In viticulture and enology, the term "clone" is used to describe a distinct sub-type within a variety. Some varieties have many different clones (e.g. Pinot Noir), the vines within each clone being identical to each other but slightly different from those of other clones. All the clones, however, are similar enough to be called by the same variety name. What is a clone really? Are clones really different? How do they get to be that way?
What is a Clone?
A group of genetically identical vines originally derived from a single mother vine by vegetative propagation.
How do Different Clones Arise?
When a genetic change (mutation) occurs in a dividing cell, all cells derived from that individual cell will carry the change. If such a mutation occurs in a developing bud it can give rise to a mutant shoot in which every cell carries the genetic change. Cuttings made from such a shoot will produce entire vines carrying the genetic change in every cell. All vines derived from this mutant shoot, and all vines subsequently propagated from these vines will constitute a new clone.
What is a Mutation?
A change in the genetic material (DNA) that specifies all structures and functions in the vine. It can be a very tiny change in a single gene (and there are thousands in each cell), such that just one specific compound or process is affected, or a gross change, such as the loss of an entire chromosome, that affects many functions and structures in the vine.
Why Does the Mutation Happen?
Mutation is a spontaneous natural phenomenon, When you consider the complexity of chemically replicating a very complicated coded sequence every time a cell divides, it is not surprising that mistakes occasionally occur. The natural mutation rate can be increased by certain chemicals and forms of radiation.
In What Ways Do Clones Differ?
The genetic changes that lead to clonal differences can, and do, occur in any gene. However, only visible clonal differences are usually detected (e.g. fruit color, leaf shape). Genetic changes that do not produce visible effects (e.g. a change in berry flavor constituent) are not usually detected but are just as frequent and may be even more important to viticulturists and enologists than visible changes.
Why Do Some Varieties Have More Clones than Others?
Some varieties (e.g. Pinot Noir, Chenin Blanc) are very ancient. They have been vegetatively propagated for centuries and mutations have been occurring in their cells all this time. Thus many different sub-types have arisen due to the accumulation of different combinations of different mutations. A new variety, such as Ruby Cabernet, has only been propagated for a few years and there has not yet been time for much genetic divergence within the variety. Also, some varieties have been subjected to deliberate clonal selection programs, in which small differences among vines in a vineyard are identified and monitored through several cycles of vegetative propagation and sue them as progenitors of new clones.
If some of my Vines Seem Different than Normal, Does that Mean I Have a New Clone?
Not necessarily. Not all differences between vines of the same variety are due to genetic changes. Other factors can profoundly affect appearance and function, e.g. soil type, water availability, rootstock. Differences due to these factors are not permanent, whereas clonal differences are. Clonal differences persist through vegetative propagation. They are confirmed by taking cuttings form plants suspected to be different clones and planting the daughter vines side by side to minimize environmental variability.