Caracterização de danos causados por pentatomídeos (Hemiptera: Pentatomidae) no rendimento e qualidade de sementes de cultivares de soja

Abstract

Insects of the Pentatomidae family (Heteroptera), known as phytophagous stink bugs, stand out among soybean pests [Glycine max (L.) Merrill] because they severely affect yield and physiological quality of grains / seeds. The study aimed to analyze the population fluctuations of pentatomids during the reproductive period of three soybean cultivars, used in commercial crops in the city of Itaqui - RS, and their influence on the reduction of grain yield and seed quality. The study was carried out under field conditions in the West Border of Rio Grande do Sul, in the couty of Itaqui ("29º 07 '31" S "56º 33' 11" W), in the 2016/17 harvest, in three soybean commercial crops, using the cultivars GMX GUAPO RR, 63i64 RSF IPRO and SYN 13561 IPRO. The population of pentatomides in the areas was raised weekly from phenological stage R1 (beginning of flowering) to R8 (physiological maturation). To quantify and compare yield-related damages, the variables analyzed for each cultivar were: weight of one thousand healthy grains (PMGS), grains with punctures (PMGP) and grains without filling (PMGC); average weight reduction, in milligrams, of sting grains (RMP) and without filling (RMC); and average weight reduction, in percentage, of the grains when chopped (RPP) and without filling (RPC). To evaluate the damage of stink bugs related to the quality of soybean seeds, the seeds classified as healthy and chopped were submitted to the following evaluations: first germination count (GPC); standard germination (G); seedling vigor (VG); sand germination (GA); emergence of seedlings (E); emergency speed index (IVE); mean length of seedlings (CMP); dry mass of seedlings (MSP) and green mass of seedlings (MVP). The Piezodorus guildinii species was highlighted, with 60% of the stink bugs sampled, followed by Euschistus heros (21.2%) and Dichelops furcatus (10.3%). All cultivars presented a significant reduction in the weight of one thousand grains when harmed by pest damage, with an average reduction of 22.66% in grain weight for GMX GUAPO RR and 11.23% for SYN 13561 IPRO, when chopped. The average reduction in the production of chopped grains for the three cultivars studied was 113.03 kg ha-¹ and 456.79 kg ha-¹ for grains without filling, ranging from 303.67 kg ha-¹ for GMX GUAPO RR and 701.46 kg ha-¹ for cultivar SYN 13561 IPRO. In general, the average reduction in grain yield among the cultivars was 0.634kg ha-¹ in the addition of one chopped grain per meter and 3.22 kg ha-¹ reduced when there was increase of one grain without filling per meter in the row of the culture. Seed germination was affected by the damage caused, with a reduction of 41.75% for the cultivar GMX GUAPO RR, and 8.75% for cultivar SYN 13561 IPRO. Still for the cultivars GMX GUAPO RR and SYN 13561 IPRO, seedling vigor decreased by 31.5 % and by 23.75%, respectively.