Pruning mature open center fruit trees involves keeping the center free of vigorous upright shoots, reducing tree height, and thinning out branches to reduce crowding. For peaches and nectarines, select 1-year-old lateral fruiting branches that originate close to main branches. Thin these fruiting branches and head them by one-third if they are longer than about 1 to 2 feet . Remove or cut back 2-year-old fruiting shoots or cut them back to 1- year-old shoots. On other species, old fruiting spurs should be renewed periodically. Table 1 shows the location of fruiting buds, the longevity of spurs, and the desired severity of pruning of selected species. When dormant pruning, become familiar with the plump fruiting buds and prune accordingly to ensure adequate flowering the following spring. Pruning of mature almonds involves few or no heading cuts; simply thin out branches—often fairly large branches—to prevent crowding.Central leader training is often used for apples and sometimes for pears, Asian pears, pecans, and quince. These trees tend to have dominant central leaders, a characteristic that lends itself to the central leader training method. However, because many apple and pear varieties are susceptible to fire blight, plastic pots 30 liters open center or other multiple-leader methods are often preferred so that if a major limb is lost the tree can be more easily redeveloped.
Central leader training involves keeping trees shaped somewhat like Christmas trees, with lateral branches arranged in separate layers, or “tiers,” separated by open areas of canopy, and branches in lower tiers wider than those in upper ones. Instead of sunlight reaching lower fruiting branches through the center, as with the open center method, it reaches them from the sides and between branches. For young central leader trees, the goal is to create three or four tiers of lateral branches, with about four branches per tier. This is done preferably during spring and summer by heading back or bending down any vigorous shoots that grow upright and compete with the central leader. Create the first tier of four lateral branches by tying or staking branches outward at an angle just above horizontal after they have grown 2 to 3 feet long. When the central leader has reached about 21⁄2 to 3 feet past the first tier, usually in the first dormant season after planting, head it just below this point and train a second tier of four branches outward from the cut leader. These branches should be offset vertically from those of the first tier. Then create the third tier in a similar manner.
Avoid bending one branch directly over another; also, maintain the tree’s pyramidal shape by keeping lower branches longer than upper branches. The entire process will take 3 to 4 years, depending on the tree’s vigor. Some side branching of these main lateral branches should be encouraged. Vigorous upright shoots should be removed or headed back during the growing season to only three to six buds, although some shoots should be left longer if fruit are exposed to hot afternoon sun. Heading these shoots a couple of times during the growing season creates fruit-bearing spurs if the tree is not too vigorous. Heading may also encourage the growth of another set of vigorous shoots; simply remove these shoots or prune them back to create more spurs.With walnuts, the first main branch originates higher than on most trees, about 5 to 8 feet , and the spacing between branches is about 3 to 5 feet . Pruning of mature walnut trees is not essential, but thinning of branches will keep trees healthy and productive. Persimmons bear on current-season shoots that originate from buds produced near the ends of 1-year-old lateral branches. For this reason, once the tree is developed, avoid heading these shoots and be sure that sunlight reaches lower shoots, or they will become less productive or die. Also, each limb must be kept strong from the start by ensuring adequate sunlight and shortening branches if necessary by cutting back to upward- and outward-growing lateral branches.
Avoid heading cuts except to stimulate branching, such as on young trees; such heading cuts are best made in late spring and summer to reduce strong upright growth of “whip” branches. Persimmons often grow taller than is desired for picking fruit. Trees that are allowed to grow unchecked can make large, beautiful trees; however, branches often break with the weight of fruit. If they are headed at a given height each year, the subsequent vigorous shoots will shade lower shoots by midsummer, so these shoots must be thinned by summer pruning. Where possible, cut to lateral branches rather than making heading cuts.“Fruit bushes” are standard trees or, preferably, trees on dwarfing rootstock that are kept small by periodic summer pruning. This method can work for nearly all fruit species. The beauty of this system is its simplicity and ease of management. Pruning begins in about late April or early May of the first growing season, when new growth is about 2 feet long. At this time, cut the new growth in half, aiming for a uniform, bushy appearance. Hedge-trimming shears may be useful in this. In about late June, cut the subsequent new growth in half. If new growth is vigorous, it may need to be cut once more during the season. These heading cuts promote an excess of branches, so thin them by removing some shoots to allow sunlight to reach the lower branches. If needed, thin out additional crowding branches in the dormant season when they are more visible. In the second year, continue cutting new growth in this manner until the trees reach 5 to 7 feet tall, a height at which you can easily prune the top. Pruning in subsequent years involves cutting off any shoots above the tree’s permanenth eight two to three times per year. Also, thin crowding branches, especially at the top of the tree, and remove unproductive fruiting wood in early spring when branches without flowers are visible.No matter which training method you choose, do some pruning in the spring and summer to train young trees and shorten the time to full fruit production. When necessary, bend and stake shoots of young trees during the spring and summer so they will grow in the desired direction. Bending branches in this manner develops the scaffold structure faster than heading them and waiting for new lateral branches to form. On mature trees, summer pruning mainly involves removing vigorous upright shoots that are not needed as permanent branches and heading or thinning shoots to control tree height and develop branches. If trees receive appropriate summer training and pruning, far less dormant pruning is necessary. However, the absence of leaves in winter provides a clear view of the framework of the tree. At that time, thin or head any branches that were not adequately pruned during the growing season. One notable feature about apricots is that they are susceptible to infection by the branch-killing disease eutypa dieback, round plastic pots which is a particularly serious problem in Northern California around the San Francisco Bay Area. Infection occurs on wounds made in fall or early winter, causing severe gumming at pruning wounds and branch dieback.
Therefore, it is best to prune apricots either in late summer, so that at least 6 weeks of rain-free weather follow the pruning, or late in the dormant season , by which time far fewer viable spores are present. If pruned in summer, be sure to prevent sunburn by leaving enough foliage to cover limbs or by painting exposed limbs white with a 50-50 mixture of interior white latex paint and water.Refrigeration is indisputably the most effective strategy to prolong shelf-life, preserve quality and delay the deterioration of many fruits and vegetables . However, in cold sensitive commodities such as tomato , storage at temperatures between 0-12°C induces the onset of molecular, biochemical, and physiological alterations known as post harvest chilling injury , which are manifested when fruit are rewarmed to room temperature . PCI is a complex and multilayered phenomenon. Its early stages are temperature-dependent and are mediated by physical changes in cellular membranes . Loss of membrane stability triggers the activation of a signal transduction cascade that transmits the cold stimulus downstream through a series of molecular players, e.g., second messengers, eliciting symptoms characteristic of this disorder . These symptoms include modifications in respiration and ethylene production, disruption in the synthesis of aroma volatiles, accumulation of reactive oxygen species , lipid peroxidation, and DNA and protein damage . These molecular and cellular processes ultimately lead to failures in fruit ripening, the development of surface pitting, seed browning and higher susceptibility to post harvest decay . Most of what is known about the cold signal transduction pathway in plants, comes from studies of Arabidopsis thaliana, which is able to cold-acclimate and endure freezing temperatures . The C-Binding Factor gene family of transcription factors are positive regulators of the cold response that interact with the cis-elements of downstream cold-responsive genes . These target genes, also known as the CBFregulon, encode protective proteins and enzymes, and are involved in the synthesis of metabolites that enhance the plant’s fitness during cold stress . In tomato fruit, SlCBF1-3 genes are also induced by cold , but the size and types of genes comprising the CBF regulon are not the same as in Arabidopsis . This might partly explain tomato’s inability to cold acclimate . Different members of the Arabidopsis CBF gene family have been ectopically expressed in tomato plants under the control of the constitutive CaMV35S promoter, resulting in increased stress tolerance, but with concomitant growth reduction and flowering delay . This, due to CBF’s involvement in gibberellin repression, and DELLA protein accumulation . A transgenic phenotype over expressing AtCBF1 in tomato fruit was characterized, and revealed this gene influenced ripening as well as fruit’s response to post harvest cold stress . In this work, we hypothesized that CBF1 over expression in tomato cv. Micro-Tom fruit during post harvest chilling would enhance fruit tolerance to cold stress and reduce the incidence of PCI. We cloned this gene from two sources: cultivated tomato and the wild tomato relative Solanum habrochaites . S. habrochaites has been extensively studied due to its tolerance to cold stress . ShCBF1 has been cloned and expressed into Arabidopsis plants conferring tolerance to freezing and salinity but displaying phenotypic abnormalities . In this study, both ShCBF1 and SlCBF1 genes were driven by the stress-inducible promoter RD29A . Our goal was to specifically induce CBF1 expression in harvested fruit stored in the cold, as well as minimize pleiotropic effects caused by constitutive over expression. To test our hypothesis, transgenic fruit were cold-stored, which elicited ectopic CBF expression, and their post harvest performance was examined and compared to wild-type fruit under the same conditions. To broaden the scope of traditional studies of chilling injury beyond fruit post harvest, we also tested if the photosynthetic responses of CBF1-overexpressing seedlings would be affected by cold stress. The goal was to understand the physiological effects of additional CBF1 transcripts at different phases of the plant life cycle. Finally, we evaluated the influence of post harvest fruit chilling on seeds and seedling traits that were measured under control or cold conditions, to explore the concept of transgenerational adaptive mechanisms transmitted from fruit to progeny.Fruit were cold-stored and transferred to 20°C for three additional days to induce PCI. The presence of surface lesions or pitting and deterioration in the form of decay, were recorded. Wild-type fruit consistently had the lowest CII scores among all genotypes, maintaining levels below 30% after 2 or 3 weeks of cold storage, and rewarming . In contrast, transgenic fruit developed pits after just one week at 2.5°C, especially in Sh-36 and Sl-2. There was a slight decrease in CII between weeks 2 and 3, which was linked to the pitted lesions becoming ‘swollen’ in appearance . The highest incidence of decay was observed in Sh-36, Sl-2, and Sl-12 . A myriad of symptoms was recorded, i.e., severe discoloration, wrinkles around the stem scar, and surface ‘translucency’ , but they were absent or minimized in the WT. Degradation of RNA samples obtained from the transgenic fruit was observed and verified during agarose gel electrophoresis and may be connected to the phenotypic deterioration induced by CBF1 over expression. Based on their contrasting PCI phenotype, further analyses were conducted on Sl-2 and Sh-13 fruit in addition to the WT.