Corn kernels or seeds that remain aft er harvest can germinate and become a troublesome volunteer plant where bean crops are grown. Th e objective of this study was to evaluate the eff ect of time of emergence ofvolunteercorn on growth parameters, photosynthetic pigments andchlorophyll fl uorescence inbean plants, competition for soil and li- ght and light resources. Th e study was conducted in completely randomised experimental design, in 2×2×2+2 factorial scheme with four replications, involving two bean cultivars in competition with volunteercorn, emerging seven days before and simultaneously with beans, besides the partitioning of the competition by soil and light, just light and two controls without competition. We measured the levels ofchlorophyll a, b, total and carotenoids, parameters related to chlorophyll fl uorescence andbeangrowth variables. Volunteercorn was more competitive when it emerged seven days before the beans. When competition was established by light resource, there was a reduction in photosynthetic pigments and morphological variables of the bean plants. When competition by soil and light resources occurred, there was a reduction not only in photosynthetic pigments and morphological characteristics, but also in the chlorophyll fl uorescence variables. Th ere were signifi cant correlations between the growth variables of the bean plants and chloro- phyll fl uorescence, which makes it an important analytical tool for quantifying the stress caused by weeds.
The experimental design was a randomized block design in a factorial scheme (2×5), with four replications. Factor A consisted of two soybean cultivars (BMX Potência RR ® and M8210 IPRO ® ), which has distinct characteristics. The cultivar BMX Potência RR ® has an indeterminate growth habit and early cycle (relative maturity group of 7.0), while M8210 IPRO ® presents a determinate growth habit and medium cycle (relative maturity group of 8.2). Factor B consisted of five infestation densities of RR ® corn plants (AS 1633 PRO2 hybrid, F1 generation) per m 2 (0, 4, 8, 12, and 16). Each experimental unit had 20 m 2 of total area, with plots composed by ten rows of 4 m in length and spaced 0.5 m from each other. The useful area consisted of the six central rows with 2 m in length (6 m 2 ).
Severe photoinhibition can give rise to photodamage in PSII, with the formation of reactive oxygen species, which are toxic, destroy pigments and affect the stability of the membrane (Lemos-Filho, 2000; Araújo et al. 2010). Damage in PSII is measured by chlorophyllfluorescence. F0 represents the initial fluorescence when all reaction centers (RCs) are open and refers to the fluorescence emission by chlorophyll molecules in the complex of the PSII light collector (Krause and Weiss, 1984). During experimental period, water deficit did not significantly affect F0 in H. speciosa seedlings, but variations were observed over time (Tab. 4). Bacarin and Mosquim (2002) also observed this kind of variation in two bean genotypes, coinciding with the increase in dry weight in the pods and nodules. Moreover, Tatagiba and Pezzopane (2007) found reductions in F0 in a eucalyptus clone during the dry season. The other variables ofchlorophyllfluorescence had the same tendency.
The first step to evaluate the bacterial interference between E. coli EC2 and Salmonella Typhi strains in the food matrix consisted on verifying the production of bacteriocin EC2 on milk agar, which was initially verified by diffusion on solid medium, using milk agar. The results showed that the activity of the bacteriocin against both tested indicators is not influenced by the milk, even though this is a compound extremely rich in carbohydrates and proteins. The inhibition zones on milk agar presented no significant difference in comparison with the control agar Casoy under the best conditions for the EC2 production (Table 2). Some studies related that the production of bacteriocin on food matrix can be affected by the food components (Stergiou et al., 2006; Galvéz et al., 2007). At least in relation to milk, bacteriocin EC2 seems to be stable.
of cover crops are collected through three sampling points per subplot. Soybean dry matter was determined through collecting five plants per plot which, as the cover crops matter, were taken to a forced ventilation oven at 65 o C for 72 hours. Plant height was evaluated by measuring from the lap to the summit of the apical meristem. For the control ofvolunteer RR® cornin soybean crops, notes were assigned according to a percentage scale that ranges from zero to 100, where zero means no plants and 100 means total presence of the plants; a witness that received only glyphosate was the main parameter. In order to evaluate the occurrence of phytotoxicity symptoms, a visual assessment was carried out using a percentage scale of notes, where zero (0) represents the absence of symptoms and one hundred (100.0) represents death of all plants of that plot.
from the seedling stage to maturity (Ayers, & Westcot, 1985), the tolerance ofcorn overcame soybean from planting to seedling development stages. Therefore, an irrigation management strategy should be taken to maximize yield in the corn-soybean crop rotation when using saline water. Saline water could be used to pro- duce soybean, being applied after crop establishment, and during the germination ofcorn, but a reduction of soil salinity is required to obtain satisfactory pro- duction ofcorn. Thus, corn-soybean crop rotation is advantageous because it allows farmers to use poor quality water and/or reuse the drainage water for irri- gation of these crops, but the irrigation management must to be accomplished to avoid high soil salinity dur- ing the germination stage for soybean and latter stages ofcorn development.
1996a; 1996b). Steckel et al. (1989) harvested seeds of carrot (Daucus carota L.) at different stages of maturation and observed an increase in germination performance of the carrot seeds. Coincidently during development the total chlorophyll content of the seed coat (as measured by the optical density of seed coat extracts) decreased. Because of this correlation, Steckel et al. proposed a simple field test using colour cards to assess the chlorophyll content of seed extracts to estimate the optimal harvest date. The relation between the amounts ofchlorophylland the maturity has been well studied in seeds of oilseed rape (Brassica napus L.) and turnip rape (Brassica rapa L.) (Ward et al., 1992; 1995). Using destructive extraction methods (ISO, 1992; Ward et al., 1995), it was found that chlorophyll is broken down during the late stages of the ripening process and that the final chlorophyll levels in rape seeds can be affected both by the genotype and the environment. Lower temperatures during seed maturation cause a slower chlorophyll degradation resulting in the so-called ‘green-seed’ problem. For the majority of seed species the amount ofchlorophyllin the seed coat decreases during maturation. At the same time the colour of the seed changes from green to a colour which depends on the species and varies with the cultivar. This process is called degreening. The chlorophyll breakdown in the seed, however, is poorly understood (Ward et al., 1995).
Chlorophyll a fluorescence analysis (CFA) is a sensitive indicator of the stability and efficiency of photosynthesis. This fundamental physiological process closely reflects the effects of internal (maturation, aging, senescence etc.) and external (salinity, drought, heat, cold stress etc.) factors on the physiological capacity or vitality of plants. In contrast to many other techniques, CFA can be actually applied remotely and non-invasively. Hence, this method has found widespread applications in plants science. During recent years, CFA has been accepted as a valuable tool to study the metabolic activity of vegetables and salad greens, and some fruits in postharvest. A number of different fluorescence parameters can be used to comprehensively characterize various aspects of photosynthetic performance. For this purpose, commercial chlorophyllfluorescence imaging (CFI) systems may be advantageous because they provided information on both spatial and temporal dynamics of photosynthesis. This yields information on various physiological aspects that are affected by postharvest handling and processing. CFI can, thus, help to objectively, rapidly and non-destructively evaluate and characterize the internal quality of green produce and its changes at many steps of the entire postharvest chain. For a proper application of CFA, a comprehensive knowledge of the physiological background ofchlorophyllfluorescenceandfluorescence analysis is helpful. Hence, a brief introduction of the physiological basics will be given here. Furthermore, information about alternative approaches to analyse fluorescence data as well as the current technical standard of an available CFI device will be provided. Finally, recent applications of this technique should illustrate the use of this method in fresh food quality research.
This study is part of the Graduate Program in Agricultural Engineering of the Federal University of the Recôncavo Baiano (Programa de Pós-Graduação em Engenharia Agrícola da Universidade Federal do Recôncavo Baiano–PPGEA-UFRB) and was conducted from July to September, 2016, in a greenhouse at the Experimental Station of the UFRB, in Cruz das Almas (latitude, 12°40'12" S; longitude, 39°6'7" W; altitude, 220 m), Bahia, Brazil. According to the classification of D'Angiolella et al. (2000), the climate of the region is humid to subhumid, with a relative humidity of 80%, mean annual temperature of 24 °C, and mean annual rainfall of 1,143 mm.
When the leaves were treated with different concentrations of atrazine, the fluorescence induction curves showed the same behaviour as the curves of leaves treated with DCMU, starting with a concentration of 50 µM (Figures 1B and 1D). Atrazine blocks the transport of electrons between Q A and Q B , since it prevents the binding of Q B in the D1 protein, and with this the flow of electrons to the PSI stops (HESS, 2000), resulting in a reduced accumulation of Q A . The results indicate that high concentrations of atrazine on the leaves directly interfere with the plant’s ability to convert the luminous energy absorbed into a biologically available form of energy. In studies of phytoplankton, Deblois, Dufresne and Juneau (2013) found the same loss in energy conversion caused by atrazine, with a significant effect on the cyanobacteria and algae.
protective down-regulation of PSII mediated by the xanthophylls cycle (Demmig-Adams and Adams, 1996). However, in fruits of D. miscolobium, the F v /F max values were constantly below the threshold value, even in the early morning, indicating a chronic photoinhibition, similarly to that observed by Mattos et al. (2002) in leaves of Miconia albicans, a cerrado shrub. The chronic photoinhibition involves photon damage to the functional integrity of the PSII reaction center when the proteolysis of the D1 protein of the reaction center core exceeds the rate of repair (Osmond, 1994). The effective quantum yield of the PSII (∆F/F ‘max ) for both leaflets and fruits dropped with the increase of incident light in the morning (figure 3B). Leaflet ∆F/F ‘max values were also higher than those of fruits with the highest difference in the afternoon, in spite of the decrease of incident light. The
The intensity of the Chl a fluorescence transients is affected not only by the activity of the PSII side electron acceptors but also by the functional state of the donor side of the same photosystem (oxygen-evolving complex, OEC) (Strasser et al., 2004). In this context, the appearance of the K-band, hidden between steps O and J, occurs due to the equilibrium established for electron transport. The K step, located at approximately 300 μs, is related to the deactivation of the OEC (Strasser et al., 2004); in leaf discs exposed to 45°C, this step displays high values. A positive K step corresponds to non-water electron donation to PSII (Strasser, 1975). A K step with large amplitude corresponds to an imbalance between the electron donor and electron acceptor sides of PSII, which reflects the dissociation of the OEC, along with a progressive decrease in the rates of photochemical processes (Gururani et al., 2012).
Silvicultural practices are important for the management of planted forests and such treatments have been recommended for increasing plantation productivity (Forrester et al. 2013). In order to increase the primary production of planted forests, practices, which improve tree photosynthesis, are extremely useful since they increase carbon assimilation. But some forestry practices such as thinning may initially have negative effects and decrease biomass gain as observed in a boreal forest in which the leaf area index decreases from 8 to 6 (Vesala et al. 2005). In addition, recent study has shown that after thinning, the remaining trees may reduce their photochemical performance [quantum yield of PSII (FV/FM) and perfor- mance index (PIABS)] as a response to excess energy, thus enhancing photoinhibition, which may decrease the net photosynthetic rates (PN) and consequently plantation productivity (Wu et al. 2018). So, some questions emerge,
Zoysiagrass (Zoysia japonica) is an important turfgrass commonly cultivated for home lawns, gardens, sports, and recreational grounds because of its relatively high drought toler- ance, disease tolerance, and slow growth [25–26]. Owing to these characteristics, several species of zoysiagrass and bentgrass including their hybrids have been introduced for commercial breeding in the USA  and elsewhere. However, because zoysiagrass is a warm-season turf- grass it suffers from cold stress as the grass usually wilts and browns by late autumn. Earlier, we have reported the development of shade-tolerant zoysiagrass cultivar expressing a hyperac- tive mutant phytochrome A (PhyA) gene, Ser599Ala-PhyA (S599A) [28,29]. Overexpression of S599A in the transgenic zoysiagrass resulted in improved shade tolerance, wider and greener leaves, and short phenotypes with increased number of tillers. Further, a delayed senescence was also noticed in S599A zoysiagrass plants that could be a manifestation of cold tolerance as phytochromes have been suggested to play a vital role in cold tolerance [30,31]. In this study, we have evaluated transgenic zoysiagrass plants carrying hyperactive mutant S599A under cold stress conditions, and demonstrated that the analysis of the recorded OJIP fluorescence tran- sients and its phenomenological and biophysical parameters can be employed for a semi-quan- titative assessment of cold tolerance in these plants. In addition, we determined the putative biochemical changes in S599A zoysiagrass subjected to cold stress by estimating the enzyme ac- tivities of certain reactive oxygen species (ROS) scavenging enzymes. Our results suggest that overexpression of hyperactive S599A mutant enhances cold stress tolerance in transgenic zoy- siagrass, and that the JIP-test is sensitive method to evaluate the response of zoysiagrass plants under cold stress.
carried out with an incomplete factorial (4x2)+1, four N rates (45, 90, 135 and 180 kg N ha -1 ), two N sources (Urea: 45% N and Urea coated with Policote ® : 41% N) and Control (without N). Each experimental plot had six rows, spaced 0.45 m, and six meters long. Four central rows were considered in these experiments and two guard rows were discarded. The hybrid DKB-240pro2 was sown on 27 th September, 2013 after 10-20-20 (310 kg ha -1 ) application in the sowing furrow. Treatments were applied on soil surface after sowing at V4 stage. Weed, pest and disease controls were made. Corn yield (with moisture corrected to 13%) was evaluated at harvest.
The experiment was conducted in a greenhouse at the experimental area of the Department of Botany of the Universidade Federal de Goiás, in Goiânia, Goiás, located at 16° 36″ S and 49° 13″ W, at an altitude of approximately 800 m. Two experiments were conducted, both with completely randomized design, with four replications. The first experiment aimed to determine the optimal concentration of PBZ needed to reduce the size of the bean plants. The second experiment examined the effect of PBZ in excessive vegetative growth inhibition, when applied after nitrogen fertilization.
agriculture to increase crop yield under drought conditions is of particular importance. Super absorbent polymer hydrogel are extremely hydrophilic and with high speed of water absorption and capacity, it provides water and nutrients for roots if required easily. These super absorbents which exist in natural and artificial forms are odorless and safe compounds for environment and plant tissue (Kabiri, 2005). Bentonite belongs to a group of super absorbent natural mineral 1:2 and is a mixture of clay minerals with high montmorillonite contents. It also shows high adhesion ability (Abedi-koupai and Sohrab, 2004). Due to the structure of the material, bentonite has the ability to absorb water and minerals, and also prevents the leaching of minerals from the soil, thus improves soil fertility (Stejskal. 1996). Further researches indicate that water limitation leads to photosynthesis decline andgrowth reduction which itself can perform in terms of lower yields (Cronic and Massacci, 1996). Photosynthesis reduction under drought stress in related to clutter biochemical pathways. Photosystem II is the most sensitive part to drought stress and oxygen receiving complex tension and recipient of the reaction center complexes in the system faces the greatest damage from drought (Giardi, 1996). Today, chlorophyllfluorescence is proposed as an index to measure the effects of environmental stresses, including water stress on crop species and determination of their drought resistance (Moffatt et al., 1990). In other words, chlorophyllfluorescence measurement proves the intact membranes of tylacoeids and shows the relative efficiency of electron transfer from the photosystem II to photosystem I. The lowest fluorescenceof the system (Fo), appears when first Kinnon Primary quinone electron acceptor of
The toxicity caused by Al interferes with enzymatic reactions, the metabolism of several elements and with plasmatic membrane permeability (Kochian, 1995). Moreover, Al inhibits root elongation and the induction of callose synthesis, which appears after a short exposure time to Al (Horst et al., 1997). Usually, the Al toxicity effect is noticed in the roots before any symptom becomes evident in the aerial regions (Pintro et al., 1995; 1996; Veloso et al., 2000; Kochian, 2000), which can be confirmed by Al accumulation in the root distal region, indicating the area of highest sensitivity. Therefore, the root apex is the primary site of toxic action of Al (Matsumoto & Motoda, 2012). Changes in the volume of the root cap were observed by Bennet & Breen (1991) in Al- treated corn plants. Bennet et al. (1987) observed that a significant alteration in the mean cell volume is limited to the cap periphery where Al causes a decrease in cell volume. Cha & Lee (1996) studied the effects of different Al levels on the growthand root anatomy of Alnus hirsute Rupr, and reported that A1-treated root
Among weeds, morning glories comprise a very important group of climbing plants that infest sugarcane crops. The objective of this study was to evaluate the shoot and root interferenceof Merremia cissoides on the initial growthof sugarcane cultivar RB 966928. The experiment consisted of five treatment groups: (i) sugarcane monocropping, (ii) morning glory monocropping, (iii) sugarcane intertwined with morning glory but inseparate boxes, (iv) sugarcane intertwined with morning glory in attached boxes and (v) sugarcane with morning glory in attached boxes with morning glory prevented from intertwining with the sugarcane. The experimental design consisted of randomized blocks with four replicates. Merremia cissoides adversely affected the initial growthof the RB 966928 sugarcane starting at 90 days after transplanting (DAT). This effect increased with the time of intercropping, reaching at 180 DAT with a reduction of 57.3% in height,15.5% in stalk diameter, 90.4% in leaf areas, 86.6 and 75.2% in stalk and leaf dry mass, respectively. These reductions primarily due to the weed intertwining with the sugarcane plants because the weed had a physical choking and shading effect. This negative effect of morning glory on the sugarcane plants increased when they shared the substrate (i.e., when they competed for space and water), which also adversely affected weed growth, reducing 50.2% leaf areas and 42.1% shoot dry mass. The leaf area and the stalk and leaf dry mass of sugarcane are the characteristics more sensitive to the weed interference. Thus, both the shoot and root of M. cissoides interferes negatively in the growthof sugarcane, with the effect proportional to the period of coexistence, highlighting the detrimental effect on the stem (greater economic interest), and may also compromise the mechanical harvesting of the crop.
The SPAD 502 portable chlorophyll meter uses red electromagnetic radiation to determine the leaf chlorophyll content, and the near-infrared to compensate for differences in leaf thickness and water content (ZOTARELLI et al., 2002). However, the absorption peak ofchlorophyll present in leaves is not only in the red band. Chlorophyll-a and -b are the pigments that most influence electromagnetic radiation in the visible region, with two absorption peaks, the larger in the red band and the smaller in the blue respectively (LIMA et al., 2011), favouring a better result for that classifier using the red (R) and blue (B) bands.