Wednesday, March 12, 2008
Abiotic stress leading to secondary pathogen invasion on Calibrachoa
Description: Calibrachoa is an ornamental plant related to the petunia but with smaller flowers. It is commonly used in hanging baskets and as a groundcover. It is propogated as cuttings and requires full sun.
Sample showed entire missing seedlings in the liners, leaf spots that began at the margins and tips, and dieback beginning at the base of the plant.
Possibilities: Rhizoctonia root rot, Phytophthora, Pythium
1) moisture chamber-showed extensive Botrytis
2) plating roots and leaves onto acidified water agar (AWA), Phytophthora agar and Pythium agar
3) check soil pH and soluble salts (SS)
4) float leaves in sterile distilled water to see if sporangia develop
1) moisture chamber-extensive Botrytis (common secondary pathogen on ornamentals)
2) plating roots and leaves onto acidified water agar (AWA), Phytophthora agar and Pythium agar-No Rhizoctonia, mixed secondary infections on other agars
3) check soil pH and soluble salts (SS)-within normal range
4) float leaves in sterile distilled water to see if sporangia develop-negative
5) replated roots and leaves onto Phytophthora agar and AWA-negative
Final diagnosis: This is likely abiotic stress (probably nutrient issues) which affected the lower leaves during transplant allowing secondary pathogens (Botrytis, etc) to invade.