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 Enquiries SEED News - july/aug 2007
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This section is coordinated by the professors from the Federal University of Pelotas-Brazil, with the objective of answering the inquiries sent by the readers.
Send your question to e-mail: silmar@seednews.inf.br
"We know that seeds reach their highest quality at the time of physiological maturity, which for maize implies 35% moisture content, whereas for soybean, the seed moisture content is of 50% at that same stage. Considering these levels, can seeds germinate before reaching this stage?"
Before reaching physiological maturity, seeds are capable of initiating the germination process, as in the case of maize and soybean. However, for species such as rice and wheat, among others, seeds are normally dormant at the time of harvest and overcoming this stage will require either artificial treatment of the seed or naturally through its storage for a few months after harvest.
Breeding programs often, harvest seeds before they reach physiological maturity as a way of reducing the time interval between successive generations.
"I've heard that maize seeds are assessed through the germination test and the cold test, among others. I would like to know the basis of the cold test."
Normally, maize seed companies carry out numerous tests to asses the quality of their seeds, among which, the cold test is one. The basis of this test is to assess the seed vigor through the exposure to adverse temperatures. The seeds are placed on a humid substrate (sand, paper or topsoil) and exposed to a temperature of 10°C for one week, after which they are placed under a standard germination environment. The germinated seeds, after the normal germination period, are considered of high vigor. The standard for maize considers seed lots with more than 80% germination, after cold test, as highly vigorous.
"I understand that during seed processing, undesirable materials are separated from the seed lot through physical procedures. Could you please explain how this happens?"
To be able to separate undesirable materials from good seeds, a physical difference in some feature between both fractions is essential. The main physical properties considered are width, length, thickness, specific gravity, weight, shape, color and surface texture. The basic machine in which all seed lots are processed is the air screen cleaner, which relies on width, thickness and weight, to separate seeds from undesirable materials. Depending on the nature of contaminants, other machines may be required to further improve the seed lot quality.
"This year my maize crop field (10ha) yielded empty ears only, something that had never happened to me in my 20 years as grower. Could you explain to me what possibly happened?"
Hybrid maize seed production can be accomplished through two basic techniques, the first, by removing the tassel from the row of plants that will perform as mother, the second, by using male-sterile plants as mothers. The process of removing the tassels is expensive, since the crop field must be inspected several times (even during bad weather), which is why many companies prefer the male sterile technique. When using this type of plants, caution should be taken in that they should have the capacity to restore male fertility, since failure to do so will determine the production of empty ears. Most probably in your case the seed company may have mistaken the maize line planted as mother. Everything leads to think that the field manager may be out of a job, since this is an inadmissible error.
"As what happens with other products, piracy has become a plague for the seed industry. In a country like Brazil, in which the agribusiness amounts to approximately 30% of the gross national produce, seed piracy can be really damaging. Could you please comment on the possible reasons for its incidence?"
Seed piracy involves the trade of seed from a specified cultivar without the breeder's permission. A lot of tricks are performed by members of the seed business that explain why it has reached such inadmissible levels. The unauthorized use of patented material is also an act of piracy, like what happens with RR soybean, Bt cotton and the Clearfield rice, among others, in which cases no royalties, whatsoever, are collected.
"Dear Sirs, I own an intermittent drier used for soybean seeds; this year the seed has been delivered with up to 19% moisture. We proceeded to dry the lot and results in physiological quality were excellent, however, the drying speed was slow, not exceeding 0.8pp/h. How could we possibly increase the speed of drying?"
Harvesting the seeds when they have high moisture content avoids their field deterioration, but requires that they be dried artificially as soon as possible. We remain satisfied that your results match the recommendations we issue. Coming back to your question, to increase the drying speed you should try only one round at a temperature of 40-45°C, after which you should heat it up to 60-65°C. This combination won't allow seed mass temperature to go over 40°C, considered the highest temperature at which soybean seeds should be dried.
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