Month: January 2006

When Greger Mendel did research on pea plants in the 1860’s, he identified a number of concepts that are important to heirloom plant growers, and people wishing to develop their own plant varieties.

His research centered around the concept of pairs of genes. He said all genetic traits were determined by these pairs of genes, and the genes within these pairs were inherited, one from each parent.

If, for example, you had two parents one with gene pair AB and another with gene pair CD, there were 4 possible outcomes for their offspring all with equal statistic probability:

AB x CD
=======
AC . AD
BC . BD

The order of the genes is not important, in other words AC is identical to CA.

Mendel’s research focused on several traits of pea plants, but for the purposes of this blog post we will look at the height of the plant. He noticed two distinct type of pea plants, those which grew tall and those which were short.

Before experimenting with cross pollinating, Mendel developed varieties of plants that only produced the traits he was interested in, in this case the height of the plant. He did this by discarding plants with the unwanted traits, and growing successive generations until the unwanted traits no longer appeared. This is a process called roguing, and it insured he was working with a gene pool that no longer contained the unwanted traits.

In this way he was able to determine that the tall plants has a pair of identical genes which made them tall, and the short plants had a pair of identical genes that made them short. For the purposes of his research, he referred to the tall gene as T, and the short gene as t.

He then took one of each type, cross pollinated them, and produced offspring as follows:

TT x tt
======= . (F1 Hybrid)
Tt . Tt
Tt . Tt

He referred to this generation as an F1 Hybrid. What he observed was that all of the resulting offspring were identical and all were tall. He explained this by saying the tall gene was dominate, and when it was present with a recessive short gene, the plant was always tall. He knew the genetic makeup of each of the plants was identical, with one of each type of gene, because they had to be inherited from parents which he had previously determined to have pairs of identical genes.

He then took pairs of plants from this generation, and crossed them again to create an F2 Hybrid as follows:

Tt x Tt
======= . (F2 Hybrid)
TT . Tt
Tt . tt

What he observed was that 75% of the resulting offspring was tall, and 25% was short. He said this was because only plants with the gene pair tt could produce short plants, otherwise as long as at least one dominate T gene was present, the resulting plant would be tall.

It was not sensible to talk about successive generations of hybrids (F3, F4, etc), because the genetic composition of the tall parents could no longer be determined, they could either be TT or Tt. This is referred to as genetically instability.

He said if it was desired to produce short plants from a genetically unstable variety, you simply needed to select 2 short plants and the resulting offspring would be short. Since then the T gene would no longer be present in the gene pool, all future offspring would also be short and the variety would be genetically stable.

He said if it was desired to produce tall plants from a genetically unstable variety, it was necessary to produce a number of successive generations of offspring and rogue out the short plants. In this way the t genes are gradually removed from the gene pool, and eventually only the T genes would remain, and the variety would become tall and genetically stable.

This turns out to be somewhat of a simplification of a much more complicated process in nature, nevertheless the basic principles here always hold true. In nature some traits are determined by more than one pair of genes, some traits are sex linked, in some pairs of genes one of them is not completely dominant, and so on. This example with pea plants deals with only one pair of genes, and since one particular plant can have hundreds or thousands of pairs of genes producing their own individual traits, a very complex situation can develop when cross pollinating two different plant varieties.

If you are trying to produce a new variety of plant through cross pollination, the basic idea is that you start by selecting two plants with traits you would like to see combined. In the first (F1) generation all the plants will always be identical, and will be an indication of the sort of plant you can hope to develop during the process of genetic stabilisation. During the stabilisation process, you rogue out plants with undesirable traits, and in the end you have a new stable variety. The stabilisation process usually ranges from a few up to 10 years.

Even if as a gardener you are not interested in in developing new strains of plants through cross pollinating, it’s still important to understand the concept of gene pools and roguing. Plants evolve by means of chance genetic variations, and you always want to preserve desirable new traits and rogue undesirable traits as they appear. You always want to select seeds from the best growing and tasting plants in your garden, to insure any genes associated with these traits are preserved. You should never save seeds from plants that bolt (go to seed) prematurely or otherwise don’t develop properly, or you risk preserving these traits.

For more information on Mendel’s work on pea and other plants, see:

http://www.visionlearning.com/library/module_viewer.php?c3=1&mid=129&l=

Exactly what an heirloom plant is can mean different things to different people. Purists will say a variety can be no younger than 60 years old, because that would ensure its origins are from before WWII, when modern agriculture emerged and varieties began to be patented. At the very least, an heirloom variety is one that is free from patents and intellectual property rights, non-genetically manipulated and not a hybrid variety. It is always possible to save the seeds from heirloom plants, and use them to grow an identical plant. In other words, you must be able to both legally and practically save them from one year to the next and pass these seeds onto your children like an heirloom. Since new varieties can be produced today but using traditional techniques, many people refer to these as modern heirloom varieties and consider them just as special as the older original heirloom varieties.

Before WWII if you wanted for example, to grow a cucumber, chances are what you would do is ask around and find someone who was growing a nice tasting cucumber and get some seeds from them. You could then save some seeds from your plants, and share them with others. If you were looking for something special and couldn’t find it anywhere else, you might create it yourself by taking two different cucumbers and cross pollinating them, thus creating a new heirloom variety.

Nowadays, if you want to grow a cucumber, chances are you would go to a garden center and buy a package of cucumber seeds. Odds are that the seeds you buy will be both patented and a hybrid variety, because these are more profitable for seed companies to sell as they can control the distribution of them. It may be that you grow excellent cucumbers with these seeds, so why should you care if they are an heirloom variety or not?

Hybrid varieties are made by combining the genetic material from two plants in a laboratory or factory, and the seeds produced by these plants are not genetically stable. In general, if you save the seeds from these plants and replant them, they will tend to revert closer to one of their original parent plants with each successive generation. Seed companies are generally able to keep the identities of the parent plants a secret, and so it is not possible for a competitor or home gardener to exactly copy the process of producing the seeds.

Let’s have a look at some of the reasons why many home gardeners choose to grow commercial seeds.

Seed companies are very adept at marketing their products and making empty claims that their F1 hybrids (common hybrids) are inherently higher quality. Often seed companies claim better taste, disease resistance or improved yields in a wider variety of climates. Much of the marketing warns you not to take a chance. You are going to spend all summer toiling in your garden, so don’t risk growing anything else.

It is true that every variety of plant, F1 hybrids included, can have unique or desirable characteristics. It’s not always true that hybrids are the only varieties with these characteristics or that heirloom varieties don’t have their own special qualities that you can’t find in hybrids. In reality, most of the characteristics seed companies are looking for in a variety have to do with long storage, ease of shipping, uniform appearance of the fruit, and so on. These characteristics are rarely interesting for the home gardener, and frequently don’t include tasting good, despite what their marketing says.

In some parts of the world heirloom varieties of plants are illegal. For example in Europe there was the 1945 treaty of Paris, which has evolved into to the current Common Agricultural Policy (CAP). The secret of the success of the CAP lies in it’s obscurity, and few people really understand how it works or what it does, and so it simply goes unchallenged. A very important part of how it functions lies in allowed seed lists. Each country maintains it’s own lists of varieties of seeds that are allowed to be used for food production and seeds to be sold to home gardeners. In theory, the purpose of these lists are to provide ‘genetically pure’ food, that has been tested for safety. Initially, it was these lists that saved Europe from genetically modified (GM) varieties, because they simply weren’t on the lists yet. In practice, the procedure for adding and taking seeds off these lists is very political. Very few heirloom varieties are on these lists, and the very fact these lists exist all but rules out the possibility of someone developing a new variety and selling it, unless you are a powerful food company. There is no credible testing for safety when adding new varieties, and there are virtually no known safety issues that they would be testing for anyway. Virtually all of the varieties on these lists are patented and the majority are hybrids. The purpose of these lists are to protect patent holders from ‘unfair competition’ from unpateneted varieties.

Most people don’t realize the huge number of heirloom varieties available, or just how special and exciting they are. For example, there are about 4000 different kinds of known tomatoes, of which about 1000 are thought to be ‘interesting’. It’s true many of them are red, but there are also yellow, green, white and purple ones. There are striped tomatoes, and tomatoes that grow hollow so you can stuff them. Some are as small as a pea, and some grow to more than 2Kg. They all taste a little different, and most are really delicious. You will never look at a store bought tomato in the same way again, after you have had one of these. It’s the same for virtually all kinds of fruits and vegetables, there are an unbelievable number of different varieties to choose from. There is particular interest now in so called ‘antique apples’. You will never want to eat an apple from the store again, after you have tasted an antique apple, they are so unbelievably good.

Okay, I hear you say, you still aren’t convinced. If you want some excuses for not growing heirlooms, here are some common ones. You want the convenience of going to the garden store and buying a package of seeds. You aren’t going to save the seeds anyway, so you don’t care if they are patented or hybrid. There is a particular trait in some hybrid variety that you want, you think it tastes good, you know it will grow in your garden and you don’t want to take a chance or go to the hassle of locating or buying an heirloom variety. You certainly don’t want to grow anything weird. So what? What does it matter? What does a package of seeds cost anyway?

The sad fact is that large seed and food companies are winning, and most people are using these excuses. So successful are these companies in fact, that by some estimates 70% of the varieties grown before WWII don’t exist anymore. They are gone and will never come back. More are disappearing every year. They are gone simply because no one bothered to grow them in their garden and keep the seeds from one year to the next. They are gone because the companies that sold these varieties couldn’t compete with the convenience of being able to go to the garden center and buy a package of commercial seeds. This is our genetic heritage, that fed many generations of our ancestors. It represents centuries of home gardeners and farmers creating varieties that tasted good to them, and they wanted to eat. It’s as much a catastrophe as losing the world’s rainforests, and the species contained within them, and few people realize it’s happening. By hunting out heirloom varieties, saving and trading seeds with others, you can do your part in saving the genetic resources we have left.