Creating an intentional cross is technically easy, though it is tedious. Here, I explain the basic procedure.
Unbagged tobacco blossoms will randomly cross with whatever varieties of N. tabacum happen to be growing within a half-mile. What you end up with, even from a single mature seed pod, will then be entirely unpredictable and varied.
One reason for intentionally crossing two varieties is to attempt to share some desirable trait of one variety (say, broad and flat leaf growth) with a different variety that has some other desirable trait (say, easy color-curing). For the best chance of possibly seeing the desired combination, you will need to do the cross in both directions: host (blossom) A crossed with pollen from B, as well as host (blossom) B crossed with pollen from A.
Some traits are supplied exclusively by the host plant (the female part of the blossom, where the seed will develop within the pod), while others are supplied by the pollen donor (the male side of the cross). [The energy machines within a cell, the mitochondria, have their own separate DNA, and this is delivered to the offspring seed only through the host (female) plant. Pollen contains no mitochondria. Most of the DNA resides within the nucleus of the plant cells, and can be contributed by either parent.] The problem is that you usually won't know if a specific trait is from nuclear DNA or from mitochondrial DNA. So creating crosses (using separate blossoms) in both directions is advisable.
Although you can perform the following procedure on a single blossom on each plant, it's a good idea to do so with at least a few blossoms in each direction. That will minimize the risk of random loss of a bud to weather, accident, budworm, etc.
I cut a waterproof stem tag from a ~2-1/2" strip of Tyvek (cut from a Tyvek envelope). The pointed end helps when inserting it into the slot. It is labeled with an "Extra Fine" Sharpie marker. These will last a long time, and will not fade in the sun. Be sure to label the tags consistently. My choice was to state the host variety first, then the pollen variety second.
The male (pollen donor) side of the cross must be from a freshly opened blossom. The female (host) blossom must be selected and pollinated the day before it opens. This sounds tricky, but if you observe some blossoms developing, you can easily identify what the blossom looks like the day before it opens. It is critical to cross the blossom before it has opened, since it will otherwise pollinate itself. Before opening, the pollen on the anthers is not yet mature, and can be simply removed with the anthers.
The process of performing the cross can be completed easily using a small pair of scissors and a hemostat clamp. A pair of small tweezers will work nearly as well as a hemostat.
I first clip the frill from the end of the immature blossom, then slit the blossom lengthwise to gain access to the sex organs. The pistil (female) appears as a light green stem in the center of the blossom. Its terminal end is usually a very dark green. The thin stems of the stamen (of which there are always 5) surround it, with a pale green anther at the end. The anther resembles a soft, pale green barley grain. If it appears to have a powdery coating, then the blossom is too mature, and a different blossom must be selected for the host.
Carefully avoiding injuring the central pistil stem, pluck out each of the 5 anthers, and discard them. You can leave the now-naked stamen stems in the blossom.
Now go to the plant that will serve as the pollen source, and locate a freshly opened blossom. The anthers here should appear dark and powder-coated. Pluck out 2 or three anthers and place them inside the previously exposed host blossom. The host blossom is then sealed by folding a strip of paper masking tape lengthwise over it. Wind motion will allow the foreign anthers to pollinate the host pistil.
You must now tag the stem of the host blossom, trimming away all but a few immature buds to use for additional crosses of the same variety. If one of the extra blossoms opens before you do the cross, it should be removed to avoid confusion.
The tape will eventually fall off with the aging blossom. If the cross is fertile, then a fat pod will develop. If the cross is infertile, then the entire tiny pod may die and fall off with the blossom and tape, leaving a bare, tagged stem.
The infertile cross on the left [N. tabacum x N. rustica] appears as an empty stalk. The fertile cross on the right boasts fat, maturing seed pods.
My practice is to use the hemostat on any crosses that use the same source of mature pollen, prior to thoroughly washing the hemostat. To handle more than one pollen source without cleaning the hemostat is likely to mix the pollen by contamination.
Successful pods should be allowed to brown on the plant, then the tagged stem removed for drying several months under shelter.
You won't know what you've accomplished until you germinate and grow out this F1 generation of seed the following year. At that time, you should germinate and plant as many of the seeds as you will have room to grow, since each one within a single pod may have combined a different set of traits from the cross. Regardless of how satisfied you may be with a plant or plants from the F1 generation, you still don't have a stable set of traits. To stabilize a new variety, you may need to then "self" it for 3 to 7 years, until most of the offspring reflect the traits of the new variety. Although this sounds like a daunting task, if you will be growing tobacco anyway, this can simply be a minor side project, which may or may not yield a useful new strain. If you are successful, then you are entitled to name it.
Bob
Unbagged tobacco blossoms will randomly cross with whatever varieties of N. tabacum happen to be growing within a half-mile. What you end up with, even from a single mature seed pod, will then be entirely unpredictable and varied.
One reason for intentionally crossing two varieties is to attempt to share some desirable trait of one variety (say, broad and flat leaf growth) with a different variety that has some other desirable trait (say, easy color-curing). For the best chance of possibly seeing the desired combination, you will need to do the cross in both directions: host (blossom) A crossed with pollen from B, as well as host (blossom) B crossed with pollen from A.
Some traits are supplied exclusively by the host plant (the female part of the blossom, where the seed will develop within the pod), while others are supplied by the pollen donor (the male side of the cross). [The energy machines within a cell, the mitochondria, have their own separate DNA, and this is delivered to the offspring seed only through the host (female) plant. Pollen contains no mitochondria. Most of the DNA resides within the nucleus of the plant cells, and can be contributed by either parent.] The problem is that you usually won't know if a specific trait is from nuclear DNA or from mitochondrial DNA. So creating crosses (using separate blossoms) in both directions is advisable.
Although you can perform the following procedure on a single blossom on each plant, it's a good idea to do so with at least a few blossoms in each direction. That will minimize the risk of random loss of a bud to weather, accident, budworm, etc.
I cut a waterproof stem tag from a ~2-1/2" strip of Tyvek (cut from a Tyvek envelope). The pointed end helps when inserting it into the slot. It is labeled with an "Extra Fine" Sharpie marker. These will last a long time, and will not fade in the sun. Be sure to label the tags consistently. My choice was to state the host variety first, then the pollen variety second.
The male (pollen donor) side of the cross must be from a freshly opened blossom. The female (host) blossom must be selected and pollinated the day before it opens. This sounds tricky, but if you observe some blossoms developing, you can easily identify what the blossom looks like the day before it opens. It is critical to cross the blossom before it has opened, since it will otherwise pollinate itself. Before opening, the pollen on the anthers is not yet mature, and can be simply removed with the anthers.
The process of performing the cross can be completed easily using a small pair of scissors and a hemostat clamp. A pair of small tweezers will work nearly as well as a hemostat.
I first clip the frill from the end of the immature blossom, then slit the blossom lengthwise to gain access to the sex organs. The pistil (female) appears as a light green stem in the center of the blossom. Its terminal end is usually a very dark green. The thin stems of the stamen (of which there are always 5) surround it, with a pale green anther at the end. The anther resembles a soft, pale green barley grain. If it appears to have a powdery coating, then the blossom is too mature, and a different blossom must be selected for the host.
Carefully avoiding injuring the central pistil stem, pluck out each of the 5 anthers, and discard them. You can leave the now-naked stamen stems in the blossom.
Now go to the plant that will serve as the pollen source, and locate a freshly opened blossom. The anthers here should appear dark and powder-coated. Pluck out 2 or three anthers and place them inside the previously exposed host blossom. The host blossom is then sealed by folding a strip of paper masking tape lengthwise over it. Wind motion will allow the foreign anthers to pollinate the host pistil.
You must now tag the stem of the host blossom, trimming away all but a few immature buds to use for additional crosses of the same variety. If one of the extra blossoms opens before you do the cross, it should be removed to avoid confusion.
The tape will eventually fall off with the aging blossom. If the cross is fertile, then a fat pod will develop. If the cross is infertile, then the entire tiny pod may die and fall off with the blossom and tape, leaving a bare, tagged stem.
The infertile cross on the left [N. tabacum x N. rustica] appears as an empty stalk. The fertile cross on the right boasts fat, maturing seed pods.
My practice is to use the hemostat on any crosses that use the same source of mature pollen, prior to thoroughly washing the hemostat. To handle more than one pollen source without cleaning the hemostat is likely to mix the pollen by contamination.
Successful pods should be allowed to brown on the plant, then the tagged stem removed for drying several months under shelter.
You won't know what you've accomplished until you germinate and grow out this F1 generation of seed the following year. At that time, you should germinate and plant as many of the seeds as you will have room to grow, since each one within a single pod may have combined a different set of traits from the cross. Regardless of how satisfied you may be with a plant or plants from the F1 generation, you still don't have a stable set of traits. To stabilize a new variety, you may need to then "self" it for 3 to 7 years, until most of the offspring reflect the traits of the new variety. Although this sounds like a daunting task, if you will be growing tobacco anyway, this can simply be a minor side project, which may or may not yield a useful new strain. If you are successful, then you are entitled to name it.
Bob