Corn seed treatment

Seeds are one of the most efficient means of disseminating fungi in corn, both in production fields and in storage conditions. That's why treating them with fungicides is an excellent option from an economic and environmental point of view.

Seeds are one of the most efficient means of spreading diseases, considering that through them pathogens can be transported great distances and introduced into new areas. Corn seeds are susceptible to various fungi, which can cause damage to the establishment of the crop, reduce the stand and weaken the seedlings.

In Brazil, the main fungi carried by corn seeds are Fusarium verticillioides e Acremonium strictum, in seed production fields, and Aspergillus spp. And Penicillium spp., under storage conditions. Mechanical damage resulting from the mechanized harvesting of corn seeds can allow the entry of storage and soil microorganisms, increasing the rot rate of the lot, especially in the embryo region. Thus, the treatment of corn seeds also aims to control soil fungi, such as species of the genera Pythium, Rhizoctonia, Fusarium e Stenocarpella. These species can cause seed rot, seedling death in pre- and post-emergence, and root rot, which promotes the formation of an irregular stand.

the fungus Fusarium verticillioides is the cause of stem and ear rot or fusariosis. It has the power to cause the death of seedlings, caused by necrosis in the coleoptile, in addition to causing rotting of the roots at the base of the plant and the lower internodes. In the physiological maturation phase of the grains, the disease becomes more severe, forming a mass of salmon-pink colored spores on the outside of the affected tissue. The disease has been increasing in recent years, mainly in areas with no-till farming systems and no crop rotation.

Corn seeds are routinely treated with chemical pesticides and this practice is an excellent option, not only for its efficiency, but also for its economy and for having a lower environmental impact, compared to products applied via foliar or in the planting furrow.  

In this sense, work was carried out to verify the efficiency of different fungicides in the treatment of seeds of corn lines and hybrids, to control Fusarium verticillioides. The study was carried out at the Seed Pathology Laboratory, located in the Department of Phytopathology and Nematology of the Luiz de Queiroz College of Agriculture (Piracicaba/SP). Seeds from six lines and three hybrids resulting from the crossing of these lines were used (Table 1). These seeds were provided by the company Melhoramento Agropastoril Ltda., specialized in corn genetic improvement.

The seeds were treated with fungicides according to the manufacturer's dose (Table 2). The products, in a syrup volume of 0,5% of the weight of the seeds, were added to the seeds in plastic bags, shaking vigorously until complete coverage and, subsequently, subjected to drying in the shade. The treatment corresponding to the control was treated with 0,5% distilled water.

The evaluation was carried out through health, germination and seedling emergence tests in a greenhouse. The health quality of the seeds was analyzed using the freezing filter paper method and germination using the germination roll method (paper towel), both according to the Rules for Seed Analysis (BRASIL, 2009). To determine seedling emergence, sowing was carried out in plastic boxes measuring 43 x 30 x 11 cm, containing substrate. They were kept in a greenhouse and, from the beginning of emergence, the number of normal seedlings emerged daily was recorded until the process stabilized. With these data, other vigor indices were obtained, namely the emergence speed index (IVE) and the percentage of seedlings emerged.

The following fungi were identified in the health test of the nine samples tested: Fusarium verticillioides, Acremonium strictum, Penicillium spp. e Aspergillus spp. All products reduced the incidence of F. verticillioides, Penicillium spp. And Aspergillus spp., with emphasis on products based on carbendazim + thiram +captan and fludioxonil + azoxystrobin + metalaxyl-M + thiabendazole, which were more efficient mainly in controlling F. verticillioides. These same treatments were those that stood out in reducing the incidence of A. strictum. This can be seen in Figure 1, where the color of the bars represents the seed treatments and the smaller bars indicate a lower incidence of the fungus carried by the seeds. The best treatments were those whose products contained the greatest number of active ingredients. This positive correlation between the products and increased efficiency in fungal control can be called substance synergism.

In the germination test, the first count (considered as a vigor parameter) showed a greater number of normal seedlings in all treatments with fungicides compared to those without fungicides. It is inferred that this increase in vigor is related to the control of the fungus F. verticillioides, observed in the sanity test. The other parameters evaluated were not efficient in discriminating the treatments in relation to the physiological quality of the seeds (Table 3).

Thus, the treatments that stood out were carbendazim+thiram+captan and fludioxonil+azoxystrobin+metalaxyl-M+thiabendazole, reducing the incidence of fungi without affecting the physiological quality of the seeds. These products can be used in corn production, in order to assist producers of both seeds, in obtaining hybrids with high yield potential, and grains, in establishing crops with the desired stand.

corn production

Corn (Zea mays L.) is the most produced cereal in the world, with Brazil being the third largest producer, behind the United States and China. In the 2015/2016 harvest, it is estimated that national production will reach 69,1 million tons (CONAB, 2016), representing one of the main productive activities, second only to sugar cane and soybean crops. . The crop plays a fundamental role in human and, especially, animal nutrition, as the majority of grains are used for the manufacture of feed. It is estimated that the world population, currently with more than seven billion people, will have, by 2050, nine billion individuals. Considering this global scenario, corn is a crop that has great potential, mainly as a source of energy to be explored in order to achieve sustainability, and also to meet humanity's increasing demand for food. 

At the beginning of the 20th century, research carried out in several areas, mainly in genetic improvement, made it possible to obtain hybrid corn (forced crossing between two plants with pure lines), which was the main cause of the spectacular increase in grain productivity in the crop. Growth in productivity directly contributes to sustainability, as more is produced in the same area, meaning less deforestation. The challenge for breeders today is to continue producing new hybrids that can replace existing ones with advantages.
In a breeding program, the choice of corn lines and hybrids is influenced by the genetic potential of the species, which is directly related to its yield. For the genetic potential to be expressed, the seeds must have high physiological and sanitary quality, that is, with high germination potential, high vigor and low incidence of pathogens.

Renata Rebellato Linhares, Maria Heloísa Duarte de Moraes, Mariane Sayuri Ishizuka and José Otávio Machado Menten, University of São Paulo (USP)

Article published in issue 208 of Cultivar Grandes Culturas.