Crop yield response to water - Cra

Fruit growth during this stage is temperature dependent; extremely high or low temperaturecan slow growth. Cell division is followed by cell enlargement. It is during this period that thepeel reaches maximum thickness. Later, as the pulp expands, the peel becomes thinner. Thefruit continues to grow as long as it is on the tree, albeit slower as temperatures fall.The potential fruit size at harvest is highly dependent on environmental factors that exist duringcell division. The conventional wisdom is that any decrease in the rate of cell division will directlytranslate into reduced potential fruit size at harvest. Once the fruit growth cycle passes from apredominant cell division phase to a primarily cell expansion phase, fruit size at harvest is not assusceptible to growing conditions. As for other fruit crops, there are trade-offs in citrus betweenfruit number and size; large numbers per tree leads to small individual size. Both very small andvery large fruit fetch lower prices in most fresh markets but there is a wide range of acceptablesizes for citrus. When citrus are grown for juice, fruit size is relatively unimportant.Fruit maturation stageThe beginning of this stage is usually characterized by the onset of fruit colour change, triggeredby the cooler night temperatures in the subtropical regions. The fruit is still increasing in sizebut at a much slower rate than previously. During fruit maturation, the juice content of thepulp increases. The acid content of the fruit decreases as the sugar content increases. Unlikemany deciduous fruit, there is no precise point that indicates maturity in citrus. In California,the basis for legal maturity of oranges is a ratio of 8-to-1 for total soluble solids to titratableacidity (TSS/TA); the so-called sugar-acid ratio. The balance between sugars, which accountsfor about 75 percent of the total soluble solids, and the sourness produced by acidity is thebest criterion in correlating fruit quality with consumer acceptance.Peel colour is also used as a maturity index but this approach is not reliable since peel colourdepends on temperature. Moreover, harvest timing is highly influenced by market pricesand processor availability. Hormonal sprays, such as gibberellic acid, are used to prolong theviability of fruit on the tree. If left on the tree too long, the fruit is subject to drop, insect/disease damage, and breakdown of the acid and flavor components.Responses to Water DeficitsThere is a large body of work on the responses of different citrus physiological processesto water stress. Many species, cultivars, and growing conditions have been studied. Sinceresponses vary with the timing of stress during the season, the year was divided into seasonsand unless otherwise noted the information focused on orange response.Spring stressIn terms of eventual impact on yields, the flowering and fruit set period has been repeatedlyidentified as the most sensitive to stress for small citrus, such as clementines (Gonzalez-Altozanoand Castel, 1999) and oranges (Pérez-Pérez et al., 2007). This resulted in the increased abortionof small fruit (June drop). On the other hand, there are reports indicating that early seasonstress significantly reduced peel creasing in a particularly vulnerable navel cv. (Frost Nucellar)without negative impacts on harvest fruit load or size (Goldhamer and Salinas, 2000).CITRUS 319