Cannabis is a fascinating plant that, when grown properly, can exhibit a variety of
morphological expressions between the multitude of cultivars available for cultivation.
Sometimes, however, despite one’s best-efforts, strange growth patterns or colorations
can occur. Sometimes this is the result of environmental stress, sometimes it is the
underlying genetics, and sometimes it is the interaction between the two. Many of these
abnormalities can be described as mutations. In this article, we present some of the
most common, and some not so common, mutations growers see in their cannabis
gardens.
Whorled Phyllotaxy:
Have you ever grown a cannabis plant that grew 3 leaves per internode instead
of the normal 2 leaves per internode? If so, then you have seen first-hand what is
known as “whorled phyllotaxy.” “Whorled” just means spiral in appearance essentially
and “phyllotaxy” is a botanical term referring to the arrangement of leaves.
Usually cannabis exhibits alternate (one leaf per node) or opposite phyllotaxy (2
leaves per node on opposite sides of the apical stalk). If your seedling or older veg plant
is showing 3 or more leaves originating from the same node then that seedling can be
described as having a whorled phyllotaxy.
Whorled phyllotaxy is caused by underlying genetics in a cultivar but is known as
a somatic mutation as this trait cannot, as far as we currently know, be inherited by
offspring. Although genetic in origin, whorled phyllotaxy can be induced by stress or
other environmental factors, yet this is uncommon. In some strains, especially those of
tropical origin, heat, nutrient imbalances, and light stress can cause whorled phyllotaxy
to appear. In many cases the plant outgrows this 3 leaf pattern as it continues to grow
and as environmental stressors are reduced or eliminated.
Whorled phyllotaxy itself is quite uncommon and is often confused with
polyploidy. Where polyploidy refers to an abnormal number of complete sets of
chromosomes inherited from the parent plants, whorled phyllotaxy is caused by a
genetic mutation that results in an altered balance between auxins and cytokinins (2 of
the most important plant hormones). This imbalance affects what are known as the
PLETHORA genes (specifically PLT1 and PLT2) which regulate the polar transport of auxins as well as the leaf arrangement at the nodes. Because whorled phyllotaxy is caused by an underlying somatic genetic anomaly involving the interaction of auxin and
cytokinin signaling, the trait is unstable and hard to breed for stability.
Whorled phyllotaxy is largely just an aesthetic trait as results are not conclusive
regarding increased or decreased yields from plants with this trait. Some growers have
found that the increased number of leaves per node allows for bushier plants with
potentially more bud sites and more photosynthetic function. Other growers have
observed that the increase in leaf coverage reduces air flow and may lead to increased
chances of bud rot or fungal growth within the plant. Some growers sit somewhere in
the middle of these opinions and state that the yield increase is only minimal and only if
the plant is trained appropriately with techniques such as SCROG. Some cultivators
appreciate the aesthetic value of this trait while others see the extra leaf per node as
more work throughout the grow cycle and during harvest.
Regardless, having a plant with a whorled phyllotaxy doesn’t mean that there is
necessarily anything wrong with that plant if your environment is dialed in and the plant
hasn’t received too much or too little nutrients. It just means that it is a little bit special, if
only visually.
Fasciation:
Fasciation is a very interesting mutation that causes stems and/or flowers to
appear “smushed” or much wider than usual. Fasciation can make flowers or a stem
look like they have been mirrored in some pretty bizarre and cool looking displays.
Fasciation can sometimes make a plant look alien due to the abnormal growth pattern
of stalk and/or flower cells.
The cause of fasciation is a disruption, or disruptions, in the apical meristem
(growing tip) of a plant which results in the flattened, ribbon-like or mirrored appearance
of flowers and stems. In a normal plant, growth in the apical meristem occurs at a single
point, which produces cylindrical growth. Fasciation causes an elongation of the apical
meristem so that flattened, ribbon-like, or mirrored growth is produced instead.
Sometimes this growth is also known as “crested” growth.
There are several causes of the disruption to apical meristem growth resulting in
a fasciated appearance to stems and flowers. One such cause is genetic factors such
as recessive genes that confer this growth structure. Other causes include
environmental stressors such as exposure to extreme heat or cold as well as hormone
imbalances within the plant, specifically auxin and cytokinin imbalances. Physical
damage from mechanical means (pruning, cutting for clones, etc.) or from insects
feeding can also sometimes cause this growth disruption.
Fasciation is not considered a trait that can be stabilized through breeding,
although some cannabis cultivators have managed to replicate it with cloning of a
fasciated plant.
What does fasciation mean for your plant’s health and your final yield? A
fasciated flower, despite looking much larger, isn’t as desirable as one may think. Often
fasciation leads to crowding of cannabis buds which can lead to secondary issues such
as botrytis or powdery mildew due to lack of proper air flow throughout the plant.
Fasciated stems are often weaker than stems under normal growth conditions and can
lead to the plant appearing as if it is wilting due to the inability of some fasciated stalks
to hold up the increasing weight of maturing cannabis flowers. Fasciation can also lead
to a higher stem to bud ratio for your plant. While rare, fasciation has also been
reportedly induced in plants by bacterial pathogens (e.g. Rhodococcus fascians) and
plant viruses (e.g. grapevine fanleaf virus (GFLV) in grapes).
For the reasons stated above fasciation generally decreases yield in cannabis as
stems are not what we are looking to harvest, nor is moldy bud anything anyone would
want to smoke. It is also doubtful that anyone would want to finish flowering out a plant
they know to have bacterial or other pathogenic issue without treating said pathogen.
Prevention methods of fasciation include maintaining a stable growing
environment, maintaining healthy nutrient levels and avoiding over-fertilization, and
avoidance of physically damaging the plant.
Many growers prefer to “top” their plants to increase the number of apical stalks
that will generate large colas. This is a fine practice and usually does not result in
fasciation but, as with all organisms, this can sometimes cause an issue if there are
underlying genetic factors or pre-existing stress conditions so reducing plant stress
however possible is key in preventing fasciation. This same idea applies to defoliation,
which is sometimes necessary to prevent mold outbreaks. As long as a grower doesn’t
overdo it and defoliate too much or too often then the vast majority, if not all, of their
cannabis plants will not show fasciated traits.
Variegation:
Have you ever noticed a leaf or leaves on your cannabis plant that have two
distinct colors on either side of the primary vein down the center (i.e. the midrib)? This
could be a case of localized chlorosis or it could be indicative of a condition known as
“variegation.”
Variegation is a condition where plant material displays abnormal patterns of
color due to a lack or excess of chlorophyll which results in patches or streaks of white, yellow, or other colors like light green (in contrast with the darker greens of the “normal”
side of the leaf). Variegation can sometimes cause mosaic patterns in addition to
streaks on plant foliage.
Variegation is most often caused by genetic mutations affecting the chloroplasts
(parts of the plant cell responsible for photosynthesis). It can also be caused by stress
from extreme temperatures, viral infections, or exposure to toxins.
One of the main genetic causes of variegation in cannabis is chimeric mutations.
This refers to the presence of two or more genetically distinct cell types within the same
organism. In cannabis this often means a combination of genetically normal cells
(green) and mutated cells producing less, or lacking, chlorophyll (white, yellow, very
light green) all contained within the same leaf.
Generally speaking, variegation is generally harmless if localized and not from a
toxin or virus in the plant. If variegation is widespread this will affect the plant’s ability to
photosynthesize and thus will affect the final yield and resin production of the plant but
again, this is rare.
It is due to the interruption and/or diminishing of photosynthesis that variegation
is seen as undesirable in cannabis despite it being desirable in ornamental plants where
final yield is not considered a factor in the reasons for said plant’s growth.
That said, variegation can make cannabis plants look quite striking and, if
localized or not on the majority of leaf surfaces, it usually doesn’t affect final yield or
resin production.
It should be noted that one or two leaves showing odd coloration doesn’t always
mean variegation. It could be localized chlorosis due to underlying genetic factors or
localized stress at the affected leaf site(s).
Due to the chance of diminished photosynthesis, and the inability to guarantee a
localized or minimal expressivity of this trait, variegation is not usually seen as a
desirable trait for breeding in cannabis.
To avoid or minimize the risk of variegation in your cannabis plants maintain
healthy growth by maintaining a consistent grow environment (temp, CO2, air
movement, light, appropriate feeding) and avoid exposing plants to extreme
temperatures.
What should you do with a variegated cannabis plant? Whatever you want! It is
not a trait that can generally be spread to other plants, and you will still get a yield from
that variegated cultivar so it is not a threat to the rest of your grow. If you have the
space, let it finish its flowering cycle if you want. If you are looking to save time and space, then discard the plant and let the others have that space to grow. The decision really comes down to personal preference and need.
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HAPPY GROWING!