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Growing Medicago Plants for Research 101

Lynne Jacobs shares her know-how on growing and handling Medicago plants after 15 years of experience in the fields and greenhouse at Noble Research Institute.

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Noble Research Institute greenhouse assistant Lynne Jacobs came to Oklahoma quite by accident. After selling a convention and tourism business in Scottsdale, Arizona, in 2004, she and her husband sought a new adventure somewhere where people were nice and land was affordable. Oklahoma fit the bill.

Growing Plants is in the Blood

By 2005, the North Dakota native was working at the Noble Research Institute, assisting with greenhouse, lab and field work. It was familiar and comforting territory.

“Growing up on an isolated farm, my companions were plants and animals,” says Jacobs, who earned an animal science degree at the University of Minnesota. “I knew how to grow things even when I was a kid. It was what we did.”

She regrets that as a young adult she wasn’t aware of the plant science career options that were available to her.

“Had I had any kind of guidance, perhaps now I would be ‘doctor’ of something plant-related,” she says.

She may not have the title, but she certainly has the knack.

Lynne Jacobs stands next to Medicago truncatula plants.Lynne Jacobs, greenhouse assistant, stands next to Medicago truncatula plants that she takes care of daily.

These days, Jacobs works with legumes, tobacco, small grains, maize, vetch and grasses in Noble’s greenhouses. She assists and provides guidance to researchers in their plant-growth projects, offering education and advice on how to handle the plants and grow the healthiest plants possible.

She also identifies plant diseases, problems with plant nutrition, and pest problems. She transplants, makes cuttings, starts plants, maintains stock populations, harvests seed and other tissues, and assists with research projects. She also handles bees for crossbreeding plants and hand-pollinates plants when needed.

Below she shares some of her best advice for researchers growing Medicago and other plants.

Are there any plant species that are easy to work with and those that are not?

There definitely are. Legumes can be way more susceptible to disease, due to their lack of tolerance to overwatering and susceptibility to pest infestation. Vetch for example is easy to germinate, but it’s very “feral” acting, growing wildly in a boisterous pile, taking up too much space, shedding leaves excessively, and getting infested by bugs quite easily. On the other hand, perennial grasses are generally pretty easy to work with — they are more tolerant of over- and under-watering, and bugs don’t tend to prefer them.

What are the most basic facilities that you need to grow Medicago?

To grow Medicago you need a climate-controlled room. Being a temperate legume, it prefers a maximum temperature of 22 degrees C and minimum of 18 degrees C. We use clear 400 watt 50,000 lumen high pressure sodium bulbs in the houses. We set the daylight hours at 16.

You also need a consistent watering regime. This can vary as the plant grows and changes in size. Also, transgenic Medicago plants generally consume less water than wild type (due to their often reduced robustness) and are more sensitive to fertilizer and pesticide. Lastly, good humidity control is essential to keep powdery mildew at bay. Radical swings in humidity and temperature is definitely an enemy.

Are there any special requirements to handle Medicago truncatula or Medicago sativa (alfalfa)?

There are lots of differences between M. sativa and M. truncatula — this is a big topic! The first big difference is that M. truncatula is an annual (lives for only one season) and M. sativa is a perennial (regrows every season). I’ve always felt a little sorry for the alfalfa in a greenhouse. Unable to put down the massive root system (dominantly tap root) it wants to and unable to go dormant in a natural cold cycle it would experience in nature, alfalfa suffers in the soil pots. It also needs insects to pollinate and create seed that are absent in an environment-controlled greenhouse.

Making cuttings from young Medicago plants.To make successful cuttings, healthy nodes from young Medicago plants should be collected by making diagonal cuts just below the node.

What kind of soil is best for Medicago?

To grow Medicago until seed set, you want to use something that will drain well. If the growth substrate is wet all the time, plants will become yellow and sickly. Especially if the plants are transgenic, don’t water them excessively. Rather, keep them moist. Soil that is too wet will deprive roots of oxygen.

Once the plants set a good population of green pods and flowering slows, I usually stop providing them with fertilizer and put them on clear water/tap water. As they start senescing, they will consume less water, and water needs to be reduced accordingly. We start hand-harvesting the pods as they mature (turn brown or gray) or bag them and move them to a dry-down area.

If someone gives you plants that have a poor root system, is there something special you can do to ensure their growth?

I do use a transplanting fertilizer, such as Fertilome Root Stimulator & Plant Starter Solution, especially in the case of weak plants. Again, transgenic plants may be sensitive to fertilizer and/or pesticides, so always take caution on what you use and don’t over-apply.

You can also propagate these plants by making cuttings once the plant takes root. The biggest obstacle here is if your plants are older and close to senescing, which makes most cuttings want to immediately flower and go to seed. Therefore, I recommend using young plant tissue.

What are the most common insect pests affecting Medicago?

Thrips are the worst. They damage the flowers, causing reduced quality and number of seed pods, and also can spread disease. Thrips are hard to control, as they rapidly develop resistance to many of the pesticides we use. Also, there are stages when they are inside the plant tissue, so they hide from the treatments. Plus they are so small, they can ride into rooms on your clothes and through cracks and you can’t see them. Thrips are not as attracted to the grasses and tobaccos as they are the legumes. They can really tear up a legume population!

There are other pests more easily controlled, such as aphids and spider mites, just to name a few of the most common. Fungus gnats and shore flies thrive in wet soils, so that is another reason to limit how wet the soil gets. While not as harmful as thrips, they can cause root damage and spread disease.

Lynne Jacobs staples together ties to ensure that creeping plants grow upright in a confined space.Lynne Jacobs, greenhouse assistant, staples together ties to ensure that creeping plants, such as Medicago truncatula, grow upright in a confined space.

How do you treat these infestations?

We use Integrated Pest Management (IPM) throughout the greenhouse. We keep an eye on pest activity every day and follow a pesticide spray program that rotates chemicals, and oils, with different modes of action to hopefully keep pests from getting resistant to the products.

Biological controls (beneficials) are a great idea and are effective for smaller populations of plants, but not for large-scale greenhouses such as what we have. “Beneficials,” as we call them, can control certain pests, but they are very target-specific.

As often as we can, we clean individual greenhouses — sanitizing them with 10% Clorox or Green-Sheild on the flood benches and floors. “Baking” the rooms at temperatures above 130 degrees F for a couple of days also helps.

Do you see many bacterial and/or fungal diseases in the greenhouse? How do you take care of them?

If we get some radical weather swings (temperature and humidity) we sometimes observe fungal infections. Here again: prevention, prevention, prevention! An application of a good general fungicide as a preventative can save you a lot of heartache.

Overwatering is always an enemy; it can get root diseases going. Because we water many of our populations by flood benches, if one plant gets sick a lot of plants could follow suit. We try to minimize this by implementing a regular schedule of cleaning and sanitizing irrigation tanks and, of course, avoiding over-watering.

Any other suggestions you might have for students/researchers just starting out with this legume?

First, lean on people who can help you — don’t be afraid to ask for help. Secondly, remember over-watering is the biggest sin of plant care. Don’t give in to the temptation to water plants if they look sickly.

Sonali Roy, Ph.D.
Former Postdoctoral Fellow