Relationship between mycelial inoculum of Sclerotinia sclerotiorum and performance of sunflower seeds under controlled conditions

Resumo

The cultivated area of sunflower in Brazil is expanding considerably over the last years as the result of the great interest in the biodiesel production derived from that crop. One consequence of that expansion is the occurrence of several diseases some of devastating nature in part of the growing areas with sunflower. This study evaluated the effects of the association of sunflower seeds infected by Sclerotinia sclerotiorum and the pathogen transmission rates from these infected seeds, considering some factors which may interfere in that interaction. Four inoculum potentials, two isolates of the cited fungus, two sunflower cultivars, 'Helio 250' and 'Helio 253' and two environmental temperatures, 20°C and 25°C, were used for the purpose in this work. Seed germination and health, emergence speed index, and plant populations were variables analyzed. From the results, increased levels of inoculum potentials led to gradual reduction of the mean values of germination, emergence rate index and plant populations, regardless the genotype, fungal isolates and temperatures. Transmission rates were higher at the highest levels of inoculum potential, the maximum reaching 80%. These results show the significance of S. sclerotiorum inoculum associated with sunflower seeds both in the establishment of plants in fields and also in spreading the pathogen inoculum between crop fields.