Orchard-grown Trees Research Articles

Phenology- and light-based parameterization of stomatal conductance model for urban woody species in northern China

Surface ozone (O3) poses a significant threat to urban vegetation health, and assessing the O3 risk across woody species is of vital importance for maintaining the health of urban infrastructure. In the present study, Jarvis-type stomatal conductance model was parameterized for ten urban species in northern China. Incorporating the effects of time of day and diurnal O3 concentration significantly enhanced the model performance. For different plant functional types (greening trees, greening shrubs, and orchard-grown trees), three parameterizations were established to estimate stomatal O3 uptake (POD1, phytotoxic O3 dose over an hourly threshold of 1 nmol m−2 s−1). The differences in POD1 between greening trees and shrubs were primarily due to the difference in their stomatal sensitivity to light. Orchard-grown trees displayed the lowest O3 removal capacity (lowest value of POD1) because of their shorter growing season despite of high stomatal conductance. These results indicated that plant phenology and light responsiveness determined stomatal O3 uptake, and the three parameterizations developed here could be applicable to various urban species in northern regions. Among climatic factors for O3 risk assessment, O3 concentration was the most important factor determining annual variation of POD1, which was primarily driven by air temperature. However, when O3 pollution decreased, O3 concentration exhibited less dependence on temperature and more dependence on light. These findings provide crucial insights for urban policy-makers and environmental scientists aiming to mitigate O3 pollution effects and enhance urban vegetation health.

Titer and Distribution of 'Candidatus Phytoplasma pruni' in Prunus avium.

'Candidatus Phytoplasma pruni' infection in cherries causes small, misshapen fruit with poor color and taste, rendering the fruit unmarketable. However, this is a disease with a long development cycle and a scattered, nonuniform symptom distribution in the early stages. To better understand the biology as well as the relationship between pathogen titer and disease expression, we carried out seasonal, spatial, and temporal examinations of 'Ca. P. pruni' titer and distribution in infected orchard-grown trees. Sequential sampling of heavily infected trees revealed marked seasonal patterns, with differential accumulation in woody stem and leaf tissues and, most notably, within fruit in the early stages of development from bloom to pit hardening. Furthermore, mapping phytoplasma distribution and titer in trees at different stages of infection indicated that infection proceeds through a series of stages. Initially, infection spreads basipetally and accumulates in the roots before populating aerial parts of the trees from the trunk upward, with infection of specific tissues and limbs followed by an increasing phytoplasma titer. Finally, we observed a correlation between phytoplasma titer and symptom severity, with severe symptom onset associated with three to four orders of magnitude more phytoplasma than mild symptoms. Cumulatively, these data aid in accurate sampling and management decision-making and furthers our understanding of disease development.

Comparison of an Immunochromatographic Assay Kit with DAS-ELISA for Large-Scale Diagnosis and Molecular Discrimination of Satsuma Dwarf Virus Collected from Citrus Orchards

Satsuma dwarf virus (SDV) seriously damages citrus production by reducing the quality and yield of fruit. To avoid contamination with SDV, mother trees are checked to be SDV-free in advance of nursery tree distribution. In this study, we compared an immunochromatographic assay (ICA) kit with double-antibody sandwich enzyme-linked immunosorbent assay (DASELISA) for large-scale diagnosis of SDV in orchardgrown trees in Shizuoka Prefecture, Japan. The two methods gave conflicting results for 11 of 1,705 samples, all of which were negative by DAS-ELISA but positive by ICA. The samples scored as positive by either DASELISA or ICA were analyzed by reverse transcription polymerase chain reaction and all were confirmed to be positive. These results validate the use of ICA as a screening method for large-scale diagnosis. Strain discrimination revealed that 16 of 22 isolates belonged to SDV, while citrus mosaic virus (CiMV) infection only and co-infection (SDV and CiMV) were in a minority.

Elicitors of Host Plant Defenses Partially Suppress Cacopsylla pyricola (Hemiptera: Psyllidae) Populations Under Field Conditions.

Defense elicitors are products that activate acquired defense responses in plants, thus rendering the plants less susceptible to attack by a broad range of pests. We demonstrated previously under laboratory conditions that foliar applications of the defense elicitors Actigard (acibenzolar-S-methyl), Employ (harpin protein), or ODC (chitosan) to potted pear trees (Pyrus communis L.) each caused an increase in mortality of Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae) nymphs and altered the settling and oviposition behavior of the adults. In this study, we monitored C. pyricola populations over a 3-yr period on orchard-grown trees treated with water (untreated control), Actigard, Employ, or ODC. Fewer nymphs were observed on trees treated with elicitors compared with untreated trees in both 2014 and 2016. A similar but statistically nonsignificant pattern was observed in 2015 when nearly 30% fewer nymphs were observed on trees treated with elicitors versus untreated controls. Observed reductions in psyllid numbers by defense elicitors were modest and do not warrant the use of these products alone for managing C. pyricola. However, these products are often used for management of fire blight, and our observations that elicitors also reduce C. pyricola populations may be useful for system-wide integrated pest management approaches.

The influence of temperature and water supply on apple fruit growth and the development of orchard-grown trees

SummaryThe growth of ‘Cox’s Orange Pippin’ apples in an orchard was studied in relation to temperature and irrigation. Temperature around a number of trees was raised by the use of polythene tunnels from bloom in May until harvest in September. These trees within the polytunnels received irrigation, while for comparative purposes some trees outside did not. Continuous measurements of the canopy environment, particularly temperature, were made until harvest. Throughout the growing season fruit size was repeatedly measured, non-destructively, on a large number of selected fruit. Despite differences in mean temperature and accumulated day-degrees between trees inside and outside the polytunnels, there was no benefit to fruit size from raised temperatures. Supplemental irrigation did have a number of effects; spur leaf area was enhanced without significant change in total leaf area, while in the absence of irrigation, final shoot length was greater. This greater shoot production was however associated with a ...

Sorbitol Dehydrogenase Gene Expression and Enzyme Activity in Apple: Tissue Specificity during Bud Development and Response to Rootstock Vigor and Growth Manipulation

Sorbitol is the primary photosynthate and translocated carbohydrate in apple (Malus ×domestica), and most of it is converted to fructose by sorbitol dehydrogenase (SDH) in sink tissues. We studied the expression of nine SDH genes, SDH activity, and sorbitol content of apple 1) in buds and floral tissues from dormancy to bloom, 2) in leaves and shoot tips of trees on two rootstocks, the moderately vigorous ‘Malling Merton 111’ (MM.111) and the dwarfing ‘Malling 9’ (M.9), and 3) in shoot tips in response to application of prohexadione-Ca to suppress shoot growth and defoliation and girdling (D/G) to deprive the shoot tip of sorbitol. In mature, orchard-grown trees, sorbitol was the main soluble carbohydrate in expressed xylem sap from dormancy to bloom at levels over 3- to 6-fold those of glucose and fructose, the other major sugars present. Sorbitol levels there increased from dormancy to its highest concentration at the half inch green stage and declined by bloom, while those of the other sugars increased. SDH activity per milligram of protein increased over 4-fold from dormancy to flowering. Three of the nine known SDH genes (SDH1, SDH2, and SDH3) were expressed in immature and mature leaves and all buds from dormancy to bloom, as well as in all floral organs, except that only SDH3 transcript was found in stamen tissue. Two genes, SDH6 and SDH9, were floral-tissue specific; SDH6 transcript was detected in all floral organs except stamens at full bloom, and SDH9 was only expressed in anthers with pollen. In buds and leaves of young, container-grown trees, SDH1 and SDH2 generally accounted for the majority of total SDH expression. There were generally no effects of rootstock on SDH expression, SDH activity, or sorbitol concentration in leaves, while apical shoot tips on M.9 rootstock exhibited greater SDH activity than those on MM.111 or lateral shoot tips on either rootstock, though SDH expression of apical and lateral shoot tips on M.9 was lower than on MM.111. Prohexadione-Ca reduced apical but not lateral shoot growth, increased apical but not lateral shoot tip sorbitol content, had no effect on SDH activity, and increased SDH1 expression of all shoot tips. D/G treatment reduced shoot growth, sorbitol content, and SDH activity, but increased SDH1 expression of apical shoot tips only and SDH2 expression of lateral shoot tips only. This work indicates that sorbitol and other sugars are abundantly available from dormancy to bloom, that SDH activity increased during this period, and that SDH expression is at least in part developmentally regulated within the individual floral and leaf tissues. In shoot tips and leaves of young trees, SDH transcript level was not correlated with sorbitol availability or SDH activity, suggesting that other factors have significant regulatory effects after SDH expression on SDH activity.

Utilizing Aboveground Rhizotrons to Study Root Growth and Pathogen Movement in Simulated Orchard Conditions

Several techniques have been used to study root growth and pathogen movement along roots between trees, including profile walls, micro-rhizotrons, and soil cores. These assessments can be very time consuming, cost prohibitive, and ineffective when studying soilborne pathogen movement across overlapping roots between adjacent trees in an orchard. Three aboveground rhizotrons were designed and constructed to study the movement of Phymatotrichopsis omnivora (Duggar) Hennebert (syn. Phymatotrichum omnivorum Duggar) along overlapping apple roots [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. (syn. M. domestica Borkh. non Poir.)] in simulated orchard conditions. Two experiments involved boxes using either observation windows or micro-rhizotron observation tubes between trees. A third experiment utilized 45-gallon containers (171,457 cm3) joined by innovative observation windows. The container rhizotrons reduced labor and material costs, were more effective at monitoring roots, were more convenient than field measurements, and more closely simulated orchard growing conditions. This method provides several advantages to better study and manipulate the rooting environment of orchard-grown trees.

Winter variation in xylem sap pH of walnut trees: involvement of plasma membrane H+-ATPase of vessel-associated cells.

We studied seasonal variation in xylem sap pH of Juglans regia L. Our main objectives were to (1) test the effect of temperature on seasonal changes in xylem sap pH and (2) study the involvement of plasma membrane H+-ATPase of vessel-associated cells in the control of sap pH. For this purpose, orchard-grown trees were compared with trees grown in a heated (> or = 15 degrees C) greenhouse. During autumn, sap pH was not directly influenced by temperature. A seasonal change in H+-ATPase activity resulting from seasonal variation in the amount of protein was measured in orchard-grown trees, whereas no significant seasonal changes were recorded in greenhouse-grown trees. Our data suggest that H+-ATPase does not regulate xylem sap pH directly by donating protons to the xylem, but by facilitating secondary active H+/sugar transport, among other mechanisms.

The Role of Autumn Infections in the Progression of Fire Blight Symptoms in Perennial Pear Branches.

The role of autumn infections in the progression of fire blight (caused by Erwinia amylovora) symptoms in perennial pear branches was studied in orchard-grown trees in Israel. The extent of symptom progression and the final length of fire blight cankers in perennial branches were variably affected by the vigor of the trees and the season of infection. Following spring infections, when all trees supported active shoot growth, fire blight symptoms progressed more rapidly and to longer distances in trees that exhibited high vigor (i.e., with numerous annual shoots on most terminal branches) than in low-vigor trees (i.e., few or no annual shoots on terminal branches). Irrespective of the vigor of the trees, the progression of fire blight symptoms in perennial branches ceased between mid-May and mid-July, and only a small proportion (0 to 14.2%) of the infections had invaded main limbs or trunks of trees. Progression of fire blight symptoms following autumn infections was related to the preceding summer (August to No-vember) shoot regrowth: in trees in which the shoots did not restore their growth in the summer, the rate of symptom progression in perennial branches was higher in trees with a low vigor than in those with a high vigor, whereas for those with summer regrowth the relationship between rates of symptom expression was reversed. Irrespective of the vigor group and of whether there was summer regrowth, symptoms in perennial branches continued to progress through the winter until the following spring. Most of the autumn infections (50 to 78.5%) that developed in susceptible trees had invaded main limbs or trunks of trees. The results of this study indicate that factors related to host phenology and physiology, rather than factors related to environmental influences (such as temperature), govern the extent, rate, and duration of fire blight progression in perennial pear branches. Furthermore, it turned out that autumn infections play a substantial role in fire blight epidemiology in Israel.

WHOLE-PLANT WATER USE OF SOME TROPICAL AND SUBTROPICAL TREE CROPS AND ITS APPLICATION IN IRRIGATION MANAGEMENT

Whole-plant water use provides a baseline for a plant's irrigation requirement. The measurement of whole-plant water use in tree crops is much more difficult than in field crops, owing mainly to their large size. The development of thermo-electrical methods for xylem sap flow measurement has provided tree physiologists with an accurate and convenient tool to study whole-tree water use and water relations. However, sap flow measurement in orchard grown trees is particularly challenging because of horticultural practices, such as grafting, training and structural pruning. Whole-tree water use on a range of tropical and subtropical tree crops, such as mango, cashew, mangosteen, banana and macadamia, was measured using a Granier sap flow measuring system. The Granier system was found suitable for tree crops with very diverse morphologies and xylem structures, e.g. mango, mangosteen and banana. For a given species, radial variation in water flux in the sapwood has a more or less regular pattern, but the circumferential (aspect) variation was substantial and random. To obtain a reasonable estimate of the whole-plant or orchard water use, a large number of sap flow sensors and several dataloggers are required. To assist in taking account of spatial variabilities, a modified Granier method was developed and proved to be effective. A summary of the quantitative estimates of the whole-plant water use of several tropical and subtropical crops was provided. Sap flow was found to be a very sensitive indicator of plant water status useful for irrigation scheduling for plants grown in containers or on soil with limited soil water holding capacity but was not so sensitive for plants with deep roots and/or on soil with high water holding capacity. In its current design the sap flow system should remain as a research tool for researchers rather than an irrigation scheduling tool for farmers.

Regeneration of almond from immature seed cotyledons

Adventitious shoots were regenerated from immature cotyledons of four almond cultivars (`Ne Plus Ultra', `Nonpareil', `Carmel' and `Parkinson'). Open-pollinated fruit were collected from orchard-grown trees 100–115 days after full bloom. The proximal ends of the cotyledons were excised and the embryonic axes discarded. The effects of different concentrations of thidiazuron (TDZ) and indole-3-butyric acid (IBA) and the presence or absence of light for the first 7 days of culture were determined. Shoot regeneration rates were highest for cotyledons cultured for 8 weeks on Murashige and Skoog (MS) basal medium containing TDZ (10.0 μM), followed by 4 weeks on medium without plant growth regulators. Regeneration levels were further improved if cotyledons were maintained in darkness for the first 7 days. IBA (0.5 μM) significantly reduced the development of adventitious shoots. The frequency of cotyledons that developed adventitious shoots under the optimum tested conditions for `Ne Plus Ultra', `Nonpareil', `Carmel', and `Parkinson' were 80.0%, 73.3%, 100.0% and 86.7%, respectively.

Thinning Peaches by Heat

Flower buds in their last stages prior to opening, open flowers and small fruitlets are the most sensitive organs to frost damage. Such effect of low temperature is well-known as it poses an economical hazard in growing stone fruits in many countries. Heat effect on flower buds and flowers is less known simply because it is not common at time of bloom in most locations where such species are grown. Many of the low-chill early maturing peaches and nectarines set very heavily in subtropical climate and require a major input of manual thinning in order to obtain marketable fruit. As the level of fruitset is usually very high, thinning is been carried out during full bloom. With increase in costs of manual labor, this element becomes the critical one in producing such fruits economically. Up till now, no chemical or physical mean can replace hand-thinning in these early cultivars effectively. During our work with greenhouse-grown stone fruits we came across the enormous sensitivity of non-dormant flower buds as well as flowers to high temperatures. Avoiding excessive heat close to, and during bloom, became number one concern in the practice of growing stone fruits in greenhouses. By using container-grown peaches and temperature-controlled chambers in a phytotron, we were able to quantify the effect of heat on flower buds with the potential of obtaining controlled damage leading to the required level of thinning. Trials with potted and with orchard grown trees will be reported.

Control of premature fruit drop in Macadamia integrifolia: effects of naphthalene acetic acid application, cincturing, and shoot-tip removal

The effects of NAA application, cincturing and shoot-tip removal on the incidence of premature fruit drop were investigated in orchard-grown trees of Macadamia integrifolia cv. Kakea. A single, post-anthesis application of NAA (1 ppm) increased (P < 0.05) the final set of macadamia fruit by 35%. Limb cincturing combined with shoot-tip removal increased (P < 0.05) initial fruit set and possibly final set. Cincturing alone was less effective and shoot-tip removal had no effect alone.