The rich experience in classical selection in the creation of new corn hybrids not only helps in deciding which initial genetic material will be used in the selection of new combinations to create top quality hybrids, but also contributes to the improvement of all agronomically important features of newly emerging hybrids.

That experience brought AGRIMAX the opportunity to develop a new, revolutionary approach in the field of classical selection.  

We have developed the AGRIMAX – STRESSAFE (STS)® method of classical selection, which involves monitoring and improvement of all important agronomic properties of the maize plant, from sowing to harvesting. Such an approach in selecting AGRIMAX hybrids and their parent components as an end result has a corn plant with increased tolerance to stressful conditions, a stable and high yield in almost all cultivation conditions, even under unsufficient precipitation and high air temperatures.

Hybrids labeled with STRESSAFFE (STS)® mark in stressful conditions ensure that the genetic potential of fertility is maximally preserved!

The STRESSAFE (STS)® mark is assigned to an AGRIMAX hybrid in the pre-commercial and/or commercial phase, when we make sure that it has the ability to tolerate more stressful conditions than the regular ones. We base this decision on various productive field trials and the production itself in a number of sites and seasons. The STS® label is not permanently assigned to a hybrid, but as such it is also monitored throughout its commercialization, so it may happen that a hybrid obtains or loses the privilege of bearing this mark, if in practice it shows better or worse performance than the other AGRIMAX corn hybrids.

From the point of view of the STRESSAFE (STS)® method of classical selection, roughly observed, the stages of maize development can be divided into four phases, which are important for all agronomic characteristics and which essentially define the grain yield itself: 



The development of the maize plant begins when the seed that was laid in the ground gets in contact with soil moisture. The seed then begins to “swell”, thus the activation of the call begins and a new, future plant begins its phenological development.

Development cycle – Phase from sowing to the emergence of 4th leaf

Corn is a thermophilic plant and for proper development it needs heat from the moment of sowing onwards. Oftenly used term “effective temperature” refers to temperatures above 10°C, considered as the limit value below which the plant’s proper development gets stopped or impeded. It is precisely the lack of effective temperatures in the early stages that is unusually important for the later manifestation of the fertility potential of a hybrid. Formation of the future yield begins as early as the seed germination initiates, continuing in the first days upon emergence.

Root system of STS® hybrids more easily tolerates the lack of heat, which ensures its balanced development and better growth

Due to insufficient heat internodes shorten, the root system gets poorly defined,  its development impeded, leaf mass decreases, the number of grain rows and the length of the cob reduce, as well as the number of secondary branches and the volume of the tassel. All this together manifests throughtout later phases of development, resulting in a shorter plant with less developed root system and leaf mass, which directly affects the ability of the plant to resist stressful conditions, such as lack of moisture or extreme temperatures. STRESSAFE (STS)® method of classical selection demands paying special attention to these early stages of development, when we are able to select genotypes that are more tolerant to coldness and more easily bear the lack of effective temperatures. This is achieved in practice by a carefully planned sowing schedule of individual genotypes, as well as conducting fertility tests in the colder soil. We follow the plant’s subsequent development, from the root system to the overhead part of the plant. For the further selection process, we pick only genotypes that have rapidly developed a strong primary root, which in future guarantees a more robustly developed root system. AGRIMAX proudly owns a genetic base hosting a large number of different genotypes that have significant tolerance towards adverse environmental conditions.


Immediately after the appearance of the first permanent leaves, a very intensive development of corn plant begins, both in the underground as well as in the above-ground segment. Of crucial importance is the development of a strong and functional root system, because only a well branched root system ensures the stability of the plant and an effective supply of water and nutrients from the soil during the entire vegetation period.

Therefore, the STRESSAFE (STS)® method of classical selection, by monitoring the process of root development, allows us to recognize those genes that contribute to the increase of tolerance to stress, among many in the rich genetic base of AGRIMAX inbred lines. Using only such inbred lines in the process of creating new hybrids, we can predict with great certainty the interaction of new hybrids with unfavorable environmental conditions. In addition to the powerful root system, STRESSAFE (STS)® method of classical selection also envisages specific plant architecture, erectile (vertical) position of the leaf, as well as the shape and number of leaves, especially those above the first piston, which remain the only photosynthetic active leaves after fertilization. The leaves below the first piston gradually die. For this reason, for the selection of new hybrids we pay huge attention to the number of leaves above the first piston. AGRIMAX hybrids bearing the (STS)® mark are the hybrids with increased number of photosynthetic active leaves. All of this is quite important, due to the fact that erect leaves allow for better photosynthetic activity.

Due to erectile position of the leaves, STS® corn hybrids make a more effective use of the solar potential

Such position and orientation of the leaves allow the sun’s light to fall at an angle nearest to the 90o and thus the use of solar energy is at maximum during the daytime. At the same time, this allows greater sowing density / more plants per unit area. Solar energy is necessary in order for the plant to develop a chemical process of photosynthesis, in which inorganic matter, in the presence of CO2, is converted into organic components that the plant consumes. The amount of absorbed solar energy depends directly on the total area covered by the leaves in the field. The larger surface area directly affects the increased intensity of photosynthesis and thus the amount of assimilated substances. These two parameters are linked by the so-called
LAI index, which denotes the relationship between the surface area and the amount of assimilated matter. It is considered that for the maize, its optimal value is 6 (which means that at least 6 hectares of leaf area is required on each hectare of land).

komparacija STS slika iz Bitolja

We also test fertility potential of STS® hybrids in the regions with significantly higher air temperatures and lack of moisture than in Serbia.
A field trial conducted in Bitola (North Macedonia) is presented in the images above

Only a proper and ballanced photosynthesis process allows hybrid plants to develop a good root system and stalk that would provide plant stability and increased tolerance to lodging, as well as proper delivery of water and nutrients to the grain on the piston throughout the entire vegetation period. Naturally, all of this ultimately means better yield. A large number of such plants per unit area allows maximum assimilation of solar energy (maximum photosynthetic activity), meaning that the fertility potential of a hybrid shall be fully evinced.


Well-developed plant, both in the underground and in the above ground segments, is ready to go through the most delicate phase of development – blooming. The stage when the plant begins to produce silk and when the tassel anthers begin to crack, spreading pollen, usually initiates when the air temperatures are sufficiently high, while air humidity and soil moisture decrease (second half of summer season for the temperate climate zone). This is why the pollination process is one of the most critical periods in the development of a plant. AGRIMAX STRESSAFE (STS)® hybrids have a distinctively high level of cellular pressure due to the intensive development of the root system at an early stage, which is very important for the vitality of silk and pollen grains. While the number of kernel rows on the piston is predominantly determined by the genetic potential, the number of kernel that actually get produced on each piston is determined during pollination. Pollen grains, upon departure from the anthers, are extremely sensitive to high air temperatures and are considered to begin losing their vitality and ability to fertilize the ovaries at temperatures of above 30oC.

In the conditions of excessive heat the pollen starts to die off. As a result, fertilization will be poor and thus the number of kernel reduced, which means that the final yield shall be reduced as well. In order to avoid these undesirable phenomena, AGRIMAX – STRESSAFE (STS)® hybrids have been selected so that the time of blooming (silking) and pollination is synchronized. This parameter is referred to as Anthesis-Silking-Interval (ASI) and is manifested during a relatively short period of pollination and silking. Such AGRIMAX – STRESSAFE (STS)® genotypes-hybrids begin to pollinate immediately upon appearance of the tassel out of the uppermost leaves; That is, as soon as the silk pops out and is ready to accept the pollen. With the (STS)® hybrids, pollen is produced in significant amounts, which certainly reduces the risk of poor fertilization.

Agrimax STS® hybrid Dimana – Pollination starts immediately upon appearance of the first silks


At this stage of the phenological development, AGRIMAX STRESSAFE (STS)® corn hybrids evince the benefit of a well developed root system, which is why, after a good fertilization and proper kernel formation on the piston, the filling of these kernel is facilitated and complete. The ability of a plant to resist adverse agroecological conditions and stress depends on its ability to “control” evapotranspiration (excessive water loss through the stomas in the leaf). AGRIMAX STRESSAFE (STS)® hybrids, by proper selection of the initial genetic material for their creation, are “predetermined” to have an increased tolerance to stress, by controlling the loss of water through the leaf notably better than the regular ones.

Mass, or weight of 1000 corn grains is a practical measure determining the total grain yield per hectare. Corn producers know that the “lean and light” grain can not achieve the top yield. Therefore, during this development phase, the STS® hybrids are expected to be more efficient in managing and exploiting their genetic potentials than the other ones. The specific methods of this type of improved classical selection, proper selection of initial genetic material, longterm field experiments and experience, ultimately result in STS® hybrids having a more developed root system, more efficient absorption of water and nutrients, better control of water loss through evapotranspiration and finally, extended photosynthetic and assimilation activity during maturation.

STS® hybrids are maximally effective at managing an excessive water loss

In difficult agroecological conditions, the combination of these enhancements contributes to the ability of AGRIMAX – STRESSAFE (STS)® hybrids to fill their kernel better than the regular ones. Only a well-filled kernel ensures that all of them will be properly positioned on the piston and that in the natural process of drydown, the piston remains “compact” and filled with kernel from the bottom to the top. One of the desirable traits of the STS® hybrids is also a quick drydown rate, as only such hybrids allow avoiding additional spendings for artificial drying. At the moment of harvest, STS® hybrids will have a low percentage of water in the kernel, while the genetic potential of the hybrid would be maximially used.

In difficult agroecological conditions STS® hybrids will fill their kernel better than the regular ones – Only well-filled kernel ensure that all of them
will be properly positioned on the piston so that the cob remains “compact” and filled with kernel from the bottom to the top

AGRIMAX – STRESSAFE (STS)® hybrids – Reduce stress, worry less!

We have been witnessing  a notable climate change over the past seasons. The competition for the top yield of corn grain is set as a priority for all seed companies on the market. In addition to the introduction of contemporary genetic material aimed at improving the fertility potential, it is necessary and extremely desirable to pay attention to the tolerance of these genotypes towards stress conditions. Our AGRIMAX team succeeded in developing a new approach in classical selection, which as an ultimate result gave birth to the AGRIMAX – STRESSAFE (STS)® line of hybrids, more tolerant of all the climatic challenges facing the plant during its entire life cycle.

In accordance with the ongoing climate changes, we are constantly monitoring all of our hybrids that have proven themselves ‘STS®-worthy’ in practice. Every year we perform a series of field trials, based on which we decide if some of the existing AGRIMAX hybrids, which were previously produced, also using the STRESSAFE (STS)® method of classical selection, can be labeled as an STS® hybrid. The best maize seed could be produced only through the best approach in selection, by professionals. Be sure that, if they get this label, such hybrids are more tolerant to unfavorable agroecological conditions and as such, will have a greater chance of exploiting their full genetic fertility potential.