Integrated Plant Genetics

Geranium blight

The most serious disease of geranium is bacterial blight, caused by Xanthomonas campestris pv. pelargonii. This disease is widespread in the U.S., Europe, Australia and Israel and may cause losses up to 80-100%--- particularly where cuttings are propagated in a large scale. In recent years, even the most diligent breeding companies have experienced losses totaling hundreds of thousands of dollars in direct costs to geranium blight. Sometimes, entire farms must be shut down due to the widespread occurrence of the disease in particular locations.

All commercial cultivars of the florists geranium (Pelargonium hortorum) are susceptible to the blight disease pathogen. Therefore, the only practical method available today for controlling the disease is eradication and the use of "culture indexed" propagating stock (free of pathogen). This requires diligent effort and expensive quarantine and sensitive, reliable and rapid diagnostic procedures.

Since production of pathogen-free geranium cuttings is crucial for the industry, diagnostic laboratories are usually employed in order to establish pathogen-free blocks of geranium, n which each plant is individually tested. The latter serve as the propagating source for geranium nurseries. All nurseries are continuously subjected to culture indexing throughout the growing season until the cuttings are exported. Current diagnostic abilities allow a small, but significant number of false negative reports, resulting in large and unpredictable losses to local nurseries, growers and retailers. Such losses are usually locally confined, but they occur with frustrating regularity.

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