Premature and excessive leaf abscission during flowering time in the late avocado (Persea americana Mill.) cultivar ‘Ryan’ is a considerable problem for avocado growers. They are especially concerned that premature and excessive leaf abscission will have a negative effect on yield. No previous investigations have been performed where premature and excessive leaf abscission in avocado has been studied in detail. This study therefore aimed to investigate the pattern of premature and excessive leaf abscission in ‘Ryan’, and compare it with two other important commercial cultivars, ‘Fuerte’ and ‘Hass’, which do not display this phenomenon. Time course studies of leaf abscission in the orchard were performed during 2006 and 2007 to determine the pattern of leaf abscission on ‘Ryan’, Fuerte’ and ‘Hass’. This also included anatomical studies to determine the time of leaf abscission zone formation. Possible stress factors, which accelerate leaf abscission were also investigated, namely unfavourable climatic conditions (temperature, solar radiation, rainfall, relative humidity and evapotranspiration), nutrient imbalances, excessive flowering and leaf area. The possible impact leaf abscission may have on yield was then assessed by determining levels of reserve carbohydrates in the bark of the tree. In addition, practical solutions, i.e. the application of fertilizers, plant growth regulators (PGRs) and kaolin, were investigated in order to reduce or eliminate premature and excessive leaf abscission. This study was carried out over the period 2005 until 2007, with experiments being modified on an annual basis as information was gathered on the phenomenon. Experiments began in 2005 with a study on the pattern of leaf abscission in ‘Ryan’, which revealed an increase in leaf abscission just prior to flowering. However, this increase was not significant. During 2006, the leaf abscission pattern for ‘Ryan’ was compared with the leaf abscission patterns of ‘Fuerte’ and ‘Hass’. Leaf abscission for ‘Ryan’ was significantly higher than for ‘Fuerte’ and ‘Hass’ during 2006. During 2006 ‘Ryan’ displayed two periods of high leaf abscission, namely the spring flush between bud dormancy and bud swell, and a drastic increase in spring and summer flush leaf abscission between inflorescence development and full bloom. These periods of increased leaf abscission were absent during the 2007 season. In addition, ‘Fuerte’ and ‘Hass’ did not display these peaks of high leaf abscission, with leaf abscission occurring in these cultivars at higher rates from full bloom onwards. Premature and excessive leaf abscission is therefore not an annual event in ‘Ryan’ and is in all likelihood influenced by external factors. Anatomical studies did not reveal any results in terms of initiation of leaf abscission, with only the protective layer of the abscission zone being visible after leaf yellowing occurred. During 2006, two peaks of extremely low temperatures (<4°C) occurred just prior to the acceleration of leaf abscission. During the second period of low temperatures, the solar radiation:temperature-ratio was also considerably higher. These periods of low temperatures were absent during 2007, indicating that cold and light stress could be contributing to premature and excessive leaf abscission in ‘Ryan’ in 2006. In addition, ‘Ryan’ flowered excessively during 2006, which could have been triggered by low temperature stress just prior to flower initiation. A significant correlation was found between excessive flowering and excessive leaf abscission in ‘Ryan’ during 2006. The occurrence of reduced flowering in ‘Fuerte’ and ‘Hass’ may possibly be due to these two cultivars being more tolerant to stress, and it is possible that ‘Ryan’ is genetically more prone to excessive flowering than ‘Fuerte’ and ‘Hass’. Excessive flowering could accelerate leaf abscission by causing an unusually high demand for water, nutrients and carbohydrates, resulting in the acceleration of leaf abscission. No significant relationship between nutrient levels and excessive leaf abscission was found for either 2006 or 2007. In addition, no significant correlation could be found between leaf abscission on a branch and the total leaf area of that branch during the 2007 season. During 2007, leaf abscission was low and it is possible that a significant correlation could be found in a season with excessive leaf abscission. During 2005, chemical applications to reduce leaf abscission did not yield any significant improvement in leaf retention. In fact, the 50 g/tree Solubor® and 50 g/tree Solubor® in combination with 2 kg/tree dolomitic lime had a significant negative effect on fruit set, possibly because too high concentrations were applied too close to fruit set. Chemical applications during 2006 were therefore made at bud dormancy and bud swell, as it was found that leaf abscission occurred before flowering time. However, no effect was observed on leaf retention or fruit set. During 2007, emphasis was placed on treatments that might reduce stress, as it became evident that stress could be responsible for premature and excessive leaf abscission in ‘Ryan’. Most treatments showed a slight positive effect on leaf retention, but no significant results were obtained possibly because that particular season was a season of low leaf abscission. Further research on application of stress-reducing treatments is therefore recommended. Best farm management practices including optimal fertilization and irrigation is therefore vital to prevent stress, accelerating leaf abscission. Copyright / Dissertation (MSc)--University of Pretoria, 2009. / Plant Science / unrestricted

Submitted by Claudia Rocha (claudia.rocha@udesc.br) on 2018-02-27T12:29:47Z No. of bitstreams: 1 PGPV16MA202.pdf: 1955049 bytes, checksum: c0487ee4e5b4f8232b76bbf8e973a9c4 (MD5) / Made available in DSpace on 2018-02-27T12:29:47Z (GMT). No. of bitstreams: 1 PGPV16MA202.pdf: 1955049 bytes, checksum: c0487ee4e5b4f8232b76bbf8e973a9c4 (MD5) Previous issue date: 2016-03-28 / FUMDES / The apple tree is a temperate fruit species with deciduous habit, where is observed the fall of the leaves at the end of the growing season. This physiological process is known as senescence, and is important for regulating the growth and development of apple plants, having a central role in the devolopment of the buds and flowering in the next cycle. In regions with autumn and winter with mild temperatures, the processes of maturation and leaf fall are delayed and may not often occur. Due to the great variability of climatic conditions for apple cultivation, many questions and hypotheses are formulated on the need to carry out the defoliation of the plants when that does not occur naturally in the fall. The objective of this research was to evaluate the effects of different concentrations of abscisic acid (ABA) in young apple trees 'Granny Smith' and 'Fuji Suprema', and adult plants in productive age 'Daiane' and 'Fuji Suprema' aiming to follow ecophysiological effects of ABA on its efficiency in inducing senescence of leaves, budbreak, nutrient levels in tissues, C/N ratio and productivity. The experiments were conducted during the fall, in a commercial orchard of apple trees in Fraiburgo, SC and in a experimental orchard in Caçador, SC, in the years of 2013 and 2014. On apple youg plants, ABA was effective in promoting the senescence of leaves. Exogenous application of ABA was effective in senescence of adult plants leaves of 'Daiane' and 'Fuji Suprema'. Was observed an increased sensitivity to treatment with ABA, regardless of concentration adopted in cv. Daiane. According with leaf analyzes, was noted that the N concentration in leaves decreases eight days after the treatment with ABA compared to control plants. The ABA anticipates the beginning of sprouting and full bloom / A macieira é uma fruteira de clima temperado de hábito caducifólio, ou seja, ocorre a queda das folhas no final do ciclo vegetativo. Esse processo fisiológico, conhecido como senescência e abscisão, é importante para a regularização do crescimento e desenvolvimento das plantas de macieira, sendo fundamental para o favorecimento da brotação e floração no ciclo seguinte. Em regiões de outono e inverno amenos, os processos de maturação e queda das folhas são retardados, podendo muitas vezes não ocorrer. Pela grande variabilidade das condições climáticas para cultivo da macieira, muitos questionamentos e hipóteses são formulados referentes à necessidade de realização da desfolha das plantas quando essa não ocorre naturalmente durante o outono. O objetivo dessa pesquisa foi avaliar os efeitos de diferentes concentrações de ácido abscísico (ABA) em mudas de macieiras ‘Granny Smith’ e ‘Fuji Suprema’, e em plantas adultas em idade produtiva de ‘Daiane’ e ‘Fuji Suprema’ visando acompanhar os efeitos ecofisiológicos e da sua eficiência na indução da senescência das folhas, brotação, teores de nutrientes nos tecidos, relação C/N e produtividade. Os experimentos foram conduzidos, durante o outono, em pomar comercial de macieira em Fraiburgo, SC, e pomar experimental em Caçador, SC, nos anos de 2013 e 2014. Em plantas jovens de macieira o ABA foi efetivo em promover a senescência das folhas. A aplicação exógena de ABA mostrou-se eficaz na senescência das folhas de plantas adultas das cultivares Daiane e Fuji Suprema. Percebeu-se maior sensibilidade ao tratamento com ABA, independentemente da concentração adotada, na cv. Daiane. A concentração de N nas folhas diminui oito dias após o tratamento com ABA em relação às plantas controle. O ABA antecipa o início das brotações e a plena floração

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Made available in DSpace on 2016-12-06T17:42:07Z (GMT). No. of bitstreams: 1 PGCS15DA024.pdf: 1709565 bytes, checksum: 102e8c7963b170e39ba16b5decf01861 (MD5) Previous issue date: 2015-03-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Entomosporium leaf spot is the most importante leaf spot and fruit spot in the culture of pear and cultivats which data are available, are all susceptible. In these cultivars, occurs defoliation in late sumer, resulting in weak trees with significant reduction in flowering buds. Whereas in Brazil there are no reports on the anticipation of leaf drop caused by Entomosporium leaf spot and the influence on the physiology of the plant. The objective of this study was to evaluate the physiology and production according to chemical defoliation and Entomosporium leaf spot. Two experiments were conducted; 1) the experiments were conducted during the 2011/12, 2012/13 and 2013/14 season, i a comercial pear orchard Mussato Company, in Vacaria city, Rio Grande do Sul state. The European pear cultivars Packham s Triumph, Abate Fetel and William s grafted on quince Adam were subjected to the treatments (dose of active ingrediente): T1 AVG aminoethoxyvinylglycine (Retain®, 15%), at 0.06 g/L¯¹; T2: ethephon (Ethrel®, 24%) at 1 g/L¯¹; T3: calcium chloride (calcium chloride, 24%) at 24 g/L¯¹; T$: control withoutapplication. The treatments were sprayed in 03/19/2012, 03/14/2013 and 03/18/2014, on average 45 days after the harvest. The variables analyzed were: percentage of leaf fall, bud quality (mass, diametr, flower/vegetative, presence of necrosis, presence of dry buds), budding return (phenology, number of flower clusters, number of flowers, fruit set) and production (number of fruits, average fruit weight, fruit diameter, number of seeds/fruit). The experimental design used was randomized block withfour replicates per treatment, each replicate consisting og three plants. 2) The experiments were conducted in the field, in a comercial orchard during the 2013/13 and 2013/14 seasons, in the Vacaria city, Rio Grande do Sul stte. The Entomosporium leaf spot severity and natural leaf dall (occurred in the autumm) datawere recorded in March and april , every two weeks, totaling five evaluations. Te disease severity was evaluated with the aid of diagrammatic scale and the values obtained integrated in ttime, processed in the área below the entomosporium leaf spot progress curve (AACPE). The data were adjusted to mono-molecular models, logistic and Gompertz. The vegetative parameters were evaluated during the dormant period: trunk diameter, plant height, canopy volume, branches fertility, and from the two years of evaluation data was obtained the incremente of each variable. The results of the dirst experimente demonstrated in the pear trees treated with ethephon the leaf fall occurred earlier compared to other treatments and the control trees. As expected the AVG showed a similar effect the control trees, because of the inhibitory action of ethylene syntheses, where the primary function is to delay senescence of tissue. Calcium chloride caused burns in the plant rissue and all tested seasons. No significant diferences were found in the bud quality, budding and production return. There were no ndesirable effects on the physiological parameters with the leaf fall induced by chemical products as a management technique. Among the tested products ethephon showed potential to induce leaf fall, no presenting undesirable effect on teh physiology of cultivars, however, further experiments must be carried out a diferente times to better evaluate the product. For the second experimente it was found that all cultivars are susceptible to entomosporiose. About the resistance of the studied cultivars, it was determined that all are susceptible to Entomosporium leaf spot leaf spot. Based on AACPE, the first crop showed significant diferences among cultivars, but in the second season did not show statistical difference. In 2012/13 sdeason, Gompertz was the model that best has adapted to the progress curve of the trhee cultivars. In the 2013/14 season the cv. Packam s Triumoph had its best adjustment to the Gompertz model, Abate Fetel to logistical model and William s ti the mono-molecular model. In the linear regression analyzes, the coefficients of tetermination (R2) obtained for yhr Entomosporium leaf spot severity versus premature leaf fall were sigificant for all cultivars and growth seasons, attesting the interference of the athogen in the leaffall in both seasons. There is a negative correlaton between the leaf, the fertility rate and plant height, indicating that the larger leaf fall, the lower will be the development of reproductive structures and smaller will be the height of these plants. It was concluded that the severity of Entomosporium leaf spot contributes to oncreased levels of prwmature leaf fall with egative correlation with the vegetative variables, indicating that the larger leaf fall, the lower will be the developement of reproductives structures and smaller will be the height of these plants / A entomosporiose é a mancha foliar e de frutos mais importante na cultura da pereira e para as cultivares que existem dados disponíveis, são todas suscetíveis. Nestas cultivares, ocorre o desfolhamento no final do verão, resultando em árvores fracas com significativa redução nas gemas floríferas. Considerando que no Brasil não existem relatos sobre a antecipação da queda de folhas provocada pela entomosporiose e a influencia sobre a fisiologia da planta, o objetivo deste trabalho foi avaliar a fisiologia e a produção de pereira europeia em função da desfolha química e entomosporiose. Foram realizados dois experimentos; 1) Os experimentos foram conduzidos a campo nas safras agrícolas de 2011/12, 2012/13 e 2013/14, em pomar comercial da Empresa Mussato, localizado no município de Vacaria, estado do Rio Grande do Sul. Plantas de pereira europeia das cultivares Packham s Triumph Abate Fetel e William s enxertadas sobre marmeleiro Adams foram submetidas a tratamentos com diferentes desfolhantes (dose do ingrediente ativo) sendo, T1: AVG - aminoethoxyvinylglycine, (Retain®, 15%), na dose 0,06 g/L-1; T2: etefon (Ethrel®, 24%), na dose 1 g/L-1; T3: cloreto de cálcio (cloreto de cálcio, 24%) na dose de 24 g/L-1; T4: testemunha sem nenhuma aplicação. Os tratamentos foram aplicados em 19/03/2012, 14/03/2013 e 18/03/2014, em média 45 dias após a colheita. As variáveis analisadas foram: percentual de desfolha, qualidade de gemas (massa, diâmetro, florífera/vegetativa, presença de necrose, presença de gema seca), retorno de brotação (fenologia, número de cachopas, número de flores, percentual de fixação), e produção (número de frutos, peso médio, diâmetro, número de sementes). O delineamento experimental utilizado foi em blocos casualizados, com quatro repetições por tratamento, sendo cada repetição constituída por três plantas. 2) Os experimentos foram conduzidos a campo, em pomar comercial, nas safras de 2012/13 e 2013/14, no município de Vacaria, RS. Os dados da severidade da entomosporiose e desfolha natural ocorrente no início do outono foram registrados no mês de março e abril, quinzenalmente, totalizando cinco avaliações. A severidade foi avaliada com o auxílio de escala diagramática e os valores obtidos integralizados no tempo, transformados em área abaixo da curva de progresso da entomosporiose (AACPE). Os dados foram ajustados aos modelos monomolecular, logístico e de Gompertz. Como parâmetros vegeto-produtivos foram avaliados durante o período de repouso vegetativo: diâmetro do tronco, altura de planta, volume de copa, fertilidade de ramos e a partir dos dados de dois anos de avaliação, obteve-se incremento de cada variável. O resultado do primeiro experimento demostraram que plantas tratadas com etefon desfolharam mais rapidamente em relação aos demais tratamentos e a testemunha. Como esperado o AVG apresentou efeito análogo à testemunha, pois apresentação ação inibidora da síntese de etileno, onde a principal função é atrasar a senescência do tecido. O cloreto de cálcio causou queima no tecido vegetal e em todas as safras avaliadas. Não foram verificadas diferenças significativas na qualidade de gema, retorno de brotação e produção. Não foram observados efeitos indesejáveis sobre os parâmetros fisiológicos da planta quanto à utilização da desfolha como técnica de manejo. Dentre os produtos testados, o etefon foi o que apresentou potencial para utilização na desfolha química, pois não apresentou efeito indesejável sobre a fisiologia das cultivares avaliadas, no entanto, novos experimentos devem ser realizados em diferentes épocas para melhor avaliação do produto. Para o segundo experimento foi possível constatar que todas as cultivares apresentam suscetibilidade à entomosporiose. Com base na AACPE, na primeira safra houve diferença significativa entre as cultivares, na segunda safra esta diferença estatística não ocorre. Na safra 2012/13, Gompertz, foi o modelo que melhor se adequou a curva de progresso das três cultivares avaliadas. Na safra 2013/14 a cv. Packham s Triumph teve seu melhor ajuste ao modelo Gompertz, Abate Fetel ao logístico e William´s ao monomolecular. Nas análises de regressão linear os coeficientes de determinação (R2) obtidos para a severidade da entomosporiose versus desfolha outonal foram significativos para todas as cultivares e safras avaliadas, confirmando a interferência do patógeno na queda das folhas nas duas safras avaliadas. Há correlação negativa entre a desfolha, o índice de fertilidade e a altura de planta, indicando que quanto maior a desfolha, menor será o desenvolvimento de estruturas reprodutivas e menor será o porte destas plantas. Conclui-se que a severidade da entomosporiose contribui para o aumento dos níveis de desfolha outonal com correlação negativa com as variáveis vegeto-produtiva, indicando que quanto maior a desfolha, menor será o desenvolvimento de estruturas reprodutivas e menor será o porte destas plantas