Choice of wheat cultivars

The use of cultivars suitable for the region in which wheat will be planted is the first step for the producer to be successful in his crop. However, it is always necessary to consider the strong dependence on the management adopted by the producer and on environmental conditions during the cycle.

wheat (Triticum aestivum L.) is the second most produced cereal in the world, with a global production of 729.5 million tons in the 2015 harvest (FAO, 2016). And for wheat grain production to reach high levels in the most diverse regions of the world, it is necessary for the cultivars to adapt to the technological conditions of the properties, therefore, it is necessary for the cultivars to be evaluated in all environments. Furthermore, it must be considered that Brazilian wheat consumption is stagnant at 10,5 million tons. However, national production never exceeded 6 million tons. Highlighting the problem of an essentially agricultural country, like Brazil, dependent on the import of approximately 50% of the volume of cereal used in Brazilian territory (CONAB, 2016).

Among the main reasons mentioned for this low national production, there is the restricted area of ​​cultivation of this cereal nationwide, which, according to the National Supply Company (Conab, 2016), was concentrated in 90% in the southern region of the country during the harvest. 2015. This concentration of production is due to the fact that this crop is characterized as one of the only ones with economic profitability in the winter period for this region. However, the expansion of this culture to central Brazil has been the subject of several studies since the 70s (TOMASINI, 1982; AMORIN et al., 2006; TRINDADE et al., 2006), and several of these found satisfactory results. However, the slow increase in crop area in the Brazilian center-west is due to cultural factors on the part of producers, and mainly due to the lower profitability of wheat when compared to other potentially competing crops for the central region of Brazil. However, in addition to the restricted area, the low productivity of national crops intensifies the problem of small internal production. It is noteworthy that Brazilian wheat crops had an average productivity of 2015 kg/ha in the 2206 harvest (CONAB, 2016), a value much lower than the average of European crops in the same harvest year, 5170 kg/ha (MARS, 2016), which shows the low efficiency of wheat farming in Brazil. Among the factors that provide an increase in the efficiency and competitiveness of national wheat farming, Embrapa (2011) highlights some crucial management practices for achieving success with the crop. It starts with complying with the sowing periods indicated by agricultural zoning, followed by investments in fertility and sowing quality, considering aspects such as spacing, depth and density. In addition, thorough management of invasive plants, diseases, pests and nitrogen fertilization must be carried out. It should be noted that for successful management, the correct choice of the exploration cultivar is extremely important, in order to express maximum production in light of the management adopted and observing the edaphoclimatic peculiarities of each region.

According to the Ministry of Agriculture, Livestock and Supply (Mapa/2016), Brazil has 244 wheat cultivars, adapted to the most diverse climatic conditions, and with the most distinct cultivation purposes. Which makes the decision to choose the most suitable cultivar unclear. Therefore, it is necessary to carry out experiments with a range of environmental conditions and with several cultivars (CARGNIN et al., 2006), in order to identify the best genotype for each particular condition.

Starting from the inference that one of the main pillars for successful wheat production is the right choice of cultivar. This text sought to provide an explanation followed by discussion, regarding different wheat cultivars and some of their productivity components for the Central region of the state of Rio Grande do Sul, in order to assist producers in deciding on the choice of cultivate for the subsequent harvest.

The experiment was carried out in the experimental area of ​​the Phytotechnics department of the Rural Sciences Center, located on the campus of the Federal University of Santa Maria. In this, 15 wheat cultivars were used, all of which were sown on July 03, 2015. Sowing took place under ideal soil moisture conditions, using a fertilizer seeder previously adjusted to distribute 300 seeds per m-² at 340 seeds per m^-², with a spacing of 0,2 meters, and 300 kg/ha of fertilizer of the commercial formula 05-20-20, according to the need predicted by the soil analysis. Following this, nitrogen fertilization was carried out on top dressing, divided into two installments totaling 110 kg/ha. The variables analyzed were number of plants per m^-2, number of ears per m^-2, mass of a thousand grains, mass of hectoliter and productivity. Analyzing data on number of plants per m^-² and ears per m^-² (Graph 1), it is observed that for the characteristic number of plants per m^-², the Mestre cultivars (344 plants m^-²) and TEC 6219 (343 plants m^-²) in relation to other cultivars.. With regard to the number of ears per m^-², it was observed (Graph 1) that the cultivar TEC 6219 (389 plants m^-²) stood out from the others. This fact is mainly due to the large number of plants per m^-² of this cultivar. The Amethyst cultivar (389 plants m-²) was the only one to have a smaller number of ears than the number of plants. This is possibly due to the death of some plants due to biotic or abiotic factors, or some plants did not produce ears due to some stress caused to them. However, it should be noted that the number of ears per m^-² is a characteristic dictated mainly by the tillering of the wheat. This, however, is essential to achieve uniformity in areas where there were problems with sowing or germination/emergence of plants. According to VALÉRIO (2009), tillering is a characteristic responsive to a set of factors, including genetics, availability of light and water, sowing density, nutrition, among others. 

Graph 2 presents the values ​​referring to productivity and hectoliter mass (MH) (kg/hl). The hectoliter mass is characterized as an indirect measure of the flour yield at the time of grinding. This value represents the amount of reserves in relation to the surrounding layers, together with the accommodation of starch and proteins in the endosperm cells. Therefore, this measure is used due to its speed and simplicity of determination, responding as an indirect assessment of grain quality (MUNDSTOCK, 1999). In Brazil, wheat is sold using MH equal to 78 kg/hl as a reference value. However, varietal characteristics, poorly formed grains and impurities in the lot determine a low MH value. Another factor adverse to MH is rain at the time of harvest, which according to (MUNDSTOCK,1999) lowers MH progressively and substantially in a short space of time.

It is observed (Graph 2) that even the BRS 327 cultivar (72 kg/ hl), which obtained the highest MH value, did not reach the basic value considered, 78 kg/ hl, which highlights the serious problem of high and subsequent rainfall rainfall at the time of harvest, in the first half of October 2015.

Analyzing the productivity values, it was observed that the cultivar BRS 327 (3056 kg/ha) obtained a better result than the others. This cultivar was also part of the group of cultivars with superior productivity in the State Trial of Wheat Cultivars in 2014 for the central region of Rio Grande do Sul (AIRES et al., 2015). However, it is noteworthy that productivity is a quantitative characteristic with strong genetic control, resulting in a high dependence on the management adopted by the producer and on environmental conditions during the cycle. 

However, when comparing the average productivity of the experiment with the average of Rio Grande do Sul in the same harvest, a superiority of the experiment of 47% is observed (CONAB, 2016).

With regard to the variable mass of 1000 grains, it can be seen (Graph 3) that the cultivars Sintonia (35,5 g), Prisma (35,3 g) and BRS 327 (34,45 g) stood out. the rest. However, it should be noted that this component is strongly influenced by the photosynthesis that the plant carries out through its green organs. Thus, the importance of plant health from the beginning of its development is emphasized. Furthermore, it should be noted that this variable has a high level of importance for the industry, which uses it for grain classification purposes, with the purpose of homogenizing the batches and ensuring the least loss by machines. (GUTKOSKI et al., 2007).

Finally, it should be noted that an environment conducive to good cultural and phytosanitary management provides the ideal conditions for maximum expression of the cultivar. However, for this, it is extremely important to choose the correct cultivar for each region. From the data presented, it is inferred that the cultivars, among those tested, most suitable for cultivation in the central region of Rio Grande do Sul, are BRS 327, Quartzo, Toruk, Iguaçu and Parrudo, as they present greater grain productivity and have A satisfactory hectoliter mass was obtained, taking into account climatic adversities at the time of harvest. However, it is always necessary to keep in mind the strong genetic control that is imposed on productivity, causing it to be highly dependent on the management adopted by the producer and on environmental conditions during the cycle. 

Luiz Fernando Teleken Grando, Luiza Kohler Durlo, Alex Taglia Pietra Schonell, Thomas Newton Martin, UFSM

Article published in issue 205 of Cultivar Grandes Culturas.