By Joe Bender, Cannabis Crop Solutions, LLC
Whorled leaf arrangements, leaf buds, hermaphroditism, fasciation and variegation are a few of the strange anomalies you might see in your cannabis garden. The larger your garden, the more likely are you are to observe abnormal plant characteristics. In this article, I’ll discuss various anomalies that you might encounter, the causes of some of these phenomena and how to determine if the symptoms are caused by genetic mutations or by pathogens.
Whorled Leaf Arrangement
In a seedling’s early vegetative stage, cannabis leaves usually arise in pairs, on opposite sides of the stem at each node. At maturity, and when flowering, it’s common for seedlings to develop an alternating leaf arrangement, with just one leaf at each node, although leaves may continue to arise in pairs. A whorled leaf arrangement (or whorled phyllotaxis) is much less common, but is far from being the rarest of cannabis’s odd displays. Whorls can have three, four or more leaves at each node. This isn’t symptomatic of any infectious disease, and it might actually increase yields. At least one breeder has attempted to stabilize the trait, but we’ve yet to see a commercially available strain bred to consistently produce a whorled leaf arrangement.
Two main types of male flowers occur on otherwise female cannabis plants: monoecious male flowers and hermaphroditic male/female flowers. Although considered abnormal, both types are still quite common in cannabis. This could be explained by the evolutionary advantage of producing both male and female flowers on a single plant: Because it’s helpful for the survival of the species, it’s not surprising that these traits are difficult to breed against.
Cannabis is normally dioecious, meaning there are separate male and female plants. When lone male flowers appear completely independent of the female flowers on the same plant, that plant is monoecious. As a visual analogy, corn (Zea mays) is monoecious. The tassels at the top of a corn plant are composed of pollen-shedding male flowers. A corn ear contains many female flowers, each connected to a strand of silk. Just like a cannabis “white hair,” a corn silk is a pistil modified to have its whole length act as an elongated stigma—the sticky, pollen-receptive part of the pistil.
When a pollen grain lands anywhere on a corn silk or a cannabis hair, the pollen grain germinates like a seed and grows a pollen tube down through the tissue of the pistil and into the ovule. Nuclei from the pollen grain travel down the pollen tube and fertilize the ovule to create a seed. Monoecious male cannabis flowers are well-developed, so a single flower can cause extensive pollination, especially in gardens with proper air circulation. These insidious flowers seem to be most commonly located hidden at the bases of axillary buds, which can allow them to easily escape detection and do their damage to a sinsemilla (which literally means “without seed”) crop.
Hermaphroditic flowers are different from monoecious flowers, in that they contain both male and female parts within the same flower. In hermaphroditic cannabis flowers, a female flower develops male stamens that arise from inside the calyx, alongside the pistils. The male stamens can be neon green or yellow. Yellow stamens are often called “bananas.” They tend to appear late in flowering, sometimes even in plants that are usually stable against hermaphroditism. You can actually spot bananas in some bud pictures of strains in seed catalogs. Bananas and green stamens can also arise earlier in flowering, at the stage when many hairs are still white and receptive to pollen. Late in flowering, most of the hairs are shriveled and red (or orange or brown) and unreceptive to pollen; hermaphroditic flowers that pop up at this stage are somewhat less threatening to sinsemilla.
Rarely, “reverse hermaphroditism” occurs, with female flowers forming on an otherwise male cannabis plants. The flowers could be of a hermaphroditic or monoecious nature.
Both monoecious male flowers and hermaphroditic flowers can be problematic. When growing seedlings, or clones you’re inexperienced with, inspect your plants thoroughly and frequently. Gently excise any suspect flowers you find with a clean razor or scissors and place them in a ziplock bag for disposal. Reconsider propagating plants with these traits.
Leaf buds are buds that form at the junction of a petiole and the leaflets of a cannabis leaf. Some might see this oddity and think, “Yay! Extra yield.” While these buds could make a small contribution to yield, it will likely be fairly negligible. The problem with these buds is that they commonly contain hermaphroditic flowers that might pollinate your sinsemilla. Regularly inspect leaf buds for male flowers, and carefully prune the cluster of flowers from the leaf if you see anything suspicious.
In architecture, a fascia is a wide, flat, horizontal surface. “Fascia” is derived from the Latin for “band.” In plant pathology, fasciation is a term used to describe a phenomenon characterized by a flattening of stems and inflorescences. Fasciation affects more than 100 plant species, and it may be caused by genetic mutations, but also by pathogens such as phytoplasmas and viruses.
In cannabis, fasciation causes wide, flat stems to form. They are hollow and flexible, and they’re susceptible to lodging (buckling into a crease from bending) in strong winds. When fasciation occurs in flowering, it causes horizontally elongated buds to form. These misshapen buds have crowded growth, and they’re susceptible to secondary infections like botrytis gray mold.
Not only is fasciation unhealthy due to the secondary problems it can encourage, it’s also possibly caused by an unidentified phytoplasma, bacterium or virus, all of which cause fasciation in other plant species. Phytoplasmas are bacterial parasites that lack cell walls, and are obligate parasites, meaning they can only survive inside their hosts and vectors. Like viruses, they cannot be cultured in a petri dish for identification. Phytoplasmas are vectored by plant-sap-sucking flying insects, the most common being plant hoppers and psyllids. Lethal yellowing of palms, including coconut palms, and citrus greening disease are examples of other diseases caused by phytoplasmas that cause devastating crop losses worldwide. Research is needed to determine the causes of fasciation in cannabis, but until proven to be an abiotic cause, the safest protocol is to destroy fasciated plants.
Variegation is an alteration of leaf or flower color, creating multicolored leaves or flowers. Variegation is caused by differential gene expression, virus infection or genetic mosaicism.
In differential gene expression, a cell’s location on a plant determines which of the cell’s genes are active, creating differences in coloration. A familiar example is the striping on watermelon rinds. Other examples include the stripes on the leaves of snake plants (Sansevieria trifasciata) and the purple rings on the leaves of some geranium varieties. The cells within the striped areas or purple rings have the same total set of genes as the rest of the plant, but have active genes causing their different color, which are dormant genes in the rest of the cells. In cannabis, differential gene expression is responsible for the purple leaves and buds seen in some varieties. These purple organs are expressing genes for anthocyanin production. Cool temperatures and bright light increase the expression of these genes.
Plant viruses commonly cause variegation in the form of mosaic patterns on the leaves of infected plants. Virus-induced mosaics typically lack a distinctive pattern, and will continue to cause symptoms on new growth. Other viral symptoms include stunting, leaf distortion and necrotic speckling.
Plant viruses are transmitted by workers moving from plant to plant, by root grafts that naturally form when plants are grown side by side, and by insect vectors such as aphids, whiteflies and thrips. In their 2000 book Hemp Diseases and Pests, J.M. McPartland, R.C. Clarke and D.P. Watson reviewed the virus research done on cannabis, and found conflicting results among experiments concerning which viruses infect cannabis. They concluded that at least five viruses commonly infect cannabis and cause debilitating symptoms. These are the hemp streak virus (HSV), the alfalfa mosaic virus (AMV), the cucumber mosaic virus (CMV), the arabis mosaic virus (ArMV) and the hemp mosaic virus (HMV). Viruses that may also infect cannabis include the tobacco mosaic virus (TMV), the tobacco ringspot virus (TRSV), the tomato ringspot virus (ToRSV) and the potato viruses X and Y (PVX and PVY).
Agdia, a plant-pathogen-testing company, offers several field test kits for diagnosing plant viruses. These test strips are dipped into a liquid buffer containing pulverized plant tissue, and work the same way as common pregnancy tests, with a control line that should always appear when the test strip is functioning properly, and another test line that appears when the virus of interest is present. The virus-assaying ImmunoStrip tests come in CMV, ArMV, TMV, TRSV, ToRSV, PVX, and PVY versions (and others for non-cannabis viruses).
Genetic mosaicism occurs when a plant has groups of cells with different sets of genes, resulting from mutations in one or more of the three layers of apical meristem tissue. Sansevieria trifasciata laurentii is exemplary of this condition. While the stripes across the leaves are caused by differential gene expression (as previously noted), the yellow margins are caused by a pigment mutation of the layer of meristematic cells that form the leaf margins. Such plants, with cells of two or more genotypes, are considered chimeras, named after the Chimera of Greek mythology, described by Homer to be a fire-breathing creature with a lion’s head, a goat’s body and a serpent’s tail. Chimeras may be vegetatively propagated (cloned), but can have varying levels of genetic stability. As seen in the photo of S. trifasciata laurentii, some shoots may revert to their original, non-variegated condition; cloning such reverted shoots will not produce chimeric plants.
Ducksfoot leaves are formed by fused leaflets. This trait has been bred into varieties marketed for stealthy outdoor growing. Plants with ducksfoot leaves are less conspicuous than normal cannabis plants, although they look quite similar in the advanced stages of flowering. This is a heritable genetic trait not caused by pathogens.
Other Random Anomalies
The anomalies discussed above are far from being the only strange conditions that can affect cannabis. Other random anomalies include extra leaflets, extra shoots, misshapen leaves and petiole webbing; all of these appear to be caused by mutations. Petiole webbing occurs in clones and seedlings that, when vegetatively propagated, will not normally produce the trait, although it pops up here and there in isolated individuals. A membrane forms between a petiole of an axillary shoot and the main stem, causing the shoot to grow downward in an abnormal orientation. Cutting the webbing will allow the shoot to reorient itself into the proper position.
One useful way to determine whether random conditions are caused by pathogens or chance mutations is by looking at how frequently they occur on a plant or within the garden. For example, if one leaf is misshapen, but the rest of the leaves on the same plant are normal, it’s unlikely that a pathogen is the cause, and more probable that it’s a random mutation.
Grafting To Diagnose Pathogenesis
Grafting can be a valuable tool for diagnosing if anomalies are caused by pathogens. Many types of pathogens, including viruses, phytoplasmas, bacterial wilts and fungal wilts, can be transferred from plant to plant via grafting. To test for such pathogens, graft a healthy scion onto a rootstock suspected of harboring a pathogen.
Several types of grafting can be used, including cleft grafting, saddle grafting and approach grafting. Here I’ll discuss cleft grafting, which is easy and effective in cannabis. Whichever method you choose, use new razors or thoroughly flame your tools between plants and keep your hands clean.
To perform cleft grafting, use a semi-woody, rooted or unrooted clone of the suspect plant as the rootstock (you can root the rootstock and create the graft union at the same time).
- If unrooted, prep the base of the rootstock by lightly wounding the sides with scissors, using a gentle scraping action. Stick the prepped cutting in a rockwool cube or another rooting medium.
- Remove the top of the rootstock with a cut that is perpendicular to the stem. Split the remaining stem down the very center, about 1.5 centimeters deep.
- Prepare the scion: Making two clean cuts, create a narrow wedge at the base of a healthy, unrooted clone with about the same stem diameter as the rootstock.
- Gently push the scion’s wedge into the cleft stem of the rootstock. If the stems are slightly different sizes, line up at least one side of the rootstock and scion stems so that their cambial layers can unite.
- Use a vegetable grafting clip, or grafting tape, to secure the graft until healed.
- Place the grafted plant in a warm humidity dome, under moderate lighting or shade, and keep evenly damp for about seven days, until roots form and/or the graft union is established.
- Gradually acclimate the plant to lower humidity and brighter light.
After establishing a graft union, the scion will begin to grow. If the condition of the suspect rootstock is genetic, it will not be transferred to the scion and the scion will grow normally. If the condition of the root-stock is pathogen-induced, the scion will be infected and will exhibit the symptoms of the rootstock.
Next time you see an unusual leaf, out-of-place flower or another oddity in your cannabis garden, you’ll be more confident in determining the cause, and what actions to take. When evaluating cannabis anomalies, it is important to establish whether or not they’re caused by pathogens. Many cannabis anomalies are genetic and aren’t threatening to your garden; however, pathogen-infected plants should be removed and discarded to prevent spreading diseases.
This feature was published in the August, 2019 issue of High Times magazine. Subscribe right here.