Cucurbit Genetics Cooperative Report 7:92-93 (article
The Reliability of a Seedling Test for Resistance to Root-Knot
Nematodes in Cucurbits
Boukema, I.W., G.T.M. Reuling and K. Hofman
Institute for Horticultural Plant Breeding (IVT), P.O.B. 16, 6700
AA Wageningen, The Netherlands
A seedling test is used to screen for resistance to root-knot
nematodes (Meloidogyne incognita Chitw.) in cucurbits (1).
The level of resistance is measured by determining the mean
number of root-knot galls per plant. To verify whether this
seedling test gives a reliable prediction of the resistance
level, the reaction of four Cucumis species (Table 1),
which showed different levels of resistance in former tests, was
compared in a) the seedling test, and b) a test which approaches
more the glasshouse situation (pot test).
The seedling test (1) was carried out in a growth cabinet at 24 C
in five replications of eight plants per plot. Each seedling was
inoculated with 50 larvae. After five weeks the number of galls
per plant was counted and the pooled larvae production per plot
was determined by hatching larvae from egg masses on the roots.
The roots were therefore cut up and placed on nematode filters in
tap water at room temperature.
The pot test was carried out in a glasshouse at a minimum
temperature of 20 C, rising to 25-28 C on sunny days. Cucumis seedlings were transplanted to pots containing
five liters of sieved glasshouse soil and inoculated one week
after transplanting with 92 larvae per plant. The test was set
up in six replications with six plants per plot. At 7, 10 and 17
weeks after inoculation two plants per plot were assessed. A
gall index was assigned to the rootballs (scale 1-10, 1 = 0-10%,
10 = 90-100% of the roots covered with galls). Larvae production
was determined by hatching larvae from egg masses on the roots
per plot, as described for the seedling test.
Of the pot test, only results of the observation at 17 weeks are
given, because they will approach most closely the value of the
resistance of the studied genotypes in practice. At that date
the gall indexes of the four Cucumis species differed
significantly from each other (Table 1). The roots of the
susceptible C. sativus were almost completely
disintegrated at that time, while those of the moderately
susceptible C. anguria var. longipes were partly
disintegrated. The rootballs of the moderately resistant C.
metuliferus and the resistant C. zeyheri 2x were still
intact, but the former showed many more galls than the latter.
Rather large numbers of larvae were produced on C.
metuliferus, only very few on C. zeyheri. It should
be noted that the C. zeyheri plants were initially growing
very slowly, with almost no side roots. This may have influenced
their high resistance level in this test.
Table 1. Means of the number of galls, of the number of larvae
and of the gall index per plant in the seedling test and in the
pot test, respectively 5 and 17 weeks after inoculation.
Cv. or Accession No.
C. anguria var. longipes
C. zeyheri 2x
zFor the analyses of variance a square root transformation was
yMeans showing a common letter are not different at p=0.05.
xNumber of larvae could not be determined because of
disintegration of the roots.
At the first and the second observation date of the pot test, the
ranking order of the gall index and the number of larvae agreed
in most cases with that of the gall index after 17 weeks.
However, the two resistant genotypes could not be distinguished.
In the seedling test the number of galls gave a good distinction
between the susceptible, the moderately susceptible and the two
resistant genotypes (Table 1). Both tests revealed that none of
the genotypes are completely resistant. For the four genotypes
studied, the level of resistance can be more precisely predicted
if, besides the number of galls, the larvae production is
measured in the seedling test.
- Nijs, A.P.M. den and K. Hofman. 1983. An efficient procedure to
screen for resistance to root-knot nematodes in cucurbits.
Cucurbit Genetics Coop. Rpt. 6:96-98.