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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Mecanismos de controle de tolerância à dissecação em sementes de Caesalpinia echinata LAM. (Pau-Brasil) e Caesalpinia peltophoroides BENTH. (Sibipiruna) /

Silva, Joao Paulo Naldi. January 2010 (has links)
Orientador: Claudio José Barbedo / Banca: Jose Maria Rocha Faria / Banca: João Rodrigues Domingos / Resumo: A aquisição da tolerância à dessecação ocorre durante a maturação da semente, após acúmulo de reservas e antes do início do processo natural de secagem, porém, com o avanço da germinação a sensibilidade a dessecação aumenta. Estresses hídricos podem induzir ou restabelecer a tolerância à dessecação em sementes, porém, não se sabe em quais processos ele atua, como na ativação de genes. O objetivo deste trabalho foi avaliar a aquisição e perda de tolerância à dessecação em sementes de Caesalpinia echinata Lam. (pau-brasil), e a possibilidade de indução deste processo avaliando as modificações nos carboidratos solúveis e de ciclitóis, nos níveis endógenos de ABA e na expressão de aquaporinas. Foram observadas diferenças na aquisição de tolerância em sementes imaturas de mesma idade, produzidas nas mesmas matrizes em 2007 e 2008, com diferentes composições de carboidratos solúveis. Sementes maduras perdem a tolerância à dessecação logo após protrusão da raiz primária, em comprimentos dependentes do grau de deterioração da semente. Sementes imaturas e maduras tolerantes de C. echinata suportaram a desidratação de formas diferentes, utilizando reservas de amido e ciclitóis, com papel da sacarose quando secas. Esses resultados foram comparados com sementes de Caesalpinia peltophoroides Benth (sibipiruna), demonstrando comportamentos fisiológicos distintos, provavelmente relacionados com o tipo de reserva que acumulam / Abstract: The acquisition of desiccation tolerance occurs during seed maturation, after reserves accumulation and before the natural process of drying, however, with seed germination the desiccation sensitivity increases. Water stress can induce or restore the desiccation tolerance in seeds, but it is unclear what processes it acts, like activation of genes. The objective of this work was to evaluate the acquisition and loss of desiccation tolerance in Caesalpinia echinata Lam (brazil-wood) seeds, and the possibility to induction this process, evaluating the soluble carbohydrates and cyclitols changes, the ABA endogenous levels and expression of aquaporins. Differences were observed in the tolerance acquisition in immature seeds of the same age, produced by the same trees in 2007 and 2008, showing different compositions of soluble carbohydrates. Mature seeds lose desiccation tolerance soon after radicle protrusion in length depending on the degree of seed deterioration lot. Immature and mature tolerant seeds of C. echinata support the dehydration by different ways, using starch reserves and cyclitols, seen sucrose when the seed dry. These results were compared with seeds of Caesalpinia peltophoroides (sibipiruna), showing different physiological parameters, probably related to the type of reserves that they accumulate / Mestre
22

Optimising the Postharvest Management Of Lychee (Litchi chinensis Sonn.) � A Study of Mechanical Injury and Desiccation

Bryant, Philippa January 2004 (has links)
The major objective of the research was to improve lychee postharvest management, through a greater understanding of mechanical injury and moisture loss. Mechanical injury is a known cause of postharvest loss in lychee, but previously published information has been limited to broad observations. In this study, the symptoms of mechanical damage in lychee were defined, including quantitative measurement of colour changes. Impact injury caused protuberance tip darkening, cracking of the pericarp and significant changes in skin colour. Compression also typically caused tip darkening, and severe loads were capable of puncture, shape distortion and skin cracking. Abrasion and vibration injuries were characterised by strong yellowing of pericarp colour, possibly due to the leakage of cell contents onto the fruit surface. Vibration also caused significant darkening and loss of colour saturation. Vibration has not previously been mentioned as an issue in lychee postharvest management, but appeared to be as important a problem as desiccation browning at the wholesale level, both in incidence and severity. Mechanically damaged fruit consistently showed increased ethylene and carbon dioxide synthesis, and moisture loss was increased by up to 30%. Some significant changes in skin biochemistry and cuticle properties were also detected. The study of damaged tissue by SEM revealed distinctive patterns of surface tissue disruption. Open pericarp cracking was a particularly detrimental injury, causing significantly increased electrolyte leakage and rapid pathogen development. The effects of load characteristics, such as magnitude, method of application, site, repetition and cushioning, on the extent of damage were defined. Fruit characteristics such as cultivar, gross morphology, temperature, hydration and surface wetness were shown to significantly affect damage levels. Small seed size was correlated with increased cracking susceptibility. Fruit surface wetness exacerbated vibration or abrasion damage. Turgid fruit were less susceptible to vibration and abrasion damage, but showed increased susceptibility to impact cracking. Previously neglected aspects of desiccation browning research were studied, including cultivar and maturity effects, sites of moisture loss and the role of air currents. Cultivar effects on moisture loss were obscured by pre-harvest factors, but consistent cultivar differences were detected in desiccation browning, possibly related to skin thickness. In contrast, maturity levels over a marketable range had little effect on weight loss or browning. Moisture was lost fairly evenly over the fruit surface, but poor postharvest handling appeared to massively increase loss from the protuberance tips. Moisture loss was shown to substantially increase ethylene synthesis. The crucial role of air currents in exacerbating lychee moisture loss was emphasised, and the relationship between air speed and weight loss was defined. The research contributed to a greater understanding of the processes of mechanical damage and moisture loss in lychee, leading to improved protocols for the postharvest management of the fruit. Improved management of mechanical damage and moisture loss will ultimately improve fruit quality and reduce postharvest losses, hence increasing returns to industry.
23

The effects of temperature and humidity on the eggs of Aedes aegypti (L.) and Aedes albopictus (Skuse) in Texas

Dickerson, Catherine Zindler 15 May 2009 (has links)
Causative influences that impact the separation of Ae. aegypti and Ae. albopictus populations in different geographic areas were determined, as well as how they are affected by the abiotic conditions as seen in the habitats they frequent in Texas. The eggs of Ae. albopictus and Ae. aegypti collected from McAllen and Brownsville, Texas, and laboratory populations of these two species were subjected to 25 different temperature and relative humidity conditions for up to three months. In most treatments, Ae. aegypti eggs had a greater percent hatch than Ae. albopictus, regardless of temperature or relative humidity. With an increase in relative humidity, the percent hatch for both species increased, but at the higher temperatures of 32° and 35°C the amount of time the eggs were exposed to those temperatures had a greater negative effect on the percent hatch than did the positive effect of increase in relative humidity. The surface area, volume and surface-area-to-volume ratio of Ae. aegypti and Ae. albopictus eggs with and without the chorionic egg pad, and the size of the chorionic egg pad were calculated for fifty eggs of each species of mosquito from populations collected in McAllen and Brownsville and from the laboratory populations. Ae. aegypti had a larger egg volume, and a larger surface area; but, it is likely their larger egg pad compensates for this high surface-area-to-volume ratio by holding moisture along the egg’s surface and that the egg pad is associated with the high desiccation resistance seen in Ae. aegypti eggs. Development rates for both species of mosquitoes from populations collected in Galveston and Brownsville, Texas, and laboratory populations were produced by measuring the development time from a hatched egg to the adult at seven temperatures. The temperature optima (28°-33°C) were similar for all populations; however, the rate of development for Ae. aegypti was significantly faster at the temperature optima. It is likely that this faster development rate in the Ae. aegypti population helps to maintain a population in climates that have this range of temperatures given that Ae. albopictus is a superior competitor in the larval and adult stages.
24

Desiccation Survival of Listeria monocytogenes in Mixed Biofilms with Pseudomonas fluorescens, Serratia liquefaciens and Shewanella putrefaciens

Daneshvar Alavi, Hessam Edin 28 November 2012 (has links)
Listeria monocytogenes has been found to withstand harsh environmental conditions including desiccation. The pathogen is also known to form biofilm when in co-culture with other bacteria found in food products. This study investigated the desiccation survival of L. monocytogenes in mixed biofilms with Pseudomonas fluorescens, Serratia liquefaciens and Shewanella putrefaciens. To this end, mono- or binary species biofilms were formed and desiccated (43% relative humidity, 21 days at 15°C) on stainless steel coupons and the double Weibull model was fitted to the resulting survivor curves. The presence of the competitor Gram-negative food spoilage bacteria with the exception of Sh. putrefaciens suppressed (p<0.05) L. monocytogenes during biofilm formation (100% relative humidity, 15°C and 48 h) and subsequently decreased (P<0.05) the desiccation survival in L. monocytogenes without affecting the resistance of individual cells. Microscopic approaches revealed different biofilm forming capabilities in the mono- and binary bacterial combinations.
25

Cotton Leaf Grade as Influenced by Harvest Aid Regimes and Cultivar Characteristics

Eder, Zachary Phillip 16 December 2013 (has links)
Cotton, Gossypium hirsutum L., leaf grade values can significantly increase with remnants of leaf and bract materials, and can result in increased ginning costs and discounts to the producer. Cotton classed through the USDA-AMS Classing Office in Corpus Christi, Texas has reported increases in leaf grade values beginning in 2000 (USDA, 2012). The impacts of the interaction of agronomic characteristics of cotton cultivars with those of various harvest aid regimes were studied over three growing seasons, and data were used to narrow possible contributors to the observed increased leaf grade values. Multiple trials were conducted throughout the Coastal Bend and Blackland Prairie of Texas, in addition to Tifton, Georgia. Cotton was harvested, lint samples were ginned in a microgin, and lint quality was quantified with HVI. Harvest aid regimes selected provided a broad range of defoliation and desiccation, from a multiple herbicidal and hormonal modes-of-action. Defoliation levels ranged from 0 to 96% and desiccation levels ranged from 0 to 90%. Harvest aid treatments had no impact (P≤0.05) on leaf grade values for either of the years of the trials. Multiple trials were conducted in five counties in Texas, including the Lower and Upper Coastal Bend and the Blackland Prairie, and were defoliated with a uniform harvest aid treatment to identify leaf and bract morphological differences, and to determine their role in leaf grade. Multi-acre module trials were conducted with a smooth leaf cultivar and a hairy leaf cultivar to obtain leaf grade values following commercial ginning. Leaf and bract pubescence, and leaf and bract area were collected to analyze the resulting impact on cotton leaf grade values. Visual quantification of leaf and bract trichome density was quantified on 10 youngest fully-expanded leaves and 10 mid-canopy full sized bolls, respectively, when cotton was at physiological cut-out. Trichome density quantification indicated substantial variation in cultivars and discrepancies from company based rating systems. Leaf grades values generally increased with increasing trichomes densities, although not always statistically significant. In the split plot cultivar and harvest aid trial, harvest aid efficacy was similar for each of the cultivars, but cultivar trichome density was positively influence the cotton leaf grade value.
26

Effect of Desiccation Cracks on Earth Embankments

Khandelwal, Siddharth 02 October 2013 (has links)
Levees are earth structures used for flood protection. Due to their easy availability and low permeability, clays are the most common material used for the construction of levees. Clays are susceptible to desiccation cracks when subjected to long dry spells during summers. There has been an increased interest in studying the occurrence of cracks in soil mass. In particular, many experimental investigations for soils have been undertaken to learn about the crack pattern in earth embankment. However, there is a dearth of work that focuses on the numerical modeling of desiccation cracks effects on levees. This study has been undertaken to analyze the effect of desiccation cracking on the hydraulic behavior of an earth embankment under flooding conditions. A numerical model was developed using the finite element package CODE_BRIGHT. The model was validated from the data obtained from a small scale embankment experiment under controlled environmental conditions. As the phenomenon of desiccation cracking is highly random, a simple random model was developed to capture the variability in crack geometry. The random crack geometry was then passed on to the finite element mesh, so that a probabilistic analysis can be carried out using a Monte Carlo approach, for assessing the embankment’s integrity. The results obtained from the analysis such as time to steady state saturation and steady state flow rate at the outward slope were very interesting to study and provided an insight on the effect of desiccation cracks on unsaturated earth embankments.
27

Optimising the Postharvest Management Of Lychee (Litchi chinensis Sonn.) � A Study of Mechanical Injury and Desiccation

Bryant, Philippa January 2004 (has links)
The major objective of the research was to improve lychee postharvest management, through a greater understanding of mechanical injury and moisture loss. Mechanical injury is a known cause of postharvest loss in lychee, but previously published information has been limited to broad observations. In this study, the symptoms of mechanical damage in lychee were defined, including quantitative measurement of colour changes. Impact injury caused protuberance tip darkening, cracking of the pericarp and significant changes in skin colour. Compression also typically caused tip darkening, and severe loads were capable of puncture, shape distortion and skin cracking. Abrasion and vibration injuries were characterised by strong yellowing of pericarp colour, possibly due to the leakage of cell contents onto the fruit surface. Vibration also caused significant darkening and loss of colour saturation. Vibration has not previously been mentioned as an issue in lychee postharvest management, but appeared to be as important a problem as desiccation browning at the wholesale level, both in incidence and severity. Mechanically damaged fruit consistently showed increased ethylene and carbon dioxide synthesis, and moisture loss was increased by up to 30%. Some significant changes in skin biochemistry and cuticle properties were also detected. The study of damaged tissue by SEM revealed distinctive patterns of surface tissue disruption. Open pericarp cracking was a particularly detrimental injury, causing significantly increased electrolyte leakage and rapid pathogen development. The effects of load characteristics, such as magnitude, method of application, site, repetition and cushioning, on the extent of damage were defined. Fruit characteristics such as cultivar, gross morphology, temperature, hydration and surface wetness were shown to significantly affect damage levels. Small seed size was correlated with increased cracking susceptibility. Fruit surface wetness exacerbated vibration or abrasion damage. Turgid fruit were less susceptible to vibration and abrasion damage, but showed increased susceptibility to impact cracking. Previously neglected aspects of desiccation browning research were studied, including cultivar and maturity effects, sites of moisture loss and the role of air currents. Cultivar effects on moisture loss were obscured by pre-harvest factors, but consistent cultivar differences were detected in desiccation browning, possibly related to skin thickness. In contrast, maturity levels over a marketable range had little effect on weight loss or browning. Moisture was lost fairly evenly over the fruit surface, but poor postharvest handling appeared to massively increase loss from the protuberance tips. Moisture loss was shown to substantially increase ethylene synthesis. The crucial role of air currents in exacerbating lychee moisture loss was emphasised, and the relationship between air speed and weight loss was defined. The research contributed to a greater understanding of the processes of mechanical damage and moisture loss in lychee, leading to improved protocols for the postharvest management of the fruit. Improved management of mechanical damage and moisture loss will ultimately improve fruit quality and reduce postharvest losses, hence increasing returns to industry.
28

Vliv odstupu sklizně od ukončení vegetace na výskyt vločkovitosti hlíz brambor / Effect of harvest interval from the end of the vegetation potato on the occurrance Rhizoctonia cancer

ZENÁHLÍK, David January 2014 (has links)
The thesis on the topic of the influence of the time period distance of the harvest from the end of the vegetation on the occurrence of "potato fenkines on the bulbs." There were 11 varieties of the potatoes chosen for the observation. Their vegetation was terminated by the desication resource called Reglone. From the end of the terminated vegetation during 10 days until the harvest there were 4 samples taken and they were evaluated on the occurrence and it's percentage of the "potato flakiness on the bulbs" in accordance with the scale of Wenzel and Demel (1976). There were there varietes selected for the evaluation; Flavia (VR), Riviera (VR), Rosara (VR), Merida (R), Adéla (R), the Baccara (R), Marabel (R), Ditta (PR), Laura (PR), Maréna (PP) and Saturn (PP). The achieved results of the "potato flakiness" weere evalunted statistically. The aim of the evlution of the ("potato flakiness on their bulls") Rhizoctonia solani. The term of the vegetation termination depends on the grover and must be in written documentation. The harvest alome can follow after the the drawal period in the desiccation resource, which uswally 15 days. The results indicale that whem the harvest of the potatoes is made at the proper time after the termination of the vegetation, the potato bulls are withhout any largen percentage accurence of the "flakiness". The results achieved during the years 2012 and 2013 indicate that in early implementation off all the working operations important for the potato growing, which begin with sorting out, followed by plantig, care, chemical sprays, selection, parades, desiccation and the harvest, the "flakiness" dinďt exceed 5% of the occurence. Another results indicate that the taken bulls were undamaged and the difference of the occurrence of the "flakiness"on each sample appeared in a variety of ways. The years of abseving the experiment proved that there was an increase in the "flakiness" on the surface for a given time period.
29

Tolerância à dissecação e armazenamento de sementes de Araticum-de-terra-fria (Annona emarginata) (SCHLTDL.) H. Rainer)

Corsato, Jaqueline Malaguti [UNESP] 22 February 2010 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:25:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-02-22Bitstream added on 2014-06-13T19:12:31Z : No. of bitstreams: 1 corsato_jm_me_botib.pdf: 479238 bytes, checksum: f0cb01da3cfdcc3e0d0cdcc7f0091f97 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho foi realizado no Departamento de Botânica, Instituto de Biociências – UNESP, Campus de Botucatu, e teve como objetivo avaliar a tolerância à dessecação de sementes de araticum-de-terra-fria (Annona emarginata (Schldtl.) H. Rainer), os açúcares envolvidos no processo e o efeito de GA4+7 N- (fenilmetil)-aminopurina na germinação das sementes submetidas aos níveis de secagem e além de avaliar o comportamento fisiológico das sementes após armazenadas no fruto (repouso pós-colheita). Foram instalados dois experimentos em delineamento inteiramente casualizado, com quatro repetições de 25 sementes por parcela. No primeiro As sementes foram secas em estufa de circulação forçada de ar (50°C) obtendo-se níveis de água de: 31% testemunha, 19%, 12% e 5%. Após secagem, as sementes foram embebidas em GA4+7 N-(fenilmetil)-aminopurina (0, 250, 500, 750 e 1000 mg L-1) por 60 horas. Já O segundo experimento foi divido em duas etapas. Na primeira os frutos maduros foram armazenados a 5°C pelo período de 0, 7, 14, 21 e 28 dias. Após armazenamento as sementes foram colocadas para embeber em água destilada e em solução de GA4+7 N-(fenilmetil)-aminopurina (800 mg L-1 ) por 60 horas. Na segunda etapa, as sementes foram armazenadas em sacos de papel tipo Kraft, envoltas por um saco de polietileno e acondicionadas em câmaras de germinação nas temperaturas de 5°C, 15°C e 25°C, onde permaneceram armazenadas por 30, 60, 90, 120 e 150 dias sendo o tempo 0 a testemunha. Após armazenamento as sementes foram colocadas para embeber em água destilada e em solução de GA4+7 N-(fenilmetil)- aminopurina (800 mg L-1 ) por 60 horas. As variáveis analisadas foram: condutividade elétrica, porcentagem, tempo médio, índice de velocidade, freqüência e sincronização da germinação, porcentagem de sementes dormentes, porcentagem de plântulas normais, comprimento... / The present study was carried out at the Department of Botany, Institute of Biosciences – UNESP, Botucatu Campus, São Paulo State, Brazil, aimed to assess the tolerance to desiccation of “araticum-de-terra-fria” (Annona emarginata (Schldtl.) H. Rainer) seeds, the sugars involved in this process, the effect of GA4+7 + N- (phenylmethyl)-1H-purine-6-amine on the germination of seeds subjected to different desiccation levels, and the physiological behavior of seeds stored in the fruit (postharvest resting period) and after fruit extraction. Two experiments were carried out in completely randomized design, including 4 replicates of 25 seeds per plot. In the first one, seeds were drought in forced aeration oven (50°C) and the following water levels were obtained: 31% control, 19%, 12% and 5%. After desiccation, seeds were immersed in GA4+7 + N-(phenylmethyl)-1H-purine-6-amine (0, 250, 500, 750 and 1000 mg L-1) for 60h. The second experiment was divided into two steps: in the first one, mature fruits were stored at 5°C for 0, 7, 14, 21 and 28 days. Then, the fruits were manually pulped and the seeds were allowed to imbibe in distilled water and in GA4+7 + N- (phenylmethyl)-1H-purine-6-amine solution at the concentration of 800 mg L-1 for 60h. In the second step, the seeds were involved with polyethylene bags, placed inside Krafttype paper bags and stored in a germination chamber at 5°C, 15°C and 25°C for 30, 60, 90, 120 and 150 days; time 0 was adopted as control. Following storage, seeds were allowed to imbibe in distilled water and in GA4+7 + N-(phenylmethyl)-1H-purine-6- amine solution at the concentration of 800 mg L-1 for 60h. The evaluated variables were electrical conductivity; germination percentage, mean time, speed index, frequency and synchronization; percentage of dormant seeds; quantitative analysis of total and reducing soluble sugars; and sugar profile by using ... (Complete abstract click electronic access below)
30

Ecofisiologia da germinaÃÃo e do crescimento inicial de Piptadenia stipulacea (Benth.) Ducke E Anadenanthera colubrina (Vell.) Brenan / Ecophysiology germination and early growth of Piptadenia stipulacea (Benth.) Ducke and Anadenanthera colubrina (Vell.) Brenan

Wanessa Nepomuceno Ferreira 25 May 2011 (has links)
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Este estudo apresenta a hipÃtese de que P. stipulacea à uma espÃcie caracterÃstica de estÃgio inicial de sucessÃo, enquanto A. colubrina de estÃgios mais avanÃados. Para caracterizar as duas espÃcies, estudaram-se alguns atributos utilizados na classificaÃÃo de grupos ecolÃgicos de florestas tropicais Ãmidas, respondendo as seguintes questÃes: a) as espÃcies apresentam dormÃncia de sementes? b) quais as condiÃÃes de temperatura e luz para germinaÃÃo? c) as sementes apresentam tolerÃncia à dessecaÃÃo? d) quais as caracterÃsticas de crescimento das plÃntulas sob diferentes graus de irradiÃncia? Dessa forma, o trabalho apresentou as seguintes previsÃes: a) as sementes de P. stipulacea apresentam dormÃncia, enquanto as de A. colubrina nÃo apresentam; b) as sementes de P. stipulacea germinam em uma ampla faixa de temperatura, enquanto as de A. colubrina germinam em uma faixa de temperatura mais estreita; c) as sementes de P. stipulacea toleram baixos nÃveis de dessecaÃÃo, enquanto as de A. colubrina nÃo toleram; d) as plÃntulas de P. stipulacea crescem melhor em maiores nÃveis de irradiÃncia, enquanto as de A. colubrina crescem melhor em menores nÃveis de irradiÃncia. Os frutos foram coletados em Ãrea de caatinga situada na fazenda âNÃo Me Deixesâ, no municÃpio de QuixadÃ-CE, e os experimentos foram realizados no LaboratÃrio de AnÃlise de Sementes e no NÃcleo de Ensino e Pesquisa em Agricultura Urbana. Resultados do teste preliminar de germinaÃÃo mostraram que sementes de P. stipulacea apresentam dormÃncia, sendo melhor superada com escarificaÃÃo quÃmica por 10 minutos. Jà as sementes de A. colubrina nÃo possuem dormÃncia. O experimento de temperatura e luz revelou que as duas espÃcies apresentam a mesma amplitude de germinaÃÃo (10ÂC a 40ÂC), com melhor germinaÃÃo a 30ÂC, porÃm, nas menores temperaturas P. stipulacea apresentou germinaÃÃo muito baixa. Quanto à tolerÃncia a dessecaÃÃo, as sementes de P. stipulacea suportaram secagem atà 5,16% de umidade sem influenciar a germinaÃÃo, representando comportamento ortodoxo. Jà com A. colubrina a germinaÃÃo diminuiu à medida que as sementes perderam Ãgua, porÃm, mesmo com teor de Ãgua de 5,81%, a germinaÃÃo permaneceu acima de 80%, indicando que esta espÃcie tambÃm apresenta sementes ortodoxas. No experimento de irradiÃncia, plÃntulas de P. stipulacea apresentaram maior diÃmetro a pleno sol e, em todos os tratamentos, acumularam maior biomassa para o caule. A. colubrina apresentou maior altura e diÃmetro em 50% de sombra e maior nÃmero de folhas e biomassa da parte aÃrea em 70% de sombra, indicando que esta espÃcie tolera nÃveis intermediÃrios de sombra. Sugere-se que caracterÃsticas utilizadas na classificaÃÃo de grupos ecolÃgicos de florestas tropicais Ãmidas tambÃm possam ser utilizadas para subsidiar a identificaÃÃo de qual estÃgio sucessional pertencem determinadas espÃcies da caatinga, com o objetivo de entender sua ocorrÃncia, distribuiÃÃo e desenvolvimento, para melhor conservaÃÃo e uso adequado no reflorestamento de Ãreas degradadas. / This study presents the hypothesis that P. stipulacea is a species characteristic of early stages of succession, while A. colubrina in later stages. To characterize the two species studied are some attributes used in classification of ecological groups of tropical rainforests, answering the following questions: a) species have seed dormancy? b) what conditions of temperature and light for germination? c) the seeds are desiccation tolerance? d) the characteristics of seedling growth under different levels of irradiance? Thus, the work made the following predictions: a) seeds of P. stipulacea present dormancy, while those of A. colubrina not present; b) seeds of P. stipulacea germinate over a wide temperature range, while those of A. colubrina germinate in a narrow temperature range; c) the seeds of P. stipulacea tolerate low levels of desiccation, while those of A. colubrina not tolerate; d) seedlings of P. stipulacea grow best at higher irradiance levels, while those of A. colubrina grow best at lower levels of irradiance. Fruits were collected in the caatinga area located on the farm "NÃo Me Deixesâ city of Quixada-CE, and the experiments were performed at the Seed Analysis Laboratory and the Core Teaching and Research in Urban Agriculture. Results of preliminary testing of germination showed that seeds of P. stipulacea present dormancy and are better solved with chemical scarification for 10 minutes. The seeds of A. colubrina have no dormancy. The experiment temperature and light was revealed that the two species have the same range of germination (10ÂC to 40ÂC), with best germination at 30ÂC, but at lower temperatures P. stipulacea showed germination very low. As for tolerance to desiccation, seeds of P. stipulacea bore drying up 5.16% moisture without influencing germination, representing orthodox behavior. Already A. colubrina germination decreased as the seeds lost water, but even with a water content of 5.81%, germination remained above 80%, indicating that this species also has orthodox seeds. In the irradiance experiment, seedlings of P. stipulacea showed larger diameter in full sun, and all treatments accumulated more biomass to the stem. A. colubrina showed greater height and diameter in 50% shade and a larger number of leaves and shoot biomass by 70% shade, indicating that this species tolerates intermediate levels of shade. It is suggested that features used for classification of ecological groups of tropical forests could also be used to support the identification of which stage of succession belongs to certain species of caatinga, with the aim of understanding their occurrence, distribution and development, for better conservation and use suitable for the reforestation of degraded areas.

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