Re: CULT: HYB: 450 Known Rotters
- Subject: Re: CULT: HYB: 450 Known Rotters
- From: B* S*
- Date: Wed, 23 May 2001 09:04:01 -0500
Adding to Linda's excellent post on soft rot--most authorities on
Erwinia seem to agree that the bacteria invade only after some kind
of damage takes place. They liquify the plant tissue by producing an
enzyme that dissolves pectins, the cement that holds cells together
and a cell wall component. The contents of the damaged loose cells
are then invaded and digested by the Erwinia and also by other
bacteria. The thing is that the wound can be microscopically small,
like an aphid puncture (hence the suspicion that aphids can transmit
rot), because the bacteria are really minute. So rot often appears
without any VISIBLE injury.
Tissue freezes and borer attacks are probably the greatest avenues
for beginning soft rot. However, I've noticed that if borers are
dealt with while they are still in the leaves, even though a slimy
mess might be present, rot follows only in a small percentage of the
cases. Only when the rhizome itself is damaged does rot seen
inevitable. This would go along with Erwinia's almost universal
presence in the soil.
Also, we seem to be forgetting that there are lots of types of irises
that don't rot at all or do so only rarely--all the beardless types.
Even after mass borer attacks, I have seen little or no rot in
Louisianas. Spurias and Siberians seem totally immune (and, hey, the
spurias are starting a potentially glorious season here).
--
Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
(804)223-6172
FAX (804)223-6374
email<wshear@email.hsc.edu>
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