Quantificação de inóculo e variabilidade de Sclerotinia sclerotiorum em sementes de soja e feijão

Abstract

The causal agent of white mold (Sclerotinia sclerotiorum) is considered one of the most important pathogens in the world, distributed in all producing regions, whether temperate, subtropical or tropical. This can cause disease in more than 200 plant genera, including 408 species of hosts. The pathogens can be transmitted through the seeds by means of dormant mycelium or through sclerotia mixed seeds, these are structures of resistance difficult to eradicate after being introduced into the area. The objective of this work was to evaluate the interaction of S. sclerotiorum with soybean and bean seeds in four different inoculum potentials (P24 -24h, P48-48h, P72-72h and P96-96h) and their quality by means of germination, vigor, sanity, besides verifying the location of the pathogen and the quantification of the inoculum in the parts of the seeds inoculated artificially and evaluated by the real time PCR technique, validating the term inoculum potential; and to detect and size the genetic variability of S. sclerotiorum isolates from different bean lots and from different seeds from the same lot from Minas Gerais state. In relation to the quality and effects of the fungus on seeds of the species under study, four potentials of pathogen inoculum in the two cultures (soybean and beans) were used, being evaluated: germination, electrical conductivity, fungus incidence by the neon method, (IVE), initial booth, final stand and dry matter, and molecular analysis by means of real-time PCR for whole seeds and dissected in integument and embryo. From the observed results, it was possible to verify that there was a correlation between the inoculum potencies and the variables analyzed for soybeans and beans, since in the higher potential (P96) it was possible to observe more severe damage in the seeds and consequently in the emerged plants. By the analysis of qPCR, it was observed that the DNA concentration of the fungus in the seeds was increasing according to the increase of inoculum potential and located in the parts that make up the seed. Regarding the variability, 103 isolates of S. sclerotiorum collected from bean seeds were characterized by colony staining, sclerotia production, mycelial growth rate index in neon medium (IVCMN), mycelial compatibility groups (GCMs) and Rep-PCR markers (REP, ERIC and BOX). The isolates of S. sclerotiorum evaluated showed broad genetic variability according to the evaluated characteristics. The predominant adult colony staining among the isolates was beige, representing more than 70% of the isolates. IVCMN and the production of sclerotia, had maximum growth above 40 mm/day and their maximum production of sclerotia was 90.66 per plaque. By GCM analysis, the isolates were grouped into nine clusters. The REP, ERIC and BOX primes separated the populations into six clusters whose AMOVA results confirmed that the greatest variability of S. sclerotiorum found was within bean seed lots.