Viruses

Q) My favorite orchid has unsightly color streaks on the flowers and I’m worried. What could this be?
Nate D.

A) Mere mention of the words Odontoglossom Ring Spot or Cymbidium Mosaic send chills through
most growers for these are dreaded orchid viruses with no known cure. Symptoms include streaky
leaves and flowers as well as compromised plant vigor. In most cases, the affected epiphytes are thrown
out.

 

 

Healthy orchids are free of all plant viruses whose symptoms can
include loss of vigor and unsightly markings in the foliage and flowers.

There are about two dozen known viruses in the world that affect orchids according to Plant Pathologist
Beth Lamb, who specializes in Virology. She presented her latest findings at the 2 nd Annual Cattleya
Symposium in Florida earlier this month. Most of the viruses are of only regional importance or
relatively obscure with few reported cases. However, 99% of the cases involve just two types:
Odontoglossom Ring Spot (ORSV) and Cymbidium Mosaic (CyMV).

 

While mites, nematodes, and flying insects such as thrips and aphids transmit many plant viruses, Lamb
explained that lack of sanitation is the primary reason for infection of ORSV and CymV. “Contaminated
tools, hands, stakes, clips, pots, etc cutting into or incidentally creating physical wounds on a previously
healthy plant” is the main culprit. In addition, water dripping from an infected plant onto a clean plant
can also act as a vector.

 

Prevention is the best practice and it starts with sanitation of all potting apparatus and tables. Prepare
a bucket of 90% water and 10% household bleach and soak used pots for an hour. Cutting tools, such as
clippers and knives, require only 10 minutes soaking. Then rinse with clean water. Some growers wear
thin surgical gloves and change them after every re-potted plant. Brand new pots, stakes, and clips are
inherently disease free.

 

Heat-treating cutting tools is also a recognized sanitizing technique. It is common to use a propane
torch to flame an instrument. Large commercial nurseries often use a boiler-fed steam chamber for high
volume applications. I have childhood memories of my father ‘baking’ his clay pots in the kitchen oven
for an hour at 300 degrees F. The distinct smell of ‘cooking clay orchid pots’ permeated the entire house
for days!

 

The question of whether a virused plant should be kept depends on the owner. For a casual grower
with just a few plants, it probably isn’t a big deal. But for a serious grower with a valuable collection, a
single infected specimen is a threat to the entire plant population. There are instances, however, where
historical and/or sentimental value as well as breeding potential warrant keeping a virused orchid. In
such a case, the designated plant is well separated from the rest of the collection. My father always
keeps a small number of virused ‘stud’ plants – some of which are up to 100 years old – and uses them
to make new hybrids. He employs a breeding method called dry seed pod harvesting so as to obtain
healthy seedlings.

 

There is an inexpensive test kit called ImmunoStrip that provides accurate virus results. A leaf tip about
the size of a quarter is cut and crushed in a small mesh bag. A sensor strip is then inserted into the
bag. Within 30 minutes, the strip shows ORSV, CymV, both, or neither. This kit is available through
www.agdia.com.

Date: 
Wednesday, August 1, 2012 - 17:00