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 Enquiries SEED News - mar/apr 2006
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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
I am finding it hard to implement the recommendation to perform seed treatment, right before sowing. Currently, I am performing the process right after the condotioning. In this sense, I ask: what is the inconvenience caused by applying fungicide treatment on the seeds six months before sowing?
The fungicide treatment on seeds will, certainly, be beneficial to the seeds during their storage, nevertheless if they are not addressed for sowing they will have to be discarded, so that they will not be used for food or industrial purposes. So, the treatment applied just after conditioning the seeds is under commercial risk in case the seeds are not sold.
I have noticed that SEED News, besides the great papers, also has such wonderful tool that is the "enquires", So, I would like to know what are the microorganisms that most affect seed germination, either in field and laboratory, and specially the fungi.
As you know, microflora associated to seeds is very variable. Such variation can be caused by many factors. Among them, we can highlight species and variety. This way, fungi that can be found in soybeans seeds belong to different species than those detected in maize seeds, for instance. So we will give you the name of the main fungi whose occurrence is associated to seeds from some species cultivated which cause seed germinative capacity to be reduced. In soybeans, we have Phomopsis sojae, Colletotrichum dematium, different species of Fusarium, Sclerotinia sclerotiorum and Rizoctonia solani. In beans, there is the occurrence of the fungi Colletotrichum lindemuthianum, Macrophomina phaseolina and different species of Fusarium. In maize, further than Fusarium species, we have the Diplodias (maydis and macrospora); in wheat there is Giberella (Fusarium) and Biploaris, Dreschlera; and in rice the most common are different Fusarium species and Helminthosporium (Dreschlera), Gerlachia oryzae and Triccoconiella padwikii.
Could you comment what is the inconvenience in having soybeans or even rice and wheat 20 tons seed lots, because for my situation larger seed lot, the better. This way I will have to make less quality analyzes and, at distribution, I can have a better control.
A seed lot is characterized for being homogeneous within given tolerable limits. If different, the sampling performed to ascertain the lot quality will not be representative. In the germination test 400 seeds are used, and they will represent the seeds of the whole seed lot (millions of seeds). This way, it is not advisable to have a very large lot because the larger it is, the lower its homogeneity.
I have heard a lot about transgenic seeds, and some conversations were about their germination capacity. I perceived that transgenic seeds once harvested do not germinate, that is, they are sterile. What can you say about it?
As every thing that is new, transgenic seeds also get the attention from the whole world. Some people who are less prepared have released the most different opinion about their performance. To have an idea of how absurd that statement is, just ask the farmers, because in Brazil more than 10 million hectares are cultivated with transgenic soybeans and great part of them is with saved seed, that is, the seed is harvested and stored to used for the next crop.
I liked the issue about tetrazolium test for bracchiaria seeds, which is very illustrative and agile to be used. However, I noticed the values of the tetrazolium test are a little higher than the ones of the germination test. Could you please comment about it?
Tetrazollium test is older than 50 years, time enough to prove its close relation to seeds physiological quality. As the tests are performed with different seeds the results are not the same and they tend to be a little higher in the tetrazolium test because the dormancy effects and seeds health do not show up in the test. It is a test indicated for a quick and reliable evaluation of seeds physiological quality.
Reygrass plays, as a matter of fact, an important role in both bovine and ovine feeding in several areas around the world. I have understood that reygrass is cross-pollinated type, but there are varieties and hybrids available in the market. Could you please talk about the varietal purity of the materials?
Really, there are high performance reygrass hybrids but in Brazil such material is not available yet. With regards to the varietal purity of a variety, it can be stated that the material already available in the market has an high heterosis content, however significantly inferior than a hybrid. Varietal purity will be high only at sites with a seed program with a cultivar maitenance process.
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