Nightmare on Elm Street. The Elms (genus Ulmus ). - >30 species in genus Europe has 5; N. America 8; Asia has 23 or more. - 2 ssp live in tropics - 6 spps native to the northeastern U.S., including Ulmus americana , the American elm. Many cultivars too.
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- >30 species in genus
N. America 8;
Asia has 23 or more.
- 2 ssp live in tropics
- 6 spps native to the northeastern U.S.,
Many cultivars too.
- New species are still
being found in China,
the center of diversity.
easily transported, tolerant
of soil compaction and
different soil types. Dense
canopy borne high above
ground, few low branches.
planted in rows, they
overhang the street
forming a Gothic-style arch. Good for windbreaks.
ssp of insect are specialized or
dependent on elm. Elm seeds are important.
isolated in 1920 by a
Dr. Schwarz in the
- Wilt disease that
attacks elm (Ulmus ssp);
caused by ascomycete
fungi (genus Ophiostoma,
Vectored bybeetles (fam. Scolytidae) and root graft. Has a saprophytic and a pathogenic stage.
1) Native elm bark beetle (Hylurgopinus rufipes) (above) is the primary vector in parts of the northern United States, New England, and all of Canada.
However, temperatures below -6F kill the larvae.
2) European elm bark beetle (Scolytus multistriatus Marsh.) (below) is the major vector of the disease.
-unknown in Europe and N. America pre-1900. Since then, 2 major pandemics.
-caused by 2 different species:
1) Ophiostoma ulmi
2) Ophiostoma novo-ulmi
(in both cases, geographic origins unknown- probably Asia)
--evolved in tropics vs. temperate
--levels of aggression (O. ulmi is moderate pathogen on European elms, O. ulmi-novo is aggressive. American elms are more susceptible to both). Different levels of the cerato- ulmil protein (see later slide).
--has the pathogenicity gene been transferred from O. ulmi to O. ulmi-novo??
( Et-Touil, Brasier, Bernier. 1999. Molecular and Plant Interactions)
--Gene acquisition of vegetative compatibility (vc) genes from O. ulmi. (occurs only where O. ulmi and O. novo-ulmi coexist or used to coexist, and the virus is present; allow for resistance to viruses.)
--Gene acquisition of virus from O. ulmi? (preliminary data suggests that it’s possible)
-- “swarms of EAN/NAN hybrids are likely to emerge in overlapping sites” (Brasier, 2001)
--so O. novo-ulmi is currently undergoing rapid evolutionary development in Europe (accelerated pathogen evolution when it is released from its endemic environment)
--Ophiostoma quercus (saprophytic on oaks) and O. novo-ulmi?
--Talk about diversity in O. ulmi and O. novo-ulmi