Pre-harvest Factors Affecting Physiological Disorder
Light, temperature and water
The taste and flavor of horticultural crops are influenced by environment, agrichemicals, nutrition, and management systems (Mattheis and Fellman, 1999). The different intensity and quality of light and temperature influence the postharvest quality (Kays, 1999). In perennial crops, light utilization is a key determinant of productivity and quality (Snelgar et al., 1998; Tustin et al., 2001) as the leaf area exposed to the sun must be adequate to provide both fruit and vegetative growth with the carbon required. For some tree crops, there is a good understanding of carbohydrate assimilation, distribution, and accumulation within the plant. However, there is a difference in understanding the variables influencing the separation of carbon into the various plant parts for others such as kiwifruit and apricots. In dry matter accumulation, seasonal variations do occur. With wine grapes, the best possible example of this.
The best Grapes (in terms of wine quality) are those where vine yields are relatively low. However, the radiation, temperature, and possibly rainfall conditions during the growing season are such that maximal partitioning of sugars (and other components that contribute to the important quality attributes of wine) are accumulated in the fruit, instead of the shoots, before harvest. There is a need to develop more robust physiological models of carbon assimilation, distribution, and accumulation on different plant organs of commercially important crops. This should provide growers with management tools to minimize the proportion of low dry matter fruit that have the potential to provide a bad taste experience for consumers and Generate an attitude of ‘no return purchase’ that will lead to falling sales. Tree canopy will influence the amount of light received and captured by fruit trees. Using size control rootstocks and adaptive pruning and thinning techniques, conventional horticultural technologies are good examples of allowing technologies to maximize fruit production and quality. These technologies do so by influencing the size and form of the tree and hence the volume occupied in an orchard. Conceptual advances in understanding the genetic plasticity of trees, or the extent to which the external or internal environment can influence tree architecture, should provide further insights into factors that control carbon assimilation and distribution within fruit trees (Seleznyova et al., 2003).
In general, growers adopt water management strategies to minimize moisture stress to allow optimal photosynthesis, plant growth, and harvestable yield. Irrigation systems vary. However, they apply water regularly (determined by evapotranspiration demand) well before serious stress conditions occur. However, for optimum efficiency, maximum yields are not always a requirement. Careful manipulation of water supply can well reduce water use and improve crop quality in some situations with certain crops without compromising sustainable plant growth.
Having very high yields can compromise the quality of wine. The best vintages of wine quality derive from those years where Ecological conditions also put stress on the vines (high temperatures, low precipitation).
In some fruits, such as kiwi fruit, high crop loads can often reduce dry matter and may affect the taste and flavor as experienced by the customer.The use of Regulated Deficit Irrigation (RDI) to minimize water applied without affecting plant performance, and sometimes increasing fruit quality, is a system that has been used successfully for a range of fruit crops (Behboudian and Mills, 1997).