of both ecotypes. The carbon dioxide assimilation rate of the southern ecotype remained high until the second decade of July, then its intensity decreased. Photosynthetic rate of the southern ecotype decreased in early August. In fully developed needles, the photosynthetic intensity between ecotypes did not differ significantly. The dark respiration of both ecotypes was maximum at the beginning of needle growth, then decreased significantly, was almost constant in July, and had minimum values at the end of the growing season. At the initial growth stages the needles of the southern ecotype had high values of dark respiration, which was 2 times higher than that of the southern ecotype. In the growth process by the first ten days of
 July, the differences between ecotypes were practically leveled. Subsequently, the dark respiration of the southern ecotype became 2 times higher than that of the southern one, however, it remained low compared to the initial stages of needle growth. The respiration of needle finished growing decreased by 8-10 times. The negative balance between photosynthesis and respiration of both ecotypes maintained until the needle length exceed 40 % and 35 % of the final length in the northern and southern ecotypes, respectively. Positive balance CO2 was observed when the needle length reached 45 % in the northern and 52 % in the southern ecotypes. During the summer months the CO2 balance was significantly higher for the Tomsk ecotype. In September and October the CO2 balance of the northern ecotype became lower than of one the southern one due to increased part of respiration of gas exchange. We believe that the high respiratory intensity of the Siberian stone pine northern ecotype is hereditary, therefore significant respiratory costs will have negative impact the productivity of high latitude plants and their adaptation to climate warming.

Comparing cell wall and membrane contributions to mesophyll conductance in plants.

Photosynthesis in plants sequesters carbon from carbon dioxide into biomass, while releasing oxygen back into the atmosphere. Gases such as carbon dioxide and oxygen must thus pass through spongy mesophyll cells, which feature both a rigid cell wall and a plasma membrane that may create barriers to gas transfer. Experimentally, this is quantified through measuring mesophyll conductance. Mesophyll conductance is a composite metric, which is controlled by the barriers between intracellular airspaces and photosynthetic membranes within plant cells, including plant cell walls and membranes. Using molecular simulation techniques, we track gas permeation events across both plant plasma membrane models as well as models for a chunk of secondary cell wall. For the membrane, we find gases accumulate within the membrane interior, consistent with prior partitioning measurements. Carbon dioxide permeability measured from observed transition events increases approximately threefold over temperature ranges experienced in the environment, similar to experimental measures for carbon dioxide assimilation. Under optimistic transport assumptions, we find that carbon dioxide membrane permeation is only ten times faster than measured carbon dioxide assimilation rates, suggesting that membrane transport may be limiting under some growth conditions where carbon dioxide availability is low. By contrast, we find that gases permeate readily through plant cell walls, with diffusion coefficients that are only approximately ten times slower than water. As a consequence, diffusion estimates reveal that a gas molecule would spend only 100 miliseconds transiting across a cell wall that is a micron thick. Thus, we find that biological membranes are likely the limiting factor in gas permeation through the plant mesophyll.

NaCl Pretreatment Enhances the Low Temperature Tolerance of Tomato Through Photosynthetic Acclimation.

Plants often need to withstand multiple types of environmental stresses (e.g., salt and low temperature stress) because of their sessile nature. Although the physiological responses of plants to single stressor have been well-characterized, few studies have evaluated the extent to which pretreatment with non-lethal stressors can maintain the photosynthetic performance of plants in adverse environments (i.e., acclimation-induced cross-tolerance). Here, we studied the effects of sodium chloride (NaCl) pretreatment on the photosynthetic performance of tomato plants exposed to low temperature stress by measuring photosynthetic and chlorophyll fluorescence parameters, stomatal aperture, chloroplast quality, and the expression of stress signaling pathway-related genes. NaCl pretreatment significantly reduced the carbon dioxide assimilation rate, transpiration rate, and stomatal aperture of tomato leaves, but these physiological acclimations could mitigate the adverse effects of subsequent low temperatures compared with non-pretreated tomato plants. The content of photosynthetic pigments decreased and the ultra-microstructure of chloroplasts was damaged under low temperature stress, and the magnitude of these adverse effects was alleviated by NaCl pretreatment. The quantum yield of photosystem I (PSI) and photosystem II (PSII), the quantum yield of regulatory energy dissipation, and non-photochemical energy dissipation owing to donor-side limitation decreased following NaCl treatment; however, the opposite patterns were observed when NaCl-pretreated plants were exposed to low temperature stress. Similar results were obtained for the electron transfer rate of PSI, the electron transfer rate of PSII, and the estimated cyclic electron flow value (CEF). The production of reactive oxygen species induced by low temperature stress was also significantly alleviated by NaCl pretreatment. The expression of ion channel and tubulin-related genes affecting stomatal aperture, chlorophyll synthesis genes, antioxidant enzyme-related genes, and abscisic acid (ABA) and low temperature signaling-related genes was up-regulated in NaCl-pretreated plants under low temperature stress. Our findings indicated that CEF-mediated photoprotection, stomatal movement, the maintenance of chloroplast quality, and ABA and low temperature signaling pathways all play key roles in maintaining the photosynthetic capacity of NaCl-treated tomato plants under low temperature stress.

EFFECT OF DROUGHT STRESS ON WHEAT AND DROUGHT BREEDING STATUS FOR IT IN NEPAL WITH THE WAY FORWARD: A REVIEW

Wheat is the third most important crop in Nepal that is grown in a dominant rice wheat cropping pattern. The productivity of wheat is at a standstill for the past decade primarily due to abiotic stress like drought and high temperature. Changing climate pattern and high vulnerability of Southeast Asian countries in the future demands extensive work under plant breeding to cope with the challenges. Wheat requires about 266.8-500mm of water for normal attainable yield, but prolonged drought has a serious effect on photosynthesis as it hampers the carbondioxide assimilation rate. It also has a pronounced effect in the reproductive and grain filling period of the wheat. This results in the reduction of yield, and this is expected to increase in the future because of climate change. Varieties like Gautam and Vijay have been reported to show positive drought adaptive traits. Vast resources of biodiversity and landraces have been underutilized in Nepal which can be useful when coupled with advanced biotechnological tools to produce drought adaptive crop.

Beauveria bassiana Enhances the Growth of Cowpea Plants and Increases the Mortality of Cerotoma arcuata.

Cowpea (Vigna unguiculata) crops stand out for their efficient adaptation to edaphoclimatic conditions. Insect pests, such as the leaf beetle Cerotoma arcuata, are among the main factors that limit cowpea yield. Chemical control methods are commonly used to control such pests; however, biological methods are an alternative to reduce the indiscriminate use of conventional pesticides. This study aimed to evaluate the effects of Beauveria bassiana inoculation on the growth and physiological parameters of the cowpea plant and assess the influence of the inoculation on the feeding performance and survival of C. arcuata adults. Colonization by B. bassiana was recorded in the stems (63.89%), roots (45.83%), and leaves (25%) of the cowpea plant. It was found that B. bassiana enhanced the plant height, number of leaves, and the dry mass of the inoculated cowpea plants as compared to the control. The treated plants exhibited higher net carbon dioxide (CO2) assimilation rates in the gas exchange evaluation as well as higher stomatal conductance, evapotranspiration rates, and chlorophyll (a + b) content than the control plants. Moreover, the Kaplan-Meier survival analysis showed that the B. bassiana negatively affected the survival of the insect in the leaf disc assays.

Deficiência de macronutrientes em <i>Cariniana estrellensis</i> (Raddi) Kintze

O conhecimento dos efeitos da nutrição mineral sobre a fisiologia vegetal de espécies nativas é um importante auxílio para que se obtenha o sucesso desejado quando estas são usadas no reflorestamento ou na recuperação de áreas degradadas. A presente pesquisa avaliou as consequências da deficiência de macronutrientes em Cariniana estrellensis (Raddi) Kintze (jequitibá-branco) nas taxas de assimilação de gás carbônico e de transpiração e na produção de biomassa desta espécie, que é amplamente utilizada na restauração florestal no Brasil. O experimento foi conduzido em casa de vegetação, em blocos ao acaso, com sete tratamentos e três repetições, empregando a técnica de diagnose por subtração de macronutrientes, com um tratamento controle no qual o jequitibá-branco foi cultivado em solução nutritiva completa, com todos os macros e micronutrientes. Os teores de nutrientes foram determinados por análise química nos diferentes órgãos do jequitibá-branco; através do analisador de gás por infravermelho portátil (Infrared Gás Analyzer – IRGA, modelo Li-cor 6400) foram determinadas as taxas de assimilação de gás carbônicoe de transpiração em folhas de três partes distintas das plantas, e ao final do experimento foi realizada a determinação da produção de biomassa seca. A deficiência dos macronutrientes, de um modo geral, prejudicou as taxas de assimilação de gás carbônico e de transpiração e, por conseguinte, a produção de biomassa seca das plantas jovens de jequitibá-branco foi menor em relação ao tratamento controle. Os resultados deste estudo sugerem que a implantação de florestas ou a recuperação de áreas degradadas por meio do reflorestamento que utilizam o jequitibá-branco certamente serão prejudicados se a complementação nutricional não for realizada quando o solo for deficiente em qualquer dos macronutrientes.

Depicting the physiological and ultrastructural responses of soybean plants to Al stress conditions

Aluminium (Al) is a toxic element for plants living in soils with acidic pH values, and it causes reductions in the roots and shoots development. High Al concentrations can cause physiological and structural changes, leading to symptoms of toxicity in plant tissue. The aim of this study was to describe the Al toxicity in soybean plants through physiological, nutritional, and ultrastructure analyses. Plants were grown in nutrient solution containing increasing Al concentrations (0; 0.05; 0.1; 1.0, 2.0 and 4.0 mmol L−1). The Al toxicity in the soybean plants was characterized by nutritional, anatomical, physiological, and biochemical analyses. The carbon dioxide assimilation rates and stomatal conductance were not affected by the Al. However, the capacity for internal carbon use decreased, and the transpiration rate increased, resulting in increased root biomass at the lowest Al concentration in the nutrient solution. The soybean plants exposed to the highest Al concentration exhibited lower root and shoot biomass. The nitrate reductase and urease activities decreased with the increasing Al concentration, indicating that nitrogen metabolism was halted. The superoxide dismutase and peroxidase activities increased with the increasing Al availability in the nutrient solution, and they were higher in the roots, showing their role in Al detoxification. Despite presenting external lesions characterized by a damaged root cap, the root xylem and phloem diameters were not affected by the Al. However, the leaf xylem diameter showed ultrastructural alterations under higher Al concentrations in nutrient solution. These results have contributed to our understanding of several physiological, biochemical and histological mechanisms of Al toxicity in soybean plants.

Atmospheric CO2 capture for the artificial photosynthetic system

The aim of these studies is to evaluate the ambient CO2 capture abilities of the membrane contactor system in the same conditions as leafs, such as ambient temperature, pressure and low CO2 concentration, where the only driving force is the concentration gradient.The polysulfone membrane employed was made by a phase inversion process and characterized by ESEM micrographs which were used to determine the thickness, asymmetry and pore size. Besides, the porosity of the membrane was measured from the membrane and polysulfone density correlation and the hydrophobicity was analyzed by contact angle measurements. Moreover, the compatibility of membrane and absorbent was evaluated, in order to exclude wetting issues by meaning of swelling, dynamic contact angle and AFM analysis. The prepared membranes were introduced into a cross flow module and used as contactors between CO2 and the absorbing media, a potassium hydroxide solution. The influence of the membrane thickness, absorbent stirring rate, solution pH and absorption time on CO2 capture were evaluated. Absorbent solution stirring rate showed no statistically significant influence on absorption. We observed a non-linear correlation between the capture rate and the increase of absorbent solution pH as well as absorption time. The results showed that the efficiency of our CO2 capture system is similar to stomatal carbon dioxide assimilation rate, achieving stable value of 20μmol/m2·s after 1h of experiment.

Selenium in lemon balm plants: Productivity, phytotoxicity and drought alleviation

ABSTRACTSince studies on the effects of selenium (Se) supplementation in water-stressed plants have mainly focused on cereal crops, the specific reports regarding Se-mediated adaptation to drought stress in medicinal vegetables are scant. Thus, we investigated the responses of Melissa officinalis to Se supplementation. Selenium contents were increased in leaves and grains by supplemental Se. Selenium foliar application at 1 mg l−1 could be useful to increase the vegetative and reproductive growth of Se-enriched plants under well-watered conditions but at 20 mg l−1 led to toxicity and caused damage to shoots. Drought stress significantly inhibited plant growth by chlorophyll degradation and reduced net carbon dioxide (CO2) assimilation rate. Although Se at 1 mg l−1 could increase biomass production under well-watered conditions in addition to the stimulation of antioxidant system under water stress, it could not ameliorate the negative effect of drought on productivity.

Effects of Grapevine leafroll‐associated virus 3 on the physiology in asymptomatic plants of Vitis vinifera

AbstractGrapevine leafroll disease is one of the most important viral diseases of grapevine (Vitis vinifera) worldwide. Grapevine leafroll‐associated virus 3 (GLRaV‐3) is the most predominant virus species causing this disease. Therefore, it is important to identify GLRaV‐3 effects, especially in plants which do not systematically show visual symptoms. In this study, effects of GLRaV‐3 on grapevine physiology were evaluated in asymptomatic plants of Malvasía de Banyalbufar and Cabernet Sauvignon cvs. Absolute virus quantification was performed in order to determine the level of infection of the treatment. The net carbon dioxide (CO2) assimilation (AN) and electron transport rate (Jflux) were the main parameters affected by the virus. The AN reduction in infected plants was attributed to restrictions in CO2 diffusion caused by anatomical leaf changes and a reduction of Rubisco activity. Those effects were more evident in Malvasia de Banyalbufar plants. The reduction of AN leads to a decrease in the total oxygen uptake rate by the activity of the cytochrome oxidase pathway, producing slight differences in plant growth. Therefore, even though no symptoms were expressed in the plants, the effects of the virus compromised the plant vital processes, showing the importance of early detection of the virus in order to fight against the infection.

Uncertainty in measurements of the photorespiratory CO2 compensation point and its impact on models of leaf photosynthesis

Rates of carbon dioxide assimilation through photosynthesis are readily modeled using the Farquhar, von Caemmerer, and Berry (FvCB) model based on the biochemistry of the initial Rubisco-catalyzed reaction of net C3 photosynthesis. As models of CO2 assimilation rate are used more broadly for simulating photosynthesis among species and across scales, it is increasingly important that their temperature dependencies are accurately parameterized. A vital component of the FvCB model, the photorespiratory CO2 compensation point (Γ*), combines the biochemistry of Rubisco with the stoichiometry of photorespiratory release of CO2. This report details a comparison of the temperature response of Γ* measured using different techniques in three important model and crop species (Nicotiana tabacum, Triticum aestivum, and Glycine max). We determined that the different Γ* determination methods produce different temperature responses in the same species that are large enough to impact higher-scale leaf models of CO2 assimilation rate. These differences are largest in N. tabacum and could be the result of temperature-dependent increases in the amount of CO2 lost from photorespiration per Rubisco oxygenation reaction.

Effects of foliar spray of nano-particles of FeSO4 on the growth and ion content of sunflower under saline condition

ABSTRACTThis study investigated the effects of foliar spray of normal and nano-particles of iron sulfate (FeSO4) on the response of sunflower cultivars to salinity. Treatments included five cultivars (Alstar, Olsion, Yourflor, Hysun36 and Hysun33), two salinity levels (0 and 100 mM sodium chloride (NaCl)), and three levels of fertilizer application. Fertilizer treatments were the foliar application of normal and nano-particles of FeSO4. Foliar application of FeSO4 in either form increased leaf area, shoot dry weight, net carbon dioxide (CO2) assimilation rate (A), sub-stomatal CO2 concentration (Ci), chlorophyll content, Fv/Fm and iron (Fe) content and decreased sodium (Na) content in leaves. The extent of increase in chlorophyll a content by foliar spray of FeSO4 nano-particles was significantly greater than normal form. The results showed that the FeSO4 nano-particles increased biomass production of sunflower plants greater in comparison with normal form, although no significant difference was found between two forms.

Atmospheric CO2 capture for the artificial photosynthetic system

The scope of these studies is to evaluate the ambient CO 2 capture abilities of the membrane contactor system in the same conditions as leaves works during photosynthesis, such as ambient temperature, pressure and low CO 2 concentration, where the only driving force is the concentration gradient. The polysulfone membrane was made by phase inversion process and characterized by ESEM micrographs which were used to determine the thickness, asymmetry and pore size. Besides, the porosity of the membrane was measured from the membrane and polysulfone density correlation and hydrophobicity was analyzed by contact angle measurements. Moreover, the compatibility of the membrane and absorbent solution was evaluated, in order to exclude wetting issues. The prepared membranes were introduced in a cross flow module and used as contactor between the CO 2 and the potassium hydroxide solution, as absorbing media. The influence of the membrane thickness, absorbent stirring rate and absorption time, on CO 2 capture were evaluated. The results show that the efficiency of our CO 2 capture system is similar to stomatal carbon dioxide assimilation rate.

Effects of seasonal change and experimental warming on the temperature dependence of photosynthesis in the canopy leaves of Quercus serrata.

The effects of warming on the temperature response of leaf photosynthesis have become an area of major concern in recent decades. Although growth temperature (GT) and day length (DL) affect leaf gas exchange characteristics, the way in which these factors influence the temperature dependence of photosynthesis remains uncertain. We established open-top canopy chambers at the canopy top of a deciduous forest, in which average daytime leaf temperature was increased by 1.0 °C. We conducted gas exchange measurements for the canopy leaves of deciduous trees exposed to artificial warming during different seasons. The carbon dioxide assimilation rate at 20 °C (A20) was not affected by warming, whereas that at 25 °C (A25) tended to be higher in leaves exposed to warming. Warming increased the optimal temperature of photosynthesis by increasing the activation energy for the maximum rate of carboxylation. Regression analysis indicated that both GT and DL strongly influenced gas exchange characteristics. Sensitivity analysis revealed that DL affected A without obvious effects on the temperature dependence of A, whereas GT almost maintained constant A20 and strongly influenced the temperature dependence. These results indicate that GT and DL have different influences on photosynthesis; GT and DL affect the 'slope' and intercept' of the temperature dependence of photosynthesis, respectively.

POTENTIALS OF KENAF FIBRE IN BIO-COMPOSITE PRODUCTION: A REVIEW

Kenaf plants are blessing to mankind. Its high carbon dioxide (CO2) assimilation rate and ability to clean the air by consuming large quantities of CO2 and also absorbs nitrogen and phosphorous from the soil, which are the main cause of the greenhouse effect has made kenaf significant from the standpoint of environmental friendliness. Today kenaf fibres are envisioned as an alternative medium to replacing conventional materials or synthetic fibres as reinforcement in composites. The low cost, no health risk, low density, high strength and modulus, and availability of kenaf fibres in some countries has made it befitting for use in composites production. This review presents the potential and recent developments of kenaf fibre and its composites. Recommendations for future work are also made.

Nitrogen, Phosphorus and Potassium Fertilization Interactions on the Photosynthesis of Containerized Citrus Nursery Trees

The objective of this research was to evaluate the nitrogen, phosphorus and potassium (NPK) fertilizer effect on the development of ‘Valencia’ sweet orange nursery trees budded on Rangpur lime rootstocks in a greenhouse using containers. The experiment was a complete (1/5) 53 factorial randomized blocks design. Treatments comprised five concentrations (g per plant) of N (1.25; 6.25; 11.25; 16.25; 21.25); K (0.42; 3.75; 6.22; 9.34; 12.45); and P (0.19; 0.89; 1.59; 2.29; 2.99). Carbon dioxide assimilation rate (A), transpiration rate (E), stomata conductance (gs), and internal carbon dioxide (CO2) concentration (Ci) and water use efficiency (WUE). Reducing sugar, sucrose and starch were evaluated. Response functions were adjusted and nutrient rates for maximum yield were presented. The results indicated that the high levels of N (>16.25 g per plant) interferes negatively on photosynthesis. Potassium at intermediate fertilization levels (from 3.75 to 6.22 g per plant) had positive effects on photosynthesis. But P had little interference on photosynthesis. Carbohydrates levels were not related to nutrients fertilized.

Foliar Applied Phosphorous Enhanced Growth, Chlorophyll Contents, Gas Exchange Attributes and PUE in Wheat (Triticum aestivum L.)

A pot experiment was conducted to evaluate the foliar applied phosphorous with and without pre-plant dose (50 kg hac.−1) of phosphorous on growth, chlorophyll contents, gas exchange parameters and phosphorous use efficiency (PUE) of wheat. The experiment was conducted in net house at Department of Crop Physiology, University of Agriculture Faisalabad, Pakistan. Two promising wheat cultivar AARI 2011 and FSD 2008 were used as a test crop with 5 foliar phosphorus (P) rates (0, 2, 4, 6, 8 kg ha−1). The foliar applied P with pre-plant performed better than without pre-plant and control treatments. Foliar treatment of phosphorus at 6 kg ha−1 P proved to be the best among other foliar treatments followed by 8 kg ha−1 P. The foliar application of phosphorous at 6 kg hac.−1 with pre-plant soil applied P increased the shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight. The chlorophyll contents (Chl. a and b) were increased with the foliar application of phosphorous. The gas exchange parameters (net carbon dioxide (CO2) assimilation rate, transpiration rate, stomatal conductance and sub-stomatal CO2 rate) were significantly improved by foliar applied P. The maximum values of net CO2 assimilation rate (5.27 μ mol m−2 sec.−1), transpiration rate (3.44 μ mol m−2 sec.−1), stomatal conductance (0.81 μ mol m−2 sec.−1) and sub-stomatal CO2 (271.67 μ mol m−2 sec.−1), were recorded in the treatment where P was foliar applied at 6 kg hac.−1 with pre-plant soil applied Phosphorous. The foliar application of phosphorous with pre-plant soil applied P enhanced Phosphorous use efficiency (PUE) in both varieties. The maximum value of PUE (15.42%) was recorded in the treatment where foliar feeding of P was done at 6 kg hac.−1 with pre-plant soil applied P in both genotypes.

Effects of foliar spray of two kinds of zinc oxide on the growth and ion concentration of sunflower cultivars under salt stress

ABSTRACTThis study investigated the effects of foliar application of normal and nano-sized zinc oxide on the response of sunflower cultivars to salinity. Treatments included five cultivars (‘Alstar’, ‘Olsion’, ‘Yourflor’, ‘Hysun36’ and ‘Hysun33’), two salinity levels [0 and 100 mM sodium chloride (NaCl)], and three levels of fertilizer application. Fertilizer treatments were the foliar application of normal and nano-sized zinc oxide (ZnO). Foliar application of ZnO in either forms increased leaf area, shoot dry weight, net carbon dioxide (CO2) assimilation rate (A), sub-stomatal CO2 concentration (Ci), chlorophyll content, Fv/Fm, and Zn content and decreased Na content in leaves. The extent of increase in chlorophyll content, Fv/Fm and shoot weight was greater as nano-sized ZnO was applied to the normal form. The results show that the nano-sized particles of ZnO compared to normal form has greater effect on biomass production of sunflower plants.

English

Rust (Uromyces appendiculatus) is a major foliar disease that reduces yield and pod quality in beans. The field trial of French beans was established at Jomo Kenyatta University of Agriculture and Technology (JKUAT). Single plant extracts and combinations of Boscia angustifolia, Zanthoxylum chalybeum and Melea volkensii were used to evaluate their effect on U. appendiculatus in the field. During the growing period, beans were infected with rust from natural inoculum at the field. Physiological responses such as carbon dioxide assimilation, transpiration (E), stomatal conductance (gs), and photosynthetic rate (Pn) of French beans treatments were examined after extracts of three antifungal plants were sprayed. B. angustifolia - Z. chalybeum combination and single plant treatment M. volkensii had positive effects on enhancing the rate of photosynthesis in bean plants. The high regressions between stomatal conductance and rate of transpiration in the treatments indicated that stomatal conductance and rate of transpiration were interdependent and it was interpreted to mean that stomatal conductance enhanced rate of transpiration at different times of the day. These plant extracts however caused an increase in the rate of transpiration of the bean plants, which resulted in loss of water. Results reveal bioactive potential of the flora from M. volkensii and a combination of B. angustifolia and Z. chalybeum to produce metabolites with potential applications as botanical pesticides.   Key words: Antifungal, beans, physiological responses, rust.