Rusts a follow up note

[Scott Vergara]

Greetings All,

Just a few comments following Paul Christian's comments on Rust.
Yes, rusts are usually quite host specific.  This specificity may be at the
generic or species level, though many cultivars or natural ecotypes may
have some level of tolerance, resistance or immunity.  However the rust
fungi mutate readily forming many strains.  This provides workers in the
Wheat Rust Resistance Breeding programs in the US with job security.

Rust are extremely complicated as a group.  Some having as many as five
spore types infecting two different hosts (heteroecious types).  While
others (autoecious) have two to five spores on one host or only one known
spore type and a single host.

Arisaema rust is caused by Uromyces caladii which has 4 of the spore stages
and has been reported from NY to FL and TX and the Pacific Northwest.
(from the 5th ed. of Westcott's Plant Disease Handbook)

I do not know if there is an alternate host or not. Perhaps some plant
pathologist on the list or on Aroid-L might volunteer more information.

A word of caution. Rust spores are windborne, thus very small and
lightweight.  It has been reported in some species that the spores can
cling to tools, clothing, (hair?) so  those who tromp though infested areas
might not want to come home to their collections and go grubbing about
immediately.

As we bring more and more species together within the range of the pathogen
it may just be a matter of time before strains appear that may cause
serious problems.

Sorry for the gloomy outlook...we pathologist types tend to have a wet
blanket side to us.

Best Regards,
Scott

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Scott Gregory Vergara
Botanical Resources
(Specialty Nursery, Horticulture Education/Training, Consulting)
P.O. Box 669
Burley, Washington  98322-0669   USA
svergara at pacific.telebyte.com     HORTULANUS at aol.com
USDA Zone 8 Ave Min Temp 10-20 deg F. Record low 0/hi 104
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