Am I a Hybrid ?

Clearing the Hybrid Misconception.

Prof. Athula Perera Emeritus Professor

What exactly is a hybrid? You may have heard about hybrid cars, hybrid fruits, hybrid vegetables, hybrid seeds etc.  During recent times, the word Hybrid has been used in a very loose manner, especially during the organic farming calamity.  Some even said that the present local rice varieties are hybrids! This is not true.  What then is a Hybrid? Let us begin  our discussion referring to biological materials first.  

The word Hybrid refers to the nature of the set of genes that a particular individual carries. If not a Hybrid, what then is the alternative? It is then a Pure variety or a Pure Line as denoted in plants and Pure breed in animals.   So, beginning with the plant world, we can find either Hybrids or Pure varieties.

Genes, Alleles and Genotypes

In order to simplify this interesting, mystifying, genetic phenomenon, let us consider a single gene (also called a Locus) and denote it as ‘A’ or ‘a’, which are the different forms of the same gene, called Alleles.  They cause changes in the same character. In the character seed colour for example, there can be just one gene for seed colour but different alleles of the same gene, giving different colours such as green, yellow, black etc. One allele is received from the female parent and another from the male parent. 

Considering this single gene, a Hybrid will always be Aa.  This is its Genotype.  Then, the genotype of a Pure variety will be either AA or aa.  So, every single gene will have 3 possible genotypes such as AA, Aa and aa. The genotype Aa is heterozygous and the genotypes AA and aa are homozygous. 

Heterozygous genes (such as Aa) are found only in Hybrids and not in Pure varieties.   All the loci / genes in a Pure variety are homozygous (AA or aa).  For example, considering many genes, a hybrid genotype may be AaBbCcDd……. and that of a pure variety AABBCCDD………..… or aabbccdd…….. or even aaBBccDD……….

Local Rice Varieties

All our Bg rice varieties are Pure varieties.  They do not carry any heterozygous genes.  Therefore, they are not Hybrids. So, for this particular locus/gene, they are either AA (homozygous dominant) or aa (homozygous recessive).

The Farmers’ Problem

When a farmer initially buys seeds of a pure variety (e.g. Bg) for cultivation, all the plants in the field grown from these seeds will be identical i.e. either AA or aa.  At harvest time, he will save some seeds to grow in the next season.  There is no necessity to buy new seeds again, because all the plants grown from these saved seeds, in the next season will also be identical i.e. either AA or aa.  This genotype will not change, season after season.  This means that the character controlled by the gene will not change season after season.  The farmer can continuously save seeds for the upcoming season.  Such are our Bg varieties and all other pure varieties. 

Let us now consider a Hybrid Aa.  All the plants in the population grown from hybrid seeds will be Aa and hence identical.  At harvest time, if the farmer saves some seeds from these hybrid plants to grow in the next season, plants of different genotypes will arise in the next population, some being Aa, some AA and the others aa, as shown below, showing differences in the character between them.  This is known as segregation. 

Again, some plants will still be Aa, some will be AA and the others aa.  Thus, the plants in the population will differ in the same character within the same field. The farmer will have huge difficulties in marketing his mixed product.  So, he cannot save seeds from a hybrid plant in order to grow in the next season.  Therefore, in order to avoid this, he will have to buy the Hybrid seed every season in order to maintain uniformity in his product. He cannot save seeds from his Hybrid plants to be grown in the next season as they will segregate, and as such, different plants will show differences in the same character. Buyers will resist.  Export potential will be doomed.

So, the farmer will have to  make one of 2 choices.  He can grow Hybrid varieties but will have to buy the seeds every season or he can buy seeds of a Pure variety only once at the beginning because he can save some seeds from the harvest to grow in the next season and repeat the same in the next season and so on….in the next…….and in the next.  His final decision will then be based on the economics of his business (relative profit), based on the yield, quality of the product etc.

The Seed Market

Logically, almost all private sector seed producers will sell Hybrid seeds, so that farmers would need to buy fresh seeds from them, every season.  If they sell seeds of pure varieties, their seed business will collapse sooner than later since the farmers will buy their seeds only once.  Hence the word ’Hybrid’ is marketed to show that such varieties are superior.  We have to be careful so as to make sure that this is not just a marketing gimmick.  Scientifically, if all hybrids are superior, it means that Aa is always superior to AA or aa.  This is not always the case.  Many experiments have shown that some hybrids are superior to AA or aa, whereas many other experiments have shown that AA is superior to Aa i.e. a Pure variety is better than the Hybrid. So, the farmer has to decide which would give him the highest profitable income

It must be mentioned that all our superior, modern rice varieties are Pure varieties produced by a technique known as Hybridization to begin with and then, after many years / seasons of  ‘selfing’ and selection, new Pure varieties are produced.   Hybridization technique does not mean that the end-product will always be a hybrid.  It can be used to produce hybrids of many types as well as Pure varieties, equally efficiently.

Right, so plants can be either hybrids or pure varieties and the farmer will have to make the ultimate decision as to which he would cultivate after getting genuine information from those officials concerned. Now, that’s another issue altogether! 

What then is a hybrid vehicle? Well, it is similar to a combination of ‘alleles’. What?  Alleles for different power generation.  If petrol power is denoted as ‘A’ and electric power as ‘a’, then a hybrid will be ‘Aa’.  All petrol only vehicles will be ‘AA’ and all electric vehicles ‘aa’. Humans carried out the hybridization, of course.  Simple. 

Then, what about me? You? Am I a hybrid? Yes, surely, we are all. We are bound to have a large proportion of heterozygous genes among the thousands we carry in our DNA, including some from our ancestors, the Neanderthals. Now, that’s another story worth discussing some other time.