I've wondered about the possibility of there being multiple strains of Erwinia
amylovora. For instance, Ethan has reported that 'Spalding' in Houston blights
badly, but here it's almost completely blight-free. I recognize that Houston may
be one of the few places in the country that are hotter & about as humid as
here in piedmont NC. However, I also considered the possibility that his
neighborhood was inhabited by a more virulent bacterial strain.
That is why I was so interested in Dr. Richard Bell's answer to this question
at the NAFEX meeting in Lexington a few years ago. He stated that there
weren't any known strains of significantly differing virulence. If that's
true, then environment becomes the biggest determinant in susceptibility of a
specific pear cultivar. With some exceptions to prove the rule, there is a
blight gradient that worsens as you go south (in the humid Eastern U.S.).
For instance, 'Honeysweet' and 'Megietsu' blight badly here, but are reported
to be quite resistant in the Mid-West.
'Magness' is known to be blight-susceptible in trunk, but resistant in leaves and flowers. So,
like you've observed, it doesn't wall off infections well when they enter the larger limbs (hail
is the classic injury that inoculates trunks). 'Magness' will produce well here for 10-20 years,
but invariably will blight out in an epiphytotic accompanied by hail. [BTW, my spellchecker
suggests, "Madness" for the word, "Magness". Hmmm.]
Anton
-----Original Message-----
From: fuwa fuwa usagi <fuwafuwausagi@muchomail.com>
Sent: Jul 3, 2009 7:50 PM
To: nafex@lists.ibiblio.org
Subject: [NAFEX] Pears/Fireblight
It was written:
The data on fireblight susceptibility of 'Wilder Early' are mixed. I rather expected my trees to perish quickly when I first grafted them.
My reply:
You might want to consider that fireblight is not a problem rather a series
of problems. Or stated differently it is very likely there are strains of
fireblight.
In my area this infamous Magness does not successfully wall of fireblight, it
consumes the tree. On the other hand Harrow Sweet, Harvest Queen, and
Potomac for wall off fireblight when it occurs. Every Magness in my yard had
been lost to fireblight unless it was branch graft on another tree, i.e I
get a few Magness from my Harvest Queen.
On the other hand plain ol' Bartlett does fine here. So do many blight susceptible trees.
tfb
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