NC State and USDA Cucumber Disease Handbook
Root-knot Nematodes
Disease:
Root-knot
Pathogen:
Meloidogyne spp., Meloidogyne incognita, M. javanica,
M. arenaria, M. hapla.
Source:
K. R. Barker, Plant Pathology Department, North Carolina State
University,, Raleigh, NC, 27695-7616.
Storage:
Root-knot nematodes must be maintained on live plant material,
since they are obligate parasites. It is necessary to reculture
them every 70-90 days. Usually they are maintained in the greenhouse
on 'Rutgers' tomato.
Inoculum Increase:
To maintain pure cultures, egg masses are picked from roots of
infected plants and placed into a small beaker (50 mL) containing
tap water. The beaker is then placed under a dissecting microscope
to make sure eggs are viable. Ten to fifteen egg masses are placed
under a 'Rutgers' tomato plant as it is being transplanted into
a moist, sterilized 1:1 sand:soil mixture. Another method that
can be used is inoculating plants with eggs that were extracted
from roots using NaOCl (described later). Usually takes 3-4 months
before inoculum is ready to use.
Inoculum Preparation:
Inoculum is prepared according to the method described by Hussey
and Barker (1973). Inoculum is prepared by first cutting infected
roots of a given species/race into 2-4 cm pieces. A 1% NaOCl solution
is then poured over roots and stirred for four minutes. This solution
is poured into a 40-mesh sieve located over a 10-liter bucket
and rinsed with cold tap water, thus washing eggs into the bucket.
The bucket is partially filled to obtain 2.5 liters of solution.
Then the water and eggs in the bucket are poured into a 500-mesh
sieve while vibrating the sieve against the side of the sink.
The 500-mesh sieve was then turned over and eggs were washed back
into the bucket and filled with 2.5 liters of water. After doing
this twice, eggs were washed to one side of the sieve and washed
into a 1-liter plastic beaker. This process of preparing eggs
to use as inoculum is done several times to obtain enough eggs.
Quantification:
The number of eggs contained within the solution was determined
by taking a 5-ml sample of eggs from the well-agitated solution
in a 1-liter beaker, and placing it into 95 ml of tap water. Five
ml of this solution is decanted into a counting dish and placed
under a dissecting microscope. The number of eggs contained within
a half-dish are counted and then multiplied by 8000 to get the
total number of eggs in the stock solution.
Inoculum Distribution and Delivery:
Seeds must be planted into a 1:1 soil:sand mixture. Plants are
ready to be inoculated when they reach the 2 to 3 true leaf stage.
The inoculum must be standardized (200 eggs/ml) to allow each
plant to be inoculated with 25 ml of solution for a total of 5000
eggs. This is accomplished by placing 1 million eggs in 5 liters
of water. Twenty-five ml of solution is removed from the bucket
and placed on the soil around the base of each plant (1 plant/pot).
The solution must be kept well agitated to prevent the eggs from
falling to the bottom of the solution during inoculation. After
all plants are inoculated, 13 mm of a 1:1 moist, sterile sand:soil
mixture is placed on top of the soil in each pot to protect eggs
from desiccation.
Host:
Cucumis sativus L., cucumber.
Source of Resistance:
LJ 90430 (M. arenaria races 1 and 2, and M. javanica)
Southern Pickler (M. arenaria race 2)
Controls:
Sumter, SMR-18 (susceptible)
Disease Response:
First symptoms are apparent 5-7 days after inoculation; however,
these symptoms are below ground. After 10-12 weeks rate plants
individually according to the gall index rating system. This is
a system that rates roots by the percentage of the root that are
galled, varies from 0% to 100%.
|
