Fábio Henrique Krenchinski

Germination and Dormancy in Seeds of Sorghum halepense and Sorghum arundinaceum

Light, temperature and dormancy are factors that influence the germination of seeds and are strictly linked to the emergence of weeds. The objective of this work was to assess the germination of Sorghum arundinaceum and Sorghum halepense subjected to different conditions of temperature and luminosity, as well as assessing seed dormancy breaking mechanisms. For this, two experiments were conducted, both arranged in a completely randomized design. Experiment 1 was installed in a 2 x 5 double factorial design. The first factor was the absence or presence of light for 12 hours, and the other was composed of five constant temperatures: 15, 20, 30, 40 and 45 oC. In experiment 2, the efficiency of nine treatments used for breaking dormancy of seeds was assessed. The variables analyzed for both experiments were germination percentage and germination speed index (GSI). For the statistical analysis were performed an analysis of variance (ANOVA) and all the necessary consequences, as well as regression, when relevant. In experiment 1 for both species greater germination occurred in the presence of light. For S. arundinaceum the temperatures at which there was the highest percentage of germination were 33.13 and 31.24 oC for presence and absence of light respectively. As for S. halepense these temperatures were 31.98 and 29.75 oC for presence and absence of light respectively. As for the treatments for breaking dormancy, the mechanical scarification of seeds with sandpaper presented the highest germination and GSI. It is concluded that the Sorghum species studied are neutral photoblastic seeds and present mechanical type dormancy.

Behavior of RR soybeans subjected to different formulations and rates of glyphosate in the reproductive period

Recent studies indicate that glyphosate applied in post-emergence in RR soybean can eventually cause phytotoxic effects. However, there are many questions that need to be clarified in the scientific and technical contexts, involving the issue of RR soybeans regarding the use of glyphosate. This study has assessed the impact of the application of different doses and formulations of glyphosate in the reproductive period of RR soybean (R1 stage). For that purpose, an experiment in the field was conducted in two harvests (2011/12 and 2012/13), in which a 2 x 5 factorial design was used (formulations versus doses) totaling 10 treatments. In these two experiments the variables related to agronomic performance were: phytotoxicity (7, 14, 21 and 28 days after application), plant height, number of pods per plant, yield and weight of 100 grains (end of soy cycle). The results obtained allowed characterizing phytotoxicity and damages to the height and yield in RR soybean, with increasing rates of glyphosate applied in the reproductive period.

Rates of Chlorimuron Applied in Glyphosate-Tolerant and Sulfonylurea-Tolerant Soybean

Susceptibility to chlorimuron varies according to soybean genotype. STS® (sulfonylurea-tolerant soybean) presents a high tolerance to some sulfonylureas; this feature is determined by semi-dominants alleles, Als1 and Als2. Experiments were conducted in the field for four seasons with two cultivars for season to evaluate the selectivity of chlorimuron rates in post-emergency (V4) of glyphosate-tolerant and sulfonylurea-tolerant soybean. Data analysis made it possible to infer that there was no significant effect on the productivity of the cultivars when they received application in post-emergency, of chlorimuron at the doses used (0, 15, 30, 45, 60, 75, and 90 g ai ha-1). The maximum recommended rate for non-STS cultivars of chlorimuron is 20 g ai ha-1, or 4.5 times less than the maximum rate employed in this study. The soybean cultivars CD 250 RR/STS, CD 236 RR/STS, CD 2630 RR/STS, and BMX Turbo RR/STS were tolerant to the application, in post-emergency (V4) of the herbicide chlorimuron, until the rate of 90 g ai ha-1.