Time filter

Source Type

IRTA, Spain

DeJong T.M.,University of California at Davis | Negron C.,University of California at Davis | Favreau R.,University of California at Davis | Day K.R.,University of California at Davis | And 3 more authors.
Acta Horticulturae | Year: 2012

One definition of horticulture is "the art of cultivating garden plants" and pruning is a horticultural practice that is traditionally approached as more of an art than a science. This is largely because of the complexity of tree growth and development and a lack of general understanding and appreciation about the processes involved in governing shoot and tree growth and development. However recent tree architectural studies have provided systematic analyses of the shoot growth and statistical and dynamic simulation models have been developed that predict tree development and responses to pruning based on scientific concepts. These concepts include apical dominance (and its subcomponents; correlative inhibition, apical control and shoot epinasty); prolepsis and syllepsis; preformation and neoformation; epicormic shoot formation and plastochron (leaf emergence rates). In this paper we will discuss how many of these concepts can be combined with hidden semi-Markov chain models of shoot bud fates and a simulation model of source-sink interactions in peach trees (L-PEACH) to understand and predict natural development of peach trees and their responses to pruning. The results of these modeling efforts help explain the architectural and physiological basis of several common, empirically-based pruning systems used in California. These concepts also provide an understanding of the limitations of relying primarily on the use of pruning to control size of trees growing on commonly used invigorating rootstocks. This research demonstrates how computer simulation modeling can be used to test and analyze interactions between environmental factors and management practices in determining patterns of tree growth and development. © ISHS 2012. Source

Debuse C.,University of California at Davis | Lopez G.,Irrigation Technology | Dejong T.,University of California at Davis
Acta Horticulturae | Year: 2010

The Californian dried plum/prune (Prunus domestica) industry is almost entirely dependent on a single cultivar, 'Improved French'. Thus the entire crop must be harvested over a relatively narrow harvest period of about three weeks with the harvest times of individual orchards varying as a function of location within the state. The mean fruit maturity dates for the 'Improved French' can vary by as much as thirty days from year to year, with weather patterns seemingly becoming more variable annually. There is a need to be able to predict fruit maturity dates early in the growing season to facilitate planning for orderly harvest and fruit drying. Recent research with peach and nectarine (Prunus persica), and fresh-market plum (Prunus salicina) cultivars indicate that fruit maturity dates can be predicted reasonably well from full bloom dates and the accumulation of growing degree hours 30 days after full bloom (GDH 30) after the relationship between GDH 30 and the length of the fruit growth period between full bloom and GDH 30 is established from historical records. Thus bloom and fruit maturity data were analyzed for the 'Improved French' cultivar for several years from two locations in California, and there was a clear relationship between the length of the fruit growth period and GDH 30. This relationship has subsequently been used to establish an industry oriented "decision support" system that allows growers and dehydration plant managers to use publicly available weather data for their local area and bloom dates from individual orchards to predict fruit maturity dates after only 30 days after bloom. Source

Lopez G.,Irrigation Technology | Girona J.,Irrigation Technology | Marsal J.,Irrigation Technology | De Jong T.M.,University of California at Davis
Acta Horticulturae | Year: 2015

Daily leaf photosynthesis was reported to be linearly related with daily leaf PAR (photosynthetic active radiation) interception, in peach trees. This relationship was considered as a fundamental step for modeling whole peach canopy photosynthesis. However, data reporting linear relationships was obtained under non-water-stressed trees. Although commercial peach orchards are usually managed under full irrigation, reduced irrigation might become inevitable in water limited areas. Water shortage is becoming increasingly frequent in peach producing areas with Mediterranean climates. Modeling the effect of water stress, on whole canopy photosynthesis, requires studies on the effect of water stress on the relationship between daily leaf photosynthesis and daily leaf light interception. We, therefore, studied the effects of water stress on the linear relationship between daily photosynthesis and light interception in a commercial 'Ryan's Sun' peach orchard. Water stress was imposed during the final stage of fruit development (50 days before harvest), because irrigation restrictions usually occur mid-summer. Under full irrigation conditions, there was a linear relationship between daily intercepted PAR and daily photosynthetic CO2 assimilation. This relationship had approximately a zero y-intercept. Under water stress conditions, the y-intercept was maintained, but there was a significant decrease in daily photosynthetic CO2 assimilation rates, at high levels of daily intercepted PAR. The higher the level of water stress, the higher the reduction in CO2 assimilation. The main consequence is that linearity between daily intercepted PAR and daily photosynthetic CO2 assimilation was not maintained under severe water stress conditions. Photosynthetic radiation use efficiency (PhRUE), for all leaves of the canopy, was similar under full irrigation conditions. However, under water stress conditions, the leaves that intercepted high values of PAR had significantly reduced PhRUE. These results can facilitate modeling the effect of water stress on whole canopy photosynthesis, in peach trees. Source

Lopez G.,Irrigation Technology | Behboudian M.H.,Irrigation Technology | Vallverdu X.,Irrigation Technology | Girona J.,Irrigation Technology | And 2 more authors.
Acta Horticulturae | Year: 2014

The effect of deficit irrigation (DI) on fruit quality has almost entirely focussed on instrumental evaluation. We were interested in assessing sensory quality and consumer acceptance of the DI fruit. DI was applied to two peach ('Ryans's Sun' and 'Tardibelle') and two nectarine ('R-28' and 'Nectalady') cultivars. Consumer acceptance data were compared to physical and chemical attributes (dry matter concentration (DMC), fruit firmness, soluble solids concentration (SSC), titratable acidity (TA), and SSC/TA ratio), and sensory traits (sweetness, sourness, juiciness, intensity of flavour, and firmness). The combination of irrigation treatments and orchard characteristics provided a wide range of tree water status values, physical and chemical parameters, sensory attributes and consumer acceptance degrees. Consumer acceptance was related to four sensory attributes (sweetness, flavour, sourness, and juiciness) and four chemical parameters (SSC, TA, SSC/TA, and DMC). According to Pearson correlation coefficients (r) between consumer acceptance and quality parameters the following ranking for best predictors of consumer acceptance was established: sweetness (r = 0.81), flavour intensity (r = 0.81), TA (r =-0.81), SSC/TA ratio (r = 0.71), sourness (r =-0.68), juiciness (r = 0.66), SSC (r = 0.56), and DMC (r =0.54). Consumer acceptance can be modified by irrigation management. Sensory evaluation is a useful tool for predicting the effects of DI on consumer acceptance. SSC/TA measured by instruments is an important predictor of consumer acceptance if complemented with information on juiciness. Source

Discover hidden collaborations