Growth, cambial activity and phloem structure in compatible and incompatible peach/plum grafts

Peach (Prunus persica L. Batsch) shoots grafted onto compatible or incompatible clones of rootstocks of myrobolan plum (Prunus cerasifera L. Ehrh. cv. myrobolan) were observed in a greenhouse for 100 days after grafting. The incompatible grafts showed foliar symptoms of incompatibility and reduced shoot growth about 60 days after grafting. Light microscopic studies revealed that cambial activity stopped earlier in the rootstocks, than in the scions, of incompatible grafts. Structural modifications were also observed in the phloem of incompatible grafts. Compared with the compatible graft rootstock, the number of sieve elements differentiated from the cambial zone was reduced in the incompatible graft rootstock, whereas the production of parenchyma cells was not affected. No important ultrastructural alteration was observed in the sieve tubes of the incompatible grafts. However, osmiophilic granulations near the plasma membrane of sieve plates were observed more frequently in the rootstocks of incompatible grafts than in ungrafted myrobolan controls. It is concluded that the external symptoms of incompatibility are not related to massive structural modifications or degeneration of the conducting tissues.     

Carbon and nitrogen partitioning in peach/plum grafts

Modifications in root-shoot relationships induced by graft incompatibility were studied in peach/plum graft combinations by means of carbohydrate and nitrogen analyses and isotope labeling. Mobilization of stored carbon, phloem transport of carbon, and mobilization, assimilation and distribution of nitrogen were studied in one compatible peach/plum graft (Prunus persica L. Batsch cv. springtime grafted on Prunus cerasifera L. Ehrh cv. myrobalan P 2032) and one incompatible graft (Prunus persica L. Batsch cv. Springtime grafted on Prunus cerasifera L. Ehrh cv. myrobalan P 18) for 89 days after grafting. Carbon and nitrogen reserves were mobilized in the rootstock in both graft combinations during the first 78 days following grafting. After that, sorbitol concentration was lower in the roots of the incompatible graft than in the roots of the compatible graft, whereas soluble sugars and starch accumulated in the peach scion of the incompatible graft. In both graft types, carbon was allocated mainly to the scion. Labeling with (13)CO(2) from 78 to 81 days after grafting showed that carbon partitioning among the different plant organs was only slightly affected by graft incompatibility. Carbohydrate concentrations provided indirect evidence that carbon transfer to the roots was hindered in the incompatible graft. Labeling with (15)NO(3) showed that nitrogen distribution and the rate of nitrogen assimilation were similar in the two graft combinations from 57 to 78 days after grafting. Nitrogen assimilation in the incompatible graft ceased 78 days after grafting, whereas it continued in the compatible graft.     

The effect of different atmospheric ozone partial pressures on photosynthesis and growth of nine fruit and nut tree species

Nursery stock of peach (Prunus persica L. Batsch, cv. O'Henry), nectarine (P. persica L. Batsch, cv. Fantasia), plum (P. salicina Lindel., cv. Casselman), apricot (P. armeniaca L., cv. Tilton), almond (P. dulcis Mill., cv. Nonpareil), prune (P. domestica L., cv. Improved French), cherry (P. avium L., cv. Bing), oriental pear (Pyrus pyrifolia Rehd., cv. 20th Century), and apple (Malus pumula Mill., cv. Granny Smith) were planted in open-top chambers on April 1, 1988 at the University of California's Kearney Agricultural Center located in the San Joaquin Valley (30 degrees 40' N 119 degrees 40' W). Trees were exposed to three atmospheric ozone partial pressures (charcoal-filtered air (C), ambient air (A), or ambient air + ozone (T)) from August 1 to November 17, 1988. The mean 12-h (0800 to 2000 h) ozone partial pressures measured in open-top chambers during the experimental period were 0.030, 0.051, and 0.117 microPa Pa(-1) in the C, A and T treatments, respectively. Leaf net CO(2) assimilation rate decreased linearly with increasing 12-h mean ozone partial pressure for the almond, plum, apricot, prune, pear, and apple cultivars. Stomatal conductances of apricot, apple, almond, and plum decreased linearly with increasing ozone partial pressure. Cross-sectional area relative growth rates of almond, plum, apricot, and pear decreased linearly with increasing ozone partial pressure. Net CO(2) assimilation rate, stomatal conductance, and trunk growth of cherry, peach and nectarine were unaffected by the ozone treatments. Reduced leaf gas exchange probably contributed to ozone-induced growth reduction of the susceptible species and cultivars. Several of the commercial fruit tree species and cultivars studied were relatively tolerant to the ozone treatments.     

Changes in polyamine concentration associated with aging in Pinus radiata and Prunus persica

Endogenous polyamine concentrations in apical buds of peach (Prunus persica (L.) Batsch cv. 'Hakuho') and monterey pine (Pinus radiata D. Don) seedlings, saplings and mature trees were analyzed by high performance liquid chromatography coupled with fluorescence detection to establish physiological correspondences and disparities between the species. Although there were many differences in polyamine metabolism between peach and monterey pine, several similarities were found. Specifically, in both species, the ratio between concentrations of free polyamines and low molecular-weight polyamine conjugates was greater than and less than unity in juvenile and adult plants, respectively. Free putrescine concentration decreased with age in both species.     

Responses of Prunus ferganensis,Prunus persica and two interspecific hybrids to moderate drought stress

Prunus ferganensis (Kost. & Riab) Kov. & Kost, a close relative of cultivated peach (Prunus persica (L.) Batsch.), is native to arid regions of central Asia. A distinguishing feature of P. ferganensis is its prominent, elongated, unbranched pattern of leaf venation. To determine whether the long-vein trait could be used as a marker in breeding for drought tolerance, we investigated the association between this trait and the leaf morphological and physiological parameters related to drought response in P. ferganensis, P. persica and two interspecific hybrids, one with the long-vein trait (BY94P7585) and one without (BY94P7589). The four genotypes were grafted onto "Guardian" peach rootstock and half of the plants were assigned to a drought treatment in which irrigation was limited to 25-50% of the evapotranspiration (ET) rate measured in the remaining well-watered plants, which were irrigated to runoff daily. The drought treatment reduced photosynthesis and leaf conductance by 49-83% and reduced total leaf area per plant by 17-24%, but generally did not affect mid-morning leaf water potential. Leaf gas exchange did not differ among genotypes in either treatment. Sorbitol accumulated in mature leaves in response to drought, but neither its amount nor its metabolism varied systematically with climatic adaptation among genotypes. Accumulation of transport sugars was highest in P. ferganensis, indicating that growth reduction may represent an important strategy for coping with drought in this species. Prunus ferganensis and the hybrids had higher ET than P. persica, and seemed to use water opportunistically, maintaining high gas exchange rates and consequently high ET when water was available, and avoiding low water potentials through stomatal closure as soil water declined. Leaf size (cm(2) leaf(-1)) and specific leaf area (cm(2) g(-1) dry mass) were lower in P. ferganensis and the hybrids than in P. persica. We conclude that the long-vein trait is not a reliable marker for drought tolerance, but leaf traits of P. ferganensis such as size and specific leaf area may be useful in P. persica breeding programs targeting drought tolerance.     

Trophic control of bud break in peach (Prunus persica) trees: a possible role of hexoses

Vegetative buds of peach (Prunus persica L. Batsch.) trees act as strong sinks and their bud break capacity can be profoundly affected by carbohydrate availability during the rest period (November-February). Analysis of xylem sap revealed seasonal changes in concentrations of sorbitol and hexoses (glucose and fructose). Sorbitol concentrations decreased and hexose concentrations increased with increasing bud break capacity. Sucrose concentration in xylem sap increased significantly but remained low. To clarify their respective roles in the early events of bud break, carbohydrate concentrations and uptake rates, and activities of NAD-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX) and cell wall invertase (CWI) were determined in meristematic tissues, cushion tissues and stem segments. Only CWI activity increased in meristematic tissues shortly before bud break. In buds displaying high bud break capacity (during January and February), concentrations of sorbitol and sucrose in meristematic tissues were almost unchanged, paralleling their low rates of uptake and utilization by meristematic tissues, and indicating that sorbitol and sucrose play a negligible role in the bud break process. Hexose concentrations in meristematic tissues and glucose imported by meristematic tissues correlated positively with bud break capacity, suggesting that hexoses are involved in the early events of bud break. These findings were confirmed by data for buds that were unable to break because they had been collected from trees deprived of cold. We therefore conclude that hexoses are of greater importance than sorbitol or sucrose in the early events of bud break in peach trees.     

Daily sap flow and maximum daily trunk shrinkage measurements for diagnosing water stress in early maturing peach trees during the post-harvest period

We compared the sensitivity of two continuously recorded plant-based water stress indicators (sap flow, SF, and maximum daily trunk shrinkage, MDS) to detect changes in the water status of 4-year-old early maturing peach trees (Prunus persica (L.) Batsch cv. Flordastar grafted on GF-677 peach rootstock) during a cycle of deficit irrigation and recovery. The feasibility of obtaining SF and MDS reference equations for use in irrigation scheduling during the post-harvest period was also studied in trees irrigated in excess of crop water requirements. We found that MDS was a more sensitive and reliable detector of changes in plant water status than SF, making it a more precise tool for irrigation scheduling. Baseline relationships between SF or MDS and the climatic variables (air temperature, vapor pressure deficit (VPD) and crop reference evapotranspiration (ETo)) were established, despite some scatter in the data. Among the climatic variables, SF correlated more closely with ETo, whereas MDS correlated more closely with mean daily air temperature (T (m)). The fits of the regressions between MDS and ETo, midday air temperature and T (m) for individual periods were better than those obtained in the overall regressions, confirming that daily stem diameter variations must be considered not only in the context of plant water status but also in the context of plant carbon status.     

Daily shoot extension growth of peach trees growing on rootstocks that reduce scion growth is related to daily dynamics of stem water potential

We studied relationships between diurnal patterns of stem water potential (PsiSTEM) and stem extension growth of the same scion cultivar growing on three rootstocks with differing size-controlling potentials. The peach trees (Prunus persica (L.) Batsch) used in this field experiment consisted of an early-maturing freestone cultivar, 'Flavorcrest,' grafted onto three different rootstocks: Nemaguard (a vigorous seed-propagated control, P. persica x P. davidiana hybrid), Hiawatha (an intermediate vigor rootstock, derived from an open pollinated seedling of a P. besseyi x P. salicina hybrid) and K-146-43 (a semi-dwarfing rootstock, P. salicina x P. persica hybrid). Diurnal patterns of PsiSTEM and stem extension growth were measured on six dates (March 29, April 12, April 26, May 10, May 24 and June 18) during the primary period of peach shoot extension growth. Rootstocks clearly affected diurnal patterns of PsiSTEM and stem extension growth. Trees on K-146-43 had the lowest midday PsiSTEM and stem extension growth. Differences among rootstocks in the amount of diurnal oscillation in PsiSTEM explained stem extension rate differences induced by the three rootstocks. The sensitivity of shoot extension growth to tree water relations tended to decrease as the season progressed and was not apparent by mid-June. The results of the study indicate that water relations may play an important role in the dwarfing mechanism induced by size-controlling peach rootstocks.     

Comparison of drought resistance among Prunus species from divergent habitats

Root and shoot characteristics related to drought resistance were compared among cultivated peach (Prunus persica (L.) Batsch.), P. andersonii (Nevada Desert almond), P. besseyi (western sand cherry), P. maritima (beach plum), P. subcordata (Sierra or Pacific plum), and P. tomentosa (Nanking cherry). In all species, shoot characteristics were more closely associated with drought adaptation than root characteristics. The most xeric species, P. andersonii, had the lowest specific leaf area, smallest leaves, highest stomatal conductance (before stress), highest rate of carbon assimilation (A), high root length/leaf area and root weight/leaf area ratios, and the highest leaf nitrogen content on an area basis. Root hydraulic conductivity was similar for all species, indicating a lack of importance of this parameter for drought resistance. During a 5-7 day drought, water use efficiency (WUE) increased as shoot water potentials (Psi) declined to -3.0 to -4.0 MPa for the xeric P. andersonii and P. subcordata, whereas after an initial increase, WUE decreased with declining Psi in the -1.5 to -3.0 MPa range for the more mesic P. maritima, P. persica and P. tomentosa as a result of non-stomatal limitations to A. Carbon assimilation rate decreased linearly with Psi during drought in all species, but the Psi at which A reached zero was not associated with drought adaptation. We conclude that the variation in leaf characteristics among Prunus species could be exploited to improve the drought resistance of commercial cultivars.     

Evaluation of sap flow and trunk diameter sensors for irrigation scheduling in early maturing peach trees

Five-year-old early maturing peach trees (Prunus persica (L.) Batsch cv. Flordastar grafted on GF-677 peach rootstock) were subjected to three irrigation treatments from March 18 to November 10, 2006. Control plants (T0 treatment) which received irrigation in excess of their crop water requirements (1089.7 mm) were compared with plants watered according to sap flow (SF; T1 treatment) or maximum daily trunk shrinkage (MDS; T2 treatment) measurements, so as to maintain SF and MDS signal intensities (control SF/SF in T1 and MDS in T2/control MDS, respectively) close to unity. When SF or MDS signal intensity on at least two of three consecutive days was at or below unity, irrigation was reduced by 10%. When the MDS signal intensity on at least two of three consecutive days exceeded unity, irrigation was increased by 10%. During the experiment, estimated crop evapotranspiration was 704.9 mm, and the cumulative amounts of applied water in the T1 and T2 treatments were 463.2 and 654.5 mm, respectively. The MDS-signal-intensity-driven irrigation schedule was more suitable than the SF-signal-intensity-driven irrigation schedule because it was more sensitive and reliable in detecting changes in plant water status, preventing the development of detectable plant water stress. Moreover, it had no effect on fruit size. We conclude that peach tree irrigation scheduling can be based on MDS measurements alone. Changes in the irrigation protocol assayed were proposed to reduce MDS signal intensity deviations above unity, for example, by increasing the irrigation scheduling frequency or the amount of water applied, or both. Irrigation schedules based on maintaining MDS signal intensities close to unity could be applied when local crop factor values are unavailable.     

Growth patterns and morphology of fine roots of size-controlling and invigorating peach rootstocks

We compared growth patterns and morphology of fine roots of size-controlling and invigorating peach (Prunus persica (L.) Batsch) rootstocks. Peach trees were grafted on five rootstocks: a vigorous control (Nemaguard), three intermediate vigor rootstocks (K119-50, P30-135 and Hiawatha), and a semi-dwarfing rootstock (K146-43). Minirhizotron tubes were installed at the base of trees on each rootstock and root images captured with a minirhizotron digital camera system. Number, visible length, and diameter of new roots were recorded at fixed soil depths from April 19, 2000 to December 19, 2001. Root diameter, specific root length, root tissue density and root length density were also measured periodically for each rootstock on roots collected from in-growth cores. Rootstocks had similar seasonal patterns of new root production. Fine root production was lowest in winter and appeared to decline during the final stages of fruit growth. A rootstock with almond in its genetic background (K119-50) produced the greatest quantity of fine roots and had the greatest number of new roots below 69 cm, whereas there were no differences among the other four rootstocks in the total number of roots produced. Rootstock K146-43 had thicker fine roots than the other rootstocks. Independent of rootstock, fine roots produced during spring had greater specific root length than those produced later in the season. The seasonal pattern of fine root production did not appear to be associated with the previously reported effects of these dwarfing rootstocks on shoot growth and stem water potential early in the growing season.     

Changes in fruit sugar concentrations in response to assimilate supply,metabolism and dilution: a modeling approach applied to peach fruit (Prunus persica)

The influence of assimilate supply, metabolism and dilution on sugar concentrations in the mesocarp of peach (Prunus persica (L.) Batsch) fruit during the main stage of fruit enlargement was analyzed with the SUGAR model of Génard and Souty (1996). The model predicts the partitioning of carbon into sucrose, sorbitol, glucose and fructose in the mesocarp of peach fruit. Based on measured data and the model, we determined values for the relative rates of sugar transformation. These rates were constant, varied with time or varied with relative fruit growth rate, depending on the type of sugar. Equations were derived to describe these rates and incorporated into the SUGAR model. The model simulated the effects of changing assimilate supply and fruit volume on sugar concentrations. The set of equations for the SUGAR model was rewritten to include the three components influencing sugar concentrations: assimilate supply, metabolism and dilution. The sugar types differed in sensitivity to these components. Sucrose was highly sensitive to changes in assimilate supply and to the dilution effect; it was not subject to intense metabolic transformation. Sorbitol was the most important carbohydrate in fruit metabolism, which explains why the sorbitol concentration was always low despite the strong positive effect of assimilate supply. The reducing sugars constituted a transitory storage pool and their concentrations were closely related to metabolism.     

Influence of arbuscular mycorrhizae and phosphate fertilization on shoot apical growth of micropropagated apple and plum rootstocks

We studied the effects of phosphate fertilization and inoculation with the arbuscular mycorrhizal fungi Glomus mosseae (Nicol. and Gerd.) Gerdmann and Trappe, Glomus intraradices Schenck and Smith or Glomus viscosum Nicolson on shoot apical growth of plantlets that had been micropropagated from MM 106 apple (Malus pumila L.) and Mr.S. 2/5 plum (Prunus cerasifera Ehrh.) rootstocks. Unfertilized and non-mycorrhizal plantlets showed no apical growth during the post in vitro acclimation phase, whereas P fertilization induced early resumption of shoot apical growth. Growth enhancement and percentage of actively growing apices of mycorrhizal-inoculated plantlets were comparable to those obtained in plantlets fertilized with P. Furthermore, tissue P concentrations of mycorrhizal plantlets were similar to those of plantlets fertilized with P. We conclude that mycorrhizal inoculation can be used as a biotechnological tool to overcome blocked apical growth and to reduce chemical inputs, especially P inputs, to micropropagated fruit trees.     

Winter embolism,mechanisms of xylem hydraulic conductivity recovery and springtime growth patterns in walnut and peach trees

Xylem vessels of Prunus persica Batsch (peach) and Juglans regia L. (walnut) are vulnerable to frost-induced embolism. In peach, xylem embolism increased progressively over the winter, reaching a maximum of 85% loss of hydraulic conductivity (PLC) in early March. Over winter, PLC in walnut approached 100%, but the degree of xylem embolism varied during the winter, reflecting the ability of walnut to generate positive xylem pressures in winter and spring. In contrast, positive xylem pressures were not observed in peach. Controlled freeze-thaw experiments showed that frost alone is insufficient to increase embolism in peach; evaporative conditions during thawing are also required. However, when both species were protected from frost, PLC was zero. At bud break, there was complete recovery from embolism in walnut, whereas PLC remained high in peach. Three mechanisms responsible for the restoration of branch hydraulic conductivity were identified in walnut: the development of stem pressure, the development of root pressure and the formation of a new ring of functional xylem, whereas only one mechanism was observed in peach (new functional ring). The climatic conditions necessary for the manifestation of these mechanisms were investigated.     

Water stress and crop load effects on fruit fresh and dry weights in peach (Prunus persica)

Effects of water stress on fruit fresh and dry weights were investigated in peach trees, Prunus persica (L.) Batsch., with varying crop loads: light, moderate and heavy. In well-watered controls, tree water status was independent of crop load. In trees receiving reduced irrigation, the degree of water stress increased with increasing crop load. Water stress induced fruit fresh weight reductions at all crop loads. Fruit dry weight was not reduced by water stress in trees having light to moderate crop loads, indicating that the degree of water stress imposed did not affect the dry weight sink strength of fruit. Water-stressed trees with heavy crop loads had significantly reduced fruit dry weights, which were likely due to carbohydrate source limitations resulting from large crop carbon demands and water stress limitations on photosynthesis.     

Preformation in vegetative buds of Prunus persica: factors influencing number of leaf primordia in overwintering buds

We investigated the influence of bud position, cultivar, tree age, tree carbohydrate status, sampling date, drought and light exposure on the number of leaf primordia formed in dormant vegetative peach buds (Prunus persica (L.) Batsch) relative to the number of primordia formed after bud break (neoformed). During winter dormancy, vegetative peach buds from California and Italy were dissected and the number of leaf primordia recorded. Between leaf drop and bud break, the number of leaf primordia doubled from about five to about 10. Parent shoot length, number of nodes on the parent shoot, cross-sectional area of the parent shoot, bud position along the parent shoot and bud cross-sectional area were correlated with the number of leaf primordia. Previous season light exposure, drought and tree carbohydrate status did not affect the number of leaf primordia present. The number of leaf primordia differed significantly among peach varieties and tree ages at leaf drop, but not at bud break. Our results indicate that neoformation accounted for all shoot growth beyond about 10 nodes. The predominance of neoformed shoot growth in peach allows this species great plasticity in its response to current-season conditions.     

Changes in fine root production and longevity in relation to water and nutrient availability in a Norway spruce stand in northern Sweden

The PEACH computer simulation model of reproductive and vegetative growth of peach trees (Grossman and DeJong 1994) was adapted to estimate seasonal nitrogen (N) dynamics in organs of mature peach (Prunus persica (L.) Batsch cv. O'Henry) trees grown with high and low soil N availability. Seasonal N accumulation patterns of fruits, leaves, stems, branches, trunk and roots of mature, cropping peach trees were modeled by combining model predictions of organ dry mass accumulation from the PEACH model with measured seasonal organ N concentrations of trees that had been fertilized with either zero or 200 kg N ha(-1) in April. The results provided a comparison of the N use of perennial and annual organs during the growing season for trees growing under both low and high N availability. Nitrogen fertilization increased tree N content by increasing organ dry masses and N concentrations during the fruit growing season. Dry mass of current-year vegetative growth was most affected by N fertilization. Whole-tree N content of fertilized trees was almost twice that of non-fertilized trees. Although N use was higher in fertilized trees, calculated seasonal N accumulation patterns were similar for trees in both treatments. Annual organs exhibited greater responses to N fertilization than perennial organs. Estimated mean daily N use per tree remained nearly constant from 40 days after anthesis to harvest. The calculations indicated that fertilized trees accumulated about 1 g N tree(-1) day(-1), twice that accumulated by non-fertilized trees. Daily N use by the fertilized orchard was calculated to be approximately 1 kg N ha(-1), whereas it was approximately 0.5 kg N ha(-1) for the non-fertilized trees. During the first 25-30 days of the growing season, all N use by growing tissues was apparently supplied by storage organs. Nitrogen release from storage organs for current growth continued until about 75 days after anthesis in both N treatments.     

樱桃李的研究进展及开发利用前景

在吸收国内外相关研究成果及学术论文的基础上,详细阐述了樱桃李的生物学和生态学特性、起源、地理分布及其地理变异类型,探讨了樱桃李果实所含营养成分及其营养与医疗保健价值;分析了种质资源保存、利用与评价的现状、新品种选育研究的进展;指出了目前资源综合开发利用过程中存在的不足;展望了樱桃李系列产品开发与应用的广阔前景。旨在实现樱桃李无公害、标准化栽培及其资源的可持续利用,为推动其功能性饮品、保健品及药品的产业化发展,提供理论依据和科技支撑。     

Carbohydrate requirements of peach fruit growth and respiration

Data on the seasonal patterns of fruit growth and dark respiration of two peach (Prunus persica (L.) Batsch) cultivars were combined with temperature data to calculate the carbohydrate requirements of an "average" peach fruit from bloom to harvest. The two peach cultivars used were June Lady (an early maturing (mid-June) cultivar) and O'Henry (a late maturing (early-August) cultivar). At harvest, the mean dry weight of the June Lady fruit was 17.8 g (139.7 g fresh weight) and of O'Henry fruits was 30.9 g (213.9 g fresh weight), and the times from full bloom to harvest were 107 and 154 days, respectively. The total calculated fruit respiration requirements were 132 and 300 mmol CO(2) fruit(-1) season(-1) for June Lady and O'Henry fruits, respectively. Total calculated carbohydrate requirements for fruit growth and respiration are 23.9 and 43.8 g CH(2)O fruit(-1) season(-1) for June Lady and O'Henry fruits, respectively. Fruit respiration accounted for 16.3% of the total carbohydrate requirements of June Lady fruits and 0.5% of the total carbohydrate requirements of O'Henry fruits.