PRODUCTION MANAGEMENT RESEARCH FOR HORTICULTURAL CROPS IN THE GULF SOUTH
Location: Southern Horticultural Research
Title: Seasonal Presence of Rhizoctonia Species in Container-grown Azalea
Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: March 15, 2009
Publication Date: August 1, 2009
Citation: Copes, W.E., Cubeta, M.A., Toda, T., Rinehart, T.A. 2009. Seasonal Presence of Rhizoctonia Species in Container-grown Azalea. Southern Nursery Association Research Conference Vol.54 pg 66-68.
Interpretive Summary: Rhizoctonia web blight annually damages some commonly sold azalea cultivars during summer months in commercial nurseries. It was not known if the fungal pathogen lives year-round on container-grown azaleas or the pathogen can die-off thus the plant become free of the pathogen. Azalea roots, stems, and leaves, and the pine bark substrate were sampled for the presence of the pathogen during December, February, May, June, and July. Rhizoctonia was found to grow on all plant surfaces during all months of the year. The information provides useful knowledge that will be used for devising practical diseaes control practices, which will be useful to nursery producers, extension scientists, and research plant pathologists.
Rhizoctonia web blight has been observed to be regularly distributed across large nursies and randomly distributed in blocks of azalea cultivars of varying susceptibility. The main objective of this project was to determine seasonal changes in the population of binucleate Rhizoctonia species in individual container-grown azaleas. Plants were destructively sampled in December, February, May, June, and July and tissue plated on an agar medium to assess frequency of recovery of Rhizoctonia species. A total of 3600 isolates were recovered over 2 years. Recovery frequency was high from the dead leaves (66 to 98%) at all sample dates. Rhizoctonia species were recovered more frequently from the top 1 1/4 inch of the bark media (17 to 55%) and the lowest 3/4 inch of the plant's trunk (68 to 100%) than from bark media and stem zones at further distances from the dead leaf layer. Recovery levels were lowest in May from the middle and lower zones of bark media and in June from stems in the upper-most canopy. Despite the population decline during early summer, the fungus was recovered from the current year's stems (5 to 20%) in early June, the time when stems are collected for propagation at many commercial nurseries. Our research suggests that once individual container-grown azalea plants become colonized by binucleate Rhizoctonia AG P the fungus persists on bark substrate and on plant surfaces from year-to-year in the container. Future studies will be needed to investigate the potential of eliminating the pathogen from stem cuttings used for propagation and of maintaining disease-free plants throught the production process.