Quality Seed Production

Transcription

1 Kerry Clark University of Missouri Quality Seed Production Before Planting Obtain high quality seed to start production. Sort through your seed supply and keep only seeds that are yellow and look healthy. Do not use seeds that are damaged, have mixed colors or have mold. The seed in the photos above have many disease problems. Everything that has purple, black or brown colors or white from mold should be sorted out and only the healthy looking seeds should be planted for Quality Seed production. The purple and brown colors are caused by a plant virus, which will affect plants that grow from these seeds. However, it is safe to eat these seeds as long as they are not moldy. The seeds in the photo to the right are very healthy and will likely produce healthy plants. The dark spots on these seeds are normal. This is the seed hilum, which is the point at which the seed connects to the pod wall while it is growing. Page 1

2 In the photo below, the majority of the seed look healthy. I have marked four seeds with black arrows that should be removed. Two seeds are cracked, one is diseased, and one does not have a nice oval shape. Soybeans have three characteristics that allow a grower to check for varietal purity by color. One is the flower color, one is the pubescence color (the hairs on the pods and stems) and the third is the color of the seed hilum. The hilum is the colored area on the seed marked with a red circle in the photo below. In a pure variety, all of the seed hilums will be the same color. In this photo some of the hilums are black and some are brown. This shows that this seed source is mixed and not all the same variety. A good Quality Seed grower would separate out these two hilum colors and plant each type of seed separately. They may find that these two varieties also have different flower and pubescence colors. Page 2

3 Planting Fields should be as well fertilized with Phosphorus (P) and Potassium (K) if possible. Applying P and K to soybean will not only improve yield, but it will also help plants resist disease. The photos below show K deficiency symptoms. P deficiency often does not have visible symptoms but plants without enough P will not yield as well as those that receive P. Photo: Seed should be inoculated. This is very important in getting good yields and having a healthy plant that can fight off disease. Inoculant can be stored in a plastic bag in a cool place, such as in a bowl of damp sand. It should never be left in the sun and the bag should remain tightly closed with all the air squeezed out of it. Air dries out the inoculant, which can cause the bacteria in the inoculant to die and become useless. Heat does the same. The man in the photo to the left is mixing inoculant with seed. A tiny bit of sugar water should be used on the seed before mixing in the inoculant. This will cause the inoculant to stick to the seed better. Some commercial inoculant in Africa comes with gum Arabic, which can be used as a sticker instead of sugar water. Seed that has been inoculated must be immediately planted or the inoculant will die and not help the plants grow better. If fungicides are available and the seed grower fully understands how to use them safely, they have been found to help produce higher quality seed. While helpful, they are not mandatory for quality seed production. Plant only the best looking seeds. They should be yellow in color, not cracked and should have no visible defects such as brown or purple coloring or mold. Seed sorting should have occurred before planting as described previously. Plant field using 50 cm rows or narrower to ensure that plants quickly canopy over and shade weeds to keep them from growing. Within a row, place seed no more than 5 cm apart. Page 3

4 Growing Season Keep field as weed free as possible. Weeds not only reduce soybean yield but they can also increase disease and insect problems in a field. The Quality Seed grower should remove diseased plants from field as they are discovered. Remove all plants that are dying from disease or any plant material from diseased plants. This keeps diseases from spreading to healthy plants. If plants have yellowing or other symptoms but do not look like they are going to die, it may not be necessary to remove them. For example, you do not need to remove plants that have nutrient deficiencies. Seed growers may benefit from keeping records of disease symptoms to know from year to year which symptoms affect seed quality and yield. Consult soybean disease book. The photo to the left shows what soybean roots look like if they are producing nitrogen. The bacteria in the inoculant forms these white balls on the root. These are called nodules. The more nodules there are on the root, the higher the yield usually is. A grower can pull a few plants during the growing season to see if they have nodulation. If they do not, they might want to find a new source of inoculant supply. In a pure soybean variety, all of the flowers should be either white or purple/pink. If your field has some plants with white flower colors and some with purple/pink, you do not have a pure variety. If there are just a few plants with different colored flowers, these could be removed. If there are a lot of plants with different flower colors, a more intense purification plan will need to be undertaken. The photos above show the two flower colors soybeans can have. Page 4

5 There are little hairs on soybean plants called pubescence. These are located on the plant stems and the pods. In a pure variety the hairs will all be either white or brown. If you have some plants in your field with white colored hairs and some with brown colored hairs, you do not have a pure variety. In the photo on the bottom left the hairs are brown and in the photo on the bottom right the hairs are white. Varietal purity may not matter much at this stage of seed development in Ghana, but you should be aware of it and as your Quality Seed producers mature in their businesses, the goal of purity should be attempted. This will require a second training module if growers advance to this stage. Harvest It is vital that seed grown for replanting and commercial sales as Quality Seed be harvested as soon as the plants have turned brown and dried down. Every day that the seed remains in the field unharvested will result in lowered seed quality and lower germination the following year. When producing Quality Seed, it is important to be selective when harvesting plants for seeds. If a producer has a large field with low disease pressure and fairly uniform plants, they can harvest the whole field for Quality Seed. However, if some plants in the field look much better than others plants, the producer should do selective harvesting. To do selective harvesting, a producer should walk through the field and pull or cut only the best looking plants. These plants will become the Quality Seed source. These plants should be harvested, processed and stored separately from other plants in the field that will not be used as Quality Seed. Characteristics to look for in good Quality Seed are: Height should be between knees and hips Plant should be standing as straight as possible Seed pods should be closed and not popping open in their own (shattering) Pods should have three seeds per pod, although some varieties may only have two Harvest plants with the most pods on them Plants should all mature at about the same time Page 5

6 The biggest enemies of seed quality are high humidity or moisture, high heat and mechanical damage during harvest. When harvest occurs after the end of the rainy season, high humidity is usually not a problem. If high humidity or rainfall is a problem, seeds can be dried in the air. Avoid putting in direct sunlight. Dry in the shade in a well ventilated area so that the wind rather than the sun and heat dries the beans down. Only place in the sun if humidity and molding are a very big problem and then only do it until the beans have dried. The ideal moisture for soybeans is between 10-12%. This is best checked with a moisture tester but if one is not available, moisture can be tested by biting the seed with the front teeth (incisorsdo not use molars in the back of your mouth). If the seed does not dent at all from the teeth it is likely at low moisture, If biting causes the seed to compress but not break it is likely at too high of a moisture level. While it is okay to harvest beans at this higher moisture level, it is not wise to store them at high moisture. In Ghana, low humidity and high heat at the time of harvest will be the most likely problem. Low moisture and high heat both cause soybeans to become brittle and break. A broken soybean seed will not grow when replanted. As you can see from the diagram to the right, the two halves of the bean seed both contain the embryonic axis, which develops into the shoot and root when the seed germinates. The seed coat holds the seed together. In addition to this visible damage, invisible damage can also occur from high heat and sub-optimum humidity conditions. Poor environmental conditions can cause the seed to use up all of its stored energy or can damage the cells inside the seed so that when planted, the seed might look healthy, but it does not germinate. If a thresher is used to harvest seed, run the threshing cylinder at as slow a speed as possible. Fast machinery speeds lead to broken and damaged seeds. Remove any damaged seeds from your Quality Seeds. If harvest is done by stick beating, remove any damaged seeds from your Quality Seeds. Use a tarp under the seeds when beating so that seeds do not get soil on them. Seeds covered with soil and dirt are more likely to lose quality and vitality during storage, become diseased, and suffer from lower germination. Page 6

7 Storage How you store your seed will greatly affect your seed quality. Poorly stored seed will have reduced germination and will upset your customers. Store your Quality Seed separately from seed that will be sold or eaten. This can either be in separate bags or in a separate building. Seed should be stored in lots. Lots are made up of seed that is grown under the exact same conditions, such as the same field, same planting time and same harvest time. Seed that comes from different fields, different planting dates or different harvest times or methods should be in separate lots. The lots should be written on the storage bags. Only store seed for Quality Seed that is clean and disease free. High heat during harvest and while soybean seed is in storage can harm a seed s ability to germinate when planted. Store seed when it is at 10-12% moisture. Use a moisture reader or the teeth test to determine this. If a producer is serious about becoming a Quality Seed Producer they might want to consider building a seed storage building. The building should use materials that keep it as cool as possible. For example, a building made with thick mud walls and a thick grass roof that does not leak will be cooler than a metal building or one with a metal roof. Mud walls help keep heat out while metal attracts sun and heat. Cross ventilation will allow wind to help cool a room. Although many grain storage buildings are built elevated to reduce rodent problems, soybean losses to rodents in a non-elevated building will be much less than losses due to heat in a noninsulated building. Mud brick construction provides good insulation in the tropics. It is possible that in areas where heat is high and moisture is very low, having bags of wet sand in the storage room can help keep seed from getting too dry. However this is just theory and has not been tested. Seed can be stored in poly, jute or cloth bags that are tied closed at the top to prevent insect entry. Bags should not be solid plastic but should be of some sort of woven material to allow trapped humidity to escape. Storage insects are not usually a big problem in soybean although there are some moths that will lay eggs on soybean. If insects become a problem in storage then the seed producer should consider using a solid plastic bag for storage that is tied shut. Purdue University developed a special bag for storing cowpea seed called the PICS bag shown in the photo to the right. Cowpea is much more vulnerable to storage pests than soybean. Page 7

8 Germination Testing Every Quality Seed Producer should test their seed for the germination percentage before they start selling it each season. They should separately test each of their seed lots. A different seed lot is seed that comes from different fields or was harvested or planted at different times. A seed dealer who is honest about their tested germination percentage will gain the trust of customers. Having high germination percentage should be a major goal of Quality Seed producers. Having high germination is a marketing tool. Following all the instructions in this training module will help producers have high germination percentage. In Ghana, many farmers plant two seeds per hole because they are unsure what their germination rate is, so they assume that at least one of the two seeds will come up. Knowing what the germination rate actually is will help them save seed costs and be more productive farmers. Recommendations to customers for different germination rates: %- plant one seed per hole and plant each seed no more than 5 cm apart 80-90%- plant one seed per hole and plant seed no more than 4 cm apart 70-80%- plant one seed per hole and plant no more than 2 cm apart 60-70%- plant seed 5 cm apart. Alternate between one seed and two seeds in each hole Under 60%- plant two seeds in every hole with seeds no more than 5 cm apart How to Conduct a Germination Test From each seed lot, count out 100 seeds. Fill a bowl with moist sand and place the 100 seeds just below the surface of the sand so that no part of the seed is showing Sprinkle more water on the bowl of sand. If any seeds can be seen after watering, rebury them. Keep the bowl of sand in the sunlight but not under direct sun. Keep in a room that is not dark. The sand must never be allowed to dry out, it must always be kept moist but not overly wet. If it is too wet the seeds will all rot. This test could also be done directly in the ground if the area where the seeds are planted has a border around it to distinguish it from adjacent areas. The advantage to doing it in the ground is that a bowl of sand may become too saturated with water while the ground will not pond water. A disadvantage is insect predation of the seed or weed competition. After 7 days, count the number of seeds that germinated. That number is your germination rate. So if 80 of the 100 seeds came up, your seed lot has 80% germination. Inform your customers what this means and give them the planting recommendations listed above for each germination rate. Page 8

9 The Quality Seed Producer attitude People who decide to become Quality Seed Producers should treat their soybean fields as a business. Soybeans that are grown as a Seed Beans (for the purpose of reselling the seed) should be treated differently from soybeans that are grown as Market Beans (grown to sell at the market or to eat). A grower must take much greater care to maintain the best possible conditions during planting, growing, harvest and storage when producing Seed Beans. If excellent care is not given to Seed Beans, they will have low germination for customers, and the producer will not be able to maintain a viable business as a Quality Seed Producer. The production of Seed Beans should be considered a serious business venture that will require some investment into inputs. However, a small farmer with no money for inputs should not be discouraged. As long as they can produce clean seeds with high germination they can still become a Quality Seed Producer. Page 9