Influência do tempo de contato de Sclerotinia sclerotiorum em sementes de girassol

Abstract

Sunflower is one of the most cultivated oilseeds on all continents because it is more resistant to heat and cold. Some diseases are considered as one of the main factors in the decline of production, among them the white mold caused by Sclerotinia sclerotiorum, because it is distributed in all the producing regions. Plants infected with the pathogen may lose their viability in the seedling stage, and pre and post-emergence tipping may occur. The objective of this work was to evaluate the influence of the contact time of the fungus Sclerotinia sclerotiorum with the sunflower seeds, before sowing, on the symptoms of the disease in the plants. The experiment was carried out at the Laboratory of Phytopathology and Soil Microbiology of Unipampa - Itaqui Campus. The experimental design was completely randomized, with four replicates being each experimental unit composed by gerbox containing 10 plants. The fungus was peeled into the BDA (Potato-dextrose-agar) culture medium and the plates were kept in a BOD heated chamber at 22 ° C for 7 days. After the fungus developed throughout the plaque, 160 sunflower seeds were seeded on the fungus and 40 seeds were divided per plate. After the fungus developed throughout the plaque, 160 sunflower seeds were seeded on the fungus and 40 seeds were divided per plate. The plates were placed back in the heated chambre. The seeds remained in contact with the fungus for up to 24 hours, and the seeds were removed in the times of 4h, 8h, 12h and 24h, using as a control the time 0h, using seeds that were not in contact with the pathogen. The seeds at time 0h (control) were sown directly in the gerboxes, filled with commercial substrate, being 10 seeds per gerbox. After 4h, 8h, 12h and 24h, 40 seeds were removed that were in contact with the fungus of the plates and were sown in gerbox, with the same procedure performed in the control treatment. Subsequently, they were irrigated and the gerboxes were covered with plastic to maintain moisture. The gerboxes were kept at room temperature on counters. The evaluation was performed daily, counting number of emerged plants per day, number of healthy plants and number of plants registered. Seeds that remained in contact with the pathogen for 4h and 8h emerged in the proportion of 65% and 25%, but post-emergence tipping of 81% and 80% occurred. In those that were in contact with the pathogen during 12h and 24h, preemergence tipping of 87.5% and 100% occurred, however in the one that was in contact with the pathogen for 12h, a 100% post-emergence tipping occurred. It is concluded that the longer the contact time of the fungus with the larger seed is the percentage of pre-emergence tipping, directly influencing the stand of the sunflower crop, according to the conditions of this work.