Mofo-branco em algodão, girassol e feijão: potencial de transmissão e efeitos na qualidade de sementes e variabilidade do patógeno

Abstract

Sclerotinia sclerotiorum is a pathogen causing disease in several economically important plant species worldwide. The infection of plants may occur through the mycelium or ascospores produced by the germination of sclerotia or mycelia associated with seed. These types of inoculum are responsible for the spread of the fungus to short and long distances. In this work, the objectives were to evaluate the effects and potential transmission and molecular detection through conventional PCR of S. sclerotiorum on cotton and sunflower seeds and variability among isolates collected in bean fields. Regarding the effects and transmission of the fungus four inoculums potentials, two cultivars of each, cotton and sunflower and two temperatures (20 and 25 °C) were used in this research. The variables analyzed were: germination, seed health, emergence rate index, initial and final stands. In relation to variability, 25 isolates of S. sclerotiorum collected in bean fields were characterized by microsatellite markers, mycelial compatibility groups (MCGs), aggressiveness and sensitivity to fungicides. From the results, there was a correlation between the level of inoculum potential and the variables analyzed, regardless of cultivar, fungal isolate and temperature. The highest potential for transmission of S. Sclerotiorum on seeds to plants was observed at the highest potential inoculum (96 hours of fungus covering seeds) reaching mean levels of 72% and 80.2% in sunflower and cotton, respectively. The detection of the fungus on seeds of both species by conventional PCR was shown to be viable and should be further evaluated for official use in certification programs. Microsatellite data grouped the 25 isolates into four clusters and seven GCMs. As for aggressiveness within and among GCMs were no significant differences among the isolates. The most aggressive isolates in resistance screening will be helpful in the identification of higher levels of resistance in bean germplasm/lines. Iprodione inhibited the mycelial growth of S. Sclerotorum at the concentration used in the field, whereas pyraclostrobin and metconazole allowed the growth of the fungus in vitro. These results demonstrate the importance of the mycelial inoculum of S. sclerotiorum both the spread of the pathogen as the causal agent of damage to the host species in cultivation condition.