Grape breeding 101

[SethDoty]

I looked in the archives and didn’t see anything similar to what I have in mind, so I thought I would create a thread about how to breed grapes & make crosses for interested amateurs. I first started growing grapes around 2008 & made my first crosses around 2012, and have continued with it every season since, making progress slowly and steadily, the way it happens in much breeding work. I am breeding for the climate conditions of the southeastern USA so my personal focus is on integration of disease resistance from wild sources into cultivated material. I hope this thread will provide encouragement and “how to” info for any grower who would like to try their hand at breeding but doesn’t know how to start. Anyone with a little space can breed grapes, the concepts are not difficult. It just takes interest, a goal, knowledge of material that possess the traits you want, and of course time. Of course any questions are welcome.

To start with, it’s helpful for the prospective hobbyist breeder to know a few facts about grapes.

1. Bunch grapes(which is everything but muscadines)are a diploid, 38 chromosome species. As a general rule, all 38 chromosome bunch grape species are fully cross compatible with each other and can pollinate each other and produce fertile offspring. This covers the majority of grapes. Muscadines are the exception. They are a more distantly related, diploid, 40 chromosome species and do not interbreed easily with bunch grapes due to the chromosome difference. It is possible to hybridize bunch grapes and muscadines with effort, particularly when the bunch grape is used as the female parent, but most offspring will have 39 chromosomes and be highly, or completely sterile. Like a mule. With enough effort, some slightly fertile hybrids can be found, and with back crossing fertility can be restored. This is how seedlessness was introgressed into muscadine varieties such as “razzmatazz” and “oh my”, but it take a huge amount of time and effort to do this successfully.

2. Grapes come with three possible flower types. Each unique vine/genotype will typically produce only one type of flower, and it will be the same every season.

First you have female flowers. Female flowers have fully formed and fertile pistils, but short, curved/twisted anthers and the pollen is infertile. Female varieties cannot be used as a pollen parent, but are the most simple varieties to use as a seed parent, since they cannot self pollinate. All that is required is to bag the flowers clusters prior to bloom to protect them from stray pollen from undesired parents, apply pollen from the desired pollen donor to the bagged cluster during bloom, and rebag till the fruit forms. As easy as it gets.

Next you have Perfect flowered varieties. Perfect flowered varieties have a fully formed and fertile pistil like a female variety, but unlike a female, they also have erect, straight stamens, and will produce viable pollen that is capable of both self fertilization, and of pollinating fertile pistils on other vines. As a result, perfect flowered vines can be used as either the pollen parent or the seed parent in breeding. This flower type is the type found in the majority of cultivated varieties, and is the most desirable flower type for most purposes.

Lastly you have male flowers. Male flowers are typically only found in wild material or rootstocks. Male flowers will have erect stamens and produce abundant pollen, but there will typically be no pistil present at all, or at most, a slight, underdeveloped and unviable indication of the beginning of a pistil. Because they have no pistil, these vines will bloom heavily but set no fruit. Typically this flower type is the least desirable to use in breeding, because roughly half of the offspring will also be fruitless males in any cross. The exception would be if you are working with rootstocks and fruit production is not a goal.

I think that’s enough for a first post in the thread. The next post will be on emasculating perfect flowered varieties so they can be used as a seed parent in breeding.

[SethDoty]

Very often, when breeding grapes, the variety you wish to use as your seed parent will have perfect flowers. To avoid self pollination, it is necessary to emasculate the flowers on such varieties before they open. Before you start you will need the following:

1. Tweezers/forceps. Tip type not super important, with the exception that super fine pointed types can damage the flowers with less pressure. Just choose a type you like.
2. A paper bag of the appropriate size. Plastic bags are NOT ok.
3. Jute twine or anything that can tie off the paper bag.
4. A sharpie or something to write on the bag.
5. Scissors(optional)

Now you’re going to want to make a cut with your scissors roughly 1.5-2 inches long in the center of the top of the bag. Additionally, cut a piece of twine 8-10 inches long. You’re also going to want to write the cross you are making on the outside of the bag. Traditionally, the female seed parent goes on top when writing top to bottom, and first when writing left to right. The easiest way to remember this order is with the saying “ladies first”. By sticking to the traditional way of indicating parentage it will help you remember the direction of the cross years down the road, and also let other breeders know which parent was the male and which was the female, should you ever pass seedlings to someone else.

At this point, we are ready to go into the vineyard and start to work on our flower cluster. You will want to select a flower cluster that is ready to open within 1-3 days. Ideally, a few flowers will already be open, but not many. A few flowers being open is an indicator that the cluster is ready to bloom. If there are any open flowers, careful pull them all off with the tweezers before you start. Once the cluster is free of open flowers, you are ready to emasculate the flowers. Grip the top one third of the unopened flower cap with the tweezers and gently squeeze till the cap splits. Don’t squeeze any tighter than you need to to split the cap or you increase the risk of damaging the flower pistil. Sometimes you will hear a slight popping sound, sometimes not, but you will see a slight split in the cap.

After the cap pops/splits, grip the top one third of the now split cap with the tweezers, and gently pull it off. If done properly, this will remove the anthers under the the half of the cap being pulled off. Repeat the same process on the other half of the cap, and the first flower should be done. It is important to make sure that you get all the anthers. If any little yellow bits of anthers remain, carefully remove those as well. You don’t want any anthers left or they could self pollinate some of the flowers.

Repeat the process on each flower until you are finished with the cluster. It is ok if you pull off some of the flowers by mistake in the process of emasculation. You will have far more flowers than you need on a cluster, so losing some is no big deal. It’s normal, although you will get better with practice. If you get tired of emasculating the cluster before you finish all the flowers(it’s a very tedious process that can take an hour or more per cluster) it’s ok to use the tweezers to just pull off all the rest of the flowers that are not open. You don’t need them all. The main thing is to not damage the pistils on the majority of emasculated flowers, and to not leave any anthers behind.

Your emasculated cluster should look like this:

You will notice there are a small number of non-emasculated flowers at the bottom of this cluster. That’s the part of the flower cluster I hold on to while emasculating the rest of the cluster. You could do that bottom part too, but on large clusters, it’s really not worth it. You have plenty of flowers. I will usually just snip off this bottom section with tweezers or scissors and be done with it.

At this point you are ready to bag up the cluster.

Put the bag over the cluster, and slide the cane into that slit you cut in the top of the bag earlier. Wrap the top of the bag around the petiole of the leaf opposite of the cluster you just emasculated, and tie it shut. Your cluster is now protected from stray pollen. In 2-3 days untie the bag and check for receptivity of the flowers. If the flowers are at peak receptivity, there will be a small drop of liquid visible on the end of the stigma. Apply pollen of your choice, either fresh plucked from a vine of your choice that’s blooming at the same time, or dried stored pollen from your freezer. All flowers in a cluster do not hit receptivity at the same time, so ideally you want to apply pollen at least three days in a row after you see receptive flowers. The next post will be about how to dry and store pollen, but it may be a week or so before I get to it.

[SethDoty]

Sometimes in grape breeding, you will want to use a pollen parent that does not bloom at the same time as the seed parent you wish to use. For these cases, which are common, knowing how to collect and store pollen is a valuable skill.

You will need the following:

Aluminum foil
A lamp with a incandescent bulb(not essential, but helpful)
Ziploc type bags
micro-centrifuge tubes
A piece of steel or aluminum screen with around 1/8 in holes

First, you will collect the clusters you wish to use for pollen. Ideally you want half the flowers or less on the cluster to be open, but at least some of the flowers should be open or the pollen may not yet be mature.

They should look something like this:

Next you should lay out a piece of aluminum foil on a flat surface in a breeze free area. Then, over the aluminum foil, you will grate the flower clusters through the mesh. The idea is to break up a lot of the unopened flowers and to leave stem of the cluster behind.
When complete, it should look something like this:

You should have a pile of mixed flower parts and pollen on the aluminum foil at this point. How big a pile, obvious depends on how many clusters you used.

If it’s a large pile, try not to leave it in a mound. Spread it to a thin layer so it can dry. At this point, turn on your lamp if you intend to use one, and let it dry for approximately 24hrs.

Look at the flower parts after 24hrs. Most should look dry. Sometimes, if you harvested a lot of clusters for pollen, it may take a little longer to dry. You don’t want to increase the heat or put the lamp too close to shorten drying time, as too much heat is bad for pollen viability. Once the pollen appears dry, you pour it off into your storage container. If the amount collected is fairly small, as in you only used a few clusters, you will probably want to put it in micro-centrifuge tubes. If the volume is large, you may want to put it directly into a Ziploc type bag. Small amounts of pollen directly into Ziploc bags doesn’t work well, as the pollen is hard to use in such cases.

Fill your tubes about half full. You can use a funnel if you want, but you will lose a little pollen that way.

If you did everything right, you can close your tube of mixed pollen/dried flower parts, shake it up, and then open the lid. On the inside of the lid there should be a fine film of pollen. When you use this pollen on a cluster, you can open the tube and touch the individual flowers to this pollen film. Periodically close the lid and shake it up for a fresh pollen film.

At this point you are pretty much done. If using a Ziploc directly, make sure to double bag. One Ziploc inside another. Label it so you know what the pollen is from. If using the tubes, one Ziploc with the tubes inside a labeled bag is fine. The purpose of this is to reduce condensation issues. You will be storing this in your freezer. When you pull it out to use it, condensation will form in the first bag. If you don’t open the bag till they both warm to room temperature, most of the condensation will be in the first bag, and not in the pollen. Water dramatically reduces the storage life of pollen. I have used pollen dried and stored in an ordinary household freezer this way that was as old as four years old and still had good set. Pollen properly prepared keeps pretty well. In general, it’s safe to say it should keep at least a year in such conditions, and often quite a bit longer, permitting you to make crosses that you otherwise could not easily make. On the other hand, pollen not dried and prepared, and left at room temperature, not frozen, tends to last a week or two at most, and often only 3-4 days.

One more tip,

If you are using large amounts of pollen directly in Ziploc bags, small glass rods are an easy way to apply the pollen to flowers. Both glass rods and the tubes can be easily purchased at places like Amazon.

I hope someone finds this information helpful/useful to them.

[SethDoty]

Harvesting seed, seed prep, stratification, and germination.

Once your grapes from your controlled crosses are mature, they are ready to be harvested for seed. The seed should be hard and brown, and should sink in water. If the seed is white, or floats(assuming no fruit residue is stuck to it) it is generally unviable and should be discarded.

You can recover the seed by either carefully eating the grapes and spitting out the seed, or by crushing the grapes in a plastic bag and sorting/straining out the seed. Whatever works for you.

Once you harvest your seed and have separated it out, you have a couple options. You can bag it, label it, refrigerate and store it in moist soil, peat moss etc. until the following spring. Grape seeds generally require cold moist stratification of at least three months to germinate well, and longer, even multiple years, does not hurt. However if it’s early enough in the season and you live in a warm southern climate, you may be able to cheat a little and germinate seeds within the same year.

If you wish to attempt to speed up the process and try to germinate seeds the same year it’s harvested, you can try this. The goal is to break down seed germination inhibitors in the seed/seed coat that preserve dormancy. First, right after they are removed from the berry, let the seeds soak for 24-48hrs in 3% hydrogen peroxide, the same stuff you can buy over the counter. After that, soak for 24hrs in 1000ppm ga3, a naturally occurring plant hormone. You can buy it relatively inexpensively in powdered form online, and it’s simple to mix it up to the proper concentration with a graduated glass cylinder. Mixing instructions are typically included and vary slightly depending on the concentration/formulation.

After the 24hr soak is complete, place the seeds in moist paper towels, or moist peat moss, etc. inside a Ziploc type bags and refrigerate for roughly 10-14 days. The purpose of this treatment is to reduce the amount of time necessary for moist, cold stratification, which is typically around 90 days for untreated seed, but often only a week or two for treated seed. After the cold, moist storage period is complete, bring the bag out to room temperature. Leave it sealed, but start checking for germination after about one week. Germination can start as soon as a few days after coming up to room temperature, or may take up to three weeks to start. Once started, seeds may largely germinate rapidly over a week or so, or slowly over a month or more. A lot depends on the genetics of the seeds, and there is much variation. Also, if you did everything right, and germination was poor or nothing germinated, don’t despair. Grape seed can be finicky about when it wants to germinate sometimes, but it lasts very well in most cases. As long as the seed is still hard(if it’s not, you can squish it between your fingers and it will turn to mush) it’s probably still good. Just return it to your refrigerator and try again the following season. There are times grape seed has a mind of its own and a batch that had poor germination one season will germinate very well the next year after further cold moist storage.

I prefer to leave seeds in the bags until after they germinate. I do this because of the previously mentioned erratic nature of germination in grape seeds. If you plant ungerminated seed directly in flats, you will end up with a lot that doesn’t germinate right away, if at all. By leaving it in bags, you can pull only the germinated seed and plant that in flats every few days, and whatever doesn’t germinate the first season can be easily returned to cold storage and tried again the following year. If using paper towels I will pull seeds at the first sign of germination as mold can become a problem for survival once the germination process begins. If using earth/peat moss instead I will let the seedling remain in the bags until the cotyledons or first few true leaves form, as mold is much less problematic on those substrates.

I will typically grow seedlings indoors under grow light till they are somewhere around 6-12in tall, roughly 2-3 months, and then plant them in nursery rows after hardening them off. I use one foot spacing between plants initially. This is far closer than is desirable for mature plants(6-8ft is typical) but the plants will be thinned heavily for foliar disease in the early years, so close spacing to start with works out ok.

[kinghat]

@SethDoty

what is the substrate/mix youre using here?

[SethDoty]

I don’t remember honestly. Most likely a mix of backyard garden dirt/sand with some compost mixed in if I was to guess. Grapes do not require particularly good soil and are pretty tolerant of such things within broad reason.