Soybean seeds

Edição XXII | 02 - Mar . 2018

Maria de Fátima Zorato - fatima@mfzorato.com.br

Rapid and continuous transformations occur and often without prior notice, whether in the urban or rural environment.


    We who work with seeds have witnessed various evolutions in recent times, which include the whole system, which involves the biological product and extends to changing user-user requirements. That is to say, the consumer is much more selective in the quality of the seed that he acquires. Because? Because it is being made aware of the linkage, specifically the vigor, with the productivity of the cultivars sown in its fields, as well as the imputed valuation in the seed, which is similar to a chip, where all innovations are being inserted. By correlating technology, biotechnology and genetic improvement, the emergence of new territorial areas and expansion with the cultivation of soybeans, which has led to the progress of the regions and can still earn high incomes, is being monitored every year. The profile of the contemporary rural producer is a constant search for improvements in practices. In addition to making use of appropriate and innovative technologies, it considers the seed a basic input and makes great investments, expecting the good establishment of its crop, an abundant harvest and the profitability sought in its planning


    The biological chip, of greater added value, is the starting point of the crops that are led to the open sky, therefore, subject to the weather conditions . The word already suggests, by itself, some unfortunate event. Something that is not controlled. In the field, there are factors that limit and interfere in the productive potential of soybean cultivars, among them are diseases. According to researchers, a large number of these, caused by fungi, bacteria, viruses and nematodes, have been and are being detected in the different producing regions of Brazil. They also point to new anomalies of unknown causes arising from the changes imposed by man's action on nature, associated with annual climate change and the various practices adopted in the agricultural system. The occurrence of attacks is subject to the host, the pathogen and the environmental condition; so it depends on the combination of the three factors. Most diseases of economic importance that occur in soybeans are caused by pathogens, transmitted via seeds. In the soybean crop 2016/17, the curiosity about the fungus Cercospora kikushii, causing purple spot of the seed and of the foliar crust, was aroused.


    Cercospora kikushii (Matsuo and Tomoy) Gardner - purple spot and blight

    It is a fungus considered to cause end-of-cycle disease (CFD), which occurs throughout the aerial part of the plant.

    The severely affected crops rapidly pass from green to dark brown and promote the acceleration of defoliation and maturation. The fungus reaches the seed through the pod, causing the purple spot on the tegument from the end of pod filling (R6), but in soils of lower fertility, symptoms may arise from the beginning of pod filling (R5 .1). The favorable conditions for its development are high temperature and humidity. The purple stain is a symptom caused by the pathogen; however, not all infected seeds show the characteristic color in the integument.

    The work carried out during a long time in several renowned research institutions showed that there was no negative effect of the fungus on the quality of the seed, as well as the rate of seed-plant-seed transferability was quite low. Thus, the infected seed did not appear to be a major source of inoculum. These studies were preponderant to claim and obtain, together with the SNPC / SARC / MAPA, the withdrawal of the tolerance pattern of seeds with purple spot (10%), valid until the 1980s.



It is worth mentioning that there has always been a divergence of opinions about it - some researchers reported a decrease in productivity and seed quality.

  

      Detecting the difference

    Over time, chemical control for diseases called CFDs was intensified, and for some time the fungus Cercospora kikushii did not draw so much attention with its purple mark on the seed. He was more restrained, without warning.

    However, from a given moment, seed production has undergone drastic changes in its range of options. The breeding program met the demand of producers who had preferences of the soybean cultivars for the habit of indeterminate growth and for the early cycle. All of us in agriculture are aware of the climatic uncertainties of soybean producing regions, especially in Central Brazil, regions of Cerrado, which were cleared and formed large areas of new oilseed borders. We can not disregard the fact that Brazil is a tropical and subtropical country. In these regions, high temperatures and high temperatures prevail, very important ingredients for the development of microorganisms, among them Cercospora kikushii.

    In the 2016/17 harvest, there was a significant change in the early harvest of some early-growing cultivars, especially in production sites where the high humidity associated with high temperatures constituted a perfect package for the establishment of end-of-life diseases cycle. Above all, the purple stain was different. More aggressive about the seed, with a much stronger purple color, quite expressive. He took all the seed and ripped it from the thread. And, a posteriori, came the complaint of the user producer that, in visualizing the physical attribute - constituent of quality -, he insisted on treating the aspect as diseased and rotted seed. In some episodes, arriving at batch returns.


    The harmony with reality

    Since the beginning of the harvest, in 2017, in some laboratories, when the collection was performed, either in pre-harvest of plants, still in the field, or in load received in the balance, in the tetrazolium test (detects the main physiological damages of the seed ), at the specific spot that there was the purple spot began to arouse attention an unprecedented fact until then. The spot was also in the cotyledons or the embryonic axis, bringing a lesion similar to that of deterioration by moisture. The difference was in color - it was a crimson red (characteristic color of the deteriorating tissue), but it was brighter, less dense. From there, the observations became constant, because the question was: could this fungus be mutating and bring about damage to the physiological potential in the future?

    At this moment, it was easy to detect the quality of work performed by attentive analysts and who monitored the other physiological quality verification tests - germination, accelerated aging, emergencies in beds or soils, among the most performed in the sowing units. What's the surprise? In all tests, the seed with the well-marked purple spot on the cotyledons or on the embryonic axis brought deterioration. The questions began and there were no questionable answers. Some accompaniments along the storage were made, so that, at the time of dispatch of the seed lots of the cultivars that had the highest incidence of the pathogen, there were no frustrations. Many seeds were losing quality when they had greater expressiveness of the fungus Cercospora kikushii (purple spot).


    New causal agents of the purple spot

    A few days later, the answer was sent to the possible clarification regarding what happened. You could not see things from the hereafter, but what had actually changed. A group of researchers discovered new causative agents of the purple spot. A scientific research published in Argentina determined that, contrary to what was thought, the causal agent of the purple spot of the soybean and the origin of cercospora is not only a fungus (Cercospora kikushii), but at least four species of this gender. According to the article, this suggests that there is a more serious epidemiological situation than hitherto known, and the reason the disease has grown in importance recently.


    Observation as primordial

    Currently, it is imperative that the analyst, in any of the tests carried out, get off the autopilot and be a good observer and bring their perceptions into the discussion. The seed market is more competitive and to serve it, there is the launch of many new cultivars each year. Living organism can suffer the influences of your universe.

    Basically, in the tetrazolium test, the analyst who cuts the seed and assigns it among the classes of the test, without having removed the integument, can stay in the blind spot and cannot perceive any different changes that are occurring. And you should still make cuts to examine the depth and connections of the incidental damages. If you do not do the thorough analysis in any of the tests, and do not stick to the details that are making the differences in contemporary practice, you are just wasting time and not collaborating for assertiveness in making decisions, a fact that can have costly consequences. Therefore, a new look must be given to the analyzes. Quality and not quantity of tests done can mean more to the system. The seed and its context have changed.

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