Necrotic Leaf Area Research Articles

Simulation of oat yield through biological and environmental variables for reducing fungicide application and increasing interval from application to grain harvest

Simulation models based on biological and environmental variables allow the analysis of scenarios in proposing more sustainable management. The objectives is to identify potential biological and environmental variables for inclusion and validation of multiple linear regression model for yield simulation and analyze scenarios that promote yield and satisfactory control of foliar diseases, with longer intervals between the last fungicide application and the grain harvest. The study was conducted in 2015, 2016, 2017, in Augusto Pestana, RS, Brazil. The soil is classified as Oxisol and the climate of the region as Cfa type, by the Köppen classification. The experimental design was randomized blocks, with three replications, in a 22 x 4 factorial, for 22 oat cultivars (10 recommended and 12 no longer recommended) and 4 fungicide use conditions (no application; one application 60 days after emergence (DAE); two applications, 60, 75 DAE; and three applications, 60, 75, 90 DAE. In 2015 and 2016, the fungicide FOLICUR® CE was used, and in 2017 PRIMO®, at a dosage 0.75 and 0.3 liters ha-1, respectively. Necrotic leaf area, rainfall depth, mean minimum and maximum temperatures, thermal sum, and crop cycle period (days) are potential variables by the Stepwise technique in the simulation of oat yield, validating the use of the multiple linear regression. The condition with three fungicide applications, at 60, 75, 90 DAE, resulted in satisfactory foliar disease control and grain yield, while maintaining a long interval between the last fungicide application and the grain harvest, thus improving the safety of the product obtained

Didymella fabae Punith.: mating type occurrence, distribution and phenotyping of the anamorph Ascochyta fabae Speg. in Tunisia.

Faba bean ascochyta blight, caused by Ascochyta fabae Speg. (teleomorph: Didymella fabae Punith.), is one of the most devastating diseases of the crop. It can cause yield losses that reach 95% in conducive weather conditions. Surveys were carried out in five regions of Tunisia: Beja, Bizerte, Jendouba, Kef and Tunis-Cap Bon. A total of 513 fungal isolates were collected from 2011 to 2013. A molecular characterization was conducted to identify the mating type of each individual using a mating type specific PCR. Results revealed that the two mating types MAT1-2 and MAT1-1 coexisted in all surveyed regions. An imbalance in favor of MAT1-2 was observed particularly in Bizerte and Jendouba regions (sex ratio was 18:85 and 32:80, respectively). Moreover, morphological and pathogenic characterization of 122 isolates among the collection revealed a significant variability in conidia type (one celled or two celled conidia) frequency, in conidia mean size and in aggressiveness toward Badii faba bean cultivar (incubation period, IP; percentage necrotic leaf area, S; and area under disease progression curve, AUDPC). A principal component analysis (PCA) performed on morphologically studied parameters (frequency of conidia cell number and conidia mean size) identified three groups of isolates based on morphological traits: one celled (1C) and two celled (2C) conidia rates, one celled and two celled conidia length and width (1L, 1W, 2L and 2W, respectively). A second PCA using aggressiveness parameters (IP: Incubation period, S1, S4 and S9: percentage of necrotic leaf area respectively 5, 20 and 45 days after inoculation) identified three distinct pathogenic groups: poorly pathogenic AG1, moderately pathogenic AG2 and highly pathogenic AG3. Morphological and pathogenic groups and mating type data were used to conduct a multiple factorial correspondence analysis (MFCA) which revealed a correlation between the variables studied. Five groups were identified, each associated with a morphological and pathogenic trait and mating type. The most pathogenic group belonged to MAT1-2 suggesting that in locations where MAT1-2 is prevalent the epidemic risk is more important.

Specific virulence patterns in Tunisian Zymoseptoria tritici strains isolated from bread and durum wheat

AbstractSeptoria tritici blotch caused by Zymoseptoria tritici is a serious threat to wheat in Tunisia, causing yield losses of up to 50%. Epidemics occur regularly, mainly on durum wheat (DW) but also to a lesser extent on bread wheat (BW), that are mainly cropped in the north‐western and north‐eastern regions, respectively. Isolates of Z. tritici exhibit both cultivar specificity and host species specificity. In this study, we investigated the extent of host specialization of Z. tritici in the Tunisian context. Cross‐inoculations of different strains derived from either BW or DW were performed at the seedling stage on a panel of the most cultivated BW and DW varieties in Tunisia using the percentage of pycnidia coverage and necrotic leaf area as disease parameters. Results showed that the effect of strains, the strain‐derived species, the wheat species and of their interactions were highly significant based on pycnidia coverage. This indicates the presence of significant virulence variability among Z. tritici strains on the tested wheat genotypes, with some strains being more virulent than others. It also suggests cultivar and host species specificity, as not only genotypes of the strains interacted differently with the genotypes of the host, but also the origin of the strain, whether BW or DW, influenced the disease outcome. Hence, future research based on comparative genomics coupled with transcriptomics of these strains and their progenies could determine genes whose expression control this host specificity or is influenced by host or strain genotype, or alternatively by life cycle stage.

Measuring resistance in durum wheat-Zymoseptoria tritici interaction using aggressiveness quantitative traits

Phenotyping for quantitative resistance to Septoria tritici blotch (STB), one of the most economically devastating diseases of durum wheat (Triticum durum Desf.) in North African region, is a limiting factor for breeding progress. Here we tested main phenotypic markers of aggressiveness affecting host damage and pathogen reproduction reported in earlier studies for measuring differences in quantitative host resistance. A collection of 11 Tunisian durum wheat genotypes varying in resistance to the pathogen was inoculated by a highly aggressive and virulent isolate of Zymoseptoria tritici in a replicated field and controlled experiments, conducted in 2017-2018 at the experimental station of the Regional Field Crops Research Center of Beja in Tunisia. The severity of infection caused by Z. tritici isolate, including percentage of leaf area covered by chlorotic lesions (PLACCL), percentage of leaf area covered by necrosis (PLACN), and percentage of leaf area covered by pycnidia (PLACP) as well as latent period (LP) and pycnidia density (PYCdens) were assessed visually and quantified. The results showed that there were significant differences in all assessed traits on the tested genotypes and significant positive correlations were obtained between PLACN, PLACP and PYCdens. Similarly, there was a significant negative correlation between LP and these last traits. The PLACP was found as the more reliable trait to discriminate genotypes to different classes of resistance, consistent with the results obtained for the remaining traits. These data suggest that using both necrotic leaf area (PLACN) bearing pycnidia and PYCdens can improve selection for quantitative STB resistance.

The Native Hymenoscyphus albidus and the Invasive Hymenoscyphus fraxineus Are Similar in Their Necrotrophic Growth Phase in Ash Leaves.

The populations of European ash and its harmless fungal associate Hymenoscyphus albidus are in decline owing to ash dieback caused by the invasive Hymenoscyphus fraxineus, a fungus that in its native range in Asia is a harmless leaf endophyte of local ash species. To clarify the behavior of H. albidus and its spatial and temporal niche overlap with the invasive relative, we used light microscopy, fungal species-specific qPCR assays, and PacBio long-read amplicon sequencing of the ITS1-5.8S-ITS2 region to examine fungal growth and species composition in attached leaves of European ash. The plant material was collected from a healthy stand in central Norway, where ash saplings in late autumn showed leaflet vein necrosis like that commonly related to H. fraxineus. For reference, leaflet samples were analyzed from stands with epidemic level of ash dieback in southeastern Norway and Estonia. While H. albidus was predominant in the necrotic veins in the healthy stand, H. fraxineus was predominant in the diseased stands. Otherwise, endophytes with pathogenic potential in the genera Venturia (anamorph Fusicladium), Mycosphaerella (anamorph Ramularia), and Phoma, and basidiomycetous yeasts formed the core leaflet mycobiome both in the healthy and diseased stands. In necrotic leaf areas with high levels of either H. albidus or H. fraxineus DNA, one common feature was the high colonization of sclerenchyma and phloem, a region from which the ascomata of both species arise. Our data suggest that H. albidus can induce necrosis in ash leaves, but that owing to low infection pressure, this first takes place in tissues weakened by autumn senescence, 1–2 months later in the season than what is characteristic of H. fraxineus at an epidemic phase of ash dieback. The most striking difference between these fungi would appear to be the high fecundity of H. fraxineus. The adaptation to a host that is phylogenetically closely related to European ash, a tree species with high occurrence frequency in Europe, and the presence of environmental conditions favorable to H. fraxineus life cycle completion in most years may enable the build-up of high infection pressure and challenge of leaf defense prior to autumn senescence.

Higher alterations in leaf fluorescence parameters of wheat cultivars predict more extensive necrosis in response to Zymoseptoria tritici

AbstractSeptoria tritici blotch (STB) is one of the main causes of wheat yield loss in the world. Apart from good agrotechnical practice, disease‐resistant cultivars are required to prevent yield losses. Breeding of such cultivars is time‐consuming and laborious, mainly due to the quantitative character of such resistance, but can be shortened using precise phenotyping. We show that fluorescence parameters, collected in a high‐throughput system, can be used for estimating wheat STB resistance. Using machine learning methods (deep learning network, random forest), we demonstrate that disease resistance based on the percentage of necrotic leaf area can be estimated by alterations in fluorescence parameters 8 days after inoculation, and before disease symptoms become visible. Moreover, we applied a random forest classifier to assess the significance of fluorescence parameters in an informative way (classification accuracy = 64.84%, p value [Accuracy >No information rate] <0.001). Based on this, we observed extensive alterations in parameters of sensitive cultivars, reflecting worse photosynthetic performance. The most highly altered parameters were fluorescence intensity measurements and descriptors of energy flux through photosystem II (PSII) reaction centres towards PSI such as F2, F3 and F4 fluorescence intensities at 0.1, 0.270 and 2 ms; initial to maximal fluorescence ratio (F0/Fm); the time derivative of relative variable fluorescence (dV/dT0); maximum quantum yield of PSII in the dark‐adapted state (Fv/Fm); maximum electron transport flux at PSII (ET0/RC); maximum trapped excitonic energy flux per excited PSII cross section (CS) at time T0 (TR0/CS0); and quantum efficiency of the reduction of end acceptors dR0 [dR0/(1 − dR0)].

Transient expression of an scFvG8 antibody in plants and characterization of its effects on the virulence factor pthA of Xanthomonas citri subsp. citri.

Citrus bacterial canker, caused by Xanthomonas citri subsp. citri (Xcc), is a major disease of citrus plants, causing a significant loss in the citrus industry. The pthA is a bacterial effector protein mediates protein-protein and protein-DNA interactions and modulates host transcription. Injection of pthA effector protein into the host cell induces the expression of the susceptibility gene CsLOB1 which is required for citrus canker disease development. In this study, we described in planta expression of a specific anti-pthA single-chain variable fragment (scFv) recombinant antibody, scFvG8, and assessed its function using molecular docking, immunoblotting, and indirect enzyme-linked immunosorbent assay (ELISA). Based on the results, homology-based molecular docking suggested that at least eight intermolecular hydrogen bonds are involved in pthA-scFvG8 interactions. Immunoblotting and indirect ELISA results reconfirmed specific binding of scFvG8 to pthA protein. Moreover, gene fragment encoding scFvG8 was cloned into plant expression vector and transiently expressed in leaves of Nicotiana tabacum cv. Samson by agroinfiltration method. Transient expression of scFvG8 (at the expected size of 35kDa) in N. tabacum leaves was confirmed by western blotting. Also, immunoblotting and indirect ELISA showed that the plant-derived scFvG8 had similar activity to purified scFvG8 antibody in detecting pthA. Additionally, in scFvG8-expressing tobacco leaves challenged with Xcc, a reduction (for up to 70%) of hypersensitive response (HR) possibly via direct interaction with pthA, was observed in the necrotic leaf area compared to control plants infected with empty vector. The results obtained in this study confirm that scFvG8 can suppress the function of pthA effector protein within plant cells, thus the induction of stable expression of scFvG8 in lime trees can be considered as an appropriate approach to confer resistance to Xcc.

Behavior of Spanish durum wheat genotypes against Zymoseptoria tritici: resistance and susceptibility

Aim of study: Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici, is one of the most important wheat diseases worldwide, affecting both bread and durum wheat. The lack of knowledge about the interaction of durum wheat with Z. tritici, together with limited resources of resistant durum wheat material, have both led to a rising threat for durum wheat cultivation, particularly in the Mediterranean Basin. In Spain, STB has increased its incidence in the last few years, leading to higher costs of fungicide applications to control the disease. Therefore, identification of new sources of resistance through wheat breeding stands out as an efficient method of facing STB.Area of study: The experimental study was conducted in growth chambers at the IFAPA facilities in Córdoba (Spain).Material and methods: The percentage of necrotic leaf area, the disease severity, and the pycnidium development through image analysis were evaluated from 48 durum wheat Spanish accessions (breeding lines and commercial cultivars) in growth chambers against an isolate of Z. tritici from Córdoba.Main results: Two breeding lines and six commercial cultivars showed resistant responses by limiting STB development through the leaf or its reproduction ability, while the other 40 accessions presented a susceptible response.Research highlights: Provided these resources of resistance in Spanish durum wheat genotypes, future breeding programs could be developed, incorporating both agronomic traits and resistance to STB.

Image-Based Methods to Score Fungal Pathogen Symptom Progression and Severity in Excised Arabidopsis Leaves.

Image-based symptom scoring of plant diseases is a powerful tool for associating disease resistance with plant genotypes. Advancements in technology have enabled new imaging and image processing strategies for statistical analysis of time-course experiments. There are several tools available for analyzing symptoms on leaves and fruits of crop plants, but only a few are available for the model plant Arabidopsis thaliana (Arabidopsis). Arabidopsis and the model fungus Botrytis cinerea (Botrytis) comprise a potent model pathosystem for the identification of signaling pathways conferring immunity against this broad host-range necrotrophic fungus. Here, we present two strategies to assess severity and symptom progression of Botrytis infection over time in Arabidopsis leaves. Thus, a pixel classification strategy using color hue values from red-green-blue (RGB) images and a random forest algorithm was used to establish necrotic, chlorotic, and healthy leaf areas. Secondly, using chlorophyll fluorescence (ChlFl) imaging, the maximum quantum yield of photosystem II (Fv/Fm) was determined to define diseased areas and their proportion per total leaf area. Both RGB and ChlFl imaging strategies were employed to track disease progression over time. This has provided a robust and sensitive method for detecting sensitive or resistant genetic backgrounds. A full methodological workflow, from plant culture to data analysis, is described.

Outdoor infrared imaging for spatial and temporal thermography: A case study of necrotic versus healthy leaf areas on woody plants

AbstractThe temperature of plants can be measured using infrared (IR) thermography. Despite the extensive use of IR imaging indoors, outdoor IR imaging is uncommon. We used IR imaging to compare leaf temperatures between necrotic spots and healthy areas of oriental cherry (Prunus serrulata var. spontanea), Japanese cornel (Cornus officinalis) and sawtooth oak (Quercus acutissima) in the field. There was a significant difference in the mean leaf temperatures between the necrotic spots (26.4°C) and healthy areas (25.6°C) of oriental cherry (p = .01). The mean temperatures in the necrotic spots of Japanese cornel and sawtooth oak leaves were 22.3°C and 29.6°C, respectively, which were not significantly different from the mean temperatures of the healthy areas. A consecutive, 2‐day temporal leaf analysis in October 2018 revealed that the temperatures in the necrotic spots were generally higher than those in the healthy areas of the three species. The temperature difference between the spots and healthy areas (up to 1.4°C) was more pronounced at 13:00 hr in all three species on both days. These results reveal differences in the spatial and temporal thermal state across the necrotic spotted leaves. There is potential for use of outdoor IR imaging to visualize the response of trees to pathogen infection and abiotic stress.

Digital picture analysis for precision screening of sour cherry progeny for necrotic leaf tissue caused by Blumeriella jaapii

Sour cherry generally holds limited resistance to attack by cherry leaf spot fungus (Blumeriella jaapii) but differences in field performance are found between cultivars and in breeding progeny. Traditionally the degree of attack is estimated visually together with the type of reaction on the leaves. A more precise and less subjective method of evaluation is of interest for screening germplasm. A method of drying leaves, scanning dried leaves and a digital picture analysis protocol was developed to provide exact data on the percentage area of attacked necrotic tissue per leaf and with options of analysing size distribution of single necrotic spots to reveal detailed patterns of infections. The new method was used to characterize leaf attack in autumn on 20 individual leaves from single trees from a sour cherry breeding genepool of over 100 genotypes in a non-sprayed situation with high inoculum present. The percentage of necrotic leaf surface varied highly within the 20 leaves from one genotype, being dependent on the level of inoculum dispersal and air humidity/precipitation over time and space. The mean percentage of attacked leaf surface varied from 0 to almost 35% of total leaf area and the maximum from 0 to 60% necrotic leaf area, indicating the potential large impact on photosynthetic capacity in attacked trees. The distribution of and absolute size of single necrotic spots demonstrated differences in how individual genotypes react to infections, from small spots in tolerant genotypes to large collapsing necrotic spots in very susceptible genotypes. A comparison of attack data with the percentage of remaining leaves on a tree in autumn revealed that some genotypes retain leaves very late even if attacked by leaf spot disease. These trees may maintain a fairly high photosynthetic capacity even if some percentages of the leaf have become necrotic.

Physiological changes in winter wheat genotypes in response to the Zymoseptoria tritici infection

Some physiological aspects of interactions between wheat and Zymoseptoria tritici were studied by measuring changes in some stress markers, photosynthetic activity, and the extent of thermal energy dissipation. Four winter wheat genotypes varying in their level of resistance, determined on the basis of necrotic leaf area and presence of pycnidia, were inoculated at a seedling stage and measurements were performed at 0, 2, 17, and 23 d after the inoculation. Physiological activity of wheat genotypes showed that keeping the membrane integrity and the extent of oxidative stress is of significant importance for pathogen resistance. It could be suggested that the changes in electrolyte leakage, malondialdehyde content, and values of quantum yield of PSII electron transport and nonphotochemical fluorescence quenching can be used to screen the degree of tolerance to Septoria tritici blotch in different wheat genotypes.

Herbaspirillum seropedicae promotes maize growth but fails to control the maize leaf anthracnose.

Herbaspirillum seropedicae is an endophytic diazotrophic bacterium and a plant growth promoting bacteria. Colletotrichum graminicola causes the anthracnose, one of the most destructive maize diseases worldwide. The main objective of this work was to evaluate the effects of H. seropedicae SmR1 strain on the plant growth and leaf anthracnose of maize plants grown in substrate amended or not amendedwith humic substances. In the first assay, plants were pre-treated with H. seropedicae and inoculated with C. graminicola at 7, 14 and 21days after treatment (DAT). In the second assay, plants were treated with H. seropedicae, grown in substrate amended with humic substances and inoculated at 3 and 7 DAT. The anthracnose severity was assessed by measurement of necrotic and chlorotic leaf area, and bacteria were quantified in leaves by quantitative PCR. H. seropedicae did not affect the disease severity in maize leaves, although it efficiently colonized the leaf tissues and it promoted maize leaf growth. Humic substances improved H. seropedicae colonization in maize.

Aqueous plant extracts for control of groundnut leaf spot in Burkina Faso

Early and late leaf spots, the two fungal diseases of groundnut (Arachis hypogaea L.) caused by Cercospora arachidicola Hori. and Phaeoisariopsis personata (Berk and Curt), respectively, cause severe groundnut crop losses in arid zone of West Africa. The objective of this study was to evaluate efficacy of aqueous extracts of four native plants species of Burkina (Lippia multiflora Moldenke, Boscia senegalensis (Pers.) Lam, Ziziphus mucronata Willd. and Securidaca longepedonculata L) against these diseases, on a susceptible groundnut variety (TS32-1) in the field during the cropping seasons of 2010 to 2012, in Gampela district in Burkina Faso. The four extracts (50 g dry weight per liter of distilled water) were sprayed by using a manual sprayer (Solo). Disease incidence and severity, defoliation rate, necrotic leaf area, pod yield, and 100 seed weight were evaluated. Disease score which attests to the severity of parasitic attack was done following ICRISAT’s disease score scale, which ranges from 1 to 9. Treatments with aqueous extracts of L. multiflora and Z. mucronata recorded the best disease control. The disease scores of these treatments were less or equal to 4 (corresponding to a resistance of plants), and increased pod yield by 2676.889 kg ha-1 (L. multiflora) and 2976.926 kg ha-1 (Z. mucronata), respectively. This field trial has confirmed that plants tested significantly control leaf spot diseases of groundnut.Key Words: Arachis hypogaea, Cercospora arachidicola, Phaeoisariopsis personata

Scaling of photosynthesis and constitutive and induced volatile emissions with severity of leaf infection by rust fungus (Melampsora larici-populina) in Populus balsamifera var. suaveolens.

Fungal infections result in decreases in photosynthesis, induction of stress and signaling volatile emissions and reductions in constitutive volatile emissions, but the way different physiological processes scale with the severity of infection is poorly known. We studied the effects of infection by the obligate biotrophic fungal pathogen Melampsora larici-populina Kleb., the causal agent of poplar leaf rust disease, on photosynthetic characteristics, and constitutive isoprene and induced volatile emissions in leaves of Populus balsamifera var. suaveolens (Fisch.) Loudon. exhibiting different degrees of damage. The degree of fungal damage, quantified by the total area of chlorotic and necrotic leaf areas, varied between 0 (noninfected control) and ∼60%. The rates of all physiological processes scaled quantitatively with the degree of visual damage, but the scaling with damage severity was weaker for photosynthetic characteristics than for constitutive and induced volatile release. Over the whole range of damage severity, the net assimilation rate per area (AA) decreased 1.5-fold, dry mass per unit area 2.4-fold and constitutive isoprene emissions 5-fold, while stomatal conductance increased 1.9-fold and dark respiration rate 1.6-fold. The emissions of key stress and signaling volatiles (methanol, green leaf volatiles, monoterpenes, sesquiterpenes and methyl salicylate) were in most cases nondetectable in noninfested leaves, and increased strongly with increasing the spread of infection. The moderate reduction in AA resulted from the loss of photosynthetically active biomass, but the reduction in constitutive isoprene emissions and the increase in induced volatile emissions primarily reflected changes in the activities of corresponding biochemical pathways. Although all physiological alterations in fungal-infected leaves occurred in a stress severity-dependent manner, modifications in primary and secondary metabolic pathways scaled differently due to contrasting operational mechanisms.

Effect of foliar-applied silicon on photochemistry, antioxidant capacity and growth in maize plants subjected to chilling stress

Low temperature is one of the major adverse climatic factors that suppress plant growth and sustainable agricultural development. In these climate conditions, silicon (Si) can mitigate various abiotic stresses including low temperature. In this study, the roles of foliar-applied silicon (10 mM potassium metasilicate) in enhancing tolerance to chilling stress were investigated in maize (Zea mays ‘Fajr’) plants. The low temperature stress caused significant reduction of plant growth and relative water content; however, Si ameliorated these effects. Si supply in maize exhibited a significantly positive effect on accumulation of free amino acids, and reduced the necrotic leaf area. The decrease in maximum quantum yield of PSII (Fv/Fm) was reversible during recovery, but not in the non-Si-treated leaves. This can be explained by enhancement of protective pigments; carotenoid and anthocyanin leading to the protection of PSII from damage. Additionally, analysis of OJIP transients revealed that Si reduced cold damaging effect on performance index (PIabs) and Fv/Fm through improvement of excitation energy trapping (TR0/CS) and electron transport (ET0/CS) per excited cross-section of leaf. The malondialdehyde (MDA) concentration, which was significantly increased under chilling stress, was decreased by Si. The reduced glutathione and ascorbate concentrations were higher in Si-treated plants as compared to those without application of Si under chilling stress. These results indicated that Si could enhance the chilling stress tolerance of maize plants through improving the biomass accumulation, maintaining a high level of glutathione, ascorbic acid, protein, protective pigments, and enhancing the photochemical reactions. This study also suggests that the foliar-applied Si increases recovery ability from chilling injury.

Caracterização de Fusarium solani f. sp. piperis, produção de fitotoxina e incidência da fusariose no norte de Minas Gerais

RESUMO A podridão das raízes causada por Fusarium solani f. sp. piperis é uma das principais doenças da pimenteira-do-reino no norte de Minas Gerais. Os objetivos deste trabalho foram quantificar a incidência da doença nas principais áreas produtoras do norte do estado de Minas Gerais, identificar o agente causal da fusariose, testar a patogenicidade dos isolados e avaliar a ação de filtrados de F. solani f. sp. piperis sobre folhas destacadas de pimenteira-do-reino e sobre Trichoderma asperellum. Avaliou-se a incidência da fusariose em 1.000 ou 500 plantas de forma arbitrária, em percurso em zigue-zague. A reação de pimenta-do-reino ‘Cingapura’ foi avaliada em relação a dois filtrados fúngicos (FPC1 e FPB2), e o isolado FPB2 foi empregado para avaliar a reação das cultivares Cingapura e Guajarina. Outro experimento foi realizado para estudar a influência das diluições do filtrado FPB2 em folhas da cultivar Cingapura. Para avaliar o efeito de toxinas dos filtrados sobre o Índice de Velocidade de Crescimento Micelial (IVCM) de T. asperellum foi implantado um ensaio com diferentes concentrações e dois filtrados. A incidência da doença nas áreas amostradas foi de 31,5 e 100% nos municípios de Bocaiúva e Montes Claros, respectivamente. De acordo com os resultados do teste de compatibilidade sexual foi possível identificar os isolados como F. solani f. sp. piperis. Nove isolados foram patogênicos quando inoculados em mudas de pimenta-do-reino com quatro meses de desenvolvimento. O filtrado FPB2 produziu maior severidade de infecção (média de 93,6% de área foliar necrosada), comparado ao isolado FPC1 (5,8%). A cultivar Cingapura foi mais sensível à ação do filtrado. A diluição do filtrado FPB2 proporcionou redução na porcentagem de área foliar lesionada. Observou-se, ainda, que o aumento das concentrações do filtrado do isolado FPC1 proporcionou o aumento do IVCM de T. asperellum, enquanto o filtrado de FPB2 gerou uma reação contrária, reduzindo o IVCM desse fungo antagonista.

Exogenous silicon leads to increased antioxidant capacity in freezing-stressed pistachio leaves

Freezing stress limits photosynthesis and growth of plants. This may be attributed to the enhancement of freezing-associated oxidative damage. In this study, we followed precisely changes in the extent of lipid peroxidation and oxidative damage in leaves of pistachio (Pistacia vera ‘Ahmadaghaii’) plants exposed to foliar-applied silicon (Si) under freezing stress. The foliar-applied Si decreased significantly damaging effects of cold on relative water content (RWC), accompanied by an increase in shoot fresh mass (SFM). In addition, pre-Si treatment caused a significant reduction of the leaf area lost by freezing. There was a remarkable increase in phenylalanine ammonia-lyase (PAL) activity during recovery. Since leaf phenolic content was not affected by supplementary Si, the possibility that exogenously applied Si directly influences the activity of PAL seems thin. In the present work, freezing stress caused great membrane damage, as assessed by lipid peroxidation, but Si application significantly reduced the membrane damage because of an efficient scavenging by superoxide dismutase (SOD) and peroxidase (POD). Under freezing, despite the increasing POD activity, Si-supplied plants accumulated the highest levels of hydrogen peroxide (H2O2) may act as a signal for recovery ability from freezing injury. A positive correlation was found between the concentration of malondialdehyde (MDA) and the percentage of necrotic leaf area. This study suggests that the possible mechanisms for Si enhanced freezing resistance may be attributed to the higher antioxidant defense activity and lower lipid peroxidation through leaf water retention, in addition to its role as a mere physical barrier.

Effect of Air-Borne Salinity on the Growth and Appearance of the Tropical Perennial Strandline Plant, Commelina erecta subsp. maritima (C.V. Morton) C.V. Morton

<p>Selection of salt spray tolerant plants with good physical appearance is of concern to ornamental growers in coastal communities. <em>Commelina erecta</em> subsp. <em>maritima</em> (C.V. Morton) C.V. Morton is a seashore plant that is widely distributed along the coast of West Africa. Therefore, the effect of salt spray was examined on the plant in a greenhouse experiment to determine its responses to various levels of air-borne salinity and to have an insight in the ecophysiological adaptations underlying these responses. It was also aimed to determine if varying levels of salt spray differentially damaged the plant. Filtered seawater was used to spray potted plants at: two sprays per week (2SS), four sprays per week (4SS) or six sprays per week (6SS) while in the control treatment (CSS), plants were sprayed with deionized water. Plants sprayed with seawater did not differ significantly (p > 0.05) in percentage necrotic leaf area compared to the control. All the plants survived but growth was inhibited by salt spray. Salt spray caused a significant (p < 0.05) reduction in leaf size and total chlorophyll content. Salt was accumulated in the shoot of salt-sprayed plants which led to ion toxicity. Salt sprays led to reduction in amount of essential nutrients in plant parts. <em>C</em>.<em> </em><em>erecta </em>subsp. <em>maritima</em> adjusted osmotically to salt stress and increased stem succulence for ion dilution. The growth of the plant was negatively affected by salt sprays but it showed no significant necrotic damage, hence it is suitable for use as a landscaping plant in coastal beaches.</p>

Limits of Active Laser Triangulation as an Instrument for High Precision Plant Imaging

Laser scanning is a non-invasive method for collecting and parameterizing 3D data of well reflecting objects. These systems have been used for 3D imaging of plant growth and structure analysis. A prerequisite is that the recorded signals originate from the true plant surface. In this paper we studied the effects of species, leaf chlorophyll content and sensor settings on the suitability and accuracy of a commercial 660 nm active laser triangulation scanning device. We found that surface images of Ficus benjamina leaves were inaccurate at low chlorophyll concentrations and a long sensor exposure time. Imaging of the rough waxy leaf surface of leek (Allium porrum) was possible using very low exposure times, whereas at higher exposure times penetration and multiple refraction prevented the correct imaging of the surface. A comparison of scans with varying exposure time enabled the target-oriented analysis to identify chlorotic, necrotic and healthy leaf areas or mildew infestations. We found plant properties and sensor settings to have a strong influence on the accuracy of measurements. These interactions have to be further elucidated before laser imaging of plants is possible with the high accuracy required for e.g., the observation of plant growth or reactions to water stress.