Leaf Abnormality: Flowers On The Petioles

Flowering on the petioles, also described as bud on leaf, is more of a growth abnormality than a mutation. Many strains will show this trait under certain conditions.

The occurence of flowers on the petioles was first published by John H. Schaffner in 1930 in The American Naturalist. This was one of several abnormalities noted in his paper about peculiar expressions in hemp.

"Hemp may be so developed in a given short-light-temperature complex that some of the petioles at the base of the inflorescence will bear one or more flowers on the upper side. Sometimes there is a regular row of flowers on the petiole. Now is it the hereditary nature of the hemp to produce flowers on the leaf petiole? I would say that it most certainly is. But again this reaction is determined by a certain specific aggregate of ecological conditions. Under one set of ecological factors the hemp has such a reaction; under another set of ecological factors no such reaction takes place."

As Schaffner explains, this developmental phenomena usually occurs with a certain combination of short days and certain temperatures, but it is different between strains and very unpredictible in general. Several variations may occur, depending on the stage of flowering or rejuvination. There may be a single flower, or a whole string of them. Sometimes additional leaves or even an entire branch emerging from the petiole. Usually these stem from the junction of the leaflets, but they may also grow from anywhere along the petiole.

What Are Mutations? And Why Should Anyone Care?

Mutations are changes in genetic material, the genotype. Typically, this means a change in the DNA sequence of a living organism, which can be inherited by the offspring of that individual. If the mutation has an observable consequence, then it is often referred to as a trait. Some mutations are dominant, or semi-dominant, where the consequences manifest even if different versions of the gene are present. Others are recessive, and can only been see if all copies of the gene are the same. Of course there are other types of observable changes in living organisms, which I will refer to as abnormalities of development or growth. Likewise, there are heritable changes in DNA sequence with no consequences, which are known as silent mutations.

Mutations can arise in a number of ways, and naturally occur during the life of any living organism. Spontaneous mutations occur through various errors in DNA replication, while induced mutations occur as a result of DNA damage from radiation or chemicals.

To begin, I will try to cover some of the more interesting morphological traits. Following that, I will move on to chemical traits and growth abnormalities. Hopefully, I will get some feedback from people who have found their own unique mutations.

The sequencing of genomes and transcriptomes from Cannabis sativa strains and sub-species has already begun, and soon genetic screens will also be conducted using various mutigens. With the cost of DNA sequencing steadily decreasing, it will not be long before many of the genetic causes of various traits will be determined. Whether you approve or not, a breeding revolution will certainly occur in Cannabis sativa along with many other organisms. It is not hard to imagine the benefit of knowing precisely the sequence of the gene alleles affecting leaf shape, pigmentation, height, branching, flowering induction, flowering speed, flower density, gender, hermaphroditism, cannabinoid synthesis, terpenoid synthesis, stress tolerance, seed size, oil content, fiber content, and many other interesting characteristics.

If you are not familiar with the benefits of knowing the gene sequences for breeding, then I will give a simple example. Perhaps someone is trying to combine two recessive traits into one plant. For example, they are crossing a ducksfoot plant with an lowryder plant to obtain an autoflower with webbed leaves. However, because they only have 1 square meter in which to grow plants, and autoflowering plants cannot be kept alive for multiple rounds of breeding, they cannot do the typical genetic tests for recessive traits. In other words, they cannot keep plants around to do test crosses. This leads to situations where a breeder has to blindly cross a small number of offspring for several generations and just hope that a suitable plant will appear by chance.

However, if the genes for the traits are known, then one of the first leaves from each plant can be tested in only a day or two to see if that plant contains the desired allele for the otherwise unobservable recessive gene. Once that has been determined, then all plants lacking at least one copy of the allele can be eliminated from the breeding program immediately. The desired traits can then be combined at a greatly accelerated pace.

With only two traits, this is not a huge advantage. After all, the double recessive combinations should show up in 1/16th of the F2 generation. However, when combining three, four, or five traits, this can easily reduce the timeline by several years. Additionally, knowing which plants contain a recessive allele is particularly useful when backcrossing, to introgress recessive traits into an otherwise "perfect" strain.

Leaf Mutation: Simple Leaves

The simple leaf mutation, also described as palmately lobed, webbed leaf, duckfoot, or pinnatifidofilla has a long history. Although it is possible that the mutation originated only once, it is likely that it has arisen several times and has been selected and maintained because of the conspicuous phenotype. There are several strains which have similar leaf morphology, including the Ducksfoot, Hawaiian Webbed Indica, Strawberry Web, Patte Canard, and some individuals of the landrace hemp from the Ferrara region of Italy.

Photographs of the webbed leaf mutation were first published by Walter Scott Malloch in 1922 in The Journal of Heredity. The mutation was presented as an interesting phenotype that was uncovered during an investigation of sex inheritance in the species. This mutation and a sectoral chlorophyll mutation were shown as evidence that Cannabis could be a useful model to study general inheritance.

“In an obligatory cross-fertilized genus like Cannabis we would naturally expect new forms to appear as a result of inbreeding. A mutant form was sent to the writer by Mr. L. H. Dewey of the United States Department of Agriculture and Professor A. H. Wright of the University of Wisconsin. This mutant is a simple leafed form which appeared in a strain of Ferramington. Instead of having the normal digitate leaf usually found in hemp, the mutant is characterized by a palmately cleft leaf as shown in Figure 20. The leaflets of the normal digitate leaf appear to have grown together as the normal number of midribs is present with an equal number of lobes. There is usually an unequal growth of tissue between the midribs which results in excess leaf surface thus causing a folded and wavy appearance of the leaf.”

The Ferramington strain of hemp, which contained the recessive mutation, was bred by Lyster Dewey, starting in 1916. The parent lines were Kymington (a selection of ‘Minnesota No. 8’ bred by Mr. Dewey beginning in 1914) and the landrace from Ferrara, Italy.

“The Ferramington variety has been developed by successive selection from the progeny of a cross made in 1916. In that year a row of Ferrara, the best hemp of northern Italy, was grown in the plot of Kymington, and all of the Ferrara staminate plants were removed before they shed any pollen. (Fig. 107.) Seed from the best Ferrara plants was saved, and this has been grown and selected at the experiment station at Madison, Wis. The cross was made for the purpose of combining the earliness and smaller diameter of stalks of the Italian hemp with the greater height and longer internodes of Kymington. This result has been achieved after many years of selection to eliminate diverse types from the progeny of the cross. This Ferramington has been tried in Wisconsin, where it gave a very good crop nearly two weeks earlier than the main hemp harvest. It has also been tried near Bologna, Italy, where it produced fiber fully equal in quality to that of the Ferrara hemp grown in the same field, and about 1 foot longer.”

The webbed leaf mutation seems to have been imported to North America from Italy within some of the Ferrara seeds. Roberto Savelli found the mutation in the Ferrara hemp in Italy, and having read about Dewey’s findings, had him send webbed Ferramington seeds so that he could compare the plants. He concluded that the mutation was the same, which is known in Italy as the “pinnatifidofilla” trait. Another leaf mutation which travelled to America was the simple leaf trait, known as “monofilla”, which also appeared in inbred Ferramington plants.

Luckily, the hemp traits have not been lost over the decades. They have been maintained in Italy, and a pinnatifidofilla strain named ‘Ermes’ may soon be used in commercial fiber and seed production.

The most well known strain with the trait is 'Ducksfoot,' bred by Wally Duck of Australia. Another well known strain is the Hawaiian Webbed Indica. If you are interested in these strains, a little history will be added soon.