CULTIVAR & GERMPLASM RELEASES
HORTSCIENCE 31(7):1246–1247. 1996.
NC-42 and NC-43: Root-Knot
Nematode–Resistant Cucumber
Germplasm
S. Alan Walters1 and Todd C. Wehner2
Department of Horticultural Science, North Carolina State University, Raleigh,
NC 27695-7609
Kenneth R. Barker2
Department of Plant Pathology, North Carolina State University, Raleigh, NC
27695-7616
Additional index words. Cucumis sativus, disease resistance, cucurbit, Meloidogyne
arenaria, Meloidogyne javanica, vegetable breeding
Root knot caused by Meloidogyne spp. is a
serious disease of cucumber (Cucumis
sativus L.) in the southeastern United States.
In North Carolina, root-knot nematodes destroy ≈11% of the cucumber crop annually (St.
Amand and Wehner, 1991). Since M. arenaria
(Neal) Chitwood and M. javanica (Treub)
Chitwood are often associated with cucumbers grown in this region (Alabama Agr. Expt.
Sta., 1960), genetic resistance is an important
breeding objective. In our breeding program
for nematode resistance, we consider a selection resistant if it has a gall index rating (0% to
100% of roots galled) consistently below 15%,
10 weeks after being inoculated with rootknot nematodes. Walters et al. (1993) identified resistance in cucumber germplasm to several root-knot nematodes, and we are now
releasing two inbreds resistant to root knot:
NC-42 and NC-43. Two other cultigens,
‘Mincu’ and PI 215589, have also been identified as resistant and are included as comparisons for this germplasm release (Table 1).
‘Mincu’ is one of the parents of NC-43 (Fig.
1), and PI 215589 is similar to NC-42 in that it
is an accession of C. sativus var. hardwickii
(R.) Alef. (Table 1).
NC-42 is a selection of C. sativus var.
hardwickii accession LJ 90430 (from the U.S.
Dept. of Agriculture program formerly located in La Jolla, Calif.). It has a high level of
resistance to four important root-knot nematodes: M. arenaria races 1 and 2, M. javanica,
and M. hapla Chitwood (Table 1). Data will
not be presented for M. hapla since all cultigens tested so far were resistant (Walters et al.,
1990). NC-43 is a selection of C. sativus var.
Received for publication 18 Jan. 1996. Accepted for
publication 22 July 1996. The use of trade names in
this publication does not imply endorsement by the
North Carolina Agricultural Research Service of the
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mentioned. The cost of publishing this paper was
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Under postal regulations, this paper therefore must
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1
Graduate Assistant.
2
Professor.
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sativus ‘Southern Pickler’, and is resistant to
M. arenaria race 2 (Table 1). The resistance
based on gall indices in NC-43 to M. arenaria
race 2 is moderate and, thus, not as good as the
resistance in NC-42. However, NC-43 has a
more acceptable fruit type than does NC-42,
which has few horticulturally useful traits.
Nematode reproduction factor (RF)
(Wehner et al., 1992) was used to verify resistance in the two germplasm releases. RF is a
method to measure resistance and is calculated
as final nematode density/initial nematode
density. An RF value >1 indicates that the
infected plant is a good host for the nematode,
whereas an RF value <1 indicates that the plant
is a poor host. NC-42 had RF values of 0 for the
four root-knot nematodes, and NC-43 had an
RF value of 0 for M. arenaria race 2 (Table 1).
RF values can differ on cucumber cultigens
that have similar gall indices, as is evident on
the susceptible cultigens infected with M.
javanica (Table 1). This difference can occur
for several reasons, including the effects of
larger root systems and root necrosis. Large
root systems have more galls than smaller root
systems while having similar gall index ratings. Root necrosis is caused by secondary
pathogens entering roots through areas opened
by nematodes. Those pathogens destroy root
tissue, which results in reduced nematode reproduction (Walters et al., 1992).
NC-42 and NC-43 are the first cucumber
inbreds to be released with root-knot nematode resistance, and are available to plant
breeders interested in resistance to M. arenaria
or M. javanica. NC-42 should be used only to
develop resistant cultivars, but NC-43 could
be used directly by growers willing to accept
its limitations in fruit yield and quality. NC-43
is not significantly different from ‘Wisconsin
SMR-18’ for M. arenaria race 2 resistance
based on gall indices, but based on RF, NC-43
is resistant and ‘Wisconsin SMR-18’ is susceptible (Table 1). The data from the germplasm test clearly show the advantage of NC43 over ‘Wisconsin SMR-18’ and ‘Sumter’
(Table 1).
Origin
NC-42 was produced by selection followed by self pollination starting with the
original bulk of LJ 90430 for five generations
to obtain an inbred line with high resistance
to M. javanica and M. arenaria race 1 and
2. LJ 90403 is a selection from PI 183967,
an accession of C. sativus var. hardwickii
(Fig. 1).
NC-43 was produced by selection followed
by self-pollination starting with a bulk of available seed sources of ‘Southern Pickler’ for six
generations to obtain an inbred line with high
resistance to M. arenaria race 2. ‘Southern
Pickler’ resulted from the cross of ‘Producer’
× ‘Ohio MR 17’ and has ‘Mincu’ in its background as the source of resistance (Fig. 1).
The two releases are inbred lines with
stable expression of root-knot nematode resistance. Plants within each inbred do not vary
more than a few percentage points for root gall
index.
Table 1. Resistance of cucumber cultigens to root-knot nematode (Meloidogyne arenaria races 1 and 2 and
M. javanica).
Cultigen
NC-42x
NC-43
Mincu
PI 215589x
Sumter
Wis. SMR 18
M. arenaria r1
Giz
RFz
11
0
33
3
31
23
43
29
5
6
10
13
Nematode species
M. arenaria r2
Giz
RFz
GTGiy
8
0
11
13
0
23
Giz
10
30
14
17
33
23
41
46
48
40
0
0
2
2
18
--57
51
M. javanica
RFz
GTGiy
0
8
6
63
3
19
25
33
63
--58
65
Mean
28
6
18
1
48
36
14
60
(P ≤ 0.05)
11
10
12
1
12
16
27
9
z
The experiment was performed once and was set up as a split plot in a randomized complete-block design
with four replications. Plants were rated for resistance using the gall index system (Gi = 0 to 100 % of roots
galled) and reproduction factor (RF) 12 weeks after planting or 10 weeks after inoculation. Reproduction
factor (RF) = (Final nematode density)/(Initial nematode density) and calculated as final number of eggs in
roots/5000 (number of eggs inoculated/pot).
y
GTGi = Germplasm test gall index rating (from Walters et al., 1993). Data from this test were single plant
means of five replications.
x
C. sativus var. hardwickii.
LSD
HORTSCIENCE, VOL. 31(7), DECEMBER 1996
produced at each node. Fruits are pickling
type, short, white to light-green, with medium
size warts, white spines, and a length : diameter ratio of 2.9 (similar to ‘Explorer’). No
other disease resistances have been evaluated
for this release.
Availability
Small amounts of breeder’s seed are available from TCW.
Literature Cited
Fig. 1. Pedigrees for NC-42 and NC-43 inbred lines of cucumber.
Description
NC-42 is C. sativus var. hardwickii, with
indeterminate, multiple lateral branching habit
and small dark-green leaves. Plant growth is
initially slow, but plants eventually surpass
the vine length of C. sativus var. sativus cultigens (Horst and Lower, 1978). Sex expression
is monoecious, with flowering promoted under short days (9 to 12 h photoperiod) (Horst,
1977). Fruits are small, extremely bitter, dark-
HORTSCIENCE, VOL. 31(7), DECEMBER 1996
green, ellipsoid, black spined, have a large
seedcell, and a length : diameter ratio of 1.6.
No other disease resistances have been evaluated for this release.
NC-43 is an indeterminate, monoecious
inbred with medium-green vines. Plants flower
39 days after seeding (5 days later than ‘Calypso’ and 1 day later than ‘Poinsett’, under
controlled 30/20C day/night conditions). Flowering is sequential, usually beginning at the
first node. Multiple pistillate flowers are often
Alabama Agr. Expt. Sta, Auburn, Ala. 1960. Distribution of plant-parasitic nematodes in the South.
Southern Coop. Ser. Bul. 74. 72 p.
Horst, E.K. 1977. Vegetative and reproductive behavior of Cucumis hardwickii and Cucumis
sativus as influenced by photoperiod, temperature, and planting density. MS Thesis, North
Carolina State Univ., Raleigh.
Horst, E.K. and R.L. Lower. 1978. Cucumis
hardwickii: A source of germplasm for the cucumber breeder. Cucurbit Genetics Coop. Rpt.
1:5.
St. Amand, P.C. and T.C. Wehner. 1991. Crop loss
to 14 diseases in cucumber in North Carolina for
1983 to 1988. Cucurbit Genetics Coop. Rpt.
14:15–17.
Walters, S.A., T.C. Wehner, and K.R. Barker. 1990.
Resistance of cucumber to the root-knot nematode, Meloidogyne hapla. Cucurbit Genetics
Coop. Rpt. 13:10–11.
Walters, S.A., Wehner, T.C., and K.R. Barker. 1992.
Effects of root decay on the relationship between Meloidogyne spp. gall index and egg
mass number in cucumber and horned cucumber. J. Nematol. 24(4S):707–711.
Walters, S.A., T.C. Wehner, and K.R. Barker. 1993.
Root-knot nematode resistance in cucumber and
horned cucumber. HortScience 28:151–154.
Wehner, T.C., S.A. Walters, and K.R. Barker. 1992.
Use of reproduction factor and gall index in
determining resistance in Cucumis spp. Cucurbit Genetics Coop. Rpt. 15:28–30.
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