M. Zibordi

Changes in vascular and transpiration flows affect the seasonal and daily growth of kiwifruit (Actinidia deliciosa) berry.

BACKGROUND AND AIMS The kiwifruit berry is characterized by an early stage of rapid growth, followed by a relatively long stage of slow increase in size. Vascular and transpiration flows are the main processes through which water and carbon enter/exit the fruit, determining the daily and seasonal changes in fruit size. This work investigates the biophysical mechanisms underpinning the change in fruit growth rate during the season. METHODS The daily patterns of phloem, xylem and transpiration in/outflows have been determined at several stages of kiwifruit development, during two seasons. The different flows were quantified by comparing the diurnal patterns of diameter change of fruit, which were then girdled and subsequently detached while measurements continued. The diurnal courses of leaf and stem water potential and of fruit pressure potential were also monitored at different times during the season. KEY RESULTS Xylem and transpiration flows were high during the first period of rapid volume growth and sharply decreased with fruit development. Specific phloem import was lower and gradually decreased during the season, whereas it remained constant at whole-fruit level, in accordance with fruit dry matter gain. On a daily basis, transpiration always responded to vapour pressure deficit and contributed to the daily reduction of fruit hydrostatic pressure. Xylem flow was positively related to stem-to-fruit pressure potential gradient during the first but not the last part of the season, when xylem conductivity appeared to be reduced. CONCLUSIONS The fruit growth model adopted by this species changes during the season due to anatomical modifications in the fruit features.

Thinning apples via shading: an appraisal under field conditions

Summary Fruit development and the fate of fruits was followed on ‘Imperial Gala’ apple (Malus × domestica Borkh.) trees thinned chemically or using shading. The percentage fruit drop, fruit growth rates using callipers and electronic gauges, and whole tree gas exchange rates were measured before, during, and after covering with a shading cloth that blocked 90% of solar radiation, applied for 1 week starting 30 d after full bloom (DAFB). While fruits were thinned to similar crop loads and all reached a similar size at harvest, their growth patterns reflected the treatments applied, with fruit growth slowing down and fruit dropping sooner in chemically-thinned trees which were treated earlier, than in the shading treatment, which took place later. Daily fruit growth patterns changed and were greatly reduced under shading, as were the net carbon exchange rates (NCER), both in total per tree and per unit of light intercepted by the trees. Regression analysis of the NCER per unit of light intercepted revealed no difference between the two treatments before and after shading, but a significantly lower relationship during shading. This work supports the hypothesis that C-starvation may induce fruit abscission at approx. 30 DAFB. Fruit growth patterns, and their changes during shading, were consistent with this hypothesis. This method of thinning, may be of interest to reduce the use of chemicals, and in organic fruit growing. However, before it can be adopted, a method to estimate the length of the period of shading is required.

The positive effect of skin transpiration in peach fruit growth

The effect of fruit transpiration on the mechanisms driving peach (Prunus persica (L.) Batsch) daily growth was investigated. In peach, fruit water losses increase during the season and might play a key role in determining fruit growth. Skin transpiration was reduced during the cell expansion stage by enclosing fruit in plastic bags fitted with holes. In the first year, diameter changes of bagged and control fruit were precisely monitored for 15 days, and percentage dry matter and soluble solids content were determined during the experiment and at harvest. In the second year, midday fruit water potential, daily patterns of fruit growth and of vascular and transpiration flows were monitored. Bagging reduced fruit daily growth on some days, and negatively affected both fruit dry matter percentage and soluble solids content. Fruit transpiration rate was reduced during the midday hours, thus increasing midday fruit water potential and lowering xylem inflows. In accordance with the Münch hypothesis on traslocation, these conditions likely decreased the necessary gradient needed for the transport of phloem sap to sink organs, as in the afternoon, bagged fruit showed lower phloem inflows. These data suggest that skin transpiration in peach has a positive effect on fruit growth, as it enhances fruit phloem import.

Increasing water stress negatively affects pear fruit growth by reducing first its xylem and then its phloem inflow

Drought stress negatively affects many physiological parameters and determines lower yields and fruit size. This paper investigates on the effects of prolonged water restriction on leaf gas exchanges, water relations and fruit growth on a 24-h time-scale in order to understand how different physiological processes interact to each other to face increasing drought stress and affect pear productive performances during the season. The diurnal patterns of tree water relations, leaf gas exchanges, fruit growth, fruit vascular and transpiration flows were monitored at about 50, 95 and 145 days after full bloom (DAFB) on pear trees of the cv. Abbé Fétel, subjected to two irrigation regimes, corresponding to a water restitution of 100% and 25% of the estimated Etc, respectively. Drought stress progressively increased during the season due to lower soil tensions and higher daily vapour pressure deficits (VPDs). Stem water potential was the first parameter to be negatively affected by stress and determined the simultaneous reduction of fruit xylem flow, which at 95 DAFB was reflected by a decrease in fruit daily growth. Leaf photosynthesis was reduced only from 95 DAFB on, but was not immediately reflected by a decrease in fruit phloem flow, which instead was reduced only at 145 DAFB. This work shows how water stress negatively affects pear fruit growth by reducing first its xylem and then its phloem inflow. This determines a progressive increase in the phloem relative contribution to growth, which lead to the typical higher dry matter percentages of stressed fruit.

A multivariate approach for assessing leaf photo-assimilation performance using the IPL index.

The detection of leaf functionality is of pivotal importance for plant scientists from both theoretical and practical point of view. Leaves are the sources of dry matter and food, and they sequester CO2 as well. Under the perspective of climate change and primary resource scarcity (i.e. water, fertilizers and soil), assessing leaf photo-assimilation in a rapid but comprehensive way can be helpful for understanding plant behavior under different environmental conditions and for managing the agricultural practices properly. Several approaches have been proposed for this goal, however, some of them resulted very efficient but little reliable. On the other hand, the high reliability and exhaustive information of some models used for estimating net photosynthesis are at the expense of time and ease of measurement. The present study employs a multivariate statistical approach to assess a model aiming at estimating leaf photo-assimilation performance, using few and easy-to-measure variables. The model, parameterized for apple and pear and subjected to internal and external cross validation, involves chlorophyll fluorescence, carboxylative activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo), air and leaf temperature. Results prove that this is a fair-predictive model allowing reliable variable assessment. The dependent variable, called IPL index, was found strongly and linearly correlated to net photosynthesis. IPL and the model behind it seem to be (1) reliable, (2) easy and fast to measure and (3) usable in vivo and in the field for such cases where high amount of data is required (e.g. precision agriculture and phenotyping studies).

The effect of two orchard light management practices on the sensory quality of apple: fruit thinning by shading or photo-selective nets

Summary The effects of innovative techniques for orchard light management on the sensory properties and quality of apple (Malus _ domestica Borkh.) fruit were measured using sensory and instrumental techniques. In the first experiment, ‘Rosy Glow’ fruit, thinned chemically or by shading, were compared. In the second experiment, ‘Fuji’ fruit were grown under five different coloured photo-selective hail nets and compared. For ‘Rosy Glow’ fruit, the efficacy of both thinning methods was comparable in terms of crop load, and no sensory differences were perceived between treatments by a trained sensory panel, based on quantitative descriptive profiling, except for the “green flesh” attribute. Nevertheless, ‘Rosy Glow’ fruit from the shade-based thinning had a higher mean fresh weight (FW; 215 g vs. 198 g) and higher titratable acidity (5.3 vs. 4.5 malic acid eq. 100 g-1 juice). Some significant differences were reported by the trained sensory panel for four out of the ten attributes rated among the ‘Fuji’ apples produced under the neutral black net (control), and the red, white, yellow, and blue photo-selective hail nets. Differences were greatest between fruit from the red and yellow hail nets. Apples from the red hail net had higher scores for yellow colour perception (average intensity 42.3 vs. 28.5, based on a linear scale anchored at 0 as the minimum and 100 as the maximum), sweet taste (score 54.9 vs. 42.4), and hardness (i.e., sensory definition for firmness; score 52.0 vs. 43.0), and a lower score for green colour (4.6 vs. 10.0). In terms of objective instrumental measurements, fruit from the red net treatment had a higher mean FW (217 g), with larger cells and larger intercellular spaces measured in terms of the number of cells mm-3 and the percentage of intercellular spaces, and a higher mean dry matter (DM) content [14.7% (w/w)], when compared to fruit from the other photo-selective net treatments. The spectrum of transmitted light influenced fruit growth by affecting cell proliferation and ripening, which changed the sensory perceptions of fruit appearance, taste, and texture.This study demonstrated that it is possible to use sensory panel analysis to measure the impact of new pre-harvest treatments on the quality of harvested apple fruit.