Re: [Aroid-l] - Serious spreading Amorph disease-Collar rot

---

Dear Adams,
The symptoms described by you are typical symptoms of
Collar rot disease of Amorphophallus caused by
Sclerotium rolfsii. We frequently observe this disease
in India. The Fungus is seed borne and also soil
borne. You might have seen white fungal mycelial
growth and mustard like structures called Sclerotia on
the infected surface. You can use systemic fungicides
like Carbendazim (0.1%) as soil drench to prevent the
disease.
For details, kindly go through my article in Aroideana
vol.26 on Field and Storage diseases of
Amorphophallus.
Sincerely
RSMisra

--- Peter Matthews <pjm@gol.com> wrote:

  

Dear Adam,

Did your garden recenty import Amorphophallus
specimens from SE Asia or
other places where the genus is native? If you could
identify possible
geographical sources, this might help narrow down
the search for a cause.

Also, I wonder if there are any insects that lay
their eggs in the lower
petiole area? In theory, a newly spreading insect
might spread a new or
existing fungus. I do not know of such happening in
Araceae, but it is
conceivable. Taro has taro-specific planthoppers
(Delphacidae) that lay
eggs in the lower petiole, and they are spread with
planting materials
when the petioles are kept attached to the corm.
There might be
planthoppers that are specific to Amorphophallus
(this is speculation).

If  you want, I could try to contacting konyakku
researchers here in
Japan. There would certainly be interested in the
outbreak you describe,
even if it is something new for them. Or they might
immediately
recognise what is happening to your plants. There is
a lot of experience
with intensive production of Amorphophallus here in
Japan.

Good luck...

Peter Matthews



On 8/7/2006, "Adam Black" <epiphyte1@earthlink.net>
wrote:

    

We are suddenly having a severe problem with the
      

Amorphophallus species
    

at the botanical gardens where I work. We are
      

seeing a localized rotting
    

of the base of the petiole an inch or two above the
      

soil line that turns
    

the petiole base to jelly and topples the leaf. It
      

is affecting all
    

three species we have - A. konjac, A. bulbifer, and
      

A. paeoniifolius,
    

and is occurring in various areas of the gardens
      

that are seperated by a
    

considerable distance and have been otherwise
      

healthy in thier locations
    

in the ground for years. I started noticing it in
      

the konjacs and the
    

bulbifers a month or so ago shortly after they put
      

up thier leaves, and
    

the rate of loss has escalated from there. I just
      

now noticed on the
    

late emerging paeoniifolius that most of them have
      

early signs of this
    

infection. I am by no means an expert on fungi, but
      

there are several
    

different colors of fungus on the affected areas,
      

but I am not sure if
    

this is secondary or not. The infection starts out
      

as a brown patch on
    

the base of the petiole a few inches above the
      

soil/leaf litter line,
    

and this progresses around the petiole and inward,
      

but does not spread
    

up or down the petiole from that point. I dug up
      

one corm from an
    

infected A. bulbifer and it appeared shrunken in
      

and clearly unhealthy,
    

felt softer than a healthy corm but no external
      

evidence of rot was
    

evident. I did not cut it open to see what it
      

looked like inside, but
    

plan to on another specimen this week.The base of
      

the petiole below
    

where the leaf had rotted off was still healthy in
      

appearance and firmly
    

connected to the corm.

Curiously, I have yet to see it affect any similar
      

aroids growing
    

side-by-side with affected Amorphs in the gardens
      

including Typhonium
    

venosum (of which we have many plants), Gonatopus
      

bovinii, Remusatia
    

vivipera, and our native Arisaema triphyllum and
      

jillions of Arisaema
    

dracontium. The Amorphs affected include both
      

potted specimens and those
    

situated in the ground for years, and among the
      

potted specimens some
    

affected plants are in a greenhouse with controlled
      

watering, while
    

other potted plants are exposed to the weather in
      

addition to
    

supplemental irrigation. I am keeping a closer eye
      

on it now, but the
    

infection appears to spread and rot through the
      

petiole relatively
    

quickly, so that the leaf itself still looks
      

unstressed and perfectly
    

healthy after it has rotted off. I have only worked
      

here since this past
    

winter, but the gardens director remembers a few
      

Amorphs having this
    

problem last year but didn't think much of it, as
      

the hundreds of others
    

in our mass plantings looked fine. If I had to
      

guess now, I would say we
    

have lost about 60 or so plants with about as many
      

showing the early
    

stages of the infection. It also seems to affect
      

our mid to largest size
    

specimens rather than the smaller plants.

Has anybody seen this before? Any recommendations?
      

I am going to try a
    

fungicide this week, but with the huge number of
      

plants we have spread
    

out all over our 60+ acre gardens, I am worried
      

about how effective any
    

methods will be in controlling this. If anyone is
      

interested I can email
    

photos of affected plants in various stages of
      

infection.
    

Thanks

Adam


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Dr.Raj Shekhar Misra
Principal Scientist & Head 
Crop Protection Division
Central Tuber Crops Research Institute
Sreekariyam, Trivandrum-695017(India)
Mobile Phone No. 91-9446557657
Fax-0471-2590063
Phone-0471-2598551 to 2598554

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