Interação com sementes de soja e sensibilidade de Phytophthora sojae a fungicidas in vitro

Abstract

The transmission and dissemination of Phytophthora sojae regarding soybean seed still remain as aspects that are poorly understood, and that they are of extreme importance in the epidemiological scope of this pathosystem. It is known that Phytophthora rot, caused by this pathogen, has been reported in a large area of soybean production in Brazil. The purpose of this work was to evaluate, under controlled conditions, the relationship of P. sojae with soybean seeds, with the main focus on evaluating the potentiality of transmission of the pathogen from plant to seed and to verify the efects and viability and longevity of this organism in seeds after harvest. It was also the purpose of this study to evaluate the sensitivity of P. sojae to some fungicides in experimental phase in Brazil aiming at the use of them in soybean seed treatment. For these studies, an isolate of P. sojae and three soybean cultivars considered susceptible to phytophthora rot were used. The transmissibility of the pathogen from inoculated plants/pods to seeds was evaluated using two inoculation methods in a greenhouse. The evaluations were carried out by using sanity and standard germination tests. To evaluate the effects and viability of P. sojae from inoculated seeds under controlled laboratory conditions, it was used the technique of water conditioning with two levels of inoculum, equivalents to the exposure of seeds to colonies of the pathogen for 48 and 96 hours. The effects of the pathogen were evaluated by the emergence test in organic compost amended with sand and the viability by the health test by plating fragments of the emerged plants. For the fungicide sensitivity test, three products with distinct active ingredients and two commercial products already registered for oomycetes and one isolate of the pathogen were used. Evaluations were made by daily measurements of mycelial growth diameter and observations of morphological characteristics of the colonies developed during the incubation period. The results of this study revealed that P. sojae was not detected in seeds harvested from inoculated pods at two developmental stages. Transmission of the pathogen from seed only occurred in freshly inoculated seed, and there was no viability of the pathogen in dry seed evaluated after the first month of storage. From freshly inoculated seed, the pathogen was able to cause significant damage to seed performance and emerged plants. By testing the sensitivity of P. sojae to fungicides, the results showed that Oxathiapiprolin was the most effective ingredient in reducing the mycelial growth of P. sojae comparable to Maxin Advanced and Apron. Such product is a potential alternative for formulation of commercial products that may be used by farmers in the treatment of soybean seeds.