Biocontrol of seed pathogens and growth promotion of common bean seedlings by Trichoderma harzianum

The objective of this work was to evaluate isolates of Trichoderma harzianum regarding biocontrol of common bean seed-borne pathogens, plant growth promotion, and rhizosphere competence. Five isolates of T. harzianum were evaluated and compared with commercial isolate (Ecotrich), Carboxin+Thiram, and an absolute control. Bean seeds of the cultivar Jalo Precoce, contaminated with Aspergillus, Cladosporium, and Sclerotinia sclerotiorum, were microbiolized with antagonists, and seed health tests were carried out. Isolates were evaluated on autoclaved substrate and in field conditions. Ten days after sowing (DAS), plant length was measured. To test rhizosphere competence, isolates were applied in boxes containing autoclaved washed sand, and root colonization was evaluated at 10 DAS, using five plants per box. The most effective isolates in the seed health tests were: CEN287 and CEN289 to control Aspergillus; the commercial isolate to control Cladosporium; and CEN287 and CEN316 to control S. sclerotiorum. Isolates CEN289 and CEN290 promoted bean growth in greenhouse and field. Seed treatment with T. harzianum reduces the incidence of Aspergillus, Cladosporium, and S. sclerotiorum in 'Jalo Precoce' common bean seeds.

Acclimatization of Tapeinochilos ananassae plantlets in association with arbuscular mycorrhizal fungi

The objective of this work was to assess the potential of three isolates of arbuscular mycorrhizal fungi to promote growth of micropropagated plantlets of Tapeinochilos ananassae during acclimatization. The experiment was carried out in greenhouse, in a completely randomized block design, with four inoculation treatments: non‑inoculated control and plants inoculated with Glomus etunicatum, Acaulospora longula or Gigaspora albida, with ten replicates. After 90 days, the following parameters were evaluated: survival rate, height, leaf and tiller number, leaf area, fresh and dry biomass, contents of macro‑ and micronutrients in the root and shoot, glomerospore number, and mycorrhizal colonization. The survival percentage was 100%, except for plants inoculated with G. albida (80%). The isolate G. etunicatum is more suitable for plant development, since it improves survival, growth, dry matter production, nutritional status, and vigor of T. ananassae micropropagated plants.

Histopathology of Colletotrichum gloeosporioides on guava fruits (Psidium guajava L.)

Anthracnose, caused by Colletotrichum gloeosporioides, produces brown lesions on guava fruits, causing severe losses on postharvest. In this study, the infection and colonization of guava fruits by C. gloeosporioides has been examined using scanning and transmission electron microscopy. Fruits at the physiologically mature stage were inoculated with a 10(5) conidia/mL spore suspension. Afterward, fruits were incubated at 25 °C in a wet chamber for periods of 6, 12, 24, 48, 96 and 120 h to allow examination of the infection and colonization process. Conidia germination and appressoria formation occurred six hours after inoculation (h.a.i). Penetration occurred directly via penetration pegs from appressoria, which penetrated the host cuticle 48 h.a.i. Notably, the appressoria did not produce an appressorial cone surrounding the penetration pore. Infection vesicles were found in epidermal cells 96 h.a.i. The same fungal structures were found in epidermal and parenchymal cells of the host 120 h.a.i. Colonization strategy of C. gloeosporioides on guava fruit was intracellular hemibiotrophic.

Poluição por mercúrio em aterros urbanos do período colonial no extremo sul do Brasil

Land reclamation fills in the city of Rio Grande (RS) are polluted by mercury with concentrations ranging from 0.3 to 18.7 mg kg-1. The level of Hg pollution decreases from the oldest landfills of 18th century to recent ones. Mercury distribution along vertical profiles resembles the same for copper, lead, and zinc, what allow supposing that mercury distribution has an autochthonous character. It is suggested that the principal source of mercury pollution was the activities related to animal skin and fair hair treatment, using ancient technology known as "carroting". Similar scenario of environmental risk could be met in other Brazilian cities with similar colonization history.

Espécies tropicais de pteridófitas em associação com fungos micorrízicos arbusculares em solo contaminado com arsênio

The symbiosis of plants with mycorrhizal fungi represents an alternative to be considered during the processes of revegetation and rehabilitation of arsenic-contaminated soil. The aim of this study was to evaluate under greenhouse conditions the effect of arsenic on the mycorrhizal association of two species of tropical fern (Thelypteris salzmannii and Dicranopteris flexuosa). T. salzmannii had higher rates of colonization and higher density of spores while D. flexuosa showed greater sensitivity to smaller concentrations of arsenic and association with mycorrhizal fungi. Our results indicate that screening and selection of mycorrhizal fungal isolates/species is possible and effective for phytoremediation of arsenic-contaminated soils.

Effect of organic amendments on sclerotial germination, mycelial growth, and Sclerotium rolfsii-induced diseases

The addition of organic residues to soil is an option to control some soil-borne diseases. Benzaldehyde and powders of kudzu (Pueraria lobata), velvetbean (Mucuna deeringiana), and pine-bark (Pinus elliottii and P. taeda) added to soil could reduce certain soil-borne diseases. This study evaluated the effects of benzaldehyde and the dried powders of kudzu, velvetbean, and pine-bark as soil amendments on germination and formation of sclerotia, on mycelial growth of Sclerotium rolfsii, on plant survival, and disease incidence. The data showed that high amounts of benzaldehyde (0.4 ml kg-1 of soil) and velvetbean (100 g kg-1) inhibited S. rolfsii mycelial growth and sclerotium germination. However, low amounts of benzaldehyde (0.1 ml kg-1), kudzu (25 g kg-1), and pine-bark (25 g kg-1) stimulated mycelial growth and sclerotium germination. Kudzu (25-100 g kg-1) and velvetbean (25-100 g kg-1) inhibited the formation of sclerotia. Nevertheless, benzaldehyde at 0.2 and 0.4 ml kg-1 stimulated the formation of sclerotia. Kudzu (50 and 100 g kg-1) and pine-bark (50 g kg-1) favored the colonization of sclerotia by Trichoderma sp. The numbers of soybean (Glycine max) plants were higher and diseased plants were lower than the non-amend soil in the following treatments: kudzu (50 and 100 g kg-1), velvetbean (50 and 100 g kg-1), and pine-bark (50 g kg-1). Disease severity on tomato (Lycopersicon esculentum) plants was low in soil treated with kudzu or velvetbean (30 and 35 g kg-1) and pine-bark (35 g kg-1). Dried powders of kudzu, velvetbean, or pine-bark added to soil can reduce disease by reducing pathogen inoculum.

Essential oil of mustard to control Rhizoctonia solani causing seedling damping off and seedling blight in nursery

The essential oil extracted from mustard (Brassica rapa) seeds was evaluated for its effect on suppression of Rhizoctonia solani growth in vitro, and in field soils, for reducing saprophytic substrate colonization and seedling damping off and blight using snap beans as indicator plant, the in vitro growth was completely inhibited at a concentration of 50 mul/l. The saprophytic substrate colonization in soils 24 h after treatment was drastically reduced to 45% at 150 mul/kg soil concentration, in contrast to 100% colonization at concentrations of 0, 50, or 75 mul/kg. This recovery rate gradually declined to 6% and 60%, respectively, in nine days. A control of pre and post-emergence seedling damping off and blight in common beans (Phaseolus vulgaris), without any apparent phytotoxic effect was achieved by irrigating R. solani infested soils with water containing the emulsified essential oil to provide 150 mul/l soil volume ten days prior to planting, gave over 95%. The effect of the mustard essential oil was not influenced by the physical soil texture, and it appears to be a good substitute for methyl bromide fumigation in nurseries for seedling production.

Influence of internal seedborne Fusarium semitectum on cotton seedlings

Fusarium semitectum was found to be the major seed colonizing fungus in the commercial acid delinted cotton (Gossypium hirsutum) seed lots. There was no correlation, however, between its incidence and seedling emergence and disease symptoms on the emerged seedlings in autoclaved sand. Inoculation technique simulating internally seedborne nature of the fungus showed that the observed non-correlation might be related to the threshold level of seed coat colonization. The internally seedborne inoculum besides reducing seedling emergence, incited an array of symptoms on the emerged seedlings, which ranged from negative geotropism, leaf tearing, collar rot leading to dry root rot and seedling mortality. The dry root rot continued to develop on the plants surviving the seedling phase. The collar rot symptoms can be confused with those caused by Rhizoctonia solani.

Is it necessary to soak rice grains to prepare Rhizoctonia solani AG-4 inoculum?

A study was conducted to evaluate the effects on the development of root rot on common bean, cv. 'Dufrix' after treatment with four volumes of water (0, 30%, 60%, and 90%, v/w) added to rice grains previously immersed in water for 24 hours before autoclaving and colonization of grains by Rhizoctoniasolani AG-4. Colonized rice grains and non-infested rice grains were mixed in pots with sterilized soil and sand (2:1), where beans were sown. Based on results of area under plant emergence curve, plant height, plant dry weight, and disease severity, we conclude that inoculum is more effective in causing disease when no water is added to the rice grains before autoclaving.

Etiology and epidemiology of Pythium root rot in hydroponic crops: current knowledge and perspectives

The etiology and epidemiology of Pythium root rot in hydroponically-grown crops are reviewed with emphasis on knowledge and concepts considered important for managing the disease in commercial greenhouses. Pythium root rot continually threatens the productivity of numerous kinds of crops in hydroponic systems around the world including cucumber, tomato, sweet pepper, spinach, lettuce, nasturtium, arugula, rose, and chrysanthemum. Principal causal agents include Pythium aphanidermatum, Pythium dissotocum, members of Pythium group F, and Pythium ultimum var. ultimum. Perspectives are given of sources of initial inoculum of Pythium spp. in hydroponic systems, of infection and colonization of roots by the pathogens, symptom development and inoculum production in host roots, and inoculum dispersal in nutrient solutions. Recent findings that a specific elicitor produced by P. aphanidermatum may trigger necrosis (browning) of the roots and the transition from biotrophic to necrotrophic infection are considered. Effects on root rot epidemics of host factors (disease susceptibility, phenological growth stage, root exudates and phenolic substances), the root environment (rooting media, concentrations of dissolved oxygen and phenolic substances in the nutrient solution, microbial communities and temperature) and human interferences (cropping practices and control measures) are reviewed. Recent findings on predisposition of roots to Pythium attack by environmental stress factors are highlighted. The commonly minor impact on epidemics of measures to disinfest nutrient solution as it recirculates outside the crop is contrasted with the impact of treatments that suppress Pythium in the roots and root zone of the crop. New discoveries that infection of roots by P. aphanidermatum markedly slows the increase in leaf area and whole-plant carbon gain without significant effect on the efficiency of photosynthesis per unit area of leaf are noted. The platform of knowledge and understanding of the etiology and epidemiology of root rot, and its effects on the physiology of the whole plant, are discussed in relation to new research directions and development of better practices to manage the disease in hydroponic crops. Focus is on methods and technologies for tracking Pythium and root rot, and on developing, integrating, and optimizing treatments to suppress the pathogen in the root zone and progress of root rot.

Macrophomina phaseolina: density and longevity of microsclerotia in soybean root tissues and free on the soil, and competitive saprophytic ability

In field experiments, the density of Macrophomina phaseolina microsclerotia in root tissues of naturally colonized soybean cultivars was quantified. The density of free sclerotia on the soil was determined for plots of crop rotation (soybean-corn) and soybean monoculture soon after soybean harvest. M. phaseolina natural infection was also determined for the roots of weeds grown in the experimental area. To verify the ability of M. phaseolina to colonize dead substrates, senesced stem segments from the main plant species representing the agricultural system of southern Brazil were exposed on naturally infested soil for 30 and 60 days. To quantify the sclerotia, the methodology of Cloud and Rupe (1991) and Mengistu et al. (2007) was employed. Sclerotium density, assessed based on colony forming units (CFU), ranged from 156 to 1,108/g root tissue. Sclerotium longevity, also assessed according to CFU, was 157 days for the rotation and 163 days for the monoculture system. M. phaseolina did not colonize saprophytically any dead stem segment of Avena strigosa,Avena sativa,Hordeum vulgare,Brassica napus,Gossypium hirsutum,Secale cereale,Helianthus annus,Triticosecalerimpaui, and Triticum aestivum. Mp was isolated from infected root tissues of Amaranthus viridis,Bidens pilosa,Cardiospermum halicacabum,Euphorbia heterophylla,Ipomoea sp., and Richardia brasiliensis. The survival mechanisms of M. phaseolina studied in this paper met the microsclerotium longevity in soybean root tissues, free on the soil, as well as asymptomatic colonization of weeds.

Histopathological features of infections caused by Fusarium oxysporum and F. solani in purple passionfruit plants (Passiflora edulis Sims)

The purple passionfruit plant, Passifloraedulis Sims, ranks second in fruit exportation in Colombia, and its main destination is the European market. However, its production is affected by several diseases, including fusariosis. This paper presents the histopathological features of different tissues affected by the pathogens Fusarium oxysporum and Fusarium solani. Both microorganisms produce similar responses on the plant: colonization of xylem vessels by hyphae and microconidia, hypertrophy and hyperplasia of the cambium, xylem and phloem; destruction of xylem fibers and amyloplasts in parenchymatous cells; and production of gels by the plant. However, there are differences in the colonization mechanism, F. solani penetrates and is concentrated especially at the collar zone, while F. oxysporum penetrates the roots and moves through the vascular system to colonize the plant.

GFP-fluorescent protein on the study of blister spot in coffee plants

In Brazil, Colletotrichum gloeosporioides is associated with a complex of symptoms in coffee culture. Although this pathogen had its pathogenesis observed and identified, its importance has still been questioned due to its several endophytic forms, raising doubts as to the real importance of the pathosystem. The aim of this study was to demonstrate, by using an isolate transformed with the gene gfp, the infection and colonization capability of C. gloeosporioides in coffee seedlings. After the fourth day of inoculation, manifestation of symptoms as punctual necrosis could be observed, which progressed during the evaluation period, culminating in the death of seedlings. Epifluorescence microscopy confirmed the presence of the pathogen in the seedlings, as well as the visualization of internal colonization of tissues, acervulus formation and conidium production, confirming that it was responsible for the observed symptoms.

Anatomical changes on coffee leaves infected by Pseudomonas syringae pv. garcae

ABSTRACTAlthough poorly studied, the bacterial halo blight is an important disease in the major coffee-producing states of Brazil. External damage and anatomical changes on leaves were measured in seedlings of Coffea arabica cv. Mundo Novo, susceptible to Pseudomonas syringae pv. garcae, by using histological sections obtained at 10 and 20 days after inoculation (DAI). The changes on the epidermis were smaller than the lesions measured in the mesophyll, irrespective of the evaluated colonization period, showing that the internal damage caused by the bacterium represent twice the damage observed externally. From the inoculation site, lysis occurred on the epidermal cells and on the palisade and spongy parenchyma cells, with strong staining of their cellular contents, as well as abnormal intercellular spaces in the palisade parenchyma, hypertrophy and hyperplasia of mesophyll cells and partial destruction of chloroplasts. Additionally, this study revealed the presence of inclusion bodies in epidermal and mesophyll cells. Bacterial masses were found in the apoplast between and within mesophyll cells. Bacteria were also observed in the bundle sheath and vascular bundles and were more pronounced at 20 DAI, not only near the inoculation site but also in distant areas, suggesting displacement through the vascular system. These results can be useful to understand this plant-pathogen interaction.

Fungi associated to bark lesions of Eucalyptus globulus stems in plantations from Uruguay

Trees with stem bark lesions are frequently observed in Eucalyptus globulus Labill. plantations, particularly in the central west region of Uruguay. These lesions constitute a problem for trunk decortications at harvest and they also facilitate the access of fungi that could cause wood decay. Seven, three and oneyear-old plantations, located at three sites in close proximity were selected. Four types of trunk lesions were present in trees regardless the age of plantation and more than one type was found in each plantation. The aim of this study was to investigate the fungal composition associated with these lesions and compare them to healthy tissues and try to find out the origin of these symptoms. Another purpose was to elucidate the real role of the fungi considered pathogens by means of experimental inoculations. Segments from lesions and healthy tissues yielded 897 fungal isolates belonging to 32 taxa, 681 isolates from bark lesions and 216 from healthy tissues. Both healthy and symptomatic tissues showed similar fungal species composition, but with differences in frequencies of colonization. Cytospora eucalypticola Van der Westhuizen, Botryosphaeria spp., Pestalotiopsis guepinii (Desm.) Stey. and Penicillium spp. were the dominant species isolated. As symptoms were not reproduced after experimental inoculation with Botryosphaeria ribis Grossenb. & Duggar and B. eucalyptorum Crous, & M.J. Wingf, it could be suggested that these lesions were originated by unfavorable environmental conditions. The frost that occurred for several days out of season and flooding may have been involved in the development of bark lesion.