G. Lopez

Postharvest regulated deficit irrigation in ‘Summit’ sweet cherry: fruit yield and quality in the following season

We examined, over the postharvest seasons of 2005–2007, regulated deficit irrigation (RDI) for its potential of saving water and maintaining fruit yield and quality in ‘Summit’ sweet cherry. The postharvest irrigation treatments were: full irrigation (Control), receiving 80% of water in Control (RDI-80%), and receiving 50% of water in Control (RDI-50%). Midday stem water potential (Ψstem) was used for assessing plant water status. In 2006, trees produced a large crop and commercial fruit thinning had to be applied, whereas 2007 was a low crop year. The RDI treatment, first applied in 2005, reduced fruit set in 2006 and also reduced root winter starch concentration. In 2006, fruit set was lower in RDI-50% than in Control. But fruit thinning had still to be done with the final yield being the same among treatments. In 2007, RDI-50% produced more fruit and higher yields than Control. Relationship between postharvest Ψstem and crop load in the following season varied according to the year. They were negatively correlated in 2006 and positively correlated in 2007. Fruit firmness did not vary with irrigation treatments in any of the years. Fruit soluble solid concentration (SSC) and fruit relative dry matter (RDM) for RDI-50% was the highest in 2006 when RDI-50% trees had the lowest fruit set. In 2007, SSC and RDM for RDI-50% were the lowest with the trees having the highest fruit set and crop load at harvest. This study indicates that RDI-50% firstly applied in an “off” year, after crop has been harvested, can maintain fruit yield at similar levels to fully irrigated trees while saving water by 45%. Correction of biennial bearing and partial saving of thinning costs are additional advantages of this treatment.

Crop coefficient (Kc) for apple: comparison between measurements by a weighing lysimeter and prediction by CropSyst

Accurate prediction of crop coefficient (Kc) is necessary for proper irrigation management. We explored CropSyst for determining irrigation requirements of apple trees and for accuracy of Kc prediction. Values of Kc were compared to those obtained, over 2002–2010, from lysimeter-grown trees. Over these years, trees had different ratios of height (H) to width (W). CropSyst predicted irrigation requirements using tree light interception and water uptake sub-model components. Parameters of the model were adjusted using data obtained from the lysimeter in 2010. Tree light interception sub-model was verified by 2007 data. After parameterization, good agreement was found between simulated and measured Kc over different seasons. The porosity coefficient of the canopy was related to changes in tree’s H/W ratio and leaf overlapping. Accordingly, different porosity values could be estimated for each year. When yearly changes in canopy porosity was considered, CropSyst improved Kc prediction and generated relevant information for managing irrigation under changing canopy shape for apple trees.

Effects of relative source-sink position within peach trees on fruit growth under water stress conditions

Summary The source-sink position of 3-year-old, potted ‘O’Henry’ peach trees was manipulated by arranging the sources and sinks in opposite positions in order to investigate the effect of directional movement of assimilates from source leaves to fruit sinks. Six different treatments were applied: 1) control-fully irrigated (C-FI), in which irrigation was applied to achieve non-stress conditions, without removal of either leaves or fruit; 2) control-deficit irrigated (C-DI), in which irrigation was reduced to obtain a moderate deficit, without removal of either leaves or fruit; 3) downward movement of assimilates-deficit irrigated (Down-DI), in which fruits from the upper part and leaves from the lower part of the tree were removed; 4) upward movement of assimilates-deficit irrigated (Up-DI), in which fruits from the lower part and leaves from the upper part of the tree were removed. The last two treatments [(5) and (6)] were identical to the Down-DI and Up-DI treatments, but source leaves and fruit sinks were isolated by girdling. Changes in stem water potential ( stem) and transpiration rate (T) were evaluated. Fruit growth analysis was based on the expected theoretical response of fruit dry mass gain to stem. The experimental conditions allowed expression of potential differences in carbon transport efficiency (i.e., the distance between leaves and fruits was sufficient to cause limitations on fruit growth) and the reserves originating from fruit-bearing shoots were relatively small (20%) in comparison with the requirements for optimum fruit growth. Under these conditions, fruits on Down-DI trees did not exhibit significant differences in their capacity to accumulate carbohydrates with respect to Up-DI fruits. The data appear to indicate that, under moderate water stress conditions, resistance to assimilate transport does not differ greatly between upward and downward movement within trees.

Influence of post-harvest deficit irrigation and pre-harvest fruit thinning on sweet cherry (cv. New Star) fruit firmness and quality

Summary The effects of tree water stress on sweet cherry (‘New Star’) fruit quality during post-harvest and pre-harvest fruit thinning were evaluated in a 2-year field experiment (2005 – 2006). Four different treatments were applied: (i) fully irrigated (Control), in which irrigation was scheduled according to a water budget approach; (ii) RDI-80%, in which the crop received 0.8× Control irrigation during post-harvest and was irrigated like the Control during pre-harvest; (iii) RDI-50% in which the crop received 0.5× Control irrigation during post-harvest and was irrigated like the Control during pre-harvest; and (iv) RDI-80%-T in which irrigation management was the same as for RDI-80%, but fruits were only thinned 1 month prior to harvest in 2006. No significant effects on fruit load or yield were observed in 2006 as a consequence of the 2005 irrigation treatments. However, the RDI-50% treatment produced a noticeable advance in ripening, as evaluated from the percentage of fruit harvested at the first pick. Post-harvest water stress did not affect fruit quality at harvest, but slightly reduced fruit firmness (FF) and soluble solids content (SSC) after cold storage, with no significant variation in fruit flesh red colour (expressed as hue angle). Fruit-thinning reduced the fruit load by 38% compared to Control trees, and significantly increased fruit fresh weight (FW), FF, and SSC for cherries with similar flesh colour to the other treatments. Reducing irrigation by 50% during post-harvest advanced the harvest date (RDI-50% treatment), but did not provide any advantage in terms of fruit quality.

Root growth following defruiting improves peach tree water status

Summary Tree growth and water status throughout the growing season and after fruit removal were studied in container-grown peach trees. Trees with fruit (F) and defruited (DF) trees were sampled destructively at bud break (8 March), 1 month after fruit removal (3 June), at harvest (6 August), and before leaf fall (15 October) to determine the mass of leaves, current season shoots, branches, trunk, and the entire root system. Tree water status was determined from the mid-day stem water potential (SWP) the day before each sampling date. Root growth in DF trees was greater than that observed in F trees, while the above-ground biomass was similar in DF and F trees. DF trees therefore had lower leaf:root biomass ratios than F trees throughout the fruit growing season. Environmental factors did not fully explain the seasonal variations in SWP, but there was a significant correlation between leaf:root biomass ratios and SWP. Reductions in leaf:root biomass ratios were accompanied by increases in SWP and, ultimately, DF trees had higher SWP values than F trees in mid-Summer. Improvements in tree water status following fruit removal can be explained, in part, by additional root growth.