Variação e efeitos de potencial de inóculo natural de Drechslera oryzae e Phomopsis sojae em lotes de sementes de arroz e soja

Abstract

Being considered one of the most important inputs in Agriculture quality of seeds is of extreme relevance for the success of all crops which are propagated by that mean. The qualification of seed lot is based on information about genetics, physiology, physics and sanitary aspects. Health condition of a seed lot may be a serious problem to obtain high yields in addition to other damages related to sustainability of the agricultural activity. for the farmers. productivity o qualify a seed lot. The detection and quantification of inoculum of phytopathogenic agents in seeds can support farmers with basic information which may help them in preventing the introduction and establishment of infectious diseases in the field. The disease development in field depends on several factors of which level of inoculum potential is extremely important. Objective of this study was to evaluate the variation in health quality, represented by the inoculum potential of Drechslera oryzae and Phomopsis sojae in rice and soybean seeds. The seed lots were selected based on the percentage of occurrence of the fungi of interest, verified by modified Blotter test. The intensity of fungal colonization on the seed surface was performed using Blotter test with the addition of Mannitol at -1.2 MPa for rice and -1.0 MPa for soybean, giving rise to a scale of grades where established: 0 without the presence of the pathogen, 1 to 10% fungal coverage, 2 for seeds with coverage between 10% and 50% and grade 3, for seeds with fungal coverage above 50%. After the evaluation period the seeds were selected and placed to dry in a natural environment for 48 hours. After this time, they were submitted to standard germination analysis, accelerated aging, electrical conductivity, substrate emergence and transmission evaluation. Both cultures showed differences in inoculum potentials within and between seed lots, where the greatest damage was caused by the highest potentials. A drop in standard germination and an increase in electrical conductivity were observed as inoculum potentials increased. Thus, it is concluded that there is a relationship between inoculum potentials and seed performance and further studies on this subject are needed.