Sexual propagation is used almost entirely for the production of rootstocks that will be grafted or budded. It cannot be used to propagate the parent tree, as the progeny will not be true to type and will be unlike the parent.
For sexual propagation, seeds extracted from mature fruit are cleaned to remove any adhering fruit pulp prior to being stratified. Seeds of temperate tree fruit have an endodormancy and do not germinate if they are directly planted at ambient temperature; the seeds must be allowed to undergo a period of stratification to overcome this dormancy. Seed dormancy is a survival mechanism that ensures that in nature the seeds will not germinate when the fruit fall to the ground in late summer but instead will germinate after adverse winter conditions are past. Seeds can be stratified naturally by planting them out doors in nursery beds; their dormancy requirements will be satisfied in the moist soil and the cold winter temperatures. If this approach is used, it is important to test the viability of the seed lot that is being planted. This can be done using embryo excision or using 2,3,5-triphenyltetrazolium chloride. These tests allow seed viability to be ascertained in a very short time period. Knowing the seed viability is important if a good stand of seedlings is to be expected in the following spring.
Seeds can be artificially stratified by placing them in moist media and holding them at 4°C. It takes approximately 60 to 90 days to fulfill the dormancy requirement, and the seeds can then be planted at the desired location.
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