Gestión de la calidad del fruto mediante prácticas culturales y aplicación de un modelo fisiológico en melocotonero

Abstract

[SPA] Esta tesis doctoral se presenta por compendio de publicaciones. La escasez de recursos hídricos constituye uno de los principales desafíos del siglo XXI al que se están enfrentando ya numerosas sociedades de todo el mundo. A lo largo del último siglo, el uso del agua aumentó a un ritmo dos veces superior al de la tasa de crecimiento de la población, siendo la agricultura la gran consumidora de agua a nivel mundial, ya que emplea actualmente más del 70% del agua dulce disponible. Por tanto, resulta de vital importancia llevar a cabo estudios encaminados a conseguir una óptima gestión de los recursos hídricos disponibles, especialmente en zonas áridas y semiáridas como el Levante Español, donde se producen la mayor parte de frutas y verduras a nivel nacional, y en la que la pluviometría es especialmente escasa. Además de intentar optimizar la eficiencia en el uso del agua mediante el estudio de nuevas estrategias y sistemas de riego de precisión, otra herramienta útil que debemos tener en cuenta es el uso de modelos de producción agraria. Estos modelos nos permiten simular un gran número de situaciones o escenarios, variando las condiciones de cultivo, la climatología, las prácticas culturales, etc., y permitiendo de este modo predecir la producción y/o calidad de la cosecha en función de nuestros “inputs” de entrada (entre los que se encuentran los aportes hídricos). De este modo es posible estimar previamente (y de forma aproximada) la relación coste-beneficio al final de cada ciclo de cultivo. En esta Tesis Doctoral, defendida el 30 de Octubre de 2014, se han planteado dos objetivos principales, el primero de ellos se centra en evaluar y conocer la calidad del fruto de dos variedades de diferente maduración de melocotonero, en función de distintos regímenes hídricos y carga de cultivo. El segundo objetivo comprende la simulación de la calidad de la cosecha por medio de la parametrización y validación de un modelo mecanístico específico adaptado a las dos variedades. Las dos variedades estudiadas han sido los cultivares “Flordastar” y “Catherine”. La primera de ellas es una variedad extra-temprana (cosechada entre finales de Abril y primeros de Mayo), cuya importancia económica radica principalmente en su precocidad, siendo ésta cualidad uno de los motivos del progresivo incremento de la superficie de cultivo dedicado a dicha variedad en los últimos años. En cambio, “Catherine” es una variedad de media estación tradicionalmente cultivada en la Región de Murcia, cuya cosecha se realiza a mediados de Julio. [ENG] Water scarcity is one of the main challenges of the XXI century, which is already being faced by many societies all over the world. Throughout the last century, water use grew at twice the rate of population growth. Agriculture is the major consumer of water worldwide and currently employs more than 70% of available freshwater. Therefore it is really important to perform studies leading to optimum management of the available water resources, particularly in arid and semi-arid areas such as the Spanish southeast, where most of the fruit and vegetables are produced at the national level and where rainfall is particularly low. Apart from trying to optimize the water use efficiency through the development of irrigation strategies and the use of precision irrigation systems, another useful tool to bear in mind is the use of physiological and agronomic models. These models allow us to simulate a large number of situations or scenarios, varying growing conditions, climatological conditions, agricultural practices, etc. Thus, these models offer an insight of the production and / or crop quality that will be obtained, taking into account our "inputs" (such as water intake). Thereby it would be possible, to estimate previously (and roughly) the cost-benefit ratio which we will obtain at the end of the growing season. To this end, it is necessary to parameterise and validate each model for each crop and variety under study. This thesis is divided into two main sections; the first one is focused on assessing the fruit quality of two different peach cultivars according to the peach tree architecture (Publications 1 and 3). In the second section it is intended to understand and simulate crop quality through the parameterisation and validation of a specific mechanistic model adapted to the two peach varieties abovementioned (Publications 2 and 4). The two varieties studied were "Flordastar" (Publication 1) and "Catherine" (Publication 3). The first one is an extra-early variety (harvested between end April and early May), whose economic importance lies mainly in its precocity, which is one of the reasons for the gradual increase in the cultivation area for this variety, in recent years. However, "Catherine" is a mid-season variety traditionally grown in the province of Murcia, harvested in mid-July. In both varieties, a detailed analysis of the fruit quality within the canopy was carried out, being also evaluated if there were any effects of the water stress and the position of the fruit within the tree canopy on the fruit quality. For "Flordastar" (Publication 1), the effect of the crop load on fruit quality was also assessed. There are several works in the literature which highlight the fruit performance variability within the tree (Forlani et al., 2002; Wu et al., 2005). This variability is associated to a great number of factors such as light interception (Génard and Baret, 1994), crop load (Marini and Sowers, 1994), pruning (Bussi et al., 2010; Kumar et al., 2010) and irrigation strategies (Buendía et al., 2008; Mercier et al., 2009; Lopez et al., 2010), but most of these studies are conducted in mid-season and late maturing cultivars, so this work aims to complement and / or extend the range of varieties studied in this area. In this way, for "Flordastar", our results showed that irrigation strategies influenced fruit growth, yielding a higher percentage of fruits which did not reach the marketable size from regulated deficit irrigation (RDI) treatments, whereas high-grade fruits were more common in the trees under full irrigation (FI). Crop load also affected fruit growth. Fruits from low-loaded trees were greater and firmer than those from commercially loaded trees. Regarding exposure to sunlight, it was a factor that greatly affected fruit-quality traits. Exposed fruits were greater than those shadowed or medium-exposed. They were redder than those that did not receive direct sunlight. Our results indicate that, for “Flordastar”, the negative effects of RDI on fruit quality can be partly compensated leaving on the tree a certain fruit distribution that enables a higher fruit exposition to sunlight. Regarding to the mid-season variety ("Catherine") (Publication 3), the effects of previously mentioned factors (water stress and fruit position within the canopy) on fruit quality, were evaluated by analyzing the evolution and sugar content within these fruits. In this sense, similar studies have been conducted in peach, where the fruit quality analysis carried out are mainly focused on attributes such as ground colour or soluble solids content (Corelli-Grappadelli et al., 1991; Miranda-Jiménez and Royo Díaz, 2002). However, only a few of them analyze in detail the sugars content and time evolution (Génard and Bruchou, 1992). These sugars are one of the main nutritional components of the fruit, and fruit sugar content varies throughout the ripening period, contributing to the characteristic fruit sweetness. Hence, the importance to assess the influence of different cultural practices (such as RDI and fruit position within the canopy) on the fruit quality, particularly on the fruit sugar content. For our cultivar (“Catherine”) irrigation strategies did not significantly affect fruit growth (total yield, numbers of fruit per tree, diameter and unitary weight, are the parameters that were not affected). These results are in disagreement with others previously reported for other peach cultivars under different management conditions (Besset et al., 2010; Mercier et al., 2010; López et al., 2010a). In our conditions our peach trees supported low crop load, which could compensate the negative effects of the water deficit. However, the irrigation treatment did exert influence on some of the fruit quality attributes. Thus, the soluble solids content, citric, malic and tartaric acids, and certain sugars (such as glucose and sorbitol) were found to be higher in fruits from the RDI treatment. These results are consistent with other previously published (Lo Bianco et al., 2000; Wu et al, 2002; Buendía et al., 2008; López et al., 2011). Both FI and RDI trees yielded a similar percentage of fruits in the highest marketable category (AAA; 12% for FI trees and 19% for RDI trees).

[ENG] This doctoral dissertation has been presented in the form of thesis by publication. Water scarcity is one of the main challenges of the XXI century, which is already being faced by many societies all over the world. Throughout the last century, water use grew at twice the rate of population growth. Agriculture is the major consumer of water worldwide and currently employs more than 70% of available freshwater. Therefore it is really important to perform studies leading to optimum management of the available water resources, particularly in arid and semi-arid areas such as the Spanish southeast, where most of the fruit and vegetables are produced at the national level and where rainfall is particularly low. Apart from trying to optimize the water use efficiency through the development of irrigation strategies and the use of precision irrigation systems, another useful tool to bear in mind is the use of physiological and agronomic models. These models allow us to simulate a large number of situations or scenarios, varying growing conditions, climatological conditions, agricultural practices, etc. Thus, these models offer an insight of the production and / or crop quality that will be obtained, taking into account our "inputs" (such as water intake). Thereby it would be possible, to estimate previously (and roughly) the cost-benefit ratio which we will obtain at the end of the growing season. To this end, it is necessary to parameterise and validate each model for each crop and variety under study. This thesis is divided into two main sections; the first one is focused on assessing the fruit quality of two different peach cultivars according to the peach tree architecture (Publications 1 and 3). In the second section it is intended to understand and simulate crop quality through the parameterisation and validation of a specific mechanistic model adapted to the two peach varieties abovementioned (Publications 2 and 4). The two varieties studied were "Flordastar" (Publication 1) and "Catherine" (Publication 3). The first one is an extra-early variety (harvested between end April and early May), whose economic importance lies mainly in its precocity, which is one of the reasons for the gradual increase in the cultivation area for this variety, in recent years. However, "Catherine" is a mid-season variety traditionally grown in the province of Murcia, harvested in mid-July. In both varieties, a detailed analysis of the fruit quality within the canopy was carried out, being also evaluated if there were any effects of the water stress and the position of the fruit within the tree canopy on the fruit quality. For "Flordastar" (Publication 1), the effect of the crop load on fruit quality was also assessed. There are several works in the literature which highlight the fruit performance variability within the tree (Forlani et al., 2002; Wu et al., 2005). This variability is associated to a great number of factors such as light interception (Génard and Baret, 1994), crop load (Marini and Sowers, 1994), pruning (Bussi et al., 2010; Kumar et al., 2010) and irrigation strategies (Buendía et al., 2008; Mercier et al., 2009; Lopez et al., 2010), but most of these studies are conducted in mid-season and late maturing cultivars, so this work aims to complement and / or extend the range of varieties studied in this area. In this way, for "Flordastar", our results showed that irrigation strategies influenced fruit growth, yielding a higher percentage of fruits which did not reach the marketable size from regulated deficit irrigation (RDI) treatments, whereas high-grade fruits were more common in the trees under full irrigation (FI). Crop load also affected fruit growth. Fruits from low-loaded trees were greater and firmer than those from commercially loaded trees. Regarding exposure to sunlight, it was a factor that greatly affected fruit-quality traits. Exposed fruits were greater than those shadowed or medium-exposed. They were redder than those that did not receive direct sunlight. Our results indicate that, for “Flordastar”, the negative effects of RDI on fruit quality can be partly compensated leaving on the tree a certain fruit distribution that enables a higher fruit exposition to sunlight. Regarding to the mid-season variety ("Catherine") (Publication 3), the effects of previously mentioned factors (water stress and fruit position within the canopy) on fruit quality, were evaluated by analyzing the evolution and sugar content within these fruits. In this sense, similar studies have been conducted in peach, where the fruit quality analysis carried out are mainly focused on attributes such as ground colour or soluble solids content (Corelli-Grappadelli et al., 1991; Miranda-Jiménez and Royo Díaz, 2002). However, only a few of them analyze in detail the sugars content and time evolution (Génard and Bruchou, 1992). These sugars are one of the main nutritional components of the fruit, and fruit sugar content varies throughout the ripening period, contributing to the characteristic fruit sweetness. Hence, the importance to assess the influence of different cultural practices (such as RDI and fruit position within the canopy) on the fruit quality, particularly on the fruit sugar content. For our cultivar (“Catherine”) irrigation strategies did not significantly affect fruit growth (total yield, numbers of fruit per tree, diameter and unitary weight, are the parameters that were not affected). These results are in disagreement with others previously reported for other peach cultivars under different management conditions (Besset et al., 2010; Mercier et al., 2010; López et al., 2010a). In our conditions our peach trees supported low crop load, which could compensate the negative effects of the water deficit. However, the irrigation treatment did exert influence on some of the fruit quality attributes. Thus, the soluble solids content, citric, malic and tartaric acids, and certain sugars (such as glucose and sorbitol) were found to be higher in fruits from the RDI treatment. These results are consistent with other previously published (Lo Bianco et al., 2000; Wu et al, 2002; Buendía et al., 2008; López et al., 2011). Both FI and RDI trees yielded a similar percentage of fruits in the highest marketable category (AAA; 12% for FI trees and 19% for RDI trees).