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Implications of green manure amendments on soil seed bank dynamicsShort, Nicolyn January 2006 (has links)
[Truncated abstract] Weeds are a major limitation to agricultural and horticultural production and the main method of control is the use of herbicides. In addition to the resulting chemical pollution of the environment, the wide spread and continues use of herbicides have resulted in many weeds developing resistance to commonly used herbicides. This study investigated the potential of using green manures as a cultural method of control of weed invasion in agricultural fields. To understand the general mechanisms involved in the suppression of seed germination in green manure amended soils, seeds of crop species with little or no dormancy requirements were used in certain studies. Lettuce (Lactuca sativa) and cress (Lepidium sativum) seeds were sown to a sandy soil amended with green manures of lupin (Lupinus angustifolius), Brassica juncea, or oats (Avena sativa) to determine if the amendments affected seed germination and/or decay. It was hypothesised that the addition of plant material would increase the microbial activity of the soil thereby increasing seed decay, under laboratory and greenhouse conditions. Initial experiments used lettuce, cress and lupin seeds. Lettuce and cress are commonly used as standard test species for seed viability studies. Subsequent experiments used seeds of annual ryegrass (Lolium rigidum), silver grass (Vulpia bromoides), wild radish (Raphanus raphanistrum) and wild oat (Avena fatua) as these weed species are commonly found throughout agricultural regions in Western Australia. Amending the soil with lupin or Brassica green manure was established as treatments capable of developing environments suppressive to seed germination. Lupin residues as green manure showed the strongest inhibition of seed germination and seed decay. The decay of certain seeds was enhanced with changes to soil microbial activity, dissolved organic carbon and carbon and nitrogen amounts in lupin amended soil. Seeds of weed species were decayed in lupin amended soil, but showed varied degree of decay. Annual ryegrass and silver grass were severely decayed and wild oat and wild radish were less decayed, in lupin amended soil.
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Bioprospecção de isolados de leveduras e bactérias, provenientes da secreção oral de Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) coletada em campo, antagônicos a Fusarium verticillioides (Nirenberg, 1976) e Colletotrichum falcatum (Went, 1893) / Bioprospection of yeast and bacteria isolates from oral secretion of field-collected diatraea saccharalis (fabricius, 1794) (Lepidoptera: Crambidae) Antagonic to Fusarium verticillioides (Nirenberg, 1976) AND Colletotrichum falcatum (Went, 1893)Silva, Larissa Chariel Domingos da 28 June 2016 (has links)
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Previous issue date: 2016-06-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Insect symbionts may have unknown functions in the interaction between insect-plant
and insect with microorganisms that co-inhabit the same space. The objective of this
study was to investigate the antagonism potential of symbiont microbiota from oral
secretion D. saccharalis collected in the field, against Fusarium verticillioides and
Colletotrichum falcatum pathogens commonly found inside the cane. For this, 4° and
5° instar caterpillars were collected inside sugarcane varieties RB-835 054 and SP-
813 250, and brought to the lab inside the cane stalks. The microbiota of oral
secretion was transferred to two selective media, NA (nutrient agar) for bacteria and
DRBC (dicloran Rose Bengal Chloramphenicol) for yeast. Based on morphology and
coloration of the colonies twenty colonies of bacteria and yeast were selected. Four
culture media were tested in co-cultivation of F. verticillioides and C. falcatum versus
bacteria or yeast isolates: PDA (potato, dextrose, agar), YEPD (yeast extract,
peptone, dextrose), CCS (supplemented cane broth) and NA (Nutrient Agar). The
most suitable culture medium for growth of most microorganisms was BDA.
Antagonism potential of 82 bacterial isolates and 87 yeast isolates to C. falcatum and
F. verticillioides was assessed using a visual scale of categories 1 to 4, with 4 being
the maximum degree of antagonism. Isolates that allocated category greater than or
equal to 2 were evaluated in co-culture with C. falcatum and F. verticillioides as the
percentage of growth inhibition. It was possible to identify four isolates of bacteria
which have the potential to inhibit growth of pathogens and 9 isolates with the same
potential but with much lower percentages. These results demonstrate that some
isolates of bacteria and yeast may influence the relationship between the bit-rot
complex and sugarcane plant, may in future be used as a biological control of these
pathogens or have some molecules of biotechnological interest extracted and
purified. / Simbiontes de insetos podem ter funções desconhecidas na interação entre insetoplanta
e do inseto com microrganismos que co-habitam o mesmo espaço. O objetivo
desse estudo foi investigar o potencial de antagonismo da microbiota simbionte,
presentes na secreção oral de Diatraea saccharalis, com os fitopatógenos Fusarium
verticillioides e Colletotrichum falcatum que habitam o colmo de cana-de-açúcar.
Para isso, foram coletadas, nas variedades de cana RB-835054 e SP-813250,
lagartas de 4° e 5° instar e trazidas para o laboratório junto aos toletes de cana. A
microbiota da secreção oral foi transferida para dois meios de cultura seletivos, NA
(nutrient agar) para bactérias e DRBC (Dicloran Rosa-de-Bengala Cloranfenicol)
para leveduras. Baseado na morfologia e coloração das colônias, foram
selecionadas, vinte colônias de bactéria e também de levedura de 5 lagartas. Foram
testados quatro meios de cultura: BDA (batata, dextrose, agar), YEPD (yeast extract,
peptone, dextrose), CCS (caldo-de-cana suplementado) e NA para os testes de
cultivo pareado. O meio de cultura mais adequado para o crescimento da maioria
dos microrganismos foi o BDA. O potencial de antagonismo de 82 isolados de
bactéria e 87 isolados de levedura a C. falcatum e F. verticillioides foi avaliado
através de uma escala visual de categorias de 1 a 4, sendo 4 o grau máximo de
antagonismo. Os isolados a que foi atribuída categoria maior ou igual a dois foram
avaliados em co-cultivo com C. falcatum e F. verticillioides quanto à porcentagem de
inibição do crescimento. Foi possível identificar 4 isolados de bactéria que tem o
potencial de inibir o crescimento dos fitopatógenos e 9 isolados com o mesmo
potencial, porém com porcentagens menores. Esses resultados demonstram que
alguns isolados de bactérias e leveduras podem influenciar na relação existente
entre o complexo broca-podridão e a planta de cana-de-açúcar, podendo,
futuramente, serem utilizados como controle biológico desses fitopatógenos ou
terem algumas moléculas de interesse biotecnológico extraída e purificada.
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Fungos endofíticos de Phaseolus vulgaris exibem atividade antimicrobiana e potencial para controle de fitopatógenos / Endophytic fungi of Phaseolus vulgaris exhibit antimicrobial activity and potential for control of phytopathogensSantos, Taides Tavares dos 20 February 2014 (has links)
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Previous issue date: 2014-02-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Endophytic fungi are those living at least a part of their life cycle within plant tissue, apparently without causing any damage to their hosts. These microorganisms have been studied for their capacity to produce secondary metabolites of biotechnological interest, and also for their ability for biological control of phytopathogens. Endophytic fungi have been isolated from a wide variety of plant species, including crops such as common bean (Phaseolus vulgaris L.). Fungi from the genus Diaporthe were abundant in the endophytic community of this legume. The objectives of this study were to evaluate the antimicrobial activity and the potential use of endophytic fungi of P. vulgaris in the control of phytopathogens of bean, and to analyze phylogenetic relationships and genetic variability of endophytic fungi of the genus Diaporthe isolated from P. vulgaris. Dual culture assays were performed between ninety endophytic fungi and four phytopathogenic fungi (Colletotrichum lindemuthianum, Fusarium oxysporum, Rhizoctonia solani and Sclerotinia sclerotiorum) to assess for the ability of endophytic fungi inhibit the growth of phytopathogens. The isolates that were able to inhibit the four phytopathogens tested were selected for cultivation and obtention of metabolites crude extracts. These extracts were evaluated for antibacterial and antifungal activity. The sequences of the ITS region of rDNA of the isolates of the genus Diaporthe from common bean, along with the partial sequences of the genes encoding translation elongation factor 1-α, β-tubulin and calmodulin were used for the study of the phylogenetic relationships of these isolates. Molecular markers based on sequences of retrotransposons, IRAP (Inter-Retrotransposon Amplified Polymorphism) and REMAP (Retrotransposon-Microsatellite Amplified Polymorphism), were used for the analysis of genetic variability. It was found that endophytic fungi of common bean are able to inhibit the in vitro growth of phytopathogenic fungi and that metabolites crude extracts of endophytic exhibit significant antimicrobial activity especially regarding the inhibitory activity against Gram-positive bacteria (Listeria monocytogenes, Bacillus cereus, B. subtilis and Staphylococcus aureus). Diaporthe sp., D. infecunda, D. melonis and D. phaseolorum are members of the endophytic fungal community in the common bean as verified by multilocus phylogenetic analysis. Cluster analysis, conducted with pooled data from IRAP and REMAP markers, was consistent regarding what was observed in multilocus phylogeny and revealed the existence of high genetic variability, particularly among isolates of D. infecunda. It was concluded that the metabolites crude extracts of endophytic fungi of common bean exhibit promising antimicrobial activity; that endophytic fungi used in this study have the potential to control phytopathogens that affect the bean crop; the multilocus phylogenetic approach was more effective than individual analysis of ITS sequences in the study of phylogenetic relationships of endophytic fungi of the genus Diaporthe from common bean and that IRAP and REMAP markers can be employed in the study of genetic variability of this genus of fungi. / Fungos endofíticos são aqueles que vivem, em pelo menos uma parte de seu ciclo de vida, no interior de tecidos vegetais, sem causar aparentemente qualquer dano a seus hospedeiros. Esses micro-organismos têm sido estudados em relação à capacidade de produzirem metabólitos secundários de interesse biotecnológico e quanto ao potencial de controle biológico de fitopatógenos. Fungos endofíticos já foram isolados de uma ampla variedade de espécies vegetais, incluindo culturas agrícolas como o feijoeiro comum (Phaseolus vulgaris L.). O gênero Diaporthe foi um dos mais abundantes na comunidade endofítica dessa leguminosa. Os objetivos do presente estudo foram avaliar a atividade antimicrobiana e o potencial de uso de fungos endofíticos de P. vulgaris no controle de fitopatógenos da cultura do feijoeiro e analisar as relações filogenéticas e a variabilidade genética de fungos endofíticos do gênero Diaporthe isolados de P. vulgaris. Ensaios de cultura dupla entre 90 isolados endofíticos e quatro fungos fitopatogênicos (Colletotrichum lindemuthianum, Fusarium oxysporum, Rhizoctonia solani e Sclerotinia sclerotiorum) foram realizados para verificar a capacidade dos isolados endofíticos inibirem o crescimento dos fitopatógenos. Os isolados que foram capazes de inibir os quatro fitopatógenos testados foram selecionados para cultivo e obtenção de extratos brutos de metabólitos. Esses extratos foram avaliados quanto à atividade antibacteriana e antifúngica. As sequências da região ITS do rDNA dos isolados do gênero Diaporthe do feijoeiro, juntamente com as sequências parciais dos genes codificam o fator de elongação da tradução 1-α, β-tubulina e calmodulina, foram utilizadas para o estudo das relações filogenéticas desses isolados. Marcadores moleculares baseados em sequências de retrotransposons, IRAP (Inter-Retrotransposon Amplified Polymorphism) e REMAP (Retrotransposon-Microsatellite Amplified Polymorphism), foram utilizados para a análise de variabilidade genética. Foi constatado que os fungos endofíticos do feijoeiro comum são capazes de inibir o crescimento in vitro de fungos fitopatogênicos e, que extratos brutos de metabólitos de isolados endofíticos exibem atividade antimicrobiana significativa, principalmente em relação à atividade inibitória sobre bactérias Gram-positivas (Listeria monocytogenes, Bacillus cereus, B. subtilis e Staphylococcus aureus). Por meio de análise filogenética multilocus, verificou-se que Diaporthe sp., D. infecunda, D. melonis e D. phaseolorum são integrantes da comunidade fúngica endofítica do feijoeiro comum. A análise de agrupamento, realizada com os dados dos marcadores IRAP e REMAP em conjunto, foi coerente em relação ao que foi verificado na filogenia multilocus e, revelou a existência de grande variabilidade genética, sobretudo entre os isolados de D. infecunda. Concluiu-se que extratos brutos de metabólitos de fungos endofíticos do feijoeiro exibem atividade antimicrobiana promissora; que fungos endofíticos utilizados neste estudo apresentam potencial para controle de fitopatógenos que acometem a cultura do feijoeiro; que a abordagem filogenética multilocus foi mais efetiva que análise individual de sequências de ITS no estudo das relações filogenéticas de fungos endofíticos do gênero Diaporthe do feijoeiro e que marcadores IRAP e REMAP podem ser empregados no estudo de variabilidade genética de fungos desse gênero.
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Caracterizaçãoda alfa-manosidase produzida por Trichoderma harzianum durante o micoparasitismoMota, Paulo Roberto da 28 August 2015 (has links)
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Previous issue date: 2015-08-28 / Fungi of the genus Trichoderma have emerged as biological control agents,
especially those belonging to the species Trichoderma harzianum with various
mechanisms involved include production of antibiotics, mycoparasitism, competition
for nutrients and host plant resistance induction. Mycoparasitism is a sequential
process that involves recognition of the host contact, adhesion, expression of specific
genes and secretion of secondary metabolites. Several hydrolytic enzymes are
involved in this process among them chitinases, beta-glucanases and proteases.
Recent studies of T. harzianum interaction with some pathogens have shown that
other enzymes may also be involved in this mechanism, among which alphamannosidase.
Alpha-mannosidase has an essential role in the recycling of
glycoproteins in filamentous fungi, but little is known about the role of these enzymes
in mycoparasitism. This study aims to characterize the expression of T. alphamannosidase
gene harzianum after growth in cell wall of Sclerotinia sclerotiorum
(SS), Fusarium solani (FS) and Fusarium oxysporum (FO) as well as during the
interaction in vivo . It was used as a control cell wall T. harzianum (TH). Also, jobs
obtaining mutants of this gene in T. harzianum were performed. Our data show that
alpha-mannosidase gene was highly expressed as T. harzianum grown in the
presence of cell wall SS (4.5X), FS (18X) and FO (75X) compared to the control TH
(1X). In comparison situation it was noticed a 75X greater expression in TH x FO
state during contact as compared with the control (TH x TH). In other situations of
confrontation did not observe a significant increase in expression. The promoter
region, the selection mark and the terminator region of the alpha-mannosidase of T.
harzianum gene was cloned into the pRS426 vector, and the deletion cassette was
assembled by the recombination technique in Saccharomyces cerevisiae. Then,
these vectors were used for transformation of T. harzianum and transformants were
obtained by selection on plates containing hygromycin b. Approximately 50
transformants were obtained, but none of the alpha-mannosidase gene was
successfully deleted. Obtaining more transformants is necessary for us to have a
mutant alpha-mannosidase gene deleted. / Fungos do gênero Trichoderma têm se destacado como agentes de controle
biológico, principalmente aqueles pertencentes à espécie Trichoderma
harzianumcom vários mecanismos envolvidos incluem produção de antibióticos,
micoparasitismo, competição por nutrientes e indução de resistência da planta
hospedeira. Micoparasitismo é um processo sequencial que envolve reconhecimento
do hospedeiro, contato, adesão, expressão de genes específicos e secreção de
metabólitos secundários. Várias enzimas hidrolíticas estão envolvidas neste
processo dentre elas quitinases, beta-glucanases e proteases. Estudos recentes de
interação de T. harzianum com alguns fitopatógenos tem demonstrado que outras
enzimas podem também estar envolvidas neste mecanismo, dentre elas as alfamanosidases.
As alfa-manosidases tem um papel fundamental na reciclagem de
glicoproteínas em fungos filamentosos, mas pouco se sabe sobre o papel destas
enzimas no micoparasitismo. Este trabalho tem como objetivo a caracterização da
expressão do gene de alfa-manosidase de T. harzianumapós crescimento em
parede celular de Sclerotinia sclerotiorum (SS), Fusarium solani (FS) e Fusarium
oxysporum (FO), bem como durante a interação in vivo. Como controle foi utilizado
parede celular de T. harzianum (TH). Além disto, trabalhos de obtenção de mutantes
deste gene em T. harzianum foram realizados. Nossos dados mostraram que o gene
de alfa-manosidase foi altamente expresso quando T. harzianum cresceu na
presença de parede celular de SS (4.5X), FS (18X) e FO (75X) quando comparado
com o controle TH (1X). Em situação de confronto foi observado uma expressão de
75X maior na situação TH x FO durante o contato, quando comparado com o
controle (TH x TH). Na outras situações de confronto não observamos um aumento
significativo de expressão. A região promotora, a marca de seleção e a região
terminadora do gene da alfa-manosidase de T. harzianumfoi clonado no vetor
pRS426 e o cassete de deleção foi montado através da técnica de recombinação em
Saccharomyces cerevisiae . Em seguida, estes vetores foram utilizados para a
transformação de T. harzianume os transformantes foram obtidos por seleção em
placas contendo higromicina b. Aproximadamente 50 transformantes foram obtidos,
mas em nenhum deles o gene da alfa-manosidase foi deletado com sucesso. A
obtenção de mais transformantes se faz necessário para que possamos ter um
mutante com o gene da alfa-manosidase deletado.
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Biological Warfare Against CropsWhitby, Simon M. January 2001 (has links)
Until now little attention has been paid to the development of military capabilities designed to target food crops with biological warfare agents. This book represents the first substantive study of state-run activities in this field. It shows that all biological warfare programmes have included a component concerned with the development of anti-crop biological warfare agents and munitions. Current concern over the proliferation of biological weapons is placed in the context of the initiative to strengthen the Biological and Toxin Weapons Convention. The book concludes by arguing that the risks posed by this form of warfare can be minimised, but that this would depend largely on the effective and efficient implementation of regimes concerning the peaceful use and control of plant pathogens that pose a risk to human health and the environment.
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Epidemiologia e controle com radiação gama de doenças pós-colheita do mamãoLOPES, Albaneyde Leite 20 March 2009 (has links)
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Previous issue date: 2009-03-20 / Papaya rot resulting from fungal infections causes high post-harvest losses. The influence of temperature (5, 10, 15, 20, 25, 30 and 35 oC) and wetting period (0, 12, 24, 36, 48, 60 and 72 h) in the incidence and severity of post-harvest rot in papaya caused by Alteraria alternata, Cladosporium herbarum, Colletotrichum gloeosporioides, Fusarium verticillioides, Geotrichum candidum and Lasiodiplodia theobromae, and their influence on physicochemical characteristics . The temperature significantly influenced the incidence and severity of rot. There was a higher incidence and severity in fruits incubated in the range of 25 to 35 ºC. The temperature in the range of 5 to 10 ºC did not allow the development of A. alternata, C. herbarum, C. gloeosporioides and L. theobromae. Analyzes of pH, titratable total acidity (TTA) and total soluble solid (TSS) showed no significant differences when compared to the control. A second experiment was carried out to verify the possibility of control through the use of gamma radiation (0, 0.6, 0.8, 1.0, 1.2, 1.4, 1.8, 2.4 And 2.8 kGy), with Cobalt 60 as a source. The parameters evaluated were: comic growth, sporulation, pathogenicity of fungi after irradiation and the physicochemical characteristics of papaya. For C. herbarum and F. verticillioides a decrease in mycelial growth occurred as the doses were increased. However, C. gloeosporioides and L. theobromae at doses of 0.6 to 1.4 kGy and G. candidum at doses of 1.4 to 2.2 kGy were more efficient in reducing the mycelial growth of these fungi. However, all the doses used stimulated the mycelial growth of A. alternata. The results demonstrated that in general, as the doses increased, there was a reduction in the number of conidia. Regarding the effect of radiation on the pathogenicity of fungal species, only L. theobromae at the doses tested, did not lose pathogenicity in relation to the other fungi. The physico-chemical characteristics of the fruits subjected to radiation did not compromise the commercialization and consumption 'in natura'. / As podridões em mamão resultantes de infecções de fungos causam perdas elevadas em pós-colheita. Diante da necessidade do conhecimento de fatores ambientais que favorecem a infecção por esses agentes, foi avaliada a influência da temperatura (5, 10, 15, 20, 25, 30 e 35 oC), e período de molhamento (0, 12, 24, 36, 48, 60 e 72 h) na incidência e severidade de podridões pós-colheita em mamão causada por Alteraria alternata, Cladosporium herbarum, Colletotrichum gloeosporioides, Fusarium verticillioides, Geotrichum candidum e Lasiodiplodia theobromae, e a influência desses sobre as características físico-químicas. A temperatura influenciou significativamente a incidência e a severidade de podridões. Ocorreu maior incidência e severidade em frutas incubadas na faixa em torno de 25 a 35 ºC. A temperatura na faixa de 5 a 10 ºC não permitiu o desenvolvimento de A. alternata, C. herbarum, C. gloeosporioides e L. theobromae. Análises de pH, acidez total titulável (ATT) e sólido solúvel total (SST) não apresentaram diferenças significativas quando comparados com a testemunha. Um segundo experimento foi realizado com o objetivo de verificar a possibilidade de controle através do uso da radiação gama (0; 0,6; 0,8; 1,0; 1,2; 1,4; 1,8; 2,4 e 2,8 kGy), tendo como fonte o Cobalto 60. Os parâmetros avaliados foram: crescimentomicelial, esporulação, patogenicidade dos fungos após irradiação e as características físico-químicas do mamão. Para C. herbarum e F. verticillioides ocorreu uma diminuição do crescimento micelial à medida que se aumentaram as doses. Já o C. gloeosporioides e L. theobromae nas doses de 0,6 a 1,4 kGy, e G. candidum nas doses de 1,4 a 2,2 kGy foram mais eficientes na redução do crescimento micelial destes fungos. Entretanto, todas as doses utilizadas estimularam o crescimento micelial de A. alternata. Os resultados demonstraram que, de modo geral, à medida que as doses foram aumentando, houve uma redução no número de conídios. Em relação ao efeito da radiação sobre a patogenicidade das espécies fúngicas, apenas L. theobromae nas doses testadas, não perdeu a patogenicidade em relação aos demais fungos. As características físico-químicas das frutas submetidas à radiação não comprometeram a comercialização e o consumo ‘in natura’.
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Ekologie patosystému Vinca minor - Puccinia cribrata v přirozených populacích / Ecology of the pathosystem Vinca minor - Puccinia cribrata in natural populationsVaníček, Jiří January 2019 (has links)
5 Absctract Environment and demographic characteristics of host population are important factors affecting incidence and severity of plant diseases. The aim of this study was to reveal possible effects of microclimatic and edaphic characteristics and host population demographic factors on the biotrophic pathogen Puccinia cribrata, microcyclic rust parasitising clonal evergreen plant Vinca minor. I studied the ecology of this pathosystem in natural populations of V. minor in the Soča valley in the Julian Alps in Slovenia. Rugged terrain of the Soča valley with different bedrocks allowed to study pathogen distribution at topographically diverse forest and scrub sites, greatly differing in soil depth and canopy structure. P. cribrata was significantly more likely to occur in the themophilous forest with shallow calcareous soils and open canopy than in the mesophilous forest types. Its prevalence (proportion of diseased stems in population) was also highest in this type of vegetation. Most important host population factors were population size and population density positively affecting incidence and prevalence respectively. Additionally, I tested various vegetation and topographic indexes derived from remote sensing for usability in prediction models. It appears that vegetation indexes connected with canopy...
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Écologie des Oomycètes et champignons phytopathogènes dans les sols de forêt de Guyane Française : éclairages sur les relations entre communautés de Phytophthora et d’arbres dans les forêts tropicales / Ecologie of Oomycetes and phytopathogenic Fungi in French Guianan forest soils : focus on the relations between Phytophthora and tree communities in tropical forestsLegeay, Jean 21 June 2019 (has links)
Les mécanismes expliquant le maintien de la diversité végétale dans les forêts tropicales sont mal connus. Une hypothèse particulièrement étudiée est l’hypothèse Janzen-Connell qui postule que ces mécanismes sont essentiellement causés par les interactions entre les plantes et leurs ennemis naturels, en particulier les organismes pathogènes. Dans cette thèse, nous nous sommes donc intéressés aux agents pathogènes présents dans les sols d’une forêt guyanaise et à leur lien de spécificité avec les plantes. Dans le cas où l’hypothèse Janzen-Connell serait vérifiée, on peut s’attendre à ce que les plantes structurent les communautés de micro-organismes pathogènes. Nos travaux se sont focalisés sur les Oomycètes et en particulier les Phytophthora, pathogènes des arbres très importants, mais nous nous sommes aussi intéressés aux champignons pathogènes. Ainsi, nous avons développé et comparé des jeux d’amorces PCR spécifiques des Phytophthora et des Péronosporomycètes afin d’étudier ces organismes par metabarcoding. Ces amorces ont ensuite servi à étudier la diversité des communautés de Phytophthora dans des échantillons de sols de deux sites forestiers de Guyane Française prélevés au pied d’arbres appartenant à 10 familles végétales. Une faible diversité a été retrouvée, avec seulement 8 taxons en tout, et la très large dominance d’un complexe d’espèces Phytophthora heveae. La structuration par la plante-hôte de ces communautés est plutôt faible. Dans une étude complémentaire, nous avons analysé la diversité des Oomycètes et des champignons pathogènes dans les sols et les litières de six plantations monospécifiques et au sein d’une forêt naturelle de Guyane. La structuration par l’hôte s’est avérée nulle pour les Oomycètes et faible pour les champignons pathogènes. Enfin, nous n’avons pas réussi à déclencher expérimentalement des mortalités ou dépérissements par des Oomycètes sur le wacapou, une espèce d’arbre guyanaise, via des inoculations de sols de forêt. Au final, les résultats de cette thèse ne supportent pas l’hypothèse selon laquelle les Oomycètes seraient d’importants acteurs du maintien de la diversité végétale dans les forêts tropicales. Par ailleurs, ils nous interrogent sur la faible diversité de ce groupe de microorganismes dans les sols et litières dans un hotspot de diversité végétale. / The mecanisms implied in the maintenance of plant diversity in tropical forests are still poorly known. One particularly studied hypothesis is the Janzen-Connell hypothesis, which posits that these mecanisms are essentially caused by the interactions between plant and their natural enemies, including pathogenic organisms. In this thesis, we looked at the pathogenic organisms present in the soils of a Guyanese forest, and the specificity of their interactions withplants. In the case where the Janzen-Connell hypothesis would be verified, we could expect that pathogenic micro-organisms communities would be structured by plants. Our works focused on Oomycetes and especially the Phytophthora, which are very important pathogens of trees, but we also took an interest on pathogenic Fungi. Thus, we developed PCR primer sets specific of the Phytophthora and Peronosporomycete groups, in order to study these organismsthroughmetabarcoding. These primers were then used to investigate the community of Phytophthora in soils sampled from two French Guiana sites, near trees belonging to 10 families. A low diversity was described, with a total of only 8 taxas, and the overwhelming dominance of the species complex P. heveae. A weak host effect was detected. In a complementary study, we looked at the diversity of Oomycetes and Fungi in soils and litters of six monospecific tree plantations and a Guianese natural forest. Structuration by host appeared to be null for Oomycetes and weak for pathogenic Fungi. Finally, we did not success in trying to experimentally provoke, through forest soil inoculations, Janzen-Connell mortalities due to Oomycetes on the Wacapou, a Guianese tree species. In the end, the results of this thesis do not support the hypothesis that Oomycetes may be important agents of the maintenance of tree diversity in tropical forests. Moreover, they bring some questions about the low diversity of this group of micro-organisms in a tree diversity hotspot.
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Nutritional water productivity of hot chilli (capsicum annuum) under infection with meloidogyne javanica and meloidogyne incognitarace 2Ramputla, Mogwale Janet January 2019 (has links)
Thesis (M.Sc. Agriculture (Soil Science)) -- University of Limpopo, 2019 / Nutritional water productivity (NWP) is an assessment tool, which describes the
amount of water that has been used to produce selected mineral malnutrition (MMN)
elements and micronutrient malnutrition (MNMN) substances. Therefore, it links
agricultural production to human nutrition. Deficiencies in MMN elements and/or
MNMN substances in human nutrition referred to as malnutrition, had been linked
with fatal diseases. Agricultural soils could be affected by soil-borne pathogens such
as plant-parasitic nematodes, which could limit the availability of MMN elements and
MNMN substances. In some communities, vegetable crops, including chilli are
regarded as a major source of MMN elements and MNMN substances. Effects of
root-knot (Meloidogyne species) nematodes on NWP of chilli (Capsicum annuum L.)
have not been documented. The objective of the study was to determine the effects
of increasing population densities of M. incognita race 2 and M. javanica on the NWP
of hot chilli plants. A microplot trial was conducted at the Green Biotechnologies
Research Centre of Excellence (GBRCE), University of Limpopo, South Africa. Pots
were filled with 10-L steam-pasteurised (300oC) sandy clay loam soil sourced from
GBRCE and Hygromix-T (Hygrotech, Pretoria North) growth medium in the ratio 3:1
(v/v). Thereafter, three-week-old hot chilli cv. 'Serrano' seedlings were transplanted
into each pot, with inoculum prepared by extracting eggs and second-stage juveniles
(J2) of M. incognita race 2 and M. javanica from roots of grown nematode
susceptible tomato cv. 'Floradade' (Solanum lycopersicum L.) in a 1% NaOCl
solution. Fourteen days after transplanting, treatments 0, 50, 125, 250, 625, 1250
and 2000 eggs and second-stage juveniles (J2) of M. incognita race 2 and M.
javanica were separately inoculated using a 20 ml plastic syringe into 5-cm-deep
holes in pots. At 56 days after the initiation of the treatments, Meloidogyne species
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decreased soil pH and increased organic carbon, contributing 29 and 43% in total
treatment variation (TTV) of the respective variables. Treatment effects caused the
pH to decrease. NWP variables against increasing nematode numbers exhibited
quadratic relations, with coefficients of determination ranging from 59 to 86% for M.
incognita race 2 trial and 80 to 98% for M. javanica trial. Meloidogyne species
population densities against plant variables did not show any significant relationship,
except for root galling and chlorophyll content where treatments contributed 76, 98
and 47% TTV of the respective variables. Generally, root galling increased with
increase in Meloidogyne species population densities, whereas chlorophyll content
decreased with increasing inoculum levels. Nematode variables against their
increasing population exhibited quadratic relationship with the model explained by 44
to 95% for M. incognita race 2 and 28 to 82%, association, respectively for M.
javanica. In conclusion, Meloidogyne species interfered with NWP of mineral
elements in chilli plant and therefore, nematode management practices should be
done to reduce the nematode population densities that would confer quality to
agricultural produce for human health benefits.
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Quality assessment of agricultural water used for fertigation in the Boland districtMgcoyi, Bulelani William January 2011 (has links)
Thesis (M. Tech. (Agriculture)) -- Central University of Technology, Free state, 2011 / Quality assessment of agricultural water used for fertigation in the Boland district. The study was undertaken to determine the influence of seasonal changes on the water quality (chemical and microbial analyses) of five different rivers in the Boland. The data was collected in the five most important water sources that are used for irrigation purposes in the district, i.e. Berg river, Eerste river, Klapmuts River, Klippies river and Krom river. The samples were collected from all sites once every three weeks for a period of six months. The sampling was carried out during specific periods in summer (December, 2006 to February, 2007) and winter (June to August, 2007). The results of the study showed that Klapmuts river recorded the highest levels of chloride and iron, especially in summer. However, chloride levels were far below the levels set by the Department of Water Affairs and Forestry. Results obtained from this study show the presence of pathogens in some of the rivers assessed which may have resulted from the leaching of these pathogens from nearby agricultural land, livestock watering or informal settlements in the catchment areas.
The bigger rivers recorded low levels of micro-elements and this might have been affected by winter rainfall. In the Berg River, many sources of nitrate pollution seem to be present in the catchment area. The levels of iron in all the rivers assessed were far more than the levels set by the Department of Water Affairs and Forestry in all rivers assessed and these might be due to the pH levels and interaction between the rivers and seasons. Iron and manganese levels should be kept low as this may cause production problems by blocking irrigation drippers.
The water samples tested for bacterial and fungal density showed Klapmuts and Eerste rivers were positive for Phytophthora cinnamomi during winter. Phytophthora citricola and Phytophthora cactorum were detected in the Klapmuts and Klippies rivers in summer. The Berg-, Klapmuts-, Krom- and Eerste rivers tested positive for species of the genera Pythium and Fusarium. Similar organisms were detected in the Eerste river mainly during summer on the fourth sampling date, while Krom river only tested positive for Pythium during summer. The total bacterial and algal density differed significantly between the seasons and was highest in winter. This might be due to high rain water influx and efflux and/or moist and aerobic conditions and air temperature. There is an increased need for farmers to sterilize feeding water (chlorination) due to high microbial count.
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