ASPECTOS EPIDEMIOLÓGICOS DE Sclerotinia sclerotiorum NA CULTURA DA SOJA E OTIMIZAÇÃO DE MÉTODO DE DETECÇÃO DE ASCÓPOROS VIA PCR EM TEMPO REAL

Abstract

The white mold disease (Sclerotinia sclerotiorum) is present in most of the soy producing regions of Brazil. It is a disease that is difficult to control due to its resistance structures, and as there are no resistant varieties and fungicides that act directly in the control of sclerotia in the soil, models or systems for predicting diseases for S. sclerotiorum help to determine the risk of the occurrence of disease. The pathogen has 4 types of propagules: sclerotia, apothecium and ascospores, infected petals and infectious hyphae. However, the main route of infection is by ascospores in floral tissues. In the first chapter, the study of the development of S. sclerotiorum epidemics in soybean was carried out. Fifty-two epidemics were studied and represented a wide variation in disease progress curves. Epidemics were analyzed using different statistical techniques and were separated according to the similarity in the development of the disease in three groups (A, B and C). Group A is composed of epidemics of slow establishment and with a low rate of development, causing epidemics with low incidence and severity of the disease. While group B and C, it is composed of intermediate and high epidemics, respectively. Considering the importance of studying the pathogen in the population and the fast and efficient detection of S. sclerotiorum ascospores in the field in the second chapter, three methods of DNA extraction from S. sclerotiorum ascospores were evaluated to optimize detection via PCR (Polymerase Chain Reaction) quantitative (qPCR). Ascospores were obtained with the aid of an automatic spore collector (Burkard) in the 2016/17 harvest in a commercial soybean crop infested with S. sclerotiorum sclerotia. For the choice and optimization of the methodology, the DNA of each sample was extracted and its quantity was measured via qPCR. The standard curve was determined from samples of ascospores collected in the laboratory. The Kurtgma & Fell (1998) and Reader & Broda (1985) extraction method was the most efficient in extracting DNA from Sclerotinia sclerotiorum from ascospores. Optimizing the detection and quantification of ascospores using qPCR are useful practices to guide preventive measures and the management of white soybean mold, as well as assist in the development of disease prediction models.