Because of the ease of performing controlled crosses, maize (or corn (Zea mays)), has been a staple of plant genetics research for decades. Barbara McClintock herself chose maize as her research organism for her Nobel Prize winning work. If you are looking to get involved but aren’t sure how to get good yields in the greenhouse, read on and for some great tips.
Know Your Maize Variety or Line
If you are new to the maize community, the first thing to understand is that all corn is not created equal. There are hundreds of different lines, each with their own characteristics and growth requirements. If you are working with one of the more traditional research lines, such as B73 or MO17, the requirements for growth will be fairly similar. This is because they all originate from the same source materials back in the early 1900s. If you are working with an ancient landrace or tropical line, the growth requirements are likely wildly different.
Getting the Setup Right
Maize requires a lot of light. Make sure that you have a greenhouse with a lot of lights on most of the day. In the summer, you might have enough sunlight to get away with turning the lights off in the middle of the day. But the winter is another story. During that time, usually the lights are required to be on a 16-hour day cycle. The plants themselves will let you know pretty quickly if there is not enough light. You will notice a delay in growth, and low-lit plants may not flower.
Compared to most model organisms, maize prefers a warm greenhouse. I have had success with lines B73 and HiII growing in a greenhouse set to 82 °F in the daytime and 77 °F at night. In my experience, the greenhouse needs to be at least 70 °F for decent pollen shed. However, warmer temperatures are certainly better. This is often the same case for decent ear development as well.
General Care for Maize
For traditional maize lines such as B73 and MO17, it is usually best to use a 10- or 12-inch pot with one seed planted per pot. Most soils available in the greenhouse will be fine but using a soil that will drain well is usually. Seeds do not need to be sterilized or pre-germinated, just stick them into the soil about an inch deep. Then, give the pots a good water. In a warm greenhouse, you can usually notice shoot emergence 3–5 days after planting.
Fertilizing plants throughout their growth allows you to obtain the highest yields. You can add long-term fertilizer, such as Osmocote, to the soil when the pots are first made. This will help to ensure proper nutrient delivery. Typically, I will also use a liquid fertilizer, such as Peter’s 20-20-20, mix once a week. Keep an eye on the plants for the tell-tale signs of nutrient deficiency. If you notice plants are starting to yellow, for instance, this can be fixed with the addition of nitrogen. There are many guides to detecting the common deficiencies online that may be of help. For example, Crop Watch at the University of Nebraska-Lincoln has a nice illustrated guide.
For the most part, maize plants do not like to be continually soaked. You usually get the best growth when the soil is allowed to dry slightly between watering. This is especially true when the plants first germinate. Seeds can rot if allowed to sit in water too long, and seedlings may die if overwatered before a proper root structure has formed.
One of the best things about working with maize is how easy it is to control crosses. Male pollen is formed on tassels at the top of the plant, and female eggs are formed on the ears which emerge towards the middle of the stalk. Maize demonstrates apical dominance, so usually only the top-most ear will produce sufficient seed. Some researchers will pollinate the top two ears if the plant is particularly important, but mostly only one ear is used from a single plant.
To make sure pollination is controlled, the ears must be covered as they emerge. After a tassel is visible, the plant should be checked daily for emerging ears. Look for ears emerging from the base of leaves at the stalk. You can usually see the leaves start separating from the stalk to make room before ears can be seen themselves. Ears will first appear as flat tissue right against the stalk but will soon become more cylindrical. Cover the ears with a paper or glycine bag as soon as they appear. If an ear is missed, simply tear it off from the plant and the plant will usually grow another, or you can use another ear on the same plant. Tassels can also be covered with a paper bag as well to ensure that pollen within the greenhouse is controlled as well.
Ears should be checked for silk formation every day. Once you see silk, use a knife to cut about a quarter to half an inch of the ear off. Recover the ear, and be sure to shake out old pollen from the tassel you wish to use. When you return the next day, you’ll see that the the silks will have grown out uniformly from the cut ear. Shake pollen from the male donor plant into a paper bag and gently tap out any captured anthers from the bag. Quickly uncover the ear to be pollinated and shake pollen onto the ear until the silks are fully covered. Cover the pollinated ear with a paper bag and tuck it tightly behind the ear to ensure that it does not fall off.
After pollination, water the plant until it does not seem to be taking up water anymore. This usually occurs about 20 to 30 days after pollination. You will see that the plant will start to yellow and dry at this point. Pull the husk back from the ear and allow the seed to dry. You can tell when the seed is ready to be harvested when you can run your fingernail across the seed and it feels smooth and glassy. At this point, the ear can be removed from the plant. It should be dried either in a commercial drier or on a benchtop until the cob is hard and fully dehydrated.
Final Tips on Maize Handling
Maize has been researched for a long time, and as a result there are tons of resources to be utilized. On top of the genetic resources, such as the Maize Genetics and Genomics Database, there are also plenty of resources to help with growing the plant in a research greenhouse. My favorite resource is from Purdue’s Greenhouse Pages. There you can find lots of specific information for the various aspects of maize greenhouse care. Good luck, I’m sure you will be aMAIZEing!