Horticultural Tree Research Articles

Changes in the temperature-dependency of the photosynthetic response to chloroplast CO2 concentrations of outdoor-grown Vitis vinifera cv. Shiraz vines with a mid-season crop removal

Removing fruit from horticultural trees and vines is a common practice in source-sink studies. What effect removal of sinks as fruit growth commences has on photosynthesis is much less addressed. The objective was to remove Shiraz bunches at the rapid growth stage and compare photosynthetic performance of vines with and without fruit. Photosynthetic responses to CO2 concentrations and leaf temperatures were followed across the season to determine performance with changes in fruit sink demand. Assimilation across all temperatures peaked in spring and declined progressively throughout the season. Detaching bunches removed about 160 g dry matter from vines and this effected assimilation immediately, a decrease of about 20% which was sustained over 30 days. For fruiting vines, bunch biomass was severely impeded by a sustained heat event, reducing berry sugar content by 50% and may have impacted on the vines without bunches, thus obscuring the effects of sink removal. There was no evidence that assimilation was impaired by the heat event but the sink removal reduced RuBP carboxylation and regeneration, probably resulting from an inactivation of Rubisco. In contrast to removal of sinks in early development, the late removal appeared to inhibit photosynthetic acclimation of the Shiraz vines, reflecting maturity of the leaves.

Do horticultural tree plant species depend on mycorrhizal inoculation under marginal soil conditions?

Do horticultural tree plant species depend on mycorrhizal inoculation under marginal soil conditions?

Juvenility and Vegetative Phase Transition in Tropical/Subtropical Tree Crops.

In plants, juvenile to adult phase transition is regulated by the sequential activity of two microRNAs: miR156 and miR172. A decline in miR156 and increase in miR172 abundance is associated with phase transition. There is very limited information on phase transition in economically important horticultural tree crops, which have a significantly long vegetative phase affecting fruit bearing. Here, we profiled various molecular cues known to be involved in phase transition and flowering, including the microRNAs miR156 and miR172, in three horticultural tree crops: avocado (Persea americana), mango (Mangifera indica), and macadamia (Macadamia integrifolia). We observed that miR156 expression decreases as these trees age and can potentially be used as a juvenility marker. Consistent with findings in annual plants, we also observed conserved regulation of the miR156-SPL3/4/5 regulatory module in these genetically distant tree crops, suggesting that this pathway may play a highly conserved role in vegetative identity. Meanwhile, the abundance of miR172 and its target AP2-like genes as well as the accumulation level of SPL9 transcripts were not related with plant age in these crops except in avocado where miR172 expression increased steadily. Finally, we demonstrate that various floral genes, including AP1 and SOC1 were upregulated in the reproductive phase and can be used as potential markers for the reproductive phase transition. Overall, this study provides an insight into the molecular associations of juvenility and phase transition in horticultural trees where crop breeding and improvement are encumbered by long juvenile phases.

Canopy architecture assessment of cherry trees by cover photography based on variable light extinction coefficient modelled using artificial neural networks

Leaf area index (LAI) is one of the most important parameters in physiological and functional plant models to estimate tree canopy vigor and photosynthesis. However, LAI requires either destructive or indirect methods for accurate assessment, which can be time consuming, costly, and requires specialized instrumentation. Cover photography to estimate canopy architectural parameters has shown to be effective and accurate for several forest species and horticultural tree crops such as apple trees, grapevines and cherry trees. The accuracy of the LAI estimation is highly dependent on the appropriate use of the variable light extinction coefficient (k) parameter per image. Canopy cover photography was tested on a commercial cherry plantation in Maule, Chile during seasons 2011-12 and 2013-14. Two cultivars were assessed, ‘Bing’ (n=80 images) and ‘Sweet Heart’ (n=80 images), with 10 trees per cultivar, and 4 photos representing each canopy quadrant per tree. Real LAI (LAI(real)) was measured allometrically from every tree photographed for both cultivars. Real k was computed based on the inverted LAI formula and LAI(real). Artificial Neural Networks (ANN) modeling for fitting was implemented per cultivar using a customized code written in MATLAB with canopy cover (f(f)), crown cover (f(c)), canopy porosity (Φ) and clumping index (Ω) obtained from image analysis algorithms as inputs, and real k as target. The ANN fitting model to obtain a variable k showed determination coefficients (R(2)) for training = 0.98 and 0.92, validation = 0.96 and 0.94, testing = 0.98 and 0.90, and final k model = 0.98 and 0.94, for ‘Bing’ and ‘Sweetheart’, respectively, in both seasons studied. This resulted in improvements in the LAI estimation for cherry trees when compared to LAI(real) with R(2) of 0.80 for ‘Bing’ and 0.90 for ‘Sweetheart’. This is a significant improvement in the assessment of canopy vigor and water requirement for tools such as VitiCanopy®, a free LAI estimation App available for iOS and Android devices based on canopy cover photography, which can incorporate a variable k.

Measuring Canopy Structure and Condition Using Multi-Spectral UAS Imagery in a Horticultural Environment

Tree condition, pruning and orchard management practices within intensive horticultural tree crop systems can be determined via measurements of tree structure. Multi-spectral imagery acquired from an unmanned aerial system (UAS) has been demonstrated as an accurate and efficient platform for measuring various tree structural attributes, but research in complex horticultural environments has been limited. This research established a methodology for accurately estimating tree crown height, extent, plant projective cover (PPC) and condition of avocado tree crops, from a UAS platform. Individual tree crowns were delineated using object-based image analysis. In comparison to field measured canopy heights, an image-derived canopy height model provided a coefficient of determination (R2) of 0.65 and relative root mean squared error of 6%. Tree crown length perpendicular to the hedgerow was accurately mapped. PPC was measured using spectral and textural image information and produced an R2 value of 0.62 against field data. A random forest classifier was applied to assign tree condition into four categories in accordance with industry standards, producing out-of-bag accuracies >96%. Our results demonstrate the potential of UAS-based mapping for the provision of information to support the horticulture industry and facilitate orchard-based assessment and management.

Morphological and molecular genetic diversity analysis using SSR markers in Jackfruit (Artocarpus heterophyllus Lam.) genotypes for pulp colour

Jackfruit (Artocarpus heterophyllus Lam.) being an important dryland horticultural tree, grows well with minimum care and maintenance. The study aimed at identifying the genetic diversity present in twenty jackfruit genotypes for different pulp colours. The genotypes were identified for commercial cultivation, based on fruit and flake quality characters viz., fruit weight, fruit rind weight per kg fruit, number of flakes per kg fruit, weight of flakes per kg fruit, individual fresh flake weight and TSS as per the Jackfruit descriptors given by IPGRI, Rome. The best genotypes identified from the study were Swarna, Lalbagh Madhura, Byrachandra, NSP, Ashoka Yellow and NEL and these can be used for commercial purpose. Molecular diversity analysis was also carried out using 22 SSR primers, out of which six primers (SSR 9, SSR 10, SSR 30, SSR 34, SSR 45 and SSR 48) showed polymorphism among twenty genotypes. The genetic similarity co-efficient ranged from 0 to 0.96, indicating a vast variation in genetic diversity for pulp colour. A dendrogram was constructed by UPGMA analysis revealed three major clusters. The genotypes with cream and yellow colour pulp grouped in cluster I and II, followed by yellow, orange and red in cluster III. These markers effectively segregated the genotypes based on different pulp colours and hence, can be used for both diversity analysis and in breeding applications.

Estimating Changes in Leaf Area, Leaf Area Density, and Vertical Leaf Area Profile for Mango, Avocado, and Macadamia Tree Crowns Using Terrestrial Laser Scanning

Vegetation metrics, such as leaf area (LA), leaf area density (LAD), and vertical leaf area profile, are essential measures of tree-scale biophysical processes associated with photosynthetic capacity, and canopy geometry. However, there are limited published investigations of their use for horticultural tree crops. This study evaluated the ability of light detection and ranging (LiDAR) for measuring LA, LAD, and vertical leaf area profile across two mango, macadamia and avocado trees using discrete return data from a RIEGL VZ-400 Terrestrial Laser Scanning (TLS) system. These data were collected multiple times for individual trees to align with key growth stages, essential management practices, and following a severe storm. The first return of each laser pulse was extracted for each individual tree and classified as foliage or wood based on TLS point cloud geometry. LAD at a side length of 25 cm voxels, LA at the canopy level and vertical leaf area profile were calculated to analyse tree crown changes. These changes included: (1) pre-pruning vs. post-pruning for mango trees; (2) pre-pruning vs. post-pruning for macadamia trees; (3) pre-storm vs. post-storm for macadamia trees; and (4) tree leaf growth over a year for two young avocado trees. Decreases of 34.13 m2 and 8.34 m2 in LA of mango tree crowns occurred due to pruning. Pruning for the high vigour mango tree was mostly identified between 1.25 m and 3 m. Decreases of 38.03 m2 and 16.91 m2 in LA of a healthy and unhealthy macadamia tree occurred due to pruning. After flowering and spring flush of the same macadamia trees, storm effects caused a 9.65 m2 decrease in LA for the unhealthy tree, while an increase of 34.19 m2 occurred for the healthy tree. The tree height increased from 11.13 m to 11.66 m, and leaf loss was mainly observed between 1.5 m and 4.5 m for the unhealthy macadamia tree. Annual increases in LA of 82.59 m2 and 59.97 m2 were observed for two three-year-old avocado trees. Our results show that TLS is a useful tool to quantify changes in the LA, LAD, and vertical leaf area profiles of horticultural trees over time, which can be used as a general indicator of tree health, as well as assist growers with improved pruning, irrigation, and fertilisation application decisions.

First report of a ‘Candidatus Phytoplasma solani‘‐related strain (16SrXII‐A subgroup) associated with pistachio leaf scorch disease in Turkey

Pistachio (Pistacia vera) is a horticultural tree grown for its edible seeds. It is of great commercial importance for Turkey which is one of the main global producers. Pistachio trees are mostly cultivated in the Sanliurfa, Siirt, …

The role of 15N-depleted fertilizers as tracers in N cycling studies in agroecosystems

A search of the literature (principally Google Scholar, using the keywords given below) revealed that 120 research papers have been published where 15N-depleted (14N-enriched) fertilizers, including ammonium sulfate, ammonium nitrate, urea and ammonia forms were used as tracers. The studies included annual cereals, vegetables, a grain legume and a fibre crop, and perennial crops including grasses, shrubs (berries), trees (fruits and nuts) and N2-fixing forage, grain and woody legumes and an actinorhizal species. Other minor examples include perennial ornamentals and trees harvested for wood. Applications included estimation of fertilizer recovery in crops, in post-harvest soil and estimation of N losses in the soil–plant system by mass balance. The residual value of 15N-depleted fertilizers and the recovery of 15N-depleted legume residues have also been reported. 15N depleted fertilizers have played an important role in differentiating the relative uptake of fertilizer N to N mobilized in storage tissues with respect to the N nutrition of deciduous horticultural trees, shrubs and vines in spring. The symbiotic dependence of N2-fixing species and transfer to companion non-legumes has been indirectly determined using 15N-depleted fertilizers. Thus 15N-depleted fertilizers have shared the same applications as their 15N-enriched counterparts. Because of their relative cheapness compared with 15N-enriched fertilizers, larger and more representative unconfined plots can be employed in field studies.

MicroRNA control of flowering and annual crop cycle in tropical/subtropical horticultural trees

The horticultural tree life cycle can be differentiated into two distinct growth stages – vegetative and reproductive. Unlike annual crops, horticultural tree crops enter into an annual flowering cycle once they attain the reproductive phase. Herein, they undergo various developmental changes including flowering, fruit set, fruit development, fruit ripening, fruit drop and vegetative growth. The annual crop cycle is critical for horticultural crops like Persea americana (avocado) and Macadamia integrifolia (macadamia) as their productivity depends upon successful flowering and fruit development. It is therefore important to understand flowering and the factors involved in the crop cycle in these horticultural trees. Various endogenous and exogenous factors are involved in flowering regulation. Among them a class of small non-coding RNAs known as microRNAs play a vital role. We investigated the expression of flowering-associated miRNAs in avocado and macadamia at distinctive time-points during their annual crop cycle. We looked at the expression of two miRNA that are known act antagonistically during flowering: the floral inhibitor miR156 and the floral promoter miR172, which regulates APETALA2 (AP2)-like transcription factors. Preliminary results from avocado showed no significant difference in the expression of miR156 during the crop cycle, while significant differences were observed for miR172. For both crops, abundance of miR172 was higher during flowering and initial fruiting but lower at fruit ripening and drop/harvest. These results will help us in understanding flowering regulation in horticultural trees by providing first insight into microRNAs and their putative targets in these crops.

Effects of Silicon Amendment on Soilborne and Fruit Diseases of Avocado.

The effects of silicon (Si) amendment have been studied in several plant/pathogen interactions; however, studies in horticultural tree crops are limited. Effects of amendment with soluble potassium silicate (AgSil®32, approximately 30% available Si), or milled cement building board by-products (Mineral Mulch (MM) or Mineral Dust (MD), containing 5% available Si) were investigated in field and greenhouse trials with avocado. Orchard soil drench applications with potassium silicate improved yield and quality of fruit, but visual health of trees declining from Phytophthora root rot (PRR) was not affected. Orchard spray or trunk injection applications with potassium silicate were ineffective. Amendment of potting mix with MM and MD reduced root necrosis of avocado seedlings after inoculation with Calonectria ilicicola, an aggressive soilborne pathogen causing black root rot. Application of MM to mature orchard trees declining with PRR had a beneficial effect on visual tree health, and Si accumulation in leaves and fruit peel, after only 10 months. Products that deliver available Si consistently for uptake are likely to be most successful in perennial tree crops.

Chemoecological Approaches for Insect Borer Pest Management

A wide range of agricultural, horticultural and forest trees are vulnerable to insect borer pests causing serious loss to the economy. Cryptic nature of the borers causes the infestations to be overlooked until sizeable damage has occurred. Employing chemical or biological control has not yielded desirable results in suppressing these, as interventions hardly reach the target site/insect. However, the hazard of pesticides remains. Understanding the ecological interaction mediated by cues, especially odours between borers and their host will aid in the development of clean and green technologies.

Isolation and characterization of wound-induced compounds from the leaves of Citrus hassaku

Citrus plants are world widely cultivated as horticultural tree crops, and nowadays their pharmacological activities have been well studied. Since research of defense responses in citrus plants have been mainly focused on the post-harvested fruits because of their commercial importance, defense mechanisms during their developmental stages have not been well understood. In the present study, two wound-induced compounds were isolated from leaves of Citrus hassaku, and their structures were elucidated by high-resolution electron spray ionization mass spectra (HRESIMS) and nuclear magnetic resonance (NMR) analyses. One of these compounds was identified as a known flavanone, hesperetin. The other was characterized as a novel furofuran lignan, and was named 'biscitrusnin-A'. Their antimicrobial activities were also evaluated.

High Efficiency Plant Regeneration from Cotyledon Explants of Pomegranate(Punica granatumL.) cv. Kandhari Kabuli

A high frequency plant regeneration pro-tocol via direct organogenesis has been develo-ped for Punica granatum L. cv. Kandhari Kabuli, a medicinally important horticultural tree. Cotyle-don explants procured from 15-20-days-old in vitro grown seedlings were used as explants. MS medium supplemented with 2.0 mg/l 6-benzylaminopurine (BAP) and 1.5 mg/l naphtha-lene acetic acid (NAA) was optimal for shoot re-generation, which resulted into highest frequen-cy of shoot regeneration (67.89%) along with maximum average number of shoots formed per explant (5.38) and average shoot length (3.62 cm). Shoot multiplication and elongation took place on the same medium. Half strength MS medium containing 0.1 mg/l NAA and 0.02% ac-tivated charcoal was found most effective for rooting of shoots resulting into 80.12% root re-generation frequency. Regenerated plantlets were transferred to plastic cups containing auto-claved peat moss and successfully acclimatized with 85% survival rate. This is the first report on in vitro plant regeneration through direct orga-nogenesis in P. granatum L. cv. Kandhari Kabuli using cotyledon explants.

Initial characterization of an unidentified Armillaria isolate from Serbia using LSU‐IGS1 and TEF‐1‐α genes

SummaryArmillaria species have a global distribution and play variable ecological roles, including causing root disease of diverse forest, ornamental and horticultural trees. Accurate identification of Armillaria species is critical to understand their distribution and ecological roles. This work focused on characterizing an unidentified Armillaria isolate from a Serbian forest using pairing, sequencing of the partial large subunit and intergenic spacer‐1 regions of rDNA (LSU‐IGS1) and the translation elongation factor‐1 alpha gene (tef‐1α) genes, and phylogenetic analyses. Despite previously obtained LSU‐IGS1 RFLP patterns that matched the newly described North American Armillaria altimontana, pairing tests and phylogenetic analyses of LSU‐IGS1 and tef‐1α sequences clearly demonstrate that the unidentified isolate is not A. altimontana. Based on LSU‐IGS1, Armillaria gallica isolates were polyphyletic, and the Serbian isolate clustered with a subset of European A. gallica isolates within a well‐supported clade (99%). Based on tef‐1α, the Serbian isolate appeared as a separate, well‐supported clade (97%) that was basal to other poorly resolved, polyphyletic clades containing European A. gallica isolates. It is speculated that the unidentified Armillaria isolate from Serbia could represent an evolutionary ancestral state because of its separate, basal position compared with other clades comprising polyphyletic European A. gallica isolates. Alternatively, this unidentified Serbian isolate could represent an unusual hybrid because of its high‐level sequence heterogeneity, represented by multiple two‐nucleotide codes, within tef‐1α. Further characterization is needed to confirm the taxonomic status and ecological/evolutionary significance of this unique, unknown Armillaria isolate from Serbia.

Breeding better cultivars, faster: applications of new technologies for the rapid deployment of superior horticultural tree crops.

Woody perennial plants, including trees that produce fruits and nuts of horticultural value, typically have long breeding cycles, and development and introduction of improved cultivars by plant breeders may require many breeding cycles and dozens of years. However, recent advances in biotechnologies and genomics have the potential to accelerate cultivar development greatly in all crops. This mini-review summarizes approaches to reduce the number and the duration of breeding cycles for horticultural tree crops, and outlines the challenges that remain to implement these into efficient breeding pipelines.

Leaf Litter Decomposition and Nutrient Dynamics Associated with Common Horticultural Cropland Agroforest Tree Species of Bangladesh

Mangifera indica,Zizyphus jujuba,Litchi chinensis, andArtocarpus heterophyllusare the most common cropland agroforest horticultural tree species of Bangladesh. This study focused on leaf litter decomposition and nutrient (N, P, and K) dynamics during the decomposition process. This experiment was conducted for 180 days by using litter bag technique during dry and wet seasons. Mass loss was the highest (49% and 57%) forA. heterophyllusand the lowest (25%) was found forL. chinensis. The highest initial rates (0.75% and 2.35%/day) of decomposition were observed forZ. jujubaand the lowest (0.50% and 0.79%/day) forL. chinensis. The highest decay constant was observed forA. heterophyllus(2.14 and 2.34) and the lowest (0.88 and 0.94) forL. chinensis. Leaf litter of all the studied species showed a similar pattern (K > N > P) of nutrient release during the decomposition process.Zizyphus jujubashowed comparatively higher return of N, P, and K than others. However, a significant (P<0.05) higher amount of mass loss, rate of decomposition, decay constant, and amount of nutrient return from leaf litter were observed during the wet season.

PC2 containment glasshouse facilities for horticultural trees and vines at PFR Mount Albert, Auckland

PC2 containment glasshouse facilities for horticultural trees and vines at PFR Mount Albert, Auckland

Detecting Plant Diseases Using Visible/Near Infrared Spectroscopy

Introduction P alestine Technical University– Kadoorie (PTUK) is one of 13 higher educational institutes in Palestine. PTUK is the first and only technical and governmental university in the West Bank. It is located on the western side of the city of Tulkarm and serves the Palestinian community in the Palestinian governorates. PTUK was established in 1930 as an agricultural school (Figure 1) and was then developed to provide Diploma programmes in various disciplines. The university went through different phases of development until it was accredited as a university on August 2007 to provide technical programmes at various levels including Diploma and Bachelor degrees in different areas in engineering and applied technology. Currently there are about 5000 students enrolled in PTUK. PTUK is particularly interested in teaching and delivering knowledge of applied science in the fields of agricultural and evnironmental sciences. On the basis of its three units (biotechnology, water and environment, and agriculture), PTUK established the Technical and Applied Research Center (TARC) in 2009. Several research projects are being conducted at TARC including phytopathology, soil, air and water pollution as well as sensor technology for non-destructive quality assesment of agricultural commodities. PTUK is very interested in the olive sector in Palestine, since olive trees cover approximately 45% of Palestinian agricultural lands. The tree is very important in the economic and social lives of the population, as it accounts for one of their main sources of income; in a good year, it can contribute about 13% of the annual agricultural production. The olive (Olea europaea L.) is one of the oldest agricultural trees and is cultivated over large areas in Palestine, with more than 10 million olive trees (about 67.3% of all horticultural trees) being grown. Olive production contributes about 12–13% of national income. The olive tree is affected by many pests and diseases. Olive leaf spot (OLS) is a foliar disease which is widespread in all olive growing regions of the world and has been reported in Mediterranean areas (Figure 2). As a result of infection, yield losses occur and these can amount to up to 20% of total production. Olive leaf spot is chemicallycontrolled by application of copper (Cu) fungicides directly after harvest but chemical treatment rarely appears to be effective. Moreover, using chemical fungicides leads to the appearance of pathogen races which are resistant to Cu as well as more general imbalance of the plant metabolism following Cu accumulation in the soil. In Palestine, the disease is common throughout many areas of the southern and northern parts of the country. The Palestinian Ministry of Agriculture, NGOs and several private institutions work with the olive sector to provide guidance and information about improving olive crop production and protection. Visible/near infrared (vis/NIR) spectroscopy is a mature sensor technology that has been successfully applied to the noninvasive analysis and detection of many parameters (for example, quality, stress and presence of disease) of a wide range of agricultural commodities. Due to its success, vis/NIR spectroscopy was used in this feasibility study to detect the severity of OLS disease in olive trees.

Special issue on water management in grapevines

Population growth, economic development, environmental demands, and climate change converge into a scenario of water scarcity worldwide (Fereres and Gonzalez-Dugo 2009). Water supply may therefore constraint grape production for quality wine. In this context, deficit irrigation (DI) strategies to stabilize yield and maintain or improve wine quality are critical. Recently, the use of regulated deficit irrigation (RDI) has expanded in vineyards to improve (sometimes to reduce) water application, yield per unit water supply, berry composition, and wine quality. The objective of RDI is to apply water deficits of predetermined levels during certain phenological stages when their effects on fruit growth and quality are neutral or positive, while keeping vineyard vigor in balance with potential production (Girona et al. 2006, 2009; Pellegrino et al. 2006; Greven et al. 2005). The short and long-term impact of deficit irrigation on production and quality vary with vineyard conditions, namely soil texture and depth, variety, atmospheric environment, and viticultural practices. These factors make it difficult to predict the best timing for imposing water deficits. Also, the desired intensity of deficit is not easy to impose uniformly over the whole vineyard, and the risks of excessive water deficits must be avoided through careful monitoring. Furthermore, there is a trade-off between regulated water deficit to improve yield per unit water supply and the need to maintain well-watered vines to reduce heat damage in warm and hot regions (Sadras and Soar 2009; Soar et al. 2009). Understanding the effects of timing and amount of irrigation on yield and berry composition is key to achieve the desired yield and berry quality. Thus, the correct determination of vineyard water requirements (or evapotranspiration, ET) and the monitoring of soil and vine water status are critical to apply the appropriate deficit irrigation strategies. The conventional crop coefficient (Kc) approach provides a simple and convenient way to estimate vineyard water requirements for a variety of soil and climatic conditions, but a major uncertainty in this approach is that the empirical nature of Kc which requires local calibration and monitoring of plant water status. Vine water status can be monitored with predawn, noon leaf, and stem water potentials, which integrate the effects of soil water status on both the environment (soil and atmosphere) and the vine (root and canopy size, stomatal conductance). However, there is no general agreement on which method is the most reliable to evaluate vine water status. This discrepancy may be explained by the combined effect of variety and rootstock, soil type and depth, range of soil water deficit, variability of weather conditions throughout the growing cycle, atmospheric evaporative demand, and source/sink ratio as affected by growing conditions and management practices shifting the balance between leaf area and fruit load. Midday stem water potential of horticultural trees, for example, is lower with high source/sink ratio (Sadras and Trentacoste 2011). Communicated by R. Evans.