Effects of drought on fruit set,yield and quality of custard apple (Annona spp. hybrid) ‘African Pride’ plants

Summary

Studies were conducted to evaluate the effects of drought during flowering for both container- and field-grown trees, and during fruit development for container-grown trees, on subsequent growth, flowering, yield and quality of the custard apple ‘African Pride’ in subtropical Australia. Moderate drought (ψ_L=–1.5 MPa) reduced shoot growth by 20–30% and increased the number of flowers per lateral by about 40% compared with well-watered controls due to reduced apical dominance and increased lateral branching. Overall fruit set was not adversely affected by drought. Drought also increased the number of fruit harvested per tree by 47% compared with well-watered controls. This response was mainly due to the increase in flower number per tree. Drought reduced average fruit size by 11% possibly due to effects on cell division in the first 4–6 weeks after fruit set or on net carbon assimilation. In summary, mild to moderate drought during the flowering period and fruit set increased flowering without adversely affecting fruit set, but decreased fruit size.     

Diversity of street tree populations in larger Danish municipalities

Healthy and sustainable tree populations require a high diversity of genera and species. This study examined the occurrence and contents of tree inventories in Denmark's 30 largest municipalities. 59% of the municipalities had a tree inventory for street trees, but only about half of these were complete and updated. Only one municipality had a registration for trees other than street trees. Based on data from the tree inventories, the diversity of road side trees was analyzed at genus level and species level. A total of 82,072 street trees are part of the study. 11 different genera account for 92% of the total street tree stock, and 2–6 genera account for 40–80% of the street tree stock in the individual municipalities. Tilia was the most dominating genera (26%). 12 species account for 73% of the total street tree stock. The 6 most common species account for almost 50% of the total tree population. The species representing the largest numbers were Tilia × europaea (12%), Acer platanoides (10.9%), Platanus × acerifolia (7.2%), Tilia cordata (7.2%), Fraxinus excelsior (6.2%) and Sorbus intermedia (5.9%). The four most urbanized municipalities had a surplus of non-native species, but all municipalities apart from one had most street trees belonging to native species. The concluding recommendation of this study is that tree managers need to start working more strategic with their tree stock, in order to reduce the vulnerability, due to potential attacks from pests or diseases and climate change effects. A risk spreading system for the urban tree population is proposed, suggesting that no genera should account for more than 10% and no species for more than 5% of the tree population.     

The Reinvigoration of Apple Trees by the Inarching of Vigorous Rootstocks

Summary

The purpose of this research was to determine if established, orchard-grown apple trees that were con®ned in root-restricting membranes received adequate water for growth when irrigated. Previous data had shown positive effects of root restriction on reducing shoot extension growth in apple. Soil matric potential (Ψ_sm), leaf stomatal conductance (g) and leaf water potentials (Ψ_l) were measured over daily cycles during the period of maximum tree water use (July and August). Measurements were also made of the Ψ_sm and fruit size throughout the growing season. Daily and seasonal Ψ_sm showed that the soil within the root restricting membranes (+R) when irrigated (+I) remained closed to field capacity (<100 HPa), which was not the case for unirrigated soil within the membranes (-I +R). Ψ_l measured before dawn, showed that similar levels of drought stress were evident between irrigated and restricted (+I +R) and unrestricted (+I -R and -I -R) trees. The Ψ_sm, and Ψ_l for trees with roots within restricting membranes were significantly more negative, in the absence of irrigation (-I +R). Measurement of g showed that root restricted trees were transpiring at similar rates in the presence of irrigation (+I +R) as unrestricted trees (+I -R) with or without irrigation. Stomatal closure could not explain the increased Ψ_l observed for the restricted irrigated (+I +R) treatment compared with unrestricted (-R) trees. A reduced stomatal aperture was the most likely explanation for the reduction in growth previously observed with the restricted unirrigated trees. Fruit size was also affected by root restriction and the effect became greater as the roots became more restricted with tree age. Similarly, there was also a negative effect, in one year, of root restriction on fruit size at harvest, even in the presence of irrigation. Data show that reductions in soil water availability, Ψ_l and g, for the root-restricted trees (+I +R), were unlikely to be the causes for the previously observed reductions in shoot growth (tree size). These results imply that other factors were in operation, among which root-synthesized chemical regulators of shoot growth are the most likely candidates.     

Assessing the performance of urban forest carbon sequestration models using direct measurements of tree growth

Across cities worldwide, people are recognizing the value of greenspace in ameliorating the health and well-being of those living there, and are investing significant resources to improve their greenspace. Although models have been developed to allow the quantification of ecosystem services provided by urban trees, refinement and calibration of these models with more accurate site- and species-specific data can increase confidence in their outcomes. We used data from two street tree surveys in Cambridge, MA, to estimate annual tree mortality for 592 trees and diameter growth rates for 498 trees. Overall tree turnover between 2012 and 2015 was relatively low (annualized 3.6% y⁻¹), and mortality rate varied by species. Tree growth rates also varied by species and size. We used stem diameter (DBH) and species identity to estimate CO₂ sequestration rates for each of 463 trees using three different model variations: (1) i-Tree Streets, (2) Urban Tree Database (UTD) species-specific biomass allometries and growth rates, and (3) empirically measured growth rates combined with UTD biomass allometries (Empirical + UTD). For most species, the rate of CO₂ sequestration varied significantly with the model used. CO₂ sequestration estimates calculated using i-Tree Streets were often higher than estimates calculated with the UTD equations. CO₂ sequestration estimates were often the lowest when calculated using empirical tree growth estimates and the UTD equations (Empirical + UTD). The differences among CO₂ sequestration estimates were highest for large trees. When scaled up to the entire city, CO₂ sequestration estimates for the Empirical + UTD model were 49.2% and 56.5% of the i-Tree Streets and UTD estimates, respectively. We suggest future derivations of ecosystem service provision models allow localities to input their own species-specific growth values. By adding capacity to easy-to-use tools, such as i-Tree Streets, we can increase confidence in the model output.     

Effect of alleviating products with different mode of action on physiology and yield of olive under drought

Two years old self-rooted Koroneiki olive trees (Olea europaea L.) were subjected to two irrigation regimes, i.e. the fully irrigated and the severely water stressed trees, while they were treated with three alleviating products of different mode of action. The products used were the osmolyte glycine betaine, the antioxidant Ambiol and the heat and irradiance reflecting kaolin clay particles. The effects of product application and water regime on leaf characteristics, shoot and root growth, photosynthesis, leaf compatible solids (carbohydrates) concentration and yield were evaluated. All products applied, exhibited significant alleviating action, based on the relative alleviation index. Irrigated trees exhibited greater growth than drought stressed ones, while the ameliorating products maintained the water content of the leaves under drought conditions and resulted in lower leaf tissue density. On the other hand carbon assimilation rate, stomatal conductance and intrinsic water use efficiency were significantly reduced under drought stress, while the opposite stood for intercellular CO₂. Drought stress resulted in elevated sucrose leaf concentration, while the application of Ambiol increased stachyose concentration and that of glycine betaine did the same with the mannitol concentration. Among the alleviating products tested in this experiment Ambiol and glycine betaine had a significant positive effect on leaf water content, photosynthesis and yield under both drought and well irrigated conditions.     

Detecting different levels of drought stress in apple trees (Malus domestica Borkh.) with selected biochemical and physiological parameters

Rational irrigation scheduling based on sensing drought stress directly in plants is becoming more important due to increasing worldwide scarcity of fresh water supplies. In order to evaluate a set of potential biochemical and physiological stress indicators and select the best drought stress markers in apple trees, two experiments with potted trees and an experiment with intensive orchard grown apple trees ‘Elstar’ and ‘Jonagold Wilmuta’ were conducted in early summer in tree following years. Biochemical parameters: ascorbic acid, glutathione, tocopherols, chlorophylls, carotenoids, free amino acids, soluble carbohydrates, and physiological parameters already known as stress indicators in apple trees: predawn and midday leaf water potential, net photosynthesis (Pn), stomatal conductance (g_s), transpiration (Tr) and intercellular CO₂ concentration (Ci) were measured in leaves of apple trees subjected to different intensities of slowly progressing drought or no drought. Our study pointed out zeaxanthin and glutathione as the best drought stress markers in apple trees. Ascorbate and sorbitol appeared to be reliable indicators of moderate drought only. Responses of other tested biochemical parameters were not consistent enough to prove their role as drought stress markers in apple trees. Relative air humidity should be taken in consideration when physiological parameters g_s, Pn, Tr and Ci are used as drought stress markers in apple trees. Our study revealed that in situations where low relative air humidity affects g_s and with g_s connected physiological parameters, biochemical markers may be better tool for determination of drought stress intensities in apple trees.     

Genotypic variation in water relations and gas exchange of urban trees in Detroit,Michigan, USA

Increasing tree species diversity has become a key underpinning for communities to improve resilience of urban and community forests. Increasingly, urban forestry researchers are examining physiological traits to aid in selecting trees for urban sites. Knowledge of physiological responses also has implications for understanding species’ resilience to increased stresses associated with climate change. Here, we compare growth, leaf SPAD chlorophyll index, water relations, and gas exchange of seven genotypes of shade trees planted in two locations in downtown Detroit, MI, USA. Genotypes included Redpointe® maple (Acer rubrum ‘Frank Jr.’), Flashfire® maple (Acer saccharum ‘JFS-Caddo2′), Pacific Sunset® maple (Acer truncatum x platanoides ‘Warrenred’), Emerald City® tulip tree (Liriodendron tulipifera ‘JFS-Oz’), Chanticleer® pear (Pyrus calleryana ‘Glen’s Form’), swamp white oak (Quercus bicolor), and Emerald Sunshine® elm (Ulmus propinqua ‘JFS-Bieberich’). Trees were planted in either Lafayette Plaisance Park (Park), a large urban greenspace, or on the median of St. Aubin Avenue (Median), a nearby major thoroughfare. Tree height growth and leaf SPAD index were higher for trees planted in the Park location than on the Median. However, genotypic variation was larger than the effects of location or the interaction of Genotype × Location for most traits. Across measurement dates, midday leaf water potential was lowest for Pyrus trees and highest for Ulmus and Liriodendron trees. Pyrus and Quercus trees had relatively high rates of net photosynthesis (A) and stomatal conductance (g_s) while Liriodendron, Acer saccharum, and Ulmus trees had low rates of A and g_s. Liriodendron trees closed their stomata rapidly as leaf water potential (Ψ_w) declined (isohydric response), while Pyrus and Quercus trees maintained g_s across a range of leaf Ψ_w (anisohydric response). Liriodendron trees also had the highest relative growth rates, suggesting that drought stress avoidance through isohydry is a viable drought tolerance mechanism in urban trees.     

New approach for using trunk growth rate and endocarp development in the irrigation scheduling of young olive orchards

Trunk diameter variation (TDV) is considered one of the most promising tools for automating the scheduling of fruit tree irrigation, and trunk growth rate (TGR) a possible indicator of TDV values. The use of TGR in commercial orchards is less common in olive trees than in other species, possibly because the influence of the environment, orchard age and the presence of developing fruit on the olive tree seasonal TGR pattern is poorly understood. In this study the trunk growth rate (TGR) seasonal progression was characterized in fully irrigated young olive trees during fruiting and non-fruiting years. In both years, at the beginning of the season, a period with an almost linear increase was found, mainly determined by temperature. In the non-fruiting year TGR remained almost constant after that initial increase, while during the fruiting year a significant decrease occurred at approximately 25 days, from values around 0.2 mm day⁻¹ to values around 0.1 mm day⁻¹. Since midday shoot water potentials were not affected, this variation was likely not produced by water stress conditions. In addition, the lack of relationship between trunk growth rate and air temperature indicated that the TGR decrease in the fruiting year was not determined either by air temperature. The period of decreasing TGR values, however, coincided with the time that the endocarp reached its maximum transverse area, a significant moment for fruit development which precedes pit hardening. These results suggest that the traditional period where regulated deficit irrigation is done, “the pit hardening”, may be indicated easier and more accurate for TGR decrease and endocarp expansion.     

Testing the accuracy of resistance drilling to assess tree growth rate and the relationship to past climatic conditions

Assessing tree growth trends over time is a central but challenging aspect of urban forest management. The potential damage caused by invasive devices used in dendrochronological analysis is a common concern among urban foresters. Thus, the development of a less-invasive method for assessing tree growth rate faster that provides reliable results is clearly beneficial. In this study, resistance drilling (RD) profiles were compared with stem core assessments (Core) to estimate the growth rate of 78 trees of three species (Quercus robur, Ulmus procera, and Platanus x acerofolia). All studied trees were core-sampled in 2013 and then resistance drilled in 2015 at a stem height of 1–1.3 m in both north (N) and west axes (W). The dependency and accuracy of paired annual ring series (CORE measurements and Resi reading) were tested using ANOVA and regression analysis. In addition, point and event year tests were determined to confirm the accuracy of the RD to assess growth trends at both population and tree level. Growth series from both methods were cross-dated to test the reliability of RD to relate historical tree growth to past climatic conditions. ANOVA analysis confirmed that average ring width values and age of 70 out of 78 trees were statistically similar for both methods and similar for both sampled stem axes. Within each tree, regression analysis indicated significant correlation between cored ring datasets and paired resistance drilled ring datasets (R² = 0.78–0.95, p < 0.05) across species. RD reliably detected pointer years at population level for Q. robur only. For all species, RD could not adequately detect event years at tree level. Regardless of species and drill axes, RD was less accurate in measuring ring width below 1 mm. For all species, RD yielded lower intercorrelation indices and greater number of “A” flagged segments as compared to CORE. Overall, RD can successfully estimate mean annual ring values to a comparable standard as conventional CORE analysis. However, the RD device used in this study did not detect the inter-annual growth pattern to the same standard as stem CORE analysis, RD should not be used to replace dendrochronology in climate-tree growth studies.     

Radial growth response of horse chestnut (Aesculus hippocastanum L.) trees to climate in Ljubljana,Slovenia

Horse chestnut (Aesculus hippocastanum L.) is a common urban tree species in Ljubljana, the capital of Slovenia. This area is forecast to experience a general reduction in precipitation and an increase in temperature, which increases water demand in plants. Because A. hippocastanum is known for its drought vulnerability, the question of the future suitability of this urban tree species in Ljubljana has arisen. To investigate how climate has influenced A. hippocastanum radial growth and how trees responded to extreme climatic events, standardized precipitation-evapotranspiration index (SPEI) was used as a proxy for water demand. Climatic signal and its stability through time were calculated using Pearson’s correlation coefficient. Additionally, to investigate whether the trees had a common response to extreme climatic events, pointer years were calculated using Cropper values. We sampled 19 trees that were growing in Tivoli Park in Ljubljana. After successful cross-dating of 15 trees, the ring count showed that the trees had up to 201 tree-rings and had 130 on average. Climate-tree growth analysis showed that in July, 3-month SPEI had the strongest influence on radial growth, but its influence on radial growth decreased over time, possibly due to the die-off process of trees. The narrowest tree-rings were a result of unusually dry periods at the time of cambium activity and/or new cell growth. With the forecast of longer, more frequent summer drought periods in Ljubljana, soil moisture stress will increase, and as a result, a decrease in radial tree growth of A. hippocastanum trees from Tivoli Park is expected.     

Use of 6-benzylamino purine and Promalin for improved canopy development in selected apple cultivars

Foliar sprays of Promalin (gibberellins A_{4 + 7} + 6-benzylamino purine) applied to 1-year-old apple (Malus domestica Borkh.) trees at the 3–5-cm growth stage significantly increased lateral branching in 5 of 9 cultivars tested. Branching response ranged from 0% (‘Winter Banana’) to 131% (‘Starkrimson Delicious’) of the untreated controls. Total shoot growth was not consistently increased by 6-benzylamino purine or Promalin in tests over 3 years on spur and non-spur 1- and 2-year-old apple trees. Sprays of 50–300 mg l⁻¹ Promalin were ineffective for increased branch development. Sprays of 300–500 mg l⁻¹ increased total shoot numbers and reduced average shoot length. Sprays applied prior to new terminal growth in spring were ineffective. Treatment during periods of active shoot growth were generally effective, but periods of stress may have reduced response. Sprays were more effective for inducing lateral shoot formation than dormant heading or delayed dormant heading (pruning) (10 days after full bloom) in ‘Criterion Golden Delicious’. No difference in branching response was observed between BA and Promalin. Addition of a spray adjuvant (Buffer-X) did not affect branching response. Repeat annual single sprays of Promalin applied to dormant pruned trees were generally less effective for stimulating lateral branching than a single application in a given year. Phytotoxicity was associated with Promalin sprays at 300–500 mg l⁻¹ on ‘Delicious’.     

Drought responses of six ornamental herbaceous perennials

Although low water use landscaping is becoming common in arid regions, little is known about drought tolerance and drought responses of many ornamental plants, especially herbaceous perennials. Drought responses were assessed for six herbaceous ornamental landscape perennials in a 38 l pot-in-pot system in northern Utah over a 2-year period. The first year was an establishment period. During the second year, drought responses were evaluated for established Echinacea purpurea (L.) Moench, Gaillardia aristata Pursh, Lavandula angustifolia P. Mill., Leucanthemum × superbum (J.W. Ingram) Berg. ex Kent, ‘Alaska’, Penstemon barbatus Roth var. praecox nanus rondo, and Penstemon × mexicali Mitch. ‘Red Rocks’. Plants were irrigated at frequencies of 1 (control), 2, or 4 weeks between June and September, simulating well-watered conditions, moderate drought, or severe drought. Osmotic potential (Ψ_s), gas exchange, visual quality, leaf area, and dry weight were assessed. In a confined root zone, P. barbatus showed the greatest tolerance to all levels of drought, avoiding desiccation by increasing root:shoot ratio and decreasing stomatal conductance as water became limiting. L. angustifolia and P. × mexicali showed tolerance to moderate drought conditions, but died after exposure to the first episode of severe drought. Neither G. aristata nor L. superbum were able to regulate shoot water loss effectively. Instead, both species displayed drought avoidance mechanisms, dying back when water was limiting and showing new growth after they were watered. Compared to control plants, G. aristata shoot dry weight was reduced by 50% and 84%, and L. superbum shoot dry weight was reduced by 47% and 99% for the 2- and 4-week irrigation intervals, respectively. Root dry weights were affected similarly for both species. E. purpurea exhibited poor visual quality at all irrigation intervals, in particular wilting severely in both drought treatments, but regaining turgor when watered again. P. barbatus is recommended for ornamental landscapes that receive little or no supplemental irrigation, while E. purpurea is not recommended for low water landscapes because of low visual quality under even mild drought.     

Trees in planters – Growth,structure and ecosystem services of Platanus x hispanica and Tilia cordata and their reaction to soil drought

Urban environments are often characterized by extensive paved surfaces, exacerbating the urban heat island effect. At the same time, limited root space due to underground infrastructure poses a challenge for planting new trees in these areas. Trees in planters have emerged as popular design elements, offering innovative and sustainable greening solutions, particularly in urban environments with limited rooting space. However, growing conditions in planters may strongly impact tree growth and the provision of environmental ecosystem services (ES). In this 3-year study, we analyzed tree growth and ecosystem services (cooling by shading, CO₂-fixation) of London plane (Platanus x hispanica Münchh.) and small-leaved lime (Tilia cordata Mill.) in four planting treatments: in-ground (G), planters in the ground (PG), non-insulated plastic planters (P), and insulated planters (PI). We also recorded soil temperature throughout the experiment and implemented soil drought conditions by reducing soil irrigation for half of the trees after one year. Our findings revealed higher thermal fluctuations in soil temperature within non-insulated plastic planters (P), reaching a maximum of 45 °C, surpassing the critical temperature threshold for plant growth (>38 °C). In contrast, insulated planters (PI) effectively mitigated soil temperatures, staying below 33.8 °C. When planted in the ground (G), P. x hispanica exhibited a significantly higher stem diameter increment (52–66%) compared to other planting treatments, aligning with the provision of ecosystem services. However, T. cordata trees showed a more moderate response to planting treatments in terms of growth and ecosystem service provision. Furthermore, the implementation of soil drought conditions resulted in a reduction of up to 34% in stem diameter increment for P. x hispanica and up to 25% for T. cordata. Our results underscore the necessity of tree species-specific knowledge about growth responses to different planting treatments for effective urban planning perspectives, as the provision of ecosystem services may be influenced differently.     

Heat tolerance of urban trees − A review

The frequency and intensity of heat stress events globally have increased over the past 20 years. Climatic modeling predicts that this trend will continue throughout the 21st century, with the global land area experiencing heat waves doubling by 2020 and quadrupling by 2040. Due to the reflective nature of buildings and infrastructure, heat temperatures tend to be higher within urban landscapes than outlying rural areas. Heat stress influences processes from the molecular level to whole-tree biology. At the leaf level, photosynthesis is reduced, photo-oxidative stress increases, premature leaf abscission occurs, and the growth of leaves decreases. Growth decreases at the whole tree level, and biomass allocation between roots, shoots, leaves, and branches is altered. When drought and heat stress are combined, detrimental effects are considerably enhanced and, without irrigation, can quickly lead to tree death. There have been few studies regarding the heat tolerance of urban tree species. However, there is evidence of genetic variation in heat tolerance between and within species within forestry, which could be essential to exploit for urban trees. Understanding the mechanisms of tree physiological, biochemical, and molecular responses to extreme heat events is also necessary for understanding how urban tree species will be affected by climate change.     

Improving productivity of four fruit species by growth regulators applied once in ultra-low doses to the collar

Summary

Two growth retardants: paclobutrazol (P, Cultar) or 2,3,5-triiodobenzoic acid (TIBA) were applied once alone, or in mixtures (in a range of 5 to 20 mg per tree) to the collar of maiden plum, sour and sweet cherries and apple trees, in early spring of the second year after planting. Plum and apple trees were also treated with benzyladenine (BA) at 10 mg per tree a.i. in a mixture with P or TIBA. Sweet and sour cherry trees were treated with natural phenolic substances: phloridzin (Phi) and quercetin (Que) alone, or in mixtures with P and TIBA. A mid-stem treatment with P and shoot bending were also applied to the plum and apple trees for comparison. Measurements of tree growth and fruiting were made within 4 or 5 years. The reaction of the four species to the treatments varied according to the growth regulator applied. Plum trees responded mostly to TIBA and its mixtures with P. A strong suppression of tree growth and increased fruit productivity, as well as improved fruit quality, were observed. The TIBA application and its mixtures with P were also effective in causing growth reduction of the sweet cherry trees. Treatments with P alone, or mixed with TIBA, were effective in growth limitation of sour cherry trees. Some increase in the reproductive processes was observed only after the TIBA treatment in both species. The apple trees responded to application of mixtures of TIBA with benzyladenine (BA), or with P, and to P alone, with effective growth reduction. But only the P + BA treatment increased significantly the fruiting of apple trees, while the other treatments resulted in crops proportional to the diminished tree sizes. The mid-stem treatment did not affect plum trees but increased growth of apple trees. Shoot bending had no effect on the plum trees but increased fruiting of apple trees. The addition of Phi to half the lower P dose or TIBA, magnified growth suppression in the sweet and sour cherry trees. When applied alone Que caused a small growth inhibition but Phi produced some increase in growth of sour cherry trees. Results obtained show the possibilities of practical applications of growth regulators to the collar. Their reduced doses mixed with natural phenolic substances are equally effective in growth suppression and make fruit production safer and more profitable, especially in plum and sour cherry trees.     

Estimating the stormwater attenuation benefits derived from planting four monoculture species of deciduous trees on vacant and underutilized urban land parcels

This paper presents research that was undertaken to determine whether planting deciduous trees, using intensive tree planting schemes, on vacant and underutilized urban land provides significant hydrologic benefits. This work contributes to an ongoing discussion on how to use vacant and underutilized land productively, and may be important to land use decision-makers, whose policies support the use of green infrastructure for stormwater management. Tree growth parameters for four monoculture planting schemes were modeled (all trees had a 50.8 mm caliper at planting) and included (i) 450 Ginkgo biloba, (ii) 92 Platanus × acerifolia, (iii) 120 Acer saccharinum, and (iv) 434 Liquidambar styraciflua, on a 1.6-acre parcel. i-Tree Hydro (formerly UFORE-Hydro) was used to derive a simplified Microsoft Excel-based water balance model to quantify the canopy interception potential and evaporation, based on 7 years (2002–2008) of historical hourly rainfall and mean temperature data in Hamilton, Ontario, Canada. This study revealed that three of the species responded similarly, while one species (L. styraciflua) performed significantly better with respect to total canopy storage potential and evaporation, capturing and evaporating 2.9 m³/tree over the 7 years analyzed, or 1280 m³ for the total tree stand of 434 trees. The analyses presented herein demonstrate that the tree canopy layer was able to intercept and evaporate approximately 6.5%–11% of the total rainfall that falls onto the crown across the 7 years studied, for the G. biloba, P. × acerifolia and A. saccharinum tree stands and 17%–27% for the L. styraciflua tree stand. This study revealed that the rate at which a species grows, the leaf area index of the species as it matures, and the total number of trees to be planted need to be determined to truly understand the behavior and potential benefits of different planting schemes; had the mature leaf area been used as the sole indicator of the stormwater attenuating potential for each species, the A. saccharinum would have been the selected species. Also, had attenuation and evaporation per unit of tree been the only measurement reported, the P. × acerifolia stand would have been deemed the best performing tree, attenuating and evaporating 8.1 m³/tree. While the actual values presented herein may be uncertain because of a lack of locally-derived tree growth models, the approach described warrants further investigation.     

Manipulating Regular Bearing in ‘Golden Delicious’/M9 Apple Trees using GA4+7 and Ethephon

Control of regular cropping in apple is considered critical for fruit growers to ensure their economical sustainability. Irregular flowering can be mitigated by plant growth regulators thanks to their promotion or inhibition effects. In this study, responses of GA₄₊₇ and ethephon on alternate bearing in ‘Golden Delicious’/M9 were examined. GA₄₊₇ and ethephon were applied on the same trees during three consecutive years (2010–12). Flowering, yield, shoot growth, and also some fruit quality parameters were assessed. GA₄₊₇ appeared to be more effectual to regulate alternate bearing. The alternate bearing index calculated with yield in successive years was high in control (0.91), moderate in ethephon (0.71), and low in GA₄₊₇ treated trees (0.41). Modified alternate bearing index, based on cluster number, indicated moderate intensity in GA₄₊₇ (0.53) and high intensity in the others. Although GA₄₊₇ reduced crop density at about 50%, there was little variation in yield per tree and crop efficiency due to increasing of fruit size. GA₄₊₇ did not increase shot length after establishment of equilibrium between vegetative and generative growth in 2012. Ethephon slightly reduced vegetative growth and relatively increased fruit size due to the decrease of fruit set.     

Factors influencing urban tree planting program growth and survival in Florida,United States

High levels of mortality after installation can limit the long-term benefits associated with urban tree planting initiatives. Past planting projects funded by the Florida Forest Service were revisited two to five years after installation to document tree survival and growth and assess program success. Additionally, various site (e.g., soil compaction, installed irrigation) and tree-related (e.g., species, nursery production method, initial size at planting) factors were noted to assess their impact on tree growth. Results show that the overall establishment rate for the 26 sites (n = 2354 trees) was high, with 93.6% of trees alive at the time of final inspection. On-site irrigation played a significant role in tree survival and growth, especially for Magnolia grandiflora (97.7% survival on irrigated sites; 73.8% survival on non-irrigated sites). Findings from this work validate the effectiveness of current program policies which include maintenance of tree quality within the first year after planting, and offer further insights regarding the impacts of season of planting and initial size of nursery stock on plant growth and development.     

The response of different almond genotypes to moderate and severe water stress in order to screen for drought tolerance

In order to screen almond genotypes for drought tolerance, three different irrigation levels including moderate and severe stress (Ψs = −1.2 and −1.8 MPa respectively) and a control treatment (Ψs = −0.33 MPa) were applied for five weeks to six different cultivated almond seedlings. A factorial experiment was conducted with a RCBD which included 3 irrigations factors, 6 genotype factors and 3 replications. Seeds were prepared from controlled pollination of the bagged trees (after emasculation and flower isolation using isolator packets in the previous year). Genotypes included: homozygote sweet (Butte), heterozygote sweet (SH12, SH18, SH21 and White) and homozygote Bitter (Bitter Genotype). Leaf and root morphological and physiological traits including; midday relative water content, midday leaf (xylem) water potential, shoot dry weight and growth, total leaf area, leaf size, total leaf dry weight, specific leaf area, leaf greenness (SPAD), stomatal size and density, root and leaf nitrogen content and chlorophyll fluorescence were measured throughout the study. Results showed the six genotypes had different reactions to water stress but all genotypes showed an ability to tolerate the moderate and severe stresses and they showed different degrees of response time to drought stress. Almond seedling leaves could tolerate Ψ_w between −3 and −4 MPa in short periods. Water availability did not significantly affect stomatal density and size of young almond plants. The analysis of leaf anatomical traits and water relations showed the different strategies for almond genotypes under water stress conditions. Although almond seedlings even in severe stress kept their leaves, they showed a reduction in size to compensate for the stress effects. All genotypes managed to recover from moderate stress so Ψ_w = −1.2 could be tolerated well by almond seedlings but Ψ_w = −1.8 limited young plant growth. Leaf greenness, leaf size, shoot growth, shoot DW, TLDW and stomatal density were not good markers for drought resistance in almond seedlings. Root DW/LA, lower stomatal size and lower SLA might be related to drought resistance in cultivated almonds. Butte had the least resistance and White showed better performance during water stress while other genotypes were intermediate. Bitter seedlings showed no superiority in comparison with other genotypes under water stress conditions except for better germination and greater root DW which might make them suitable as rootstocks under irrigation conditions.     

Selection-pressure effects of medium pH during regeneration on successive performances of leaf-derived Tomuri’ and ‘Hayward’ kiwifruit (Actinidia deliciosa) somaclones cultured on proliferation culture media with variable pH

Summary

The aims of the work were in vitro selecting for tolerance to high culture pH (CpH) in kiwifruit and evaluating the effects of selection pressure exerted by pH variations during regeneration. Leaf-derived ‘Tomuri’ and ‘Hayward’ kiwifruit (Actinidia deliciosa) somaclones, which had been regenerated at pH 5.7, 7 and 7.5, were compared to each other and to controls (i.e. cultures derived from ‘Tomuri’ and ‘Hayward’ mother plants through standard micropropagation techniques) for shoot growth, proliferation and appearance when cultured at up to pH 8. The proliferation rate (PR), the number of nodes (NN) produced by each shoot and axillary shoot length (ASL) decreased in all ‘Tomuri’ and ‘Hayward’ somaclones and in controls as culture pH increased. At CpH 8, ‘Tomuri’ somaclones regenerated at pH 7.0 generally tended to have higher average PR and NN than the other somaclones and control; their ASL also exceeded that of the other somaclones and was just slightly higher than in control. Regardless of CpH, ‘Hayward’ somaclone 7.5-1 tended to have higher PR, NN and ASL than other female somaclones. When shoot growth and appearance (tissue hyperhydricity, leaf yellowing or browning) were considered together through a multivariate data analysis, most ‘Tomuri’ and ‘Hayward’ somaclones which appeared less sensitive than controls to high CpH had been regenerated at pH 7 and 7.5. These regeneration and culture methods, especially the selection pressure exerted by the high pH during regeneration, thus seem to be effective in obtaining ‘Tomuri’ and ‘Hayward’ variants tolerant to high culture pH.