Genetic abnormalities

Tobacco, like many crops, may show genetic abnormalities which can usually be observed on the plant by modified habit, colour and shape of some of its organs. Thus, several genetic abnormalities are reported in the Solanaceae in literature. These can be, for example, an ability to produce deformed leaves which are strangely curled along their length or width, as is the case on the tobacco plant shown in figure 1.
 
More specifically, the abnormality referred to as "ruffle leaf" results in leaves that tend to curve downward. Those near the apex may consist of a midrib only, giving them an appearance of a rat tail. There are many enations (figure 2) of variable length and width, located along the veins producing ruffle-like appearance. The flowers of these plants exhibit morphological variations.
 
The leaf abnormality referred to as "toad-skin" is characterised by dark green leaves topped with finger- or wing-like protrusions (figure 3). The larger veins are knotted and puckered. The leaves have a toad skin appearance.
 
Plants affected by the abnormality named "leaf curl" (or "leaf roll"), as its names suggest, show leaves more or less strongly rolled upward (figures 4 and 5).

These three genetic abnormalities that occur exceptionally in the field, cause more or less generalised symptoms to all leaves of one or more plants. There are others, whose symptoms can be much more localised. It can be seen in the  tobacco plant shown in figure 6, where one can observe a tobacco leaf with an enormous and irregular blister whose origin is also genetic.

Some plants may have an ability to produce deformed leaves which are strangely rolled up along their length or breadth.
 
In general, these genetic aberrations are real curiosities that are expressed only by certain genotypes. They are sometimes found in the collections of tobacco breeders who avoid to introduce them in crops or keep them in cultivated genotypes. They are unduly rare in the latter.
 
Other genetic abnormalities produce symptoms similar to leaf mosaics.