Tolerance of cultivars and clonal selections of peach rootstocks to excess aluminum / Tolerância de cultivares e seleções clonais de porta-enxertos de pessegueiro ao excesso de alumínio

Forms of aluminum (Al) present in the solution of tropical and subtropical soils can cause toxicity in rootstocks and peach cultivars, impairing growth and productivity. This can be minimized by growing Al-tolerant rootstocks and cultivars. However, this is not sufficiently known, especially because plant breeding programs do not always consider tolerance as a selection variable for genetic materials. The study aimed to (a) select cultivars and clonal selections of Al-tolerant peach rootstocks, (b) identify variables that confer Al tolerance for use in genetic improvement programs, and (c) propose critical levels (NC) and ranges of toxicity (TF) of Al in relation to morphological variables of the root system. The experimental design was completely randomized, comprising a factorial of 13 (cultivars and clonal selections) x 2 (with and without Al) with three replications. Own-rooted 'BRS Mandinho' peach seedlings (without rootstock) and grafted seedlings of 'BRS Mandinho' on different cultivars and clonal rootstock selections were cultivated in a hydroponic system, composing two levels for the Al factor (absence and presence at 100 mg L−1). The morphological variables of the canopy and root system, Al accumulation in tissues, translocation factor, and the critical level (NC) and toxicity range (TF) of Al in the roots were evaluated. Rootstocks FB-SM-09-43, JB-ESM-09-13, SAS-SAU-09-71, SS-CHI-09-40, 'Sharpe' and VEH-GRA-09-55 were tolerant at high Al concentrations. The NC of Al in the roots in relation to the root surface area of peach rootstocks was 1400 mg Al kg−1, and the FT was between 1200 and 1500 mg Al kg−1.(AU)

Formas de alumínio (Al) presentes na solução de solos tropicais e subtropicais podem causar toxicidade em porta-enxertos e cultivares de pessegueiro, prejudicando o crescimento e a produtividade. Isso pode ser minimizado pelo cultivo de porta-enxertos e cultivares tolerantes ao Al. Porém, isso não é suficientemente conhecido, principalmente porque os programas de melhoramento vegetal nem sempre consideram a tolerância como uma variável de seleção de materiais genéticos. O estudo teve como objetivo (a) selecionar cultivares e seleções clonais de porta-enxertos de pessegueiro tolerantes ao Al, (b) identificar variáveis que confiram tolerância ao Al para uso em programas de melhoramento genético e (c) propor níveis críticos (NC) e faixas de toxicidade (FT) do Al em relação às variáveis morfológicas do sistema radicular. O delineamento experimental foi inteiramente casualizado, compreendendo fatorial 13 (cultivares e seleções clonais) x 2 (com e sem Al) com três repetições. Mudas de pessegueiro 'BRS Mandinho' autoenraizadas (sem porta-enxerto) e mudas enxertadas de 'BRS Mandinho' em diferentes cultivares e seleções de porta-enxertos clonais foram cultivadas em sistema hidropônico, compondo dois níveis para o fator Al (ausência e presença a 100 mg L−1). Foram avaliadas as variáveis morfológicas da parte aérea e do sistema radicular, acúmulo de Al nos tecidos, fator de translocação, NC e FT do Al nas raízes. Os porta-enxertos FB-SM-09-43, JB-ESM-09-13, SAS-SAU-09-71, SS-CHI-09-40, 'Sharpe' e VEH-GRA-09-55 foram tolerantes a altas concentrações de Al. O NC do Al nas raízes em relação à área radicular dos porta-enxertos de pessegueiro foi de 1400 mg Al kg−1, e o FT ficou entre 1200 e 1500 mg Al kg−1.(AU)

Efeito do raleio manual em frutos de ameixeira japonesa (Prunus salicina Lind) sobre algumas qualidades / Effect of manual thinning on japanese plum fruits (Prunus salicina Lind) on some qualities

A fruticultura de clima temperado possui grande potencial para desenvolvimento no Brasil, o uso de produtos químicos cada vez mais aumenta nos dias atuais podendo se tonar um problema se utilizados de forma errada, por isto a utilização de outras formas de realização de tratos culturais como é o caso do raleio manual em frutos apresenta-se como uma alternativa para pequenas áreas produtoras. Este trabalho teve como objetivo analisar as datas de início e final dos ciclos de florescimento e frutificação e algumas e qualidades físicas e químicas em frutos de ameixeira japonesa (Prunus salicina Lind) assim como a influência do raleio manual nestas qualidades nos frutos obtidos de diferentes acessos de ameixa produzidos pelo IAPAR. O experimento foi realizado na cidade de Ponta Grossa-PR no Polo Regional de Pesquisas do IAPAR. O experimento foi realizado em esquema fatorial 7x2, composto de sete acessos de ameixeira japonesa (Prunus salicina Lind) e dois tratamentos com realização do raleio manual nos frutos e sem realização do raleio manual e seis repetições. As análises realizadas foram data de início e final do florescimento e início e final frutificação, após a maturação os frutos foram colhidos e analisados as características de diâmetro dos frutos, massa dos frutos, massa do caroço massa da polpa dos frutos, sólidos solúveis totais, acidez total titulável e ratio. O raleio manual realizados nos frutos de ameixeira apresentou um acréscimo significativo nos valores do diâmetro dos frutos e na massa do frutos, massa do caroço e massa da polpa, este aumento ocorreu devido principalmente a retirada de frutos diminuindo a competição por seiva e fotoassimilados entre os frutos, entretanto os frutos não apresentaram variações nos resultados nas análises de sólidos solúveis totais, acidez total titulável e ratio mostrando que mesmo com a realização deste trato cultura não afetou estas características, com isso é possível concluir que os...

Temperate fruit growing has great potential for development in Brazil, the use of chemical products is increasing more and more in the present day, being a problem if used in a wrong way, therefore the use of other forms of cultural the case of manual thinning in fruits presents itself as an alternative to small producing areas. The objective of this work was to analyze the start and end dates of flowering and fruiting cycles and some physical and chemical qualities of Japanese plum fruits (Prunus salicina Lind) as well as the influence of manual thinning on these qualities in fruits obtained from different accessions of plum produced by IAPAR. The experiment was carried out in the city of Ponta Grossa-PR at the Regional Research Center of IAPAR. The experiment was carried out in a 7x2 factorial scheme, composed of seven Japanese plum accesses (Prunus salicina Lind) and two treatments with manual thinning in the fruits and without manual thinning and six replications. The fruits were harvested and the characteristics of fruit diameter, fruit mass, seed mass, fruit pulp mass, total soluble solids, titrizable total acidity and ratio. The manual thinning performed on the plum fruits showed a significant increase in fruit diameter and fruit mass, stone mass and pulp mass. This increase was mainly due to the removal of fruits, reducing the competition for sap and photoassimilates between the fruits. However, the fruits did not show any variation in the results in the analyzes of total soluble solids, total acidity and titrable ratio, showing that even with the accomplishment of this tract culture did not affect these characteristics, with this it is possible to conclude that the accesses studied present a capacity of launching as new cultivars adapted to the climate of the city of Ponta Grossa-PR, and that the manual thinning in the fruits is an alternative to the realization of small areas bringing positive results in the physical qualities of the fruits.

Efeito do raleio manual em frutos de ameixeira japonesa (Prunus salicina Lind) sobre algumas qualidades / Effect of manual thinning on japanese plum fruits (Prunus salicina Lind) on some qualities

A fruticultura de clima temperado possui grande potencial para desenvolvimento no Brasil, o uso de produtos químicos cada vez mais aumenta nos dias atuais podendo se tonar um problema se utilizados de forma errada, por isto a utilização de outras formas de realização de tratos culturais como é o caso do raleio manual em frutos apresenta-se como uma alternativa para pequenas áreas produtoras. Este trabalho teve como objetivo analisar as datas de início e final dos ciclos de florescimento e frutificação e algumas e qualidades físicas e químicas em frutos de ameixeira japonesa (Prunus salicina Lind) assim como a influência do raleio manual nestas qualidades nos frutos obtidos de diferentes acessos de ameixa produzidos pelo IAPAR. O experimento foi realizado na cidade de Ponta Grossa-PR no Polo Regional de Pesquisas do IAPAR. O experimento foi realizado em esquema fatorial 7x2, composto de sete acessos de ameixeira japonesa (Prunus salicina Lind) e dois tratamentos com realização do raleio manual nos frutos e sem realização do raleio manual e seis repetições. As análises realizadas foram data de início e final do florescimento e início e final frutificação, após a maturação os frutos foram colhidos e analisados as características de diâmetro dos frutos, massa dos frutos, massa do caroço massa da polpa dos frutos, sólidos solúveis totais, acidez total titulável e ratio. O raleio manual realizados nos frutos de ameixeira apresentou um acréscimo significativo nos valores do diâmetro dos frutos e na massa do frutos, massa do caroço e massa da polpa, este aumento ocorreu devido principalmente a retirada de frutos diminuindo a competição por seiva e fotoassimilados entre os frutos, entretanto os frutos não apresentaram variações nos resultados nas análises de sólidos solúveis totais, acidez total titulável e ratio mostrando que mesmo com a realização deste trato cultura não afetou estas características, com isso é possível concluir que os...(AU)

Temperate fruit growing has great potential for development in Brazil, the use of chemical products is increasing more and more in the present day, being a problem if used in a wrong way, therefore the use of other forms of cultural the case of manual thinning in fruits presents itself as an alternative to small producing areas. The objective of this work was to analyze the start and end dates of flowering and fruiting cycles and some physical and chemical qualities of Japanese plum fruits (Prunus salicina Lind) as well as the influence of manual thinning on these qualities in fruits obtained from different accessions of plum produced by IAPAR. The experiment was carried out in the city of Ponta Grossa-PR at the Regional Research Center of IAPAR. The experiment was carried out in a 7x2 factorial scheme, composed of seven Japanese plum accesses (Prunus salicina Lind) and two treatments with manual thinning in the fruits and without manual thinning and six replications. The fruits were harvested and the characteristics of fruit diameter, fruit mass, seed mass, fruit pulp mass, total soluble solids, titrizable total acidity and ratio. The manual thinning performed on the plum fruits showed a significant increase in fruit diameter and fruit mass, stone mass and pulp mass. This increase was mainly due to the removal of fruits, reducing the competition for sap and photoassimilates between the fruits. However, the fruits did not show any variation in the results in the analyzes of total soluble solids, total acidity and titrable ratio, showing that even with the accomplishment of this tract culture did not affect these characteristics, with this it is possible to conclude that the accesses studied present a capacity of launching as new cultivars adapted to the climate of the city of Ponta Grossa-PR, and that the manual thinning in the fruits is an alternative to the realization of small areas bringing positive results in the physical qualities of the fruits.(AU)

Susceptibility, Oviposition Preference, and Biology of Grapholita molesta (Lepidoptera: Tortricidae) in Prunus Spp. Rootstock Genotypes.

Studying the susceptibility of peach trees to Grapholita molesta (Busck) is one of the major steps in the development of pest-resistant peach varieties. This work evaluated the susceptibility of 55 genotypes of the "Prunus Rootstock Collection" ("Coleção Porta-enxerto de Prunus") of Embrapa Temperate Climate (Pelotas, Rio Grande do Sul, Brazil) to the natural infestation of G. molesta, assessed the oviposition preference of G. molesta in choice and no-choice bioassays, and estimated the biological parameters and the fertility life table on different Prunus spp. genotypes in the laboratory. Genotypes Prunus kansuensis (Rehder), I-67-52-9, and I-67-52-4 were the most susceptible to G. molesta infestation in the field (>60% of branches infested), while 'Sharpe' (Prunus angustifolia x Prunus spp.) and Prunus sellowii (Koehne) were the least infested (0% of branches infested). In choice and no-choice bioassays, G. molesta preferred to oviposit on P. kansuensis when compared with Sharpe. The Sharpe genotype also showed an antibiosis effect, resulting in negative effects on the fertility life table parameters when compared with the genotypes P. kansuensis and 'Capdeboscq.' The results found in the present study can provide information to initiate a long-term breeding program moving desired G. molesta resistance traits from the rootstock into the Prunus spp. cultivars.

Generalist dispersers promote germination of an alien fleshy-fruited tree invading natural grasslands.

Plants with animal-dispersed fruits seem to overcome the barriers that limit their spread into new habitats more easily than other invasive plants and, at the same time, they pose special difficulties for containment, control or eradication. The effects of animals on plant propagules can be very diverse, with positive, neutral or negative consequences for germination and recruitment. Moreover, the environmental conditions where the seeds are deposited and where the post-dispersal processes take place can be crucial for their fate. Prunus mahaleb is a fleshy-fruited tree invading natural grasslands in the Argentine Pampas. In this study, we analyzed the importance of pulp removal, endocarp scarification and the effects of vectors on its germination response, by means of germination experiments both in the laboratory and under semi-natural conditions. Our laboratory results demonstrated that endocarp scarification enhances germination and suggests that vestiges of pulp on the stones have inhibitory effects. Frugivores exert a variety of effects on germination responses and this variation can be explained by their differing influence on pulp removal and endocarp scarification. Most frugivores produced a positive effect on germination under laboratory conditions, in comparison to intact fruits and hand-peeled stones. We observed different degrees of pulp removal from the surface of the stones by the dispersers which was directly correlated to the germination response. On the other hand, all the treatments showed high germination responses under semi-natural conditions suggesting that post-dispersal processes, like seed burial, and the exposure to natural conditions might exert a positive effect on germination response, attenuating the plant's dependence on the dispersers' gut treatment. Our results highlight the need to consider the whole seed dispersal process and the value of combining laboratory and field tests.

Use of plant woody species electrical potential for irrigation scheduling.

The electrical response of plants to environmental stimuli can be measured and quantitatively related to the intensity of several stimulating sources, like temperature, solar radiation, soil water content, evapotranspiration rates, sap flow and dendrometric cycles. These relations can be used to assess the influence of different environmental situations on soil water availability to plants, defined as a steady state condition between leaf transpirative flow and soil water flow to plant roots. A restricted soil water flow due to soil dryness can trigger water stress in plants, if the atmospheric evaporative demand is high, causing partial stomata closure as a physiological response to avoid plant dehydration; water stressed and unstressed plants manifest a differential electrical response. Real time plant electrical response measurements can anticipate actions that prevent the plant reaching actual stress conditions, optimizing stomata gas exchange and photosynthetic rates. An electrophysiological sensor developed in this work, allows remote real-time recording information on plant electrical potential (EP) in the field, which is highly related to EP measurements obtained with a laboratory Keithley voltmeter sensor used in an highly controlled experimental setup. Our electrophysiological sensor is a wireless, autonomous devise, which transmits EP information via Internet to a data server. Using both types of sensors (EP electrodes with a Keithley voltmeter and the electrophysiological sensor), we measured in real time the electrical responses of Persea americana and Prunus domestica plants, to induced water deficits. The differential response for 2 scenarios: irrigation and water restriction is identified by a progressive change in slope on the daily maximal and minimal electric signal values in stressed plants, and a zero-slope for similar signals for well-watered plants. Results show a correspondence between measured signals obtained by our electrophysiological sensor and the EP electrodes connected to the Keithley voltmeter in each irrigation stage. Also, both sensors show a daily cyclical signal (circadian cycle).

Electrophysiological assessment of water stress in fruit-bearing woody plants.

Development and evaluation of a real-time plant water stress sensor, based on the electrophysiological behavior of fruit-bearing woody plants is presented. Continuous electric potentials are measured in tree trunks for different irrigation schedules, inducing variable water stress conditions; results are discussed in relation to soil water content and micro-atmospheric evaporative demand, determined continuously by conventional sensors, correlating this information with tree electric potential measurements. Systematic and differentiable patterns of electric potentials for water-stressed and no-stressed trees in 2 fruit species are presented. Early detection and recovery dynamics of water stress conditions can also be monitored with these electrophysiology sensors, which enable continuous and non-destructive measurements for efficient irrigation scheduling throughout the year. The experiment is developed under controlled conditions, in Faraday cages located at a greenhouse area, both in Persea americana and Prunus domestica plants. Soil moisture evolution is controlled using capacitance sensors and solar radiation, temperature, relative humidity, wind intensity and direction are continuously registered with accurate weather sensors, in a micro-agrometeorological automatic station located at the experimental site. The electrophysiological sensor has two stainless steel electrodes (measuring/reference), inserted on the stem; a high precision Keithley 2701 digital multimeter is used to measure plant electrical signals; an algorithm written in MatLab(®), allows correlating the signal to environmental variables. An electric cyclic behavior is observed (circadian cycle) in the experimental plants. For non-irrigated plants, the electrical signal shows a time positive slope and then, a negative slope after restarting irrigation throughout a rather extended recovery process, before reaching a stable electrical signal with zero slope. Well-watered plants presented a continuous signal with daily maximum and a minimum EP of similar magnitude in time, with zero slope. This plant electrical behavior is proposed for the development of a sensor measuring real-time plant water status.

Deciphering the metabolic pathways influencing heat and cold responses during post-harvest physiology of peach fruit.

Peaches are highly perishable and deteriorate quickly at ambient temperature. Cold storage is commonly used to prevent fruit decay; however, it affects fruit quality causing physiological disorders collectively termed 'chilling injury' (CI). To prevent or ameliorate CI, heat treatment is often applied prior to cold storage. In the present work, metabolic profiling was performed to determine the metabolic dynamics associated with the induction of acquired CI tolerance in response to heat shock. 'Dixiland' peach fruits exposed to 39 °C, cold stored, or after a combined treatment of heat and cold, were compared with fruits ripening at 20 °C. Dramatic changes in the levels of compatible solutes such as galactinol and raffinose were observed, while amino acid precursors of the phenylpropanoid pathway were also modified due to the stress treatments, as was the polyamine putrescine. The observed responses towards temperature stress in peaches are composed of both common and specific response mechanisms to heat and cold, but also of more general adaptive responses that confer strategic advantages in adverse conditions such as biotic stresses. The identification of such key metabolites, which prime the fruit to cope with different stress situations, will likely greatly accelerate the design and the improvement of plant breeding programs.

Breeding in peach, cherry and plum: from a tissue culture, genetic, transcriptomic and genomic perspective.

This review is an overview of traditional and modern breeding methodologies being used to develop new Prunus cultivars (stone fruits) with major emphasis on peach, sweet cherry and Japanese plum. To this end, common breeding tools used to produce seedlings, including in vitro culture tools, are discussed. Additionally, the mechanisms of inheritance of many important agronomical traits are described. Recent advances in stone fruit transcriptomics and genomic resources are providing an understanding of the molecular basis of phenotypic variability as well as the identification of allelic variants and molecular markers. These have potential applications for understanding the genetic diversity of the Prunus species, molecular marker-assisted selection and transgenesis. Simple Sequence Repeat (SSR) and Single Nucleotide Polymorphism (SNPs) molecular markers are described as useful tools to describe genetic diversity in peach, sweet cherry and Japanese plum. Additionally, the recently sequenced peach genome and the public release of the sweet cherry genome are discussed in terms of their applicability to breeding programs.

Breeding in peach, cherry and plum: from a tissue culture, genetic, transcriptomic and genomic perspective

This review is an overview of traditional and modern breeding methodologies being used to develop new Prunus cultivars (stone fruits) with major emphasis on peach, sweet cherry and Japanese plum. To this end, common breeding tools used to produce seedlings, including in vitro culture tools, are discussed. Additionally, the mechanisms of inheritance of many important agronomical traits are described. Recent advances in stone fruit transcriptomics and genomic resources are providing an understanding of the molecular basis of phenotypic variability as well as the identification of allelic variants and molecular markers. These have potential applications for understanding the genetic diversity of the Prunus species, molecular marker-assisted selection and transgenesis. Simple Sequence Repeat (SSR) and Single Nucleotide Polymorphism (SNPs) molecular markers are described as useful tools to describe genetic diversity in peach, sweet cherry and Japanese plum. Additionally, the recently sequenced peach genome and the public release of the sweet cherry genome are discussed in terms of their applicability to breeding programs.

Peach (Prunus persica) fruit response to anoxia: reversible ripening delay and biochemical changes.

The use of modified atmospheres has been successfully applied in different fruits to delay the ripening process and to prevent physiological disorders. In addition, during normal ripening, hypoxic areas are generated inside the fruit; moreover, anaerobic conditions may also arise during fruit post-harvest storage and handling. In consequence, the fruit is an interesting model to analyze the metabolic modifications due to changes in oxygen levels. In this work, a 72 h anoxic treatment by using an N(2) storage atmosphere was applied to peaches (Prunus persica L. Batsch) after harvest. Ripening was effectively delayed in treated fruits, preventing fruit softening, color changes and ethylene production. Metabolic changes induced by anoxia included induction of fermentative pathways, glycolysis and enzymes involved in both sucrose synthesis and degradation. Sucrose, fructose and glucose contents remained unchanged in treated fruit, probably due to sucrose cycling. Sorbitol was not consumed and citrate was increased, correlating with citric acid cycle impairment due to O(2) deprivation. Malate content was not affected, indicating compensation in the reactions producing and consuming malate. Changes in malic enzymes and pyruvate orthophosphate dikinase may provide pyruvate for fermentation or even act to regenerate NADP. After fruit transfer to aerobic conditions, no signs of post-anoxia injury were observed and metabolic changes were reversed, with the exception of acetaldehyde levels. The results obtained indicate that peach fruit is an organ with a high capacity for anoxic tolerance, which is in accord with the presence of hypoxic areas inside fruits and the fact that hypoxic pre-treatment improves tolerance to subsequent anoxia.

Differential expression levels of aroma-related genes during ripening of apricot (Prunus armeniaca L.).

Fruit aroma is a complex trait, particularly in terms of the number of different biosynthetic pathways involved, the complexity of the final metabolites, and their regulation. In order to understand the underlying biochemical processes involved in apricot aroma, four cDNAs (Pa-aat, EU784138; Pa-adhEU395433; Pa-pdcEU395434; and Pa-loxEU439430) encoding an alcohol acyl transferase (AAT), alcohol dehydrogenase (ADH), pyruvate decarboxylase (PDC), and lipoxygenase (LOX), respectively, were isolated and characterized at four stages of maturity in Prunus armeniaca L. cv. Modesto. We observed a reduction in aldehyde and alcohol production between early-harvested fruit and late-harvest fruit, concomitant with an increase in ester production. qPCR analyses showed that the expression levels of the adh gene and the lox gene stayed constant at all stages. Interestingly, aat levels showed a sharp increase in the late-harvest stages concurrent with the changes observed in ester levels. The significance of these changes in relation to aroma production in apricot is discussed.

Identification of woolliness response genes in peach fruit after post-harvest treatments.

Woolliness is a physiological disorder of peaches and nectarines that becomes apparent when fruit are ripened after prolonged periods of cold storage. This disorder is of commercial importance since shipping of peaches to distant markets and storage before selling require low temperature. However, knowledge about the molecular basis of peach woolliness is still incomplete. To address this issue, a nylon macroarray containing 847 non-redundant expressed sequence tags (ESTs) from a ripe peach fruit cDNA library was developed and used. Gene expression changes of peach fruit (Prunus persica cv. O'Henry) ripened for 7 d at 21 degrees C (juicy fruit) were compared with those of fruit stored for 15 d at 4 degrees C and then ripened for 7 d at 21 degrees C (woolly fruit). A total of 106 genes were found to be differentially expressed between juicy and woolly fruit. Data analysis indicated that the activity of most of these genes (>90%) was repressed in the woolly fruit. In cold-stored peaches (cv. O'Henry), the expression level of selected genes (cobra, endopolygalacturonase, cinnamoyl-CoA-reductase, and rab11) was lower than in the juicy fruit, and it remained low in woolly peaches after ripening, a pattern that was conserved in woolly fruit from two other commercial cultivars (cv. Flamekist and cv. Elegant Lady). In addition, the results of this study indicate that molecular changes during fruit woolliness involve changes in the expression of genes associated with cell wall metabolism and endomembrane trafficking. Overall, the results reported here provide an initial characterization of the transcriptome activity of peach fruit under different post-harvest treatments.

Effects of irrigation deprivation during the harvest period on yield determinants in mature almond trees.

Effects of irrigation deprivation during the harvest period on yield determinants in mature almond (Prunus dulcis (Mill.) D.A. Webb cv. Nonpareil) trees were investigated during a 3-year field experiment. Return bloom and fruit set were measured on 2185 individually tagged spurs. Water stress resulting from irrigation deprivation during the harvest period, which purportedly coincides with the time of flower initiation, had no effect on the percentage of spurs that flowered or set fruit during subsequent years. Although water stress had no apparent effect on spur mortality, 66% of the tagged spurs died within 3 years. In addition, many spurs were vegetative by the third year, indicating the importance of spur renewal for sustained fruit production. Reductions in nut yield were evident after two successive years of irrigation deprivation during the harvest period. Regression analysis indicated a loss in yield of 7.7 kg tree(-1) in response to each 1 MPa decrease in stem water potential below -1.2 MPa during the previous seasons. The number of fruiting positions per tree (estimated indirectly for whole trees based on weight of current-year shoots > 5 cm in length) was negatively associated with water stress. Yield reduction in response to water stress during harvest appears to be a compound, multiyear effect, associated with reduced annual growth and renewal of fruiting positions.

Effects of irrigation deprivation during the harvest period on nonstructural carbohydrate and nitrogen contents of dormant, mature almond trees.

Effect of irrigation deprivation during the harvest period on the nonstructural carbohydrate (NC) content of dormant, mature, field-grown almond (Prunus dulcis (Mill.) D.A. Webb cv. Nonpareil) trees was studied. Roots, trunk, branches, spurs and stems of 12 trees were subsampled in February 1997, across a gradient of irrigation treatments (FI = fully irrigated, MS = moderately stressed and SS = severely stressed) to relate NC concentration to the degree of water stress experienced by individual trees during the previous (1996) harvest period. To assess the effect of water stress on whole-tree NC content, three dormant FI trees and three dormant SS trees were excavated on December 10, 1997, and dry weights and NC and N concentrations of the tree components were determined. Whole-tree biomass did not differ significantly between FI and SS trees, although SS trees tended to have less total dry weight. Although roots constituted just 13% of tree biomass, they stored 36 and 44% of tree NC and N contents, respectively. There were negative relationships between the seasonal minimum values of both midday (Psi(ms)) and predawn (Psi(pd)) stem water potentials during the harvest period and root NC content of dormant trees. Severe water stress during the harvest period resulted in a 26% reduction in NC content and a 50% reduction in biomass of current-year stems (> 5 cm in length) per tree. The reduction in NC content is consistent with the previously reported late season reductions in leaf function and persistence. The SS trees exhibited a reduction in NC content but not in N content per tree, indicating that late season accumulation of NC and N were uncoupled in trees subjected to severe harvest-period water stress.