Pathogenic diversity of Sclerotium rolfsii isolates from Mexico, and potential control of southern blight through solarization and organic amendments

Pathogenic diversity and cultural control of Sclerotium rolfsii are two fields of knowledge not well understood. In this work, two onion isolates of S. rolfsii from the States of Morelos and Guanajuato, Mexico were inoculated to 51 plant species and disease severity levels were determined. Subsequently, 12 out of 51 plant species were selected for the determination of pathogenic reaction to 20 isolates of S. rolfsii from different regions of Mexico. Onion isolates from Morelos and Guanajuato produced variable levels of disease severity for half of the plants tested. Five plant species were susceptible or highly susceptible to all isolates. The remaining plants tested showed differential reactions to individual isolates, ranging from highly resistant to highly susceptible. Three organic soil amendments alone or combined with solarization were tested for control of S. rolfsii on microplots containing onion seedlings in naturally infested soil. A combination of solarization and incorporation of Parthenium hysterophorus into soil was effective in reducing damage and sclerotial numbers of S. rolfsii. However, the amendment alone was associated with increased damage and high sclerotial populations.