This study screened eight varieties of oil radish for their potential as trap crops and biofumigants against root-knot and reniform nematodes. Two experiments were conducted: 1) a greenhouse pot experiment that found 'Sodbuster' and 'Discovery' varieties most reduced nematode populations and increased zucchini growth; 2) a bench experiment that found 'Summer Cross' and 'April Cross' did not support nematode reproduction or root galling, indicating potential as non-host trap crops. The results suggest oil radish, particularly certain varieties, could be effective biofumigants and trap crops for managing root-knot nematodes, though further research is needed on reniform nematodes.

1. Introduction
Screening oil radish (Raphanus sativus) varieties for nematode management through trap
cropping and biofumigation effect
Philip Waisen* and Koon-Hui Wang
Department of Plant and Environmental Protection Sciences, College of Tropical Agriculture and Human Resources
Results
Conclusion
Acknowledgment
Materials and Methods
Root-knot (Meloidogyne spp.) and reniform (Rotylenchulus reniformis) nematodes cause
substantial economic loss in vegetable and fruit crops. Most of the efficacious chemical
pesticides have been withdrawn from the markets and recently organic farming
approaches of managing crop pests and diseases are gaining popularity. Oil radish
(Raphanus sativus) is susceptible to the root-knot nematodes, thus it can be used as a
dead-end trap crop to manage the nematodes by trapping the nematodes inside its
roots when terminated within four weeks of the plant growth. During this time, nematode
eggs can not fully develop, thus it prevents them from attacking subsequent crop roots.
Oil radish also produces glucosinolates that are converted into isothiocyanates which
are allelopathic to several plant-parasitic nematodes when added as soil amendment.
Information is needed to determine oil radish varieties with the best biofumigation and
trap cropping potentials in Hawaii. Fig. 1. Numbers of A) root-knot, and B) reniform nematodes affected by leaf amendment of eight varieties of oil radish
(1% w/w) in field soil contained in greenhouse pot planted with a zucchini seedling. Means (n=4) for each nematode
species followed by the same letter(s) are not different according to Waller-Duncan k-ratio (k=100) t-test.
Fig. 3. A) Numbers of Meloidogyne javanica juveniles recovered from the soil, and B) root-gall index (1-5) on oil radish
varieties and tomato at 1-month after the nematode inoculation. Means (n=4) are presented. Bars with the same letters
are not different (P<0.01) based on Duncan’s Multiple Range Test.
To determine oil radish varieties with the best biofumigation and trap cropping effects
against root-knot and reniform nematodes.
Experiment I: A pot experiment was conducted in greenhouse conditions at Magoon
facility (21°18'24.90"N and 157°48'33.11"W). Eight oil radish varieties (‘Alpine’, ‘April
Cross’, ‘Discovery’, ‘Miyashige’, ‘Oshin’, ‘Sodbuster’, ‘Summer Cross’, and ‘Tillage
Radish’) were selected based on local farmers’ preference, or availabilities as cover
crop seeds with cheap seed price. Field soil infested with root-knot (Meloidogyne spp.)
and reniform (Rotylenchulus reniformis) nematodes were collected and amended with
oil radish at 1% dry leaf weight/dry soil weight (w/w). A ‘Felix’ zucchini (Cucurbita pepo
var. cylindrica) was germinated and planted singly in 6 inch diameter clay pots. A non-
amended control was included. The experiment was arranged in RCBD with 4
replications, and terminated 1-month after planting zucchini. At termination, chlorophyll,
height, shoot and root weights were measured from each plant. Nematodes were
extracted from 250 cm3
soil subsampled from each pot by elutriation (Byrd et al, 1976)
and density-dependent centrifugal sugar floatation (Jenkins, 1964; Barker, 1985)
method. Data were log transformed where necessary and subjected to analysis of
variance in SAS, and means are presented.
Experiment II: A pot experiment was conducted on a bench outside the greenhouse in
the Magoon facility. Sterile soil:sand mix (1:1 v/v) was potted into tree pots (6’’ x 16’’;
Greenhouse Megastore, CA, USA). Seeds of 8 oil radish varieties were used with an
addition of ‘Orange Pixie’ tomato (Solanum lycopersicum) as a root-knot nematode
susceptible host control. The oil radish varieties were planted (3 seeds/pot) and thinned
to one per pot. Eleven days post-planting, 2,700 second stage juveniles (J2s) were
inoculated per pot. The experiment was arranged in RCBD with 4 replications, and
terminated 1-month post-inoculation. Nematodes were extracted from 250 cm3
soil
subsampled from each pot by elutriation (Byrd et al, 1976) and density-dependent
centrifugal sugar floatation (Jenkins, 1964; Barker, 1985.) method. Fine roots were
examined and rated for root gall index according to Taylor and Sasser (1978). Data
were log transformed where necessary and subjected to analysis of variance in SAS.
Means of the soil nematode population and root gall rating are presented.
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Photograph 1. A) Tomato (foreground) and zucchini (background) growing in experiment I. B) Oil radish growing in tree
pots in experiment II C) Root of oil radish ‘Sodbuster’ variety (arrowheads pointing root galls on fine roots).
Discussion
Fig. 2. Response of zucchini chlorophyll,height, root and shoot parameters affected by oil radish leaf amendment.
Means (n=4) for each zucchini plant growth parameter followed by the same letter(s) are not different according to
Waller-Duncan k-ratio (k=100) t-test.
A
A B
Objective
This project is supported in part by Western SARE PDP project
no. OW15-019, and in part by HAW09022-H. The authors would
like to thank Steve Yoshida, Donna Mayer Jari Sugano, Gareth
Nagai, Josiah Marquez, Shelby Ching, and Shova Mishra.
C
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Experiment I: All the oil radish varieties reduced (P<0.01) the PPNs per 250 cm3
soil. ‘Sodbuster’ and ‘Discovery’ showed the maximum reduction of root-knot and
reniform nematodes, respectively (Fig.1). Compared to unamended control,
‘Sodbuster’ and ‘Miyashige’ suppressed the root-knot nematodes by 94% and 92%,
respectively (Fig. 1A). Although no difference between varieties, oil radish
suppressed reniform nematode by 77% on average compared to unamended
control. Oil radish amendments increased the zucchini plant growth parameters.
Compared to unamended control, chlorophyll production was increased (P<0.01) by
35% (Fig. 2A) and also increased (P<0.01) shoot by almost 5 folds on average (Fig.
2D). While numerically increasing the root by 50% (Fig. 2C), oil radish also increased
(P<0.01) zucchini plant height (Fig. 2B) by 87% on average, compared to the
unamemded control. In overall. oil radish amendments suppressed root-knot
nematodes better than reniform nematode.
Experiment II: Varietal variations were observed in the oil radish varieties screened
for susceptibility to M. javanica. Compared to other varieties, no nematode was
recovered from the soil nor galls formed on the roots from ‘Summer Cross’ and ‘April
Cross’ (Fig. 3). Root galling index was different (P<0.01) between the oil radish
varieties (Fig.3B). While ‘April Cross’ and ‘Summer Cross’ serve as non-host,
‘Sodbuster’, ‘Miyashige’ and ‘Oshin’ serve as good hosts for M. javanica. Thus, the
oil radish varieties that serve as host to M. javanica can be used as trap crops in the
field experiments. Time plays a major role whether or not to detect soil nematode
population as shown in ‘Sodbuster’ (Fig. 3A). Unlike ‘Summer Cross’ and ‘April
Cross’, ‘Sodbuster’ formed root galls (Fig. 3B) but no nematode was recovered from
the soil (Fig. 3A). Considering the time of termination of the experiment, 1-month
post-infection, this indicates that nematodes are likely to be all in the roots, thus
forming root galls.
A B C
Based on the results from this study, oil radish would be a good cover crop to be
used against root-knot nematodes as it serves as a good biofumigant and and shows
good host status. However, further research needs to be conducted to determine if
the use of oil radish could be useful for the management of reniform nematodes.
References
Barker, K. R. 1985. Nematode extraction and bioassays, pp. 19-35 in An advanced
treatise on Meloidogyne. Vol. 2. Methodology, ed. K. R. Barker, C. C. Carter, and J.
N. Sasser. North Carolina State University Graphics, Raleigh, North Carolina, USA.
Byrd, D. W., Barker, K. R., Ferris, Jr. H.m, Nusbaum, C. J., Griffin, W. E., Small, R.
H., and Stone, C. A. 1976. Two semi-automatic elutriators for extracting nematodes
and certain fungi from soil. Journal of Nematology 8:206-2012.
Jenkins, W. R. 1964. A rapid centrifugal flotation technique for extracting nematodes
from soil. Plant Disease Reporter 48:692.
Taylor, A. L., and Sasser, J. N. 1978. Biology, identification and control of root-knot
nematodes. North Carolina State University Graphics.