© Benaki Phytopathological Institute
Meloidogyne javanica
and
M. incognita
infecting resistant tomato
61
ceptible crops, where no nematode resis-
tant tomato hybrid had been used in the
last 4-5 year crop rotation scheme. The nem-
atode populations were established as cul-
tures, by inserting pieces of root galls, in soil
around seedlings of the susceptible tomato
(
Solanum lycopersicum
L
.
) cv. ACE grown in
pots. The RKN populations originating from
pepper were established as cultures on the
susceptible pepper (
Capsicum annuum
L.)
cv. California Wonder. The plants were wa-
tered and fertilized as required; they grew
in a controlled environment with 16 h pho-
toperiod and soil temperature 24-26
o
C, at
which the
Mi
gene is effective (Williamson,
1998). Every seven weeks, the plants were
uprooted and ten egg masses were trans-
ferred to new plants to maintain the nema-
tode populations.
Preliminary tests
Egg masses were used to inoculate resistant
tomato plants cv. Silvana (with the
Mi
gene)
and the susceptible pepper cv. California
Wonder at a rate of 20 egg masses/plant,
and were maintained in the conditions de-
scribed above. Seven weeks after the inocu-
lation, the roots of the resistant tomato and
pepper plants were examined. If there were
no egg masses, new plants of resistant to-
mato and pepper were inoculated again us-
ing inoculum from the original nematode
cultures. In case that there was no reproduc-
tion of the nematodes in the second test,
the populations were discarded.
From the 20 RKN populations tested, 12
were discarded as they did not reproduce on
resistant tomato and pepper. The remain-
ing eight populations, originating exclusive-
ly from greenhouse crops, were selected for
subsequent studies according to the results
of the preliminary tests:
Five populations which reproduced on
1.
resistant tomato but not on pepper (I1,
I2, I3, S and V).
One population which reproduced on
2.
both resistant tomato and pepper (I4).
One population which reproduced on
3.
pepper but not on resistant tomato (K).
One population which did not repro-
4.
duce in both, resistant tomato and pep-
per, was kept as control (I5).
RKN population virulence tests
The populations which reproduced on re-
sistant tomato and pepper were maintained
in the same cvs for 4-5 further generations,
using each time ten egg masses originating
from the tomato cv. Silvana or the pepper
cv. California Wonder. All the original pop-
ulations were simultaneously maintained in
the susceptible tomato cv. ACE or in pepper
cv. California Wonder.
Females of each population were ex-
tracted from the roots and used for identifi-
cation. Protein extracts were obtained from
females and the electrophoretic analysis
was carried out using the Mini-Protean Tet-
ra cell system (Bio-Rad) according to Esben-
shade and Triantaphyllou (1985ab) and Pais
et al.
(1986), with some modifications. The
origins and species of these eight
Meloid-
ogyne
populations are presented in Table 2.
In all cases the same species per population
was identified in both the susceptible toma-
to and resistant tomato or pepper, indicat-
ing that selection in these plants did not al-
ter the constitution of the initial nematode
population.
The reproductive ability of all the orig-
inal nematode populations, which were
maintained either on the susceptible toma-
to cv. ACE or the susceptible pepper cv. Cal-
ifornia Wonder for at least four generations,
was studied on the resistant tomato cv. Sil-
vana and on the susceptible pepper cv. Cal-
ifornia Wonder in a pot experiment. Egg
masses were left to hatch in extraction dish-
es and plants of both tomato cvs and pepper
grown in 250 ml pots were inoculated with
400 second stage juveniles (J
2s
) with five rep-
licates per treatment. In each test, the pop-
ulation I5 was used as control to prove the
resistance of the tomato cv. Silvana and
the non host status of pepper cv. California
Wonder, towards the avirulent
M. javanica
.
Plants were maintained at 16 h photoperi-
od and soil temperature 24-26
o
C. The num-
ber of egg masses on roots was assessed
seven weeks after inoculation. Egg masses
