Peach Tree Growth Research Articles

Impact of Plum pox virus (PPV-D) infection on peach tree growth, productivity and bud cold hardiness

In 2000, the Dideron (D) strain of Plum pox virus (PPV) was detected in commercial peach and nectarine orchards in the Niagara region of Ontario where most of Canada’s stone fruit crops are produced. As part of a disease management research programme, peach (Prunus persica L. Batsch) trees in a commercial orchard at Niagara-on-the-Lake were assayed for PPV annually for 3 years. The orchard consisted of two blocks of the cultivars ‘Allstar’ and ‘Brighton’, of which 4 of 288 and 5 of 252 trees, respectively, were infected with PPV-D. The growth and health of these PPV-infected and non-infected trees were evaluated based on the annual growth rates, vigour (chlorophyll content) and bud winter hardiness. Comparative fruit quantity and quality index values were based on total yield and marketable yield per tree, fruit size and weight, fruit pH, titratable acidity, total soluble solids, flesh firmness, and fruit skin colour. Results from these preliminary studies showed that trees infected with this mild Ontario isolate of PPV produced slightly more fruit of smaller size that ripened earlier than non-infected trees. However, yield efficiencies based on weight of fruit relative to the trunk cross-sectional area did not differ statistically. Screenhouse studies on three graft-inoculated fresh market peach cultivars (‘Babygold’, ‘Catherina’, and ‘Garnet Beauty’) similarly did not demonstrate any differences in growth or fruit production in the second and third year post inoculation, but fruit on infected trees matured somewhat earlier.

Differential effect of regulated deficit irrigation on growth and photosynthesis in young peach trees intercropped with grass

The effects of a moderate soil water deficit on several shoot growth variables (1st and 2nd order shoot growth and final leaves number, final height and final number of 2nd order shoots) and on net photo- synthesis were studied in young peach trees during the two years following plantation (January 2014). Trees were either fully irrigated (C), subjected to moderate water deficit (RDI) or subjected to moderate water deficit and associated with a grass-legume mixture on the entire orchard floor (RDI +G). Irrigation was scheduled according to soil water potential target ranges in order to keep C trees above −0.02 MPa, i.e. at field capacity, and RDI and RDI + G trees between −0.04 MPa and −0.06 MPa. The level of water deficit obtained was moderate but yet significantly reduced by 50% overall tree growth in 2014 in RDI. This reduction was enhanced when water deficit lasted longer and when it was associated with grass in RDI + G. No reduction in growth variables occurred in RDI in 2015 due to the shorter duration of water deficit. Overall reduction was observed in 2015 in RDI + G mostly due to a carry-over effect of the pre- vious year. Net photosynthesis was reduced by the longer and more intense water deficit in 2014, but was not reduced during the soil water deficit in 2015. An indicator of plant process sensitivity to water deficit, taking into account the variable reduction with regards to the control, the water deficit intensity and its duration was used to classify shoot growth variables and net photosynthesis according to their sensitivity to water deficit. Variables could be classified according to the following order of ascending sensitivity: net photosynthesis <1st order final leaf number < final tree height <1st order final shoot length <2nd order final leaf number <2nd order final shoot number <2nd order final shoot length. Applying a moderate water deficit combined with full grass cover drastically reduces overall tree size due to grass competition

Influence of rhizosphere ventilation on soil nutrient status, root architecture and the growth of young peach trees

The peach tree root respiration rate is high, which requires large amounts of oxygen. When the rhizosphere oxygen content is poor, the root respiration and energy metabolism are restrained which will have negative impacts on peach trees growth, fruit quality and yield, especially during high temperature and rainy season. Our objectives were to investigate the relationship between rhizosphere ventilation and orchard soil enzyme activity, nutrient status, root architecture and growth of young peach trees. Two-year-old ‘Chunmei’ peach (Prunus persica L. Batsch) was subjected to various treatments (Treatment 1 [T1]: ventilation every three days; T2: ventilation every six days; T3: natural ventilation; Control: no ventilation) under field cultivation conditions. The soil oxygen content decreased and subsequently increased during the growth period, reaching a minimum in August. The rhizosphere soil oxygen content was higher under ventilation treatment than control, and T1 markedly increased the rhizosphere soil oxygen content. The rhizosphere soil available K and organic matter decreased while the rhizosphere soil available N and available P content increased and the soil enzyme activity was improved under ventilation treatments. The root activity and root nitrate reductase activity increased under ventilation treatments. Under T1, the total root surface area, total root length and number of first lateral root and second lateral root were increased significantly, but the average root diameter and the average length of first lateral root was reduced significantly, the branching angle between first lateral root and vertically downward direction was decreased, the number of small angle was increased. T1improved leaf functions and increased the net photosynthetic rate. Under T1, the leaf chlorophyll content and leaf protective enzyme activity (Superoxide dismutase, Guaiacol peroxidase and Catalase) increased markedly in the middle- and late-growth period and leaf senescence was postponed. The total nitrogen, phosphorus and potassium contents of young peach roots, shoots and leaves, as well as shoot growth, leaf weight and leaf area, increased under T1.

Effect of Biochar Amendments on Peach Replant Disease

The use of biochar as a soil amendment has generated interest all over the world, and it has been advocated as a means to improve soil fertility and sequester carbon. The objective of this study was to test if the use of pinewood biochar could reduce the detrimental effects of replant disease (RD) on peach tree growth and biomass production. An RD-susceptible peach rootstock, Lovell, was grown in soil from a peach replant site (control), sterilized soil (sterilized), and biochar-amended soil at 10% and 20% (v/v) [low biochar (LB) and high biochar (HB), respectively], all from the same site. Trunk diameter increase was measured weekly; total aboveground and belowground biomass was determined by harvesting a subsample of plants at 11, 22, and 33 weeks after planting. Soil samples, and foliar and root tissue samples were collected before each harvesting date and analyzed for nutrient content. Total aboveground and belowground biomass production was significantly higher in the biochar and sterilized soil treatment (S) compared with the control. Root carbon (C*) content was significantly greater in the HB treatment compared with the control. Soil nitrate-N was significantly greater in the HB treatment by the third harvesting date, and foliar magnesium (Mg) concentrations were significantly higher in both biochar treatments for all harvesting dates. The results from this study provide evidence that biochar may alleviate RD in peach trees.

Vegetation-free Width and Irrigation Impact Peach Tree Growth, Fruit Yield, Fruit Size, and Incidence of Hemipteran Insect Damage

Orchard floor vegetation competes with peach trees for water and nutrients and may harbor pathogens and insects. Tree growth, fruit yield, and fruit size can be optimized through management of vegetation in the tree row and irrigation. Under-tree vegetation-free strip widths (0, 0.6, 1.2, 2.4, 3.0, and 3.6 m) and irrigation were studied in years four through eight of a young peach orchard to determine their effects on peach tree growth and fruit yield, harvest maturity, and fruit size. Immature fruit samples were collected during thinning in years four through six to determine the effect of the treatments on the incidence of hemipteran (catfacing) insect damage. Trunk cross-sectional area (TCSA), as a measure of tree growth, increased with increasing vegetation-free strip width; trees grown in the 3.6-m vegetation-free strip had TCSAs 2.2 times greater, on average, than trees grown in the 0-m vegetation-free strip. TCSA also increased with irrigation; trees grown with irrigation had TCSAs 1.2 times greater, on average, than trees grown without irrigation. Yield increased with increasing vegetation-free strip width, from 9.6 kg per tree in the 0-m plot to 26.5 kg per tree in the 3.6-m plot in year four, to 24.3 kg per tree in the 0-m plot and 39.6 kg per tree in the 3.6-m plot in year eight, for a total yield over years 4–8 per tree of 100 kg in the 0-m plot compared with 210 kg per tree in the 3.6-m plot. Yield, average fruit weight, and average fruit diameter increased with irrigation in three of 5 years; the other 2 years had higher than average rainfall reducing the need for supplemental irrigation. In 3 out of 5 years fruit in irrigated plots matured earlier than fruit in nonirrigated plots. In all years, fruit grown in the 0-m strip matured earliest and had the smallest diameter. Establishing a vegetation-free strip of as narrow as 0.6 m reduced the incidence of catfacing damage compared with the 0-m treatment, even though the orchard was on a commercial pesticide spray schedule. The least damage was seen with the industry standard vegetation-free strip widths greater than 3.0 m with or without irrigation.

Auxin levels and MAX1–4 and TAC1 gene expression in different growth habits of peach

Branch orientation and distribution determine tree architecture that can influence orchard design and management. Peach [Prunus persica L. (Batch)] trees with three different branching genotypes were evaluated: fewer, nearly vertical branches (pillar), less vertical and more spreading branches (upright), and more abundant, least vertical branches (standard). Auxin concentrations and expression of genes that regulate branch development in herbaceous species, MAX1, 2, 3, 4 and TAC1 were determined. Shoots and roots of peach trees in the field and greenhouse were studied following pruning and during periods of growth when bud break and branch spatial orientation develop. Expression of MAX3 and MAX4 decreased in stems of field-grown peach trees that remained on the tree following pruning. In the greenhouse elevated auxin concentrations and higher gene expression of MAX3 in roots and MAX4 in stems were found in pillar rather than standard trees. Upright trees had auxin and MAX1–4 expression that was intermediate between pillar and standard trees. Temporal differences were found with MAX1–4 expression being greater in April or May but auxin concentrations were greater only in shoots in May. Expression of TAC1 was inversely related with auxin concentrations in shoots and was greatest in standard and least in pillar trees. The current work indicates that in stems, auxin, MAX3–4 genes, and TAC1 genes may influence regulatory processes that affect growth and development of peach trees with different growth habits. In addition to breeding, new plant growth regulators that affect the modes of action of root-originating signals may provide new cultural tools for managing tree growth and development.

High and low root zone temperatures at bud-break reduce growth and influence dry matter partitioning in peach rootstocks

Previous studies with actively growing peach [Prunus persica (L.) Batsch] rootstocks have shown that low root zone temperatures (RZTs) affect growth and partitioning of dry mass. However, whether plants show similar responses at other phenological stages has not been examined, nor has the influence of high RZTs. Consequently, we examined the effects of high and low RZTs on dry matter accumulation and its partitioning using five rootstocks (Fay Elberta, Green Leaf Nemaguard, Golden Queen, Okinawa and Red Leaf Nemaguard) that were emerging from dormancy. The rootstocks were grown at diurnally variable (29/21°C) or at constant RZTs of 5, 13, 21 and 29°C; the above ground parts were at a day-time temperature of 27°C and a night-time temperature of 21°C. Total growth and its components could be described by cubic functions of RZT, all of which were maximised at a RZT of ∼21°C. Thus, both sub- and supra-optimal RZTs reduced growth and influenced dry matter partitioning independently of air temperature and light intensity. At ∼21°C, the root mass ratio was maximised whilst the leaf, stem and shoot mass ratios were minimised. With the exception of their roots, the growth of plants exposed to diurnally variable 29/21°C RZTs was similar to those whose roots were constantly maintained at 29°C with root growth being intermediate between that of plants whose roots were kept constantly at 21 or 29°C. The partitioning of growth, however, was similar to that at a constant RZT of 21°C. The rootstock cultivars differed in response to RZT with respect to total growth and in partitioning. This research illustrates that the growth of plants exiting dormancy is significantly influenced by RZT. The different responses of the rootstocks to RZT offer an explanation for comparative differences in tree growth and development of rootstock-scion combinations at different locations, particularly in the spring. The data also indicate that RZTs should be incorporated into tree growth and development models for peaches and has implications for the mitigation of the deleterious effects of global changes in climate on peach tree growth.

PROTECTED CULTIVATION OF PLUM IN SOUTH CENTRAL LIAONING: PRESENT STATUS AND FUTURE PERSPECTIVES

Inspired by the protected vegetable production methods in south central Liaoning, which was the cradle of Chinese greenhouse vegetable production in, protected fruit production began to flourish approximately twenty years ago. Protected fruit culture first occurred in Liaoning and then it extended to north central China, mainly to advance the time of ripening to meet the demand of off-season fruit consumption. The main fruits that were grown were the perishable fruit types such as stone fruits and berry fruits, including peach, cherry, apricot, plum and table grape. Table grape and peach were relatively easy to cultivate in protected conditions since the growth of grapevines or peach trees is easy to control and fruit set readily occurs, while plum, apricot and cherry tree are more difficult to work with. The purpose of this paper is to describe the growing technology of the protected plum cultivation system including the greenhouse structure, cultivar selection, the methods of forcing dormancy, heating the greenhouse etc. The present status and future perspectives of this system are also discussed.

Effect of hail nets on the microclimate, irrigation requirements, tree growth, and fruit yield of peach orchards in Catalonia (Spain)

SummaryHail nets protect orchards from storm damage, but also offer potential water savings for fruit trees grown in arid areas. We investigated the effects of black nets on water use, growth, yield, and fruit quality in peach trees growing in Catalonia, Spain, over 2 years (2006 and 2007). Water savings were quantified by irrigating the netted trees to a similar midday stem water potential (Ψstem) as the control trees. This method was only partially successful in 2006, with the netted trees being over-watered early in the season (i.e., higher Ψstem than the controls), and under-watered (i.e., lower Ψstem than the controls) later in the season. A combination of water stress and a hail net resulted in lower yields because of a smaller fruit size. Skin colour was more enhanced in control fruit. In 2007, Ψstem values were similar between treatments. Any difference in tree performance was therefore due to the hail net per se. Fruit size was similar between treatments, and the lower yields of netted trees were due to decreased fruit number. There were no treatment differences in fruit skin colour or flesh firmness. Soluble solids concentrations were higher in nonnetted fruit. In both years, water savings amounted to approx. 25%, if irrigation replaced the potential evapotranspiration that was measured. Hail nets are therefore recommended for their effects on water saving in arid areas, despite lower fruit yields.

Changes in the vegetative growth of the low-chill peach tree in response to reproductive shoot pruning after harvesting

The effect of reproductive shoot pruning (after harvesting) on the vegetative growth of peach trees was studied. After the harvest period, one group of plants was left unpruned; however, a second group of plants was pruned by heading back or thinning out their bearing shoots. Summer pruning improved the rejuvenation of wood and enhanced the growth of basal shoots thus increasing the proportion of shoots that arose on older wood or directly from the scaffold (+15%). Summer pruning was shown to affect branch regrowth, leaf restoration and radial expansion of the trunk; the leaf area removed was completely restored in 80 days by the increase of new branches (+108%) in the remaining shoots; however, the annual expansion of the trunk cross-sectional area was significantly reduced (−37.4%). Summer pruning also reduced the plant size from −7% to −26% and delayed autumn leaf fall (+10 days).

Radiometric properties of photoselective and photoluminescent greenhouse plastic films and their effects on peach and cherry tree growth

SummaryTwo photoselective and three photoluminescent greenhouse plastic films were studied for their effects on the spectral distribution of solar radiation and their influence on the growth of cherry and peach trees in the field and in laboratory tests.The two photoselective films modified the ratio of the photon fluence rate in the red to that in the far-red (R/FR), while the three photoluminescent films increased both the blue and red solar radiation by moving energy from the ultra-violet range to the blue and red wavelength range.The photoselective film that reduced the R/FR ratio, from 1.14 (open-field) to 0.93, enhanced shoot growth in peach (46.1 cm) and cherry trees (68.7 cm) compared to trees grown in the open-field (13.5 cm and 39.3 cm for peach and cherry trees, respectively). Trees grown under the red-emitting photoluminescent film showed increases in shoot length of 27.2 cm and 55.8 cm for peach and cherry trees, respectively; while plants grown under the blue-emitting photoluminescent film showed increases of 22.4 cm and 48.9 cm for peach and cherry trees, respectively. This research showed that a significant enhancement of shoot growth in peach and cherry trees can be obtained using plastic films that modify the spectral distribution of solar radiation. Further research should explore the potential for the development of film-additives that promote more compact vegetative growth.

Long-term effects of managed grass competition and two pruning methods on growth and yield of peach trees

Ground cover competition and tree training strongly affect development of newly planted peach trees and eventual productivity of peach orchards. This experiment characterized the long-term interactive effects of three levels of competition and two pruning criteria on yield, fruit size, and marketable yield efficiency. Trees of two cultivars (’Jersey Dawn’, JD, and ‘Redskin’, RS, on Lovell) of peach ( Prunus persica (L.) Batsch) were planted in an orchard in 1993 and grown for 14 years in a vegetation free area (VFA) width of 0.6 or 2.4 m. A separate group of trees that were in the 2.4 m VFA had grass seeded beneath them in 1998 to obtain 0 m VFA. All trees were pruned to maintain canopy size with wide-angled scaffold limbs and intense pruning (IP) or upright branch form with reduced pruning (RP). In general, RS had greater yield than JD and yield was greatest in the 2.4 m VFA with RP and least in the 0.6 m VFA with IP. Cumulative marketable (≥6.35 cm) and average annual total yield of both cultivars was similar for RP trees in 0 m VFA and IP trees in 2.4 m VFA's although more of the fruit were in the largest size class (>6.98 cm) in the IP trees. Reduced pruning increased crop load. Fruit weight decreased with increased crop load more in RS than JD and this response was similar for all VFA's within each cultivar. Grass competition tended to reduce both the number and weight of fruit per tree but the average weight of individual marketable fruit was reduced only in the 0.6 m VFA of RS. Tree size was reduced by grass competition and pruning times measured from 1995 to 2000 were less in RP than IP. Consequently, marketable yield efficiency of marketable fruit (grams fruit ≥6.35 cm/cm 2 trunk cross-sectional area, TCSA) measured from 2004 to 2007 was generally greater in trees with RP than IP and in the 0.6 than the 0 and 2.4 m VFA. The results indicate that persistent competition will reduce total annual yield per tree but with reduced pruning the concomitant increased crop load can help maintain marketable yield.

GREENHOUSE PLASTIC FILMS CAPABLE OF MODIFYING THE SPECTRAL DISTRIBUTION OF SOLAR RADIATION

The aim of this paper was to investigate the radiometric properties of innovative covering films for protected cultivation capable of modifying the spectral distribution of the transmitted radiation and thus the vegetative activity. Two photoselective films, three photoluminescent films and one low-density polyethylene film were used as greenhouse coverings for cherry trees and peach trees, grown in pots. The photoselective films were characterised by a reduction of the R/FR ratio in comparison to the natural solar radiation. Tree growth parameters, such as the apical shoot of cherry trees and the shoot of peach trees, were monitored. Different responses to vegetative activities were observed under the films, depending on the species, with a higher shoots growth rate in the peach with respect to the cherry. The photoselective film characterised by the lowest R/FR ratio significantly enhanced the growth of cherry and peach trees in comparison to the trees cultivated under the other greenhouse films

Growth and cropping of two cultivars of peach and nectarine in the conditions of the Sandomierska Plateau

Abstract In this experiment, the growth of peach and nectarine trees was determined to be related to the cultivar. ‘Inka’ peach trees grew weaker than ‘Harbinger’ trees. The ‘John Rivers’ nectarine was characterized by stronger growth than the ‘Harko’. The amount of crops produced by the trees was related to the cultivar and the meteorological conditions during winter and spring. ‘Inka’ produced higher yields and bigger fruits as compared to ‘Harbinger’. The ‘Harko’ cultivar provided significantly higher yields than the ‘John Rivers’ only in 2006. Peach and nectarine fruit production in the Sandomierska Plateau in the years 2004 − 2007 was risky. In 2006, damage to the flower buds during winter caused no crop yield in young peach trees and the older ones of the ‘Harbinger’ cultivar. A minor reaction to the temperature drop, down to -26.8oC, was found for nectarines in comparison with peach trees. In 2007, the spring frost injured flower pistils and caused a lack of crops from the studied cultivars.

Functional–structural plant modelling in crop production. Wageningen UR Frontis Series, vol. 22

Functional–structural plant modelling in crop production. Wageningen UR Frontis Series, vol. 22

Analysis of the ‘A72’ Peach Tree Growth Habit and Its Inheritance in Progeny Obtained from Crosses of ‘A72’ with Columnar Peach Trees

Since the first report of the ‘A72’ semidwarf peach [Prunus persica (L.) Batsch] tree in 1975, no new information has become available on this genotype. We evaluated the growth habit and verified the inheritance of ‘A72’ in a population of 220 progeny derived from self-pollination. Detailed tree and branch measurements revealed a unique forked-branch (FBR) character of the ‘A72’ (Nn) phenotype. The progeny segregated into 1 NN:2 Nn:1 nn. NN trees were indistinguishable from standard peach trees, Nn were FBR, and nn were dwarf. Hybrids between ‘A72’ and columnar (brbr) peach trees confirmed that FBR is inherited as a monogenic trait that appears to express incomplete dominance. ‘A72’ (Nn) trees were later blooming than sibling NN trees. The relationship (linkage or pleiotropy) between the growth habit of ‘A72’ and late bloom is not known. The structure of ‘A72’ trees presents new opportunities to breeder/geneticists, physiologists, and horticulturists to further explore the plasticity of peach tree growth and architecture that can be achieved through breeding. Applications of the ‘A72’ growth habit for commercial fruit production and as an ornamental, particularly in the dwarf form (nn) and in combination with the columnar tree (brbr) form, present opportunities that await exploration.

Mechanical Thinning of Peach and Apple Trees Reduces Labor Input and Increases Fruit Size

Hand thinning is a necessary but costly management practice in peach (Prunus persica) production. Organic apple (Malus ×domestica) production also may require hand thinning to adjust crop load. Mechanical devices to aid in thinning have been developed, but none has proven highly efficient and capable of completely replacing hand thinning. Narrow canopy training systems and novel peach tree growth habits offer new opportunities to examine mechanical methods for thinning peach and apple trees. Our studies evaluated mechanical thinning devices on peach and organically grown apple trees. In 2005 and 2006, a U.S Department of Agriculture-designed spiked-drum shaker was used to thin pillar (columnar) peach trees at 52 to 55 days after full bloom. The drum shaker, driven at two different speeds in the orchard, reduced crop load an average of 58% and follow-up hand thinning time by 50%, and increased fruit size by 9% at harvest compared with conventional hand-thinned or nonthinned control trees in 2005. In 2006, the shaker was driven at one speed but operated at two different frequencies. At 260 cycles/minute, the drum shaker removed more fruit and reduced crop load to a greater extent than when operated at 180 cycles/minute, however, fruit size at harvest did not differ between the two operating frequencies. The drum shaker reduced follow-up hand thinning time between 54% and 81%. Horticultural and economic evaluations of the drum shaker and/or a German-designed blossom string thinner were conducted in 2007 in four commercial peach orchards trained to a perpendicular V or quad V system and an organic apple block trained to a narrow vertical axis system. Mechanical thinners reduced peach crop load by an average of 36%, decreased follow-up hand thinning time by 20% to 42%, and increased fruit in higher market value size categories by 35%. The net economic impact of mechanical thinning versus hand thinning alone ranged from $175/ha to $1966/ha. Mechanical thinning at 20% full bloom resulted in more fruit in the large size categories (2.75 inches in diameter and larger) than thinning at 80% full bloom. Detailed counts of flowers on branches with different orientations indicated that pruning may be adjusted to improve thinner performance. The string thinner effectively thinned dwarf apple trees trained to a vertical axis system in a certified organic orchard, resulting in a reduction in hand thinning time and an increase in fruit size. Based on our tests, mechanical thinning appears to be a promising technique for supplementing hand thinning in apple and peach trees.

Inhibiting peach-tree growth with abscisic acid, hinokitiol and tropolone applied to partially ringed bark strips

SummaryThe dwarfing effects of growth inhibitors [abscisic acid (ABA), hinokitiol and tropolone] applied to a connecting bark strip on a partially ringed trunk were evaluated using 2-year-old peach trees. A 2 cm strip of bark was removed from the circumference of the trunk, leaving a 2 mm-wide connecting bark band to which aqueous solutions of the chemicals were applied. Positive correlations were found between bark regeneration and tree growth. High concentrations of tropolone and hinokitiol retarded both bark regeneration and shoot growth. Tropolone at 500 µg ml–1 and 1,000 µg ml–1 completely inhibited bark regeneration, even resulting in tree-death similar to complete ringing. Regenerated bark at 1,000 µg ml–1 ABA was half that in the partially ringed water control, and regeneration was completely inhibited at 2,000 µg ml–1 ABA. Root weight was also reduced in accordance with the decline in bark regeneration. These results indicate that tree growth can be controlled by chemically modifying bark regeneration, or by translocation to the shoots of partially ringed trees. The cost of chemicals will be less than that of whole-tree sprays for growth inhibition.

Effects of post-harvest regulated deficit irrigation on carbohydrate and nitrogen partitioning, yield quality and vegetative growth of peach trees

The aim of the present work was to evaluate the effects of regulated deficit irrigation (RDI) applied in the post-harvest stage of peach trees. The 3-year trial was carried out in Italy (N 40°20′, E 16°48′) on mature peach plants (cv “Springcrest”) trained to transverse Y. From bud break to harvest, irrigation was carried out by applying 100% ETc, while from harvest to early autumn, plants were separated into three groups and subjected to different irrigation treatments (100, 57 and 34% ETc). The decrease in soil water content caused a reduction in the values of tissue water potential and gas exchange both in 57% ETc and 34% ETc treatments. RDI determined the reduction in the growth of waterspouts and lateral shoots but did not influence the growth of fruiting shoots. During the trial, no significant reductions in crop yield and quality were observed in the 57% ETc treatment, whereas about 1,100, 1,800 and 2,500 m3 ha−1 of water were saved in the first, the second and the third year, respectively. In the second year of the trial, the use of RDI in the post-harvest stage determined carbohydrate and nitrogen accumulation in roots, branches, shoots and floral buds. The results demonstrate that, under scarce water supply conditions, a clear benefit can be obtained through the use of RDI during the post-harvest stage. This confirms the possibility to reduce the irrigation water by applying RDI during phenological stages less sensitive to water deficit without negatively affecting peach growth and yield.

Relationship of water status to vegetative growth and leaf gas exchange of peach (Prunus persica) trees on different rootstocks

We investigated relationships between tree water status, vegetative growth and leaf gas exchange of peach trees growing on different rootstocks under field conditions. Tree water status was manipulated by partially covering (0, approximately 30 and approximately 60%) the tree canopies on individual days and then evaluating the effects of tree water status on vegetative growth and leaf gas exchange. Early morning stem water potentials were approximately -0.4 MPa for trees in all treatments, but mean midday values ranged from -1.1 to -1.7 MPa depending on rootstock and canopy coverage treatment. Relative shoot extension growth rate, leaf conductance, transpiration rate and net CO2 exchange rate differed significantly among trees in the different rootstocks and canopy coverage treatments. Shoot extension growth rate, leaf conductance, leaf transpiration rate and leaf net CO2 exchange rate were linearly correlated with midday stem water potential. These relationships were independent of the rootstock and canopy coverage treatments, indicating that tree water relations are probably directly involved in the mechanism that imparts vegetative growth control by selected peach rootstocks.