Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop Progress Report — September1996
in Flower Crops
Investigate the epidemiology of powdery mildew. Areas recently
addressed include the epidemiology of powdery mildew on poinsettia with
emphasis on the events occurring after the conidia (spore) lands on the
plant and the effects of heat treatments on the germination of conidia.
For time series experiments which documents the appearance and development
of fungal structures, leaf disks were inioculated with conidia and observed
2, 6, 12, 24, 36, and 48 hours after inoculation using light and electron
microscopy. Data from this experiment, performed twice, indicate that appressoria
(the structure that powdery mildew uses to penetrate the plant) can develop
two to six hours after the conidia lands on the plant. After six hours,
most germinated conidia have formed primary appressoria. Primary haustoria
(the structure that powdery mildew uses to absorb nutrients from the plant),
as well as additional germ tubes, developed 12 to 24 hours after conidia
land on the plant. The heat treatement experiment involved leaf disks with
conidia that were exposed to 20 and 30 C. A higher percentage of conidia
germinated at 20 than 30C. Heat did not affect the production of the primary
appressoria, but had a significant inhibitory effect on the production
of primary haustoria and additional germ tubes.
Future plans. Expand research on the environmental and cultural
factors affecting disease development of Botrytis, downy mildew, and powdery
mildew on gerbera, delphinium, snapdragon, and rose, expand efficacy trials
and develop grower recommendations.
