Chemical Scarification

It seems that many seeds are blessed with an extremely hard and thick seed coat. Though this might seem like a great means of protection it is also a barrier to germination. You see, germination requires that the small embryo within the seed have access to both water and oxygen, a hard shell prevents such access. When this is the case the seed will remain in dormancy until the coat is altered to allow these essential makings of plant growth to reach the embryo.

Any action taken to alter the seed coat is known as scarification. In a natural setting this can occur in a number of ways. The seed can freeze (expand) and then thaw (contract) causing an alteration in the seed coat. Or, a seed can be consumed by an animal – often a bird – and the animal’s stomach acids will thin the seed coat just enough to allow access of even the smallest amount of water and oxygen, breaking dormancy and allowing germination.

Yes, I know acid does not sound like a growth enhancer! However, this artificial process is not a new idea; in fact, acid scarification has been a recommended method of improving successful plant germination and growth for more than 100 years. 

Further investigation taught me that commercial operations use sulfuric acid in their chemical scarification. If I were not fortunate enough to have a full lab at my disposal I would be taking a quick trip to Pep Boys – sulfuric acid is sold in the battery department of most automotive stores. Though, website authors recommend vinegar for home scarification; noting that although not as effective it is a much, much safer route for the novice. 

So, today we began to submit some of our seeds to a little pre-treatment with sulfuric acid, a forced method of chemical scarification, to see if this might improve the germination of our precious seeds of the lower Sonoran Desert.

For our scarification process we chose four different species and two different techniques.

First we counted 125 seeds of Lupinus arizonicus (Arizona Lupine) and 50 seeds of Cercidium microphyllum (Palo Verde) and bathed them for three minutes in sulfuric acid. After the short three minutes we washed them thoroughly with water (I wonder if the chlorine in water causes scarification?). Our little seeds were then divided (25 seeds per dish for Arizona Lupine and 10 seeds per dish for Palo Verde) and put into - paper towel lined and labeled - Petri dishes with 5mL of distilled water. The final step was sealing them with parafilm. 

Next we counted 125 seeds of Opuntia Phaecantha (Desert Prickly Pear) and 125 seeds of Encelia farnosaI (Brittle Bush) and bathed for one hour in sulfuric acid. After this long hour (It is emotionally hard to put a living thing in acid for such a long time!) we washed them thoroughly with water. The seeds were then divided (15 seeds per dish for Bursage and 25 seeds per dish for Brittle Bush) and put into - paper towel lined and labeled - Petri dishes with 5mL of distilled water. The final step was sealing them with parafilm.

All of the Petri dishes were left in full light.

As I have discussed in previous blogs, our project has been haunted by the presence of mold on our darling little seedlings. It seems that chemical scarification may also serve to kill fungi! We shall keep our fingers crossed!

Mold, mold and more mold.

Upon arrival at the lab on Tuesday I was excited at the prospect of what my little seedlings had accomplished over Spring Break 2013. It had been twelve long, restful days since I had last seen them and I had visions of leaves and possibly a trimming dancing in my head! Unfortunately, the vast majority of growth was not plant growth, but an overwhelming massacre. The perpetrator was (of course) the devastating effects of fungi growth!

Yes, molds are a fungi. Which fungi is growing on my little seedlings I am sorry to report I do not know. I do know that there are estimated to be possibly more than three hundred thousand different species of mold. They grow everywhere, but prefer warm and damp or humid conditions. They reproduce – and quite effectively I might add – by making spores. Clearly, mold is an insidious organism and I have deemed all three hundred thousand species my foe, particularly in terms of my current project!

As you can see from my pictures, the mold has overtaken and in many cases killed my little seedlings.
The questions that I am now asking are:

Is there anything I can do to kill the mold that won’t kill my remaining seedlings?

Is there anything I can do, on my next batch, to prevent the mold from every growing?

In order to find the answers I went straight to Google. Finding the internet version of The Complete Idiot’s Guide to Seed Saving and Starting I learned that once germination has begun there truly is little that can be done to save the molded seedlings. Mold quickly reaches the embryo and once it has reached this delicate origin of the plant there is no hope, as the seed at this point is dead. It does mention that, if the embryo has not succumbed, a hydrogen peroxide bath can destroy the mold and give the damaged seedling a chance, albeit small, at survival.

Preventing mold in future batches is my best hope. Suggestions to prevent mold include: sanitizing the paper towel medium before placing the seeds, use a minimum amount of moisture, place in an entirely dark area, check seeds frequently and remove infected seeds immediately, use cinnamon as an anti-mold agent.

Thankfully, Matt is a resource even greater than Google and under his remarkable tutelage Ainsley and I began labeling and preparing a new batch of Petri dishes for our ever more interesting allelopathy project. We are counting seeds and starting the growing process once again – a few changes made and a new hope for the growth and happiness of our little seedlings.

Let the Germination Begin

As of today, March 7, 2013, it has officially been one week since we watered and sealed our first batch of carefully counted seeds. Though many of the seeds have begun the process of germination others have not. Unfortunately, many of our specimens are covered in mold and I think this means we will not have an accurate picture of germinating conditions.

Ambrosia deltoidea (triangle bursage)

-        0%   germination (excessive mold present)

Cercidium microphyllum (palo verde)

-        35% germination (slight mold present)

Larrea tridentata (creosote bush)

-        0% germination (slight mold present)

Encelia farinosa (brittlebush)

-        2% germination (no mold)

Cylindropuntia acanthocarpa (buckhorn cholla)

-        0% germination (slight mold present)

Phacelia campanularia (desert bluebell)

-        94% germination (no mold)

Opuntia phaeacantha (prickly pear)

-        0% germination (no mold)

Eschscholzia Mexicana (golden poppy)

-        4% germination (slight mold present)

Sphaeralcea ambigua (desert globemallow)

-        2% germination (no mold)

Lupines arizonicus (Arizona Lupine)

-        0% germination (slight mold)

Lesquerella gordonii (bladder pod)

-        0% germination (slight mold present)

Carnegiea gigantea (saguaro)

-        56% germination (no mold)

Because our project revolves around plants of the lower Sonoran Desert, I have been trying to learn about this vast area that occupies much of Arizona. The Sonoran Desert covers approximately 120,000 square miles. Its borders reach across the states of the Southwest and into Northwest Mexico. The low and much hotter desert is referred to as the lower Sonoran, and is – at least at first glance – very barren in appearance. It is actually home to a vast array of endemic plants, more than 500 species of which are used by humans for both nutritional and medicinal purposes. Some of these unique plants have been included in our project.

For example:

Larrea tridentata (creosote bush) – this amazing plant has been used by the peoples of the Sonoran Desert for thousands of years. It has been used to treat a variety of conditions including; congestion, idney stones, snakebite, tuberculosis, sexually transmitted diseases and cancer. It contains nordihydroguaiaretic acid which is a proven and strong antioxidant, however chronic use has been shown to result in both renal and hepatotoxicity.

Opuntia phaeacantha (prickly pear) – this plant has traditionally been used for both nutritional and medicinal purposes. As a food source, they add a tart flavor to a number of Mexican dishes including pies and jellies and they are also eaten fresh. Medicinally it is used as an anti-inflammatory or in larger doses as a laxative. In western culture it has been used for reducing the effects of alcohol hangovers.