Relationship between hydraulic conductance and citrus dwarfing by the Flying Dragon rootstock (Poncirus trifoliata L. Raft var. monstruosa)

This work studied the hydraulic characteristics and physiological behavior of two trifoliate orange (Poncirus trifoliata L. Raft) varieties—Flying Dragon (FD) and Rubidoux (RT)—with contrasting size-controlling potential when used as rootstocks for citrus trees. Thus, Valencia orange scions growing on RT root system develop about 40 % more biomass than scions on FD. The anatomical study of xylem root tissue of both rootstocks showed that the number of vessels per cross-sectional area in RT almost doubled that found in FD, whereas diameter distribution did not vary significantly. Hydraulic resistance determined in rootstocks, and bud union segments were, respectively, 2- and 3.4-fold higher in trees on FD than in trees on RT. Root systems accounted for 46.5 and 55.2 % of whole-plant hydraulic resistance, whereas bud union segments represented 7.5 and 14.6 % of this parameter, the dwarfing rootstock (FD) having the highest values. Reduced hydraulic conductance in plants on FD rootstock diminished water potential in high evaporative demand periods, causing a reduction in stomatal conductance with respect to plants on RT. This leads to lower net photosynthetic CO₂ assimilation, which may affect biomass production. Translocation of ¹³C-labeled photoassimilates from leaves to roots was lower in plants on FD than in plants on RT, indicating that in the dwarfing rootstock (FD) there may be a vascular resistance to sucrose transport at the budding union level. Findings show that reduced hydraulic conductance may be the main cause of rootstock-induced dwarfing in citrus grafted onto FD.     

Influence of rootstock on antioxidant system in leaves and roots of young apple trees in response to drought stress

Grafting rootstocks are widely used to enhance plants resistance to various biologic and abiotic stresses. We determined how the rootstock genotype might influence plant responses to drought, using 2-year-old ‘Gale Gala’ apple trees grafted onto Malus sieversii and M. hupehensis. Under water stress, trees with the former as their rootstock had smaller reductions in rates of relative growth and photosynthesis, total biomass, leaf area, levels of leaf chlorophyll, and relative water content compared with those grafted onto the latter. They also had greater maximum photochemical efficiency and water-use efficiency. On the other hand, trees growing on M. sieversii rootstock had less production of superoxide radicals and hydrogen peroxide in both leaves and roots than those growing on M. hupehensis in response to drought stress. Furthermore, under drought conditions, leaves and roots from trees grafted onto M. sieversii had greater synthesis of ascorbic acid and glutathione, as well as higher activities of superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase. These results suggest that the choice of grafting rootstock can enhance drought resistance by improving the antioxidant system in a plant. Here, ‘Gale Gala’ trees grafted onto M. sieversii were more drought-resistant than those on M. hupehensis rootstock.     

Influence of the Sting Nematode, Belonolaimus longicaudalus,on Young Citrus Trees

The sting nematode, Belonolaimus longicaudatus, was associated with poor growth of citrus in a central Florida nursery. Foliage of trees was sparse and chlorotic. Affected rootstocks included Changsha and Cleopatra mandarin orange; Flying Dragon, Rubidoux, and Jacobsen trifoliate orange; Macrophylla and Milam lemon; Palestine sweet lime; sour orange; and the hybrids - Carrizo, Morton, and Rusk citrange and Swingle citrumelo. Root symptoms included apical swelling, development of swollen terminals containing 3-5 apical meristems and hyperplastic tissue, coarse roots, and a reduction in the number of fibrous roots. Population densities as high as 392 sting nematodes per liter soil were detected, with 80% of the population occurring in the top 30 cm of soil; however, nematodes were detected to 107 cm deep. Although an ectoparasite, the nematode was closely associated with citrus root systems and was transported with bare root nursery stock. Disinfestation was accomplished by hot water treatment (49 C for 5 minutes).     

Photosynthetic responses of citrus trees to soil flooding

Continuous soil flooding reduced leaf photosynthetic rate, stomatal conductance to water vapor, chlorophyll concentration and activity of ribulose bisphosphate carboxylase-oxygenase (Rubisco, EC 4.1.1.39) of sweet orange [ Citrus sinensis (L.) Osbeck cv. Hamlin] trees, grafted onto rough lemon (RL; C. jambhiri Lush.) and sour orange (SO; C. aurantium L.) rootstocks. After 24 days of waterlogging, trees showed senescence, wilting and abscission of leaves, and these symptoms were more evident with flooded Hamlin/SO than Hamlin/RL. Reduction of leaf photosynthetic rate at day 24 was ca 94%, of stomatal conductance, 71%, of chlorophyll, 38% and of Rubisco, 62% for flooded Hamlin/SO, compared with 22, 5, 18 and 33%, respectively, for flooded Hamlin/RL. For both Hamlin/RL and Hamlin/SO, leaf photosynthetic rate and stomatal conductance to water vapor were closely correlated (r²= 0.87). Leaf internal CO₂ concentration of flooded trees, however, was not decreased by reduced stomatal conductance. Dark respiration rates of fibrous roots of flooded trees were greatly reduced, but not in leaf tissues. Total nonstructural carbohydrate concentrations were higher in leaves (50 and 80% increases for Hamlin/SO and Hamlin/RL, respectively), but drastically reduced in roots (60 and 45% reductions for Hamlin/SO and Hamlin/RL, respectively), as a result of flooding. The data indicate that Hamlin grafted onto RL rootstocks was more tolerant to soil flooding than Hamlin grafted onto SO rootstocks.     

Etiology of three recent diseases of citrus in São Paulo State: sudden death, variegated chlorosis and huanglongbing

The state of S?o Paulo (SSP) is the first sweet orange growing region in the world. Yet, the SSP citrus industry has been, and still is, under constant attack from various diseases. In the 1940s, tristeza-quick decline (T-QD) was responsible for the death of 9 million trees in SSP. The causal agent was a new virus, citrus tristeza virus (CTV). The virus was efficiently spread by aphid vectors, and killed most of the trees grafted on sour orange rootstock. Control of the disease resided in replacing sour orange by alternative rootstocks giving tolerant combinations with scions such as sweet orange. Because of its drought resistance, Rangpur lime became the favourite alternative rootstock, and, by 1995, 85% of the SSP sweet orange trees were grafted on this rootstock. Therefore, when in 1999, many trees grafted on Rangpur lime started to decline and suddenly died, the spectre of T-QD seemed to hang over SSP again. By 2003, the total number of dead or affected trees was estimated to be over one million. The new disease, citrus sudden death (CSD), resembles T-QD in several aspects. The two diseases have almost the same symptoms, they spread in time and space in a manner strikingly similar, and the pathological anatomy of the bark at the bud union is alike. Transmission of the CSD agent by graft-inoculation has been obtained with budwood inoculum taken not only on CSD-affected trees (grafted on Rangpur lime), but also on symptomless trees (grafted on Cleopatra mandarin) from the same citrus block. This result shows that symptomless trees on Cleopatra mandarin are tolerant to the CSD agent. Trees on rootstocks such as Sunki mandarin or Swingle citrumelo are also tolerant. Thus, in the CSD-affected region, control consists in replacing Rangpur lime with compatible rootstocks, or in approach-grafting compatible rootstock seedlings to the scions of trees on Rangpur lime (inarching). More than 5 million trees have been inarched in this way. A new disease of sweet orange, citrus variegated chlorosis (CVC), was observed in 1987 in the Triangulo Mineiro of Minas Gerais State and the northern and north-eastern parts of SSP. By 2000, the disease affected already 34% of the 200 million sweet orange trees in SSP. By 2005, the percentage had increased to 43%, and CVC was present in all citrus growing regions of Brazil. Electron microscopy showed that xylem-limited bacteria were present in all symptomatic sweet orange leaves and fruit tissues tested, but not in similar materials from healthy, symptomless trees. Bacteria were consistently cultured from twigs of CVC-affected sweet orange trees but not from twigs of healthy trees. Serological analyses showed the CVC bacterium to be a strain of Xylella fastidiosa. The disease could be reproduced and Koch's postulates fulfilled, by mechanically inoculating a pure culture of X. fastidiosa isolate 8.1.b into sweet orange seedlings. The genome of a CVC strain of X. fastidiosa was sequenced in SSP in the frame of a project supported by FAPESP and Fundecitrus. X. fastidiosa is the first plant pathogenic bacterium, the genome of which has been sequenced. Until recently, America was free of huanglongbing (HLB), but in March 2004 and August 2005, symptoms of the disease were recognized, respectively in the State of S?o Paulo (SSP) and in Florida, USA. HLB was known in China since 1870 and in South Africa since 1928. Because of its destructiveness and its rapid spread by efficient psyllid insect-vectors, HLB is probably the most serious citrus disease. HLB is caused by a phloem sieve tube-restricted Gram negative bacterium, not yet available in culture. In the 1990s, the bacterium was characterized by molecular techniques as a member of the alpha proteobacteria designated Candidatus Liberibacter africanus for the disease in Africa, and Candidatus Liberibacter asiaticus for HLB in Asia. In SSP, Ca. L. asiaticus is also present, but most of the trees are infected with a new species, Candidatus Liberibacter americanus.     

Seasonal and diurnal changes in photosynthetic limitation of young sweet orange trees

This study tests the hypothesis that potted sweet orange plants show a significant variation in photosynthesis over seasonal and diurnal cycles, even in well-hydrated conditions. This hypothesis was tested by measuring diurnal variations in leaf gas exchange, chlorophyll fluorescence, leaf water potential, and the responses of CO₂ assimilation to increasing air CO₂ concentrations in 1-year-old ‘Valência’ sweet orange scions grafted onto ‘Cleopatra’ mandarin rootstocks during the winter and summer seasons in a subtropical climate. In addition, diurnal leaf gas exchange was evaluated under controlled conditions, with constant environmental conditions during both winter and summer. In relation to our hypothesis, a greater rate of photosynthesis is found during the summer compared to the winter. Reduced photosynthesis during winter was induced by cool night conditions, as the diurnal fluctuation of environmental conditions was not limiting. Low air and soil temperatures caused decreases in the stomatal conductance and in the rates of the biochemical reactions underlying photosynthesis (ribulose-1,5-bisphosphate (RuBP) carboxylation and RuBP regeneration) during the winter compared to the values obtained for those markers in the summer. Citrus photosynthesis during the summer was not impaired by biochemical or photochemical reactions, as CO₂ assimilation was only limited by stomatal conductance due to high leaf-to-air vapor pressure difference (VPD) during the afternoon. During the winter, the reduction in photosynthesis during the afternoon was caused by decreases in RuBP regeneration and stomatal conductance, which are both precipitated by low night temperature.     

Variation in the content of bioflavonoids of orange as affected by scion,rootstock, and fruit part

Fruits of citrus cultivars contain bioflavonoids and some other important secondary metabolites in pharmaceutical and nutritional industries. The present experiment was designed to investigate the correlation between the content of flavonoid components like naringin, hesperidin, and neohesperidin of the scions fruits and the same parameters in rootstocks fruits. Six-year-old trees including four citrus cultivars of ‘Moro’, ‘Mars’, ‘Salustiana’, and ‘Italian’ which were previously grafted on the four different rootstocks including ‘Yuzu’, ‘Shelmahalleh’, ‘Citromelo’, and ‘Sour orange’ were selected as experimental trees. The content of the mentioned flavonoids was investigated in the peel and pulp of the fruits of both scions and rootstocks. The results showed that the measured parameters were significantly influenced by scions, rootstocks, and tissues. Based on the obtained results, it can be suggested that the accumulation of chemicals in citrus fruit depends on genetic and inherent abilities of the scion, more than what was previously believed, while the rootstock can also play an important role in the accumulation of these substances.     

Growth, gas exchange, water-use efficiency, and carbon isotope composition of ‘Gale Gala’ apple trees grafted onto 9 wild Chinese rootstocks in response to drought stress

To determine the effects of rootstock choice on the scion response to drought stress, we compared the vegetative growth, biomass accumulation, gas exchange, and water-use efficiency (WUE) of ??Gale Gala?? apple (Malus domestica Borkh.) trees grafted onto nine wild Chinese Malus rootstocks. Compared with the well-watered control, drought treatment limited growth, as manifested by smaller increments in plant height (PH), trunk diameter (TD), total fresh biomass (TB), total dry biomass (TDB), total leaf area (LA), and relative growth rate (RGR). The extent of this effect differed among rootstocks. Stress conditions led to increases in the root/shoot ratio (RSR), leaf thickness (LT), water-holding capacity (WHC), carbon isotope composition (??¹³C), and WUE. Decreases were noted in stomatal density (SD), leaf relative water content (RWC), chlorophyll content (Chl), net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s), again varying by rootstock. Those that are generally considered more drought-tolerant, e.g., M. sieversii, M. prunifolia, and M. toringoides, had smaller declines in PH, TD, TB, TDB, LA, RGR, SD, RWC, Chl, P _N, E, and g _s and proportionally greater increases in RSR, LT, WHC, ??¹³C, and WUE compared with the droughtsensitive M. hupehensis and M. sieboldii. These results suggest that moisture stress has a significant dwarfing effect in the latter two species. Based on WUE calculations, trees on drought-tolerant rootstocks showed higher tolerance when stressed, whereas those on drought-sensitive rootstocks were less tolerant, as indicated by their lower WUE values.     

Drought tolerance in faster- and slower-growing black spruce (Picea mariana) progenies: II. Osmotic adjustment and changes of soluble carbohydrates and amino acids under osmotic stress

The possibility was considered that osmotic adjustment, the ability to accumulate solutes in response to water stress, may contribute to growth rate differences among closely-related genotypes of trees. Progeny variation in osmotic adjustment and turgor regulation was investigated by comparing changes in osmotic and pressure potentials, soluble carbohydrates, and amino acids in osmotically stressed seedlings in 4 full-sib progenies of black spruce [ Picea mariana (Mill.) B. S. P.] that differed in growth rate under drought. Osmotic stress was induced by a stepwise increase in the concentration of polyethylene glycol (PEG)-3350 from 10 (w/v) to 18 and 25%, which provided osmotic potentials in solution culture of -0.4, -1.0 and -2.0 MPa each for 3 days. All 4 progenies maintained a positive cell turgor even at 25% PEG, due to a significant decline in osmotic potential. Although total amino acids, principally proline, increased, ca 60% of the decrease in osmotic potential was attributable to soluble carbohydrates and glucose was the major osmoregulating solute. There was little progeny variation in any of measured parameters in unstressed seedlings. Compared to two slower-growing progenies, the two progenies capable of more vigorous growth under drought in the field accumulated more soluble carbohydrates (mainly glucose and fructose), developed lower osmotic potential and maintained higher turgor pressure when osmotically-stressed in solution culture. The ability to adjust osmotically and maintain turgor under drought stress could thus be a useful criterion for the early selection of faster-growing, drought-tolerant genotypes.     

Osmotic relations of the drought-tolerant shrub Artemisia tridentata in response to water stress

Turgor maintenance, solute content and recovery from water stress were examined in the drought-tolerant shrub Artemisia tridentata. Predawn water potentials of shrubs receiving supplemental water remained above ?2 MPa throughout summer, while predawn water potentials of untreated shrubs decreased to ?5 MPa. Osmotic potentials decreased in conjunction with water potentials maintaining turgor pressures above 0 MPa. The decreases in osmotic potentials were not the result of osmotic adjustment (i.e. solute accumulation). Leaf solute contents decreased during drought, but leaf water volumes decreased more than 75% from spring to summer, thereby passively concentrating solutes within the leaves. The maintenance of positive turgor pressures despite decreases in leaf water volumes is consistent with other studies of species with elastic cell walls. Inorganic ion, organic acid, and carbohydrate contents of leaves declined during drought. The only solutes accumulating in leaves of A. tridentata with water stress were proline and a cyclitol, both considered compatible solutes. Total and osmotic potentials recovered rapidly following rewatering of shrubs; solute contents did not change except for a decrease in proline. Maintaining turgor through the passive concentration of solutes may be advantageous compared to synthesis of new solutes for osmotic adjustment in arid environments.     

Diurnal and Seasonal Changes in Leaf Water Potential Components and Elastic Properties in Response to Water Stress in Apple Trees

Apple trees are very drought tolerant, having the capability to grow and carry on photosynthesis even at low water potentials. Much of the tolerance is due to the ability of apple leaves to maintain turgor potentials at levels conducive to growth and stomatal opening. Diurnally, leaf turgor is maintained through decreases in osmotic potentials (due to active solute accumulation), osmotic adjustment, or to concentration of solutes via tissue water loss. These two processes combined may decrease osmotic potentials by as much as 1.65 MPn during the day. Seasonally, osmotic potentials remain fairly constant, but leaf elasticity increases, allowing growth to continue and stomata to remain open us water and turgor potentials become progressively lower. Release of stored water from plant tissues to the transpiration stream is another means of preventing water potentials from reaching critical values for stomatal closure. A combination of a number of these physiological adaptations may account for much of the drought tolerance in apple trees.     

Genome-wide identification and expression analysis of the molecular chaperone binding protein <Emphasis Type="Italic">BiP</Emphasis> genes in <Emphasis Type="Italic">Citrus</Emphasis>

Here, we report for the first time the genome-wide identification and expression analysis of the molecular chaperone BiP genes in Citrus. Six genes encoding the conserved protein domain family GPR78/BiP/KAR2 were identified in the genome of Citrus sinensis and C. clementina. Two of them, named here as CsBiP1 and CsBiP2, were classified as true BiPs based on their deduced amino acid sequences. Alignment of the deduced amino acid sequences of CsBiP1 and CsBiP2 with BiP homologs from soybean and Arabidopsis showed that they contain all the conserved functional motifs of BiPs. Analysis of the promoter region of CsBiPs revealed the existence of cis-acting regulatory sequences involved in abiotic, heat-shock, and endoplasmic reticulum (ER) stress responses. Publicly available RNA-seq data indicated that CsBiP1 is abundantly expressed in leaf, flower, fruit, and callus, whereas CsBiP2 expression is rarely detected in any tissues under normal conditions. Comparative quantitative real-time PCR (qPCR) analysis of expression of these genes between C. sinensis grafted on the drought-tolerant “Rangpur” lime (C. limonia) and -sensitive “Flying Dragon” trifoliate orange (Poncirus trifoliata) rootstocks showed that CsBiP1 was upregulated by drought stress on the former but downregulated on the latter, whereas the CsBiP2 mRNA levels were downregulated on drought-stressed “Flying Dragon,” but remained constant on “Rangpur.” CsBiP2 upregulation was only observed in C. sinensis seedlings subjected to osmotic and cold treatments. Taken together, these results indicate the existence of two highly conserved BiP genes in Citrus that are differentially regulated in the different tissues and in response to abiotic stresses.     

Two minuses can make a plus: waterlogging and elevated CO2 interactions in sweet cherry (Prunus avium) cultivars

The increase in the ambient concentration of CO₂ and other greenhouse gases is producing climate events that can compromise crop survival. However, high CO₂ concentrations are sometimes able to mitigate certain stresses such as salinity or drought. In this experiment, the effects of waterlogging and CO₂ are studied in combination to elucidate the eventual response in sweet cherry trees. For this purpose, four sweet cherry cultivars (‘Burlat’, ‘Cashmere’, ‘Lapins and ‘New Star’) were grafted on a typically hypoxia‐tolerant rootstock (Mariana 2624) and submitted to waterlogging for 7 days at either ambient CO₂ concentration (400 µmol mol^?1) or at elevated CO₂ (800 µmol mol^?1). Waterlogging affected plants drastically, by decreasing photosynthesis, stomatal conductance, transpiration, chlorophyll fluorescence and growth. It also brought about the accumulation of proline, chloride and sulfate. Nonetheless, raising the CO₂ supply not only mitigated all these effects but also induced the accumulation of soluble sugars and starch in the leaf. Therefore, sweet cherry plants submitted to waterlogging were able to overcome this stress when grown in a CO₂‐enriched environment.     

Leaf Water Potential Response to Transpiration by Citrus

This paper reports on further studies of a model for interpreting leaf water potential data for Citrus. Experimental data confirmed the assumption that the ratio of vapor pressure deficit to leaf diffusion resistance adequately estimates transpiration when leaf-to-air temperature differences are small. Data collected diurnally indicated that the relationship between leaf water potential and transpiration followed a sequence of steady states without hysteresis. No difference in water transport characteristics was found for Valencia orange on three rootstocks in well-watered soil, but the two rootstocks Cleopatra mandarin and Rangpur gave slightly greater leaf water stress in Valencia orange leaves than‘Troyer’ citrange rootstock at high transpiration rates under mild soil water deficits. In laboratory studies, previously unstressed seedlings had higher leaf water potentials than field trees at equivalent transpiration rates. After several drying cycles, however, leaf water potentials were similar to those observed in the field.     

Global analysis of plasticity in turgor loss point,a key drought tolerance trait

Many species face increasing drought under climate change. Plasticity has been predicted to strongly influence species' drought responses, but broad patterns in plasticity have not been examined for key drought tolerance traits, including turgor loss or ‘wilting’ point (π_tlp). As soil dries, plants shift π_tlp by accumulating solutes (i.e. ‘osmotic adjustment’). We conducted the first global analysis of plasticity in Δπ_tlp and related traits for 283 wild and crop species in ecosystems worldwide. Δπ_tlp was widely prevalent but moderate (?0.44 MPa), accounting for 16% of post‐drought π_tlp. Thus, pre‐drought π_tlp was a considerably stronger predictor of post‐drought π_tlp across species of wild plants. For cultivars of certain crops Δπ_tlp accounted for major differences in post‐drought π_tlp. Climate was correlated with pre‐ and post‐drought π_tlp, but not Δπ_tlp. Thus, despite the wide prevalence of plasticity, π_tlp measured in one season can reliably characterise most species' constitutive drought tolerances and distributions relative to water supply.     

Biological and Molecular Detection of Citrus Psorosis Virus in Citrus in the Eastern Mediterrenean Region of Turkey

Fifty bud sticks exhibiting vein flecking, vein clearing and oak-leaf pattern symptoms of ‘Satsuma’ and ‘Clementine’ mandarins, and ‘Washington navel’ and local oranges in the field in Mersin, Kozan and Adana provinces were collected and grafted on one-year-old sour orange seedlings to maintain Citrus psorosis virus (CPsV) in indicators. Thirty two indicator plants showed typical symptoms of vein flecking, vein clearing, and vein banding with oak-leaf pattern. Eighteen plants gave mild leaf symptoms. CPsV was detected by RT-PCR from CPsV-infected sources. Leaf samples for RT-PCR were collected from symptomatic field trees. In all, thirty samples from different trees of mandarin and twenty samples from different trees of sweet oranges were collected. A 434 by specific DNA for the coat protein was amplified from the cDNA of CPsV-infected leaf samples. This specific DNA product was not amplified from healthy leaf samples or asymptomatic leaves collected from CPsV-infected trees.     

Does turgor limit growth in tall trees?

The gravitational component of water potential contributes a standing 0.01 MPa m^?1 to the xylem tension gradient in plants. In tall trees, this contribution can significantly reduce the water potential near the tree tops. The turgor of cells in buds and leaves is expected to decrease in direct proportion with leaf water potential along a height gradient unless osmotic adjustment occurs. The pressure–volume technique was used to characterize height‐dependent variation in leaf tissue water relations and shoot growth characteristics in young and old Douglas‐fir trees to determine the extent to which growth limitation with increasing height may be linked to the influence of the gravitational water potential gradient on leaf turgor. Values of leaf water potential (Ψ_l), bulk osmotic potential at full and zero turgor, and other key tissue water relations characteristics were estimated on foliage obtained at 13.5 m near the tops of young (approximately 25‐year‐old) trees and at 34.7, 44.2 and 55.6 m in the crowns of old‐growth (approximately 450‐year‐old) trees during portions of three consecutive growing seasons. The sampling periods coincided with bud swelling, expansion and maturation of new foliage. Vertical gradients of Ψ_l and pressure–volume analyses indicated that turgor decreased with increasing height, particularly during the late spring when vegetative buds began to swell. Vertical trends in branch elongation, leaf dimensions and leaf mass per area were consistent with increasing turgor limitation on shoot growth with increasing height. During the late spring (May), no osmotic adjustment to compensate for the gravitational gradient of Ψ_l was observed. By July, osmotic adjustment had occurred, but it was not sufficient to fully compensate for the vertical gradient of Ψ_l. In tall trees, the gravitational component of Ψ_l is superimposed on phenologically driven changes in leaf water relations characteristics, imposing potential constraints on turgor that may be indistinguishable from those associated with soil water deficits.     

Influence of Scion/Rootstock reciprocal effects on post-harvest and metabolomics regulation in stored peaches

Peach is an important stone fruit crop cultivated at commercial scale in Pakistan. While, appropriate selection of rootstock has significant impact on the quality of peach fruit. Therefore, in the current study the influence of three rootstocks viz. ‘GF-677′, ‘Peshawar Local’ and ‘Swat Local’ were evaluated on the quality of ‘Flordaking’ peaches following cold storage during two consecutive years. The fruit from these rootstocks were kept at 0 °C for five weeks were studied for various fruit physical (weight loss, colour, firmness) and biochemical (pH, soluble solids content (SSC), titratable acidity (TA), SSC:TA ratio, fruit juice pH, sugars (total, reducing and non-reducing sugars), ascorbic acid (vitamin C) and free radicals scavenging activities) were evaluated. During both years, fruit harvested form trees grafted on ‘GF-677′ exhibited reduced fruit weight loss, changes in Chroma (C*) and highest fruit firmness, Lightness (L*), ascorbic acid contents and radical scavenging activities as compared to fruit harvested from tree grafted on other rootstocks. In conclusion, the post-harvest quality of scion ‘Flordaking’ peach fruit was significantly influenced and best quality can be obtained when it is grafted on ‘GF-677′ rootstock.     

立地条件和树龄对刺槐和小叶杨叶水力性状及抗旱性的影响

以形成黄土高原“小老树”的2种典型树种刺槐和小叶杨为对象,研究了立地条件(沟谷台地和沟间坡地)和树龄对两种树木叶水力学性质和抗旱性的影响,探讨“小老树”形成的水力生理机制.结果表明:水分较好的沟谷台地上生长的两种树木的叶最大水力导度(Kmax)明显大于水分较差的沟间坡地,叶水力脆弱性(P50)也较高;随树龄增加,两种树木的Kmax明显下降,但P50差异不大.台地上生长的两种树木的叶表皮导度和PV曲线参数(膨压损失点时的相对含水量RWCtlp、膨压损失点时的水势ψtlp饱和含水量时的渗透势ψsat)均大于 坡地;随树龄增加,两种树木的叶表皮导度显著下降,PV曲线参数出现不同程度的下降.两种树木Kmax与ψtlp呈显著正相关,P50与PV曲线参数之间存在一定的相关性,表明Kmax与抗旱性之间存在一种权衡关系,P50是反映两种树木的抗旱性特征之一.