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Ash fruit trees are the best choice for commercial production of fruit at the present time because they have high yields and are free from diseases. Apple, apricot, peach and quince are examples of fruit tree species that grow well in arid and semi-arid regions. These tree species typically produce a much greater yield per tree than grapefruit trees. The fruit are well adapted for both fresh and processed markets and they are less susceptible to insects and disease. However, asexual reproduction of arid-region fruit trees is severely restricted.
Sexual reproduction is accomplished in arid-region fruit trees by flowering and fertilization of the female and male gametes that result in seeds. In arid-region fruit trees, flowering occurs at specific times of the year following which pollen is distributed over the orchard and fertilization of the female gametes occurs. This fertilization occurs at a lower elevation (i.e. at the soil level) compared to the male gametes resulting in seeds being carried along the branches of the fruit tree.
As a result of these biological processes, it is extremely difficult to propagate fruit trees using conventional practices in an arid region. To overcome this difficulty, scientists in the research community have conducted extensive studies to optimize the breeding of fruit trees. Over the past several years, many different breeding programs have been attempted and tested to generate new varieties of fruit trees. However, these attempts have not been successful and only very limited success has been obtained in the past.
In the past, many attempts have been made to produce hybrid orchards with fruit trees. Most of these programs were designed to propagate trees that produce high quality fruit having large fruits and attractive colors and that exhibit a reduced incidence of disease and other undesirable characteristics. The fruit produced in such programs were propagated by using the male or female gametes to obtain seeds for breeding. However, few hybrids resulted from these breeding programs and the techniques used have not been commercially successful.
Other breeding programs have attempted to introduce new disease resistant varieties of fruit trees. Such programs have been more successful in identifying fruit trees that produce high quality fruit but the methods used have not been commercially successful because of the tremendous labor and expense involved in creating the programs. For example, in order to select parents of a desired cross-hybridization, it is necessary to plant many thousands of seedlings from each variety. Such seeds are planted in the spring and the resulting seedlings are maintained under the most favorable conditions for growth until late summer. At this time, the seedlings are planted in field plots to ensure that they survive and can produce fruit. Many of these seedlings are produced in nurseries from seeds harvested in fall and winter. Nurseries are labor intensive and require a large volume of seeds and seedlings to produce the desired number of seedlings needed to create new varieties. The labor and expense involved in creating the seedlings needed to make new varieties of fruit trees is extremely high.
Some of these nursery propagated seedlings are planted each year and some are stored. For example, it is necessary to store the propagated seedlings in order to preserve the vitality of the trees. It is also necessary to store fruit trees in order to ensure that a fruit tree produces fruit for the next season. In order to preserve the trees, the propagated trees are kept in storage and are grown in the spring. This method of storing propagated seedlings ensures that the seedlings will survive the winter months. However, this technique results in a reduced percentage of seedlings that survive the winter and also results in a reduced growth rate in spring.
Other breeding programs have attempted to select for certain properties that have little or no correlation with disease resistance and other desirable characteristics. For example, most fruit trees have a life cycle that produces reproductive maturity and yields fruit in a highly predictable manner. This life cycle allows breeders to determine the age of fruit, when it is mature, and when it will begin to ripen. Fruit growth in trees, whether it be for apples, plums, peaches, or other fruits, has been described as a “shingle effect” as the fruit becomes larger in size as it ages.
The shingle effect, also called bifurcation, or growth rings, occurs in almost all woody plant fruits. As the fruit ripens, the flesh starts to shrink.This shrinkage creates an opening in the fruit that allows the flesh to dry and harden. At the same time, the skin around the opening of the fruit thins and separates from the main fruit, causing the fruit to bifurcate.
The ripening time for fruit is also predictable. Fruit ripens on the stem or “peduncle”. The time to ripen varies from species to species, but the process occurs within 2 to 4 months of harvest. Trees are propagated from cuttings or are grown from seed. At some point the tree is harvested. When this occurs, the time remaining until harvest is highly predictable. If the fruit still has some growth remaining, the tree will grow another crop, or the fruits will be harvested. At some point the fruit stops ripening, and if the tree is still harvested the fruit will be harvested and placed in a cooler to retain the ripening cycle.
A problem arises when the fruit has ripened and there is still some residual growth. For example, a tree can be selected for growth that has superior fruit characteristics and fruit is harvested. But when the fruit reaches harvest maturity, it still has some residual growth that will cause the fruit to bifurcate at harvest. Harvesting fruit in this manner is not preferred, since it can cause the fruit to fall to the ground. In addition, harvesting fruit in this manner will cause the fruit to remain on the tree in an unripe state for an extended period of time. When this happens, the fruit will not ripen as expected by the grower.
It would be desirable to provide a harvesting system that allowed fruit to be harvested while still retaining some residual growth. This would allow growers to harvest fruit at an earlier stage than would otherwise be possible. This could also reduce the amount of fruit that is wasted.