Crop yield response to water - Cra

Figure 2Seasonal pattern of the leaf area index (LAI) in a A. deliciosa (Hayward) mature orchard inItaly (Pergola, 625 plants/ha). The day 0 is the April 10 th (Xiloyannis et al., 1999).4.54.03.53.0LAI2.52.01.51.00.50.00 20 40 60 80 100 120 140Days from leaf outare around 2.5-3 in orchards trained to T-bar (~400 vine/ha), and up to 4-5 in orchards trainedto the pergola system (~700 vine/ha). Different vigour rootstocks could greatly affect the LAI(Figure 3) particularly during the early years after planting. The evolution of LAI during thefirst years of planting is shown in Figure 4. Because the fraction of shaded leaves may representup to 60 percent of LAI in pergola trained vines (Figure 5), it is important to control growthby summer pruning so that the proportion of leaves with high water use efficiency increases(Figure 6) and some fruit quality traits (e.g. calcium content) related to light availability areenhanced (Montanaro et al., 2006).After fruit set, the development of a fruit entails an initial rapid growth (predominant celldivision stage) which spans about 50 days and is followed by the cell enlargement stage thatslows down late in the season. The pattern of fruit growth, described as changes in fruit lengthor surface area, is shown in Figure 7.Responses to Water DeficitsKiwifruit is quite sensitive to water deficit; vines do not survive stress levels associated withpredawn leaf water potential values (LWP) below -1.5 MPa. Even mild water deficits determinerapid stomatal closure and increase in leaf temperature, which results initially in leaf tip burn andlater leads to necrosis of the entire lamina. Restriction of water supply over the summer easilyreduces fruit size at harvest. Mild water stress (about -0.5 MPa predawn LWP) occurring duringthe early growth of fruit (cell division stage) or later during fruit growth, causes a reduction infruit size (Figure 8). However, in the case of deep soils with high water-holding capacity, an initialirrigation deficit may be tolerated without affecting fruit size (Reid et al., 1996) as long as the soil490crop yield response to water