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

Abstract

ABSTRACT: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.

Transmission potential of Colletotrichum lindemuthianum (race 65) in association with bean seeds under controlled conditions

“…Siqueira et al (2014;2016) report that transmission rates of the fungi S. macrospora and S. maydis in asymptomatic plants of maize were higher in the plant root collar region than in the top leaf node region. In contrast, Zancan et al (2015) did not observe the presence of S. sclerotiorum in tissues of asymptomatic sunflower plants grown from infected seeds.…”

“…At the temperature of 26 °C, the total transmission rate was 56% (Figure 4). Pathogens in other pathosystems, such as Sclerotinia sclerotiorum in common bean seeds and S. macrospora and S. maydis in maize seeds, led to total transmission rates at varying levels, depending on the growing temperature and inoculum potential (Siqueira et al, 2014;Siqueira et al, 2016;Zancan et al, 2015).…”

Quantification and conceptual validation of the inoculum potential of Sclerotinia sclerotiorum in soybean and bean seeds

“…phaseoli in beans, Stenocarpella maydis in corn, S. sclerotiorum in beans and sunflower, were reported in the literature as responsible for causing severe damage to the performance of seeds when subjected to longer periods in contact with the fungus. Consequently, germination and vigor tests showed a significant reduction (Costa et al, 2003;Siqueira et al, 2014;Guimarães et al, 2017;Botelho et al, 2013;Zancan et al, 2015).…”

“…In addition to its devastating nature, S. sclerotiorum is a fungus that associates with the seeds of its hosts in the form of sclerotia or as a dormant mycelium inside infected seeds. In this condition, some studies have demonstrated the transmission of the pathogen by soybean and bean seeds, with variable transmission rates on the basis of factors such as temperature, inoculum potential and genotypes (Zancan et al, 2015).…”