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 Main subject - sept/oct 2003
Adding Value to Soybean Seed Through Quality Control
Fancisco Krzyzanowski
Embrapa
fck@cnpso.embrapa.br
José de Barros França-Neto
Embrapa
franca@cnpso.embrapa.br
Seed quality influences directly on the success of the crop and contributes significantly so that high productivity levels are reached. Low quality seeds compromise the proper plant stand, influencing directly on the productivity of the crop. In situations where plant population is below the recommended for cultivation, replanting will be necessary and such procedure is associated with losses regarding the increase of production cost and the risks inherent to this procedures, such as cultivating exchange, loss of the best sowing period, problems of herbicide efficiency or risks of product overlapping in the area, toxicity occurrence. All these factors contribute to low productivity.
The production of high quality seeds requires the adoption of a good quality control program (QCP). The non-use of this program can result in the production of inferior quality seeds, mainly when the seeds are produced in tropical and subtropical areas. The adoption by the producers of quality control techniques in seed production has the purpose to supply information that will be helpful in the process of taking decisions to overcome limitations imposed by several factors that can affect seed quality.
The quality of soybean seeds, for instance, can be influenced by several factors that can occur during the production phase in the field before harvesting and during harvesting, drying, processing, storage, transport and sowing. These factors include extreme temperatures during maturation, fluctuation of moisture conditions, including droughts, weathering, plant nutrition deficiencies, occurrence of insects, improper handling, drying and storage. Several pathogens also affect soybean seed quality. Phomopsis spp., Colletotrichum truncatum, Cercospora kikuchii and Fusarium spp. are among the fungi most frequently associated with soybean seeds. The action and the interaction of all these physiological, physical, entomological and pathological factors contribute to a common result - seed deterioration.
Seed deterioration is a natural process that involves the interaction of cytological, physiological, biochemical and physical changes in each seed. These changes reduce vigor, viability and eventually lead to the seeds' death.
Quality control involves government action as well as activities of seed producers. The government can act through specific laws, seed analysis and seed certification. These actions permit a series of procedures enabling seed production programmes to be monitored and regulated to ensure that technically sound methods are followed, thereby safeguarding the integrity of cultivars. This system, which may encompass all phases of seed production, ensures that only seeds of known quality are accepted for marketing.
The quality control includes all the production phases: field, harvesting, drying, processing, storage and commercialization.
In the internal quality control, through a series of systematic activities carried out during all the seed production phases, seed companies can check quality to identify and correct possible problems in order to protect the reputation of the company, as well as satisfy the consumer. The objective of this type of QC is to produce and to market seeds of high physical, physiological, sanitary and genetic qualities. A good QC system supplies information to correct possible problems, helps in decisions making, and reduces environmental contamination, through the reduction of agrochemicals used in the control of pests and diseases. Internal QC also avoids problems with the official system of quality control.
A good QC system self pays. It helps seed producers to detect and to adopt measures to correct seed quality problems. The QC system proves information to seed producers which will contribute to avoid quality losses, as well as the rejection of good quality seed lots, when inadequately evaluated only through the germination test, as for instance the occurrence of Phomopsis due to weathering during maturation in tropical and subtropical climate conditions. QCP reduces seed preparation costs, and prevents stand failures and problems of low seedling emergency in the field. Such problems can result in seed replacement for the farmers, because of the replanting needed, activity that is related with serious losses and damages to soybean farmers.
The internal QC system includes several phases:
a) Exploratory phase: this phase begins with the selection of adapted cultivars, suitable seed production regions, selection of good cooperators and initial material for multiplication of known origin. To be a seed multiplier, the farmer should have a good knowledge about technological aspects of the species production, good quality field equipment, tractors, implements and harvesting machine with wide resources of threshing adjustments and enough amount of area, required for seeds production.
b) Sowing phase: the selected areas for seed production, pre-sowing and sowing operations and field emergence are checked in loco. Field isolation conditions, prevalent weeds and the occurrence of voluntary plants are also examined.
c) Vegetative and harvesting phases: three additional field inspections are made in those phases: during the vegetative phase of the crop, to evaluate the incidence of diseases, the occurrence of insects mainly the stink bugs, the occurrence of weeds and the presence of off types plants; in the flowering, to identify and to rogue plants out of the pattern regarding the cycle, the height and the flower color; pre-harvesting, seeking the evaluation of cultivar mixture, through some genetic descriptors, as pubescence color and plant cycle. Special attention should be given for the stink bugs occurrence that is responsible for the occurrence of green stem in the soybean crop and, consequently, of green seeds. It should also detect diseases caused by pathogens transmitted by seeds, diseases that occur in the final of the cycle, Cercospora kikuchii and Septoria glycines, as well as Fusarium, since these last ones can propitiate the occurrence of greenish seeds that are immature and have low physiologic quality. These inspections permit a final decision on whether the harvested crop should be sold for seed or grain.
Insect damage
Another important aspect is to monitor mechanical damage occurrence during harvesting operation. Lots with more than 3% of splits are inappropriate to be used for seed production due to high final percentage of mechanical damage imposed to the seed. To follow field deterioration due to weathering through the tetrazolium test (TZ), is an important procedure to make decision in the use of the field for seed.
Mechanical damage
d) Processing phase: QC is also exercised during seed receiving, pre-cleaning, drying, cleaning, classification, packing and storage;
e) Finishing phase: QC is performed through seed analysis, proper identification of the lots, marketing, sales, and distribution and during the period that seeds remain with the distributors for sale to consumers.
CERTIFICATION OF SEEDS AND QUALITY CONTROL
The certification system ensures standards of seed quality concerning seed origin, physical and genetic seed purities and physiological and sanitary qualities. Seed certification is performed to meet the needs of the seed producer.
Field emergence
page 2 ->> Adding Value to Soybean Seed Through Quality Control
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