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The potential yield of wheat is mainly determined by temperature, solar radiation and the photothermal quotient. The objective of this study was to determine the temporal and spatial variability of the photothermal quotient and the frost risk to identify suitable sowing dates for wheat in Parana State, Brazil. The results showed that the photothermal quotient has greater spatial variability than temporal variability. The sowing date affects crop conditions that can in turn affect yield. However, the photothermal quotient and frost risk fluctuate differently in different Value for Cultivation and Use (VCU) regions. The regions VCU 1 and VCU 2 showed greater temporal variability of the photothermal quotient. The photothermal quotient ranged from 1.5 to 2.0 MJ m-2 day ºC in VCU 1, from 1.1 to 1.5 MJ m-2 day ºC in VCU 2 and from 1.0 to 1.2 MJ m-2 day ºC in VCU 3. Sowing performed in June provided the greatest photothermal quotient in all VCU regions. However, June sowing increased the frost risk in VCU 1. Thus, the sowing date can be used as a management tool for the attainment of higher yield in wheat.

Choosing the right sowing dates can maximize the outcomes of the interaction between genotype and environment, thus increasing grain yield and baking quality of wheat (Triticum aestivum L.). The present study aimed at determining the most appropriate sowing dates that maximize grain yield and baking quality of wheat cultivars. Seven wheat cultivars (BRS 179, BRS Guamirim, BRS Guabiju, BRS Umbu, Safira, CD 105 and CD 115) were evaluated at four sowing dates (the 1st and the 15th of June and July) in two harvesting seasons (2007 and 2008). The study was setup in a completely randomized block design with four repetitions. The effects of the year and sowing date when combined explained 93% of the grain yield variance. In 2007, the CD 105 and Safira cultivars had the highest grain yield (GY) for all sowing dates. Only the BRS Guabiju and Safira cultivars possessed high baking quality for all sowing dates assessed. In 2008, the environmental conditions were favorable for superior GY, but the baking quality was inferior. Considering adapted cultivars and sowing dates, it is possible to maximize grain yield and baking quality of wheat.

Understanding the environmental factors that influence genotype performance is an important step in a breeding program because large interactions can complicate the identification and recommendation of superior cultivars. The objective of this study was to evaluate the effects of years, locations and sowing dates on the performance of wheat genotypes in two growing regions of the State of Paraná, Brazil. The grain yield data for 17 wheat genotypes at two locations (Cascavel and Palotina, PR) over five years (2007 to 2011) for three sowing dates at each location in each year were used. Analyses of joint variance were performed, and the repeatability,adaptability and stability statistics of the genotypes were calculated for the different sowing dates. The effects of years (24.3%) and locations (12.5%) had greater contributions to the genotype-by-environment interaction (GEI), and the effect of the sowing dates contributed less (7.0%) to the GEI. To identify superior wheat genotypes with regard to grain yield with 80% precision, a total of 21 trials distributed across different years, locations and sowing dates must be used. The trials for the evaluation of wheat genotypes must include a greater number of years and lower numbers of sowing dates and locations. The CD 105, CD 114 and CD 150 cultivars at Cascavel and the CD 150, Onix and CD 119 cultivars at Palotina were shown to be stable and broadly adapted across different sowing dates, with high grain yield.

Understanding the environmental factors that influence genotype performance is an important step in a breeding program because large interactions can complicate the identification and recommendation of superior cultivars. The objective of this study was to evaluate the effects of years, locations and sowing dates on the performance of wheat genotypes in two growing regions of the State of Paraná, Brazil. The grain yield data for 17 wheat genotypes at two locations (Cascavel and Palotina, PR) over five years (2007 to 2011) for three sowing dates at each location in each year were used. Analyses of joint variance were performed, and the repeatability,adaptability and stability statistics of the genotypes were calculated for the different sowing dates. The effects of years (24.3%) and locations (12.5%) had greater contributions to the genotype-by-environment interaction (GEI), and the effect of the sowing dates contributed less (7.0%) to the GEI. To identify superior wheat genotypes with regard to grain yield with 80% precision, a total of 21 trials distributed across different years, locations and sowing dates must be used. The trials for the evaluation of wheat genotypes must include a greater number of years and lower numbers of sowing dates and locations. The CD 105, CD 114 and CD 150 cultivars at Cascavel and the CD 150, Onix and CD 119 cultivars at Palotina were shown to be stable and broadly adapted across different sowing dates, with high grain yield.

Wheat plants use different strategies for achieving grain yield. Among them, one can point out the compensatory mechanisms among the grain yield components: number of ears per unity of area, number of grains per ear and grain weight. Grain yield in wheat is mostly represented by tiller production, providing that plants are adequately spaced from each other and that weather conditions are favorable to stimulate tillering. Thus, it is necessary to understand the different factors that are related to tiller production and development. The signalling pathways and the morphophysiological responses to environmental factors such as light quality, soil fertility and water availability are also important. The correct adjustment of these factors, as presented in this review, is essential for maximizing grain yield. In the breeding programs it is important make efforts to use genotypes with low number of tillers, even with a higher number of seeds per hectare, to maximize grain yield, reducing the dependence on environmental variables., As plantas de trigo utilizam estratégias diferenciadas para a composição do rendimento de grãos. Entre elas se destacam os mecanismos compensatórios entre os componentes do rendimento de grãos: espigas por unidade de área, grãos por espiga e massa de grãos. A produção de grãos em trigo é representada, em grande parte, pela produção de afilhos, desde que as plantas estejam suficientemente espaçadas entre si e haja condições climáticas e de manejo adequadas para estimular um adequado afilhamento. Portanto, se faz necessário o entendimento dos diferentes fatores relacionados à produção e desenvolvimento de afilhos, desde o conhecimento das rotas sinalizantes até as respostas morfo-fisiológicas dos genótipos aos fatores de ambiente, principalmente da qualidade da luz, da fertilidade do solo e da disponibilidade hídrica. O ajuste correto desses fatores, conforme abordado nesta revisão, é de fundamental importância para a maximização da produtividade de grãos. Além disto, parece evidente a necessidade de esforços no melhor aproveitamento de genótipos com reduzido número de afilhos, mesmo com um maior gasto de sementes por hectare, buscando-se a maximização em rendimento de grãos e uma menor dependência das variáveis de ambiente.