Hindawi
International Journal of Agronomy
Volume 2018, Article ID 6715909, 9 pages
https://doi.org/10.1155/2018/6715909
Research Article
Screening Selected SolanumPlants as Potential Rootstocks for the
Management of Root-Knot Nematodes (Meloidogyne incognita)
Benjamin A. Okorley , Charles Agyeman , Naalamle Amissah, and Seloame T. Nyaku
Department of Crop Science, University of Ghana, P.O. Box LG 44, Legon-Accra, Ghana
Correspondence should be addressed to Seloame T. Nyaku; seloame.nyaku@gmail.com
Received 15 May 2018; Revised 3 July 2018; Accepted 30 July 2018; Published 25 September 2018
Academic Editor: Maria Serrano
Copyright © 2018 Benjamin A. Okorley et al. ,is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
Root-knot nematodes (RKNs) (Meloidogyne spp.) represent agricultural pest of many economic crops, including tomatoes and
potatoes. ,ey advance a complex parasitic relationship with roots of tomato plants leading to modification of host structural and
physiological functions in addition to significant yield loss. Resistance in solanaceous plants to RKNs has been identified and
associated with the possession of Mi gene. ,e reaction of four Solanum rootstocks (S. aethiopicum L., S. macrocarpon L., S.
lycopersicum L.“Mongal F1,” and S. lycopersicum L. “Samrudhi F1”) was evaluated in pots and in a naturalMeloidogyne spp.-infested
field in a two-year trial (2015–2016), to identify RKN-resistant rootstock(s), which can be utilized in tomato grafting as amanagement
measure against these nematodes. A rootstock’s reaction to RKNs was assessed using root gall scores (GSs), egg count/g of root, and
reproductive factors (Rfs) at the end of 6 and 12 weeks after transplanting (wat) in infested fields, respectively. Solanummacrocarpon,
S. aethiopicum, and Mongal F1 showed tolerant responses with reduced root galling and low to high reproductive factors in pot and
field experimentation. Although Samrudhi F1 was resistant in both pot and field trials and consistently decreased nematode root
galling (<1.00) and reproduction (Rf< 1.00), it failed to significantly increase yield, as compared with the highest yield obtained by the
tolerant rootstock, Mongal F1 (870.3 and 1236.6 g/plant, respectively). Evaluation of the four rootstocks against four (0, 500, 1,000,
and 5000) RKN inocula levels (Juveniles) showed no significant differences among the growth parameters (fresh and dry shoot and
root weights). Root-knot nematode-susceptible tomato varieties, for example, Pectomech F1, a popular tomato variety in Ghana, can
be grafted onto the RKN-resistant and RKN-tolerant rootstocks for increased yields.
1. Introduction zones because of the derived income and nutritional ben-
efits. Pectomech F1, Power Rano, and “Wosowoso” are
Tomato (Solanum lycopersicum L.) is an annual crop of the popular varieties cultivated for high yield and quality fruits.
Solanaceae family, and the second most widely consumed However, domestic production levels over the years have
vegetable after potatoes [1]. Tomato fruits are highly nu- been low, mainly due to its vulnerability to pest and diseases,
tritious, and constitute a rich source of vitamins A, C, and E, including plant-parasitic nematodes [8].
and essential minerals, namely, potassium, phosphorus Plant-parasitic nematodes are economic pests of agri-
calcium, magnesium, and iron [2, 3]. Tomato and its culture worldwide, with more than 3000 plants species as
products contain the antioxidant lycopene, which reduces host [9–11]. Global losses associated to root-knot nematodes
cancers and development of atherosclerosis [4, 5]. ,e large (RKNs) alone from 75 countries as at 2000 was valued at
diversity in the crop makes it adaptable to different climatic $121 billion [12] and cost about $500 million for their annual
conditions, ranging from temperate to tropical environ- control [13, 14]. In Ghana, RKNs are responsible for 33% of
ments, production methods, and uses [6]. Ghana has vegetable losses per season [15], in which 73–100% are re-
a young tomato industry (production estimated at 366, 722 alized in tomato production alone [16]. ,e RKNs thus
tonnes from 47,000 hectares of land [7]), with the potential impact a key limitation to tomato production, as the crop is
to increase production in the savannah and transitional considered the most vulnerable in the tropics [17, 18].
2 International Journal of Agronomy
Currently, crop rotation, soil solarization, nematode-free tomato rootstocks because of their slow growth rate. A week
seedlings, and the use of nematicides are adopted by after seedling emergence, N-P-K: 15-15-15 (6 g/L) nutrient
Ghanaian farmers for managing nematodes [16, 19]. ,e solution was applied once every week by immersing in a bath
withdrawal of extensively used fumigants such as ethylene for 5-6 minutes. A shade cover was placed over the seedlings
dibromide, because of its carcinogenic nature and its ability to minimize the solar radiation on the leaves. Suncozeb 80
to contaminate groundwater [12, 20], has necessitated the WP at 20 g/L of H20 was sprayed, until runoff close to the
adoption and worldwide use of tolerant/resistant rootstocks, crown of the seedlings, to prevent damping-off on seedlings.
as an alternative for nematode control because they are safe Two weeks before transplanting the seedling, the shade cover
to both farmers and the environment [21]. was completely removed to allow them harden-off.
Nematode-resistant plants or rootstocks have the in-
trinsic ability, to be unaffected significantly upon nematode
attack, and will greatly contribute to reducing nematode 2.3. Experimental Area (Field Trials). ,e field experiments
infestations in tomato fields [22–24]. Grafting utilizing re- were conducted at the Biotechnology and Nuclear Agri-
sistant rootstocks has proven to effectively manage RKNs cultural Research Institute (BNARI) of Ghana Atomic En-
and improve yield in tomato and eggplant cultivated in ergy Commission, Legon-Accra on a natural RKN-infested
naturally infested nematode soils [25]. Resistance to RKN field. ,e experimental site had a sandy loam soil, humid
species (M. incognita, M. javanica, and M. arenaria) is tropical climate with average low-high day temperatures of° °
conferred by a single dominant Mi gene, introduced from 25–34 C (dry season) and 25–29 C (rainy season), pH≈ 6.4,
the wild relative S. peruvianum accession (P.I. 128657), and a history of being used continuously for growing veg-
through embryo rescue technique, into commercially cul- etables, thus making the site a hot spot for RKNs. Laboratory
tivated tomatoes [26, 27]. Dhivya et al. [28] reported re- and nursery activities were carried out in the Department of
sistant and susceptible reaction, in wild Solanum plants after Crop Science, University of Ghana.
assessing their response to RKN. In another study, 33 tomato
genotypes were evaluated against RKN, and variable re- 2.4. Experimental Design (Field Trials). ,e experimental
sponses in gall development and nematode reproduction field was slashed and debris collected; then, three beds each
existed [29]. Plants with the Mi gene also effectively in- measuring 23.2m× 2.0m were raised and pegged at
creased yields to about ten-fold, compared with susceptible a planting distance of 80 cm× 40 cm. A randomized com-
plants at high nematode inoculum levels of about 200, 000 plete block design (RCBD) with three replicates partitioned
eggs/plant [24]. Solanaceous plants, for example, S. by two alleys of 0.5m each was used. A block contained five
aethiopicum, S. macrocarpon, S. torvum, and S. lycopersicum plots, each measuring 4.0m× 1.6m. ,irty (30) plants
cultivars, are commercially available, and common among constituted a plot, with ten plants in a row and three plants
local farmer seed stocks in Ghana. However, the use of between rows. Eight middle row plants were used as record
resistant rootstocks in tomato cultivation remains less ex- plants, from which data were taken. ,e experimental setup
plored, due to the unknown response of this Solanum spp. to was repeated for the succeeding trial in 2016. ,e layout for
RKNs. Grafting of tomato scions with superior traits onto the pot experiments was a 4× 4 factorial, arranged in a split
RKN-resistant rootstocks will help manage this biotic stress plot design with three replicates.
in a healthy and environmentally friendly manner [30],
reduce production cost, and improve yields [31].
,e use of resistant Solanum plants in grafting experi- 2.5. Agronomic Practices and Parameters Taken on Tomato
ments in Ghana is in its infancy; therefore, there is a need to Plants (Field Trials). Four-week-old seedlings were trans-
identify sources of resistance in the available Solanum planted (one per stand), and a starter solution (N-P-K: 15-
rootstocks for managing the RKN problem in tomato fields. 15-15 at 6 g/L of water) applied at 100mL/plant. Two (2) kg
,is study was thus initiated to screen and identify potential N.P.K was mixed with 1 kg NH3 and was also applied at
rootstock(s) among four selected Solanum plants for re- 15 g/plant as a side dressing. Agricombi (fenitrothion 30%
sistance to M. incognita. + fenvalerate 10%) were sprayed twice, at a rate of 50mL/L ofH2O, to control whiteflies, aphids, and red spider mites. ,e
plants were cared for by regular watering and weed control.
2. Materials and Methods Plant height, plant girth, and chlorophyll contents were
taken 5, 7, and 9 weeks after seedling transplant.
2.1. Plant Materials. Seeds of the test rootstocks, S.
aethiopicum and S. macrocarpon “Gboma,” were obtained
from the Department of Crop Science, University of Ghana. 2.6. Experimental Design (Pot Trials). ,e layout for the pot
Solanum lycopersicum “Mongal F1” and S. lycopersicum experiment was a 4× 4 factorial experiment, with a control
“Samrudhi F1” were supplied by Agriseed Company and arranged in a split plot design with three replicates, each
East-West Seed Ltd., respectively. experimental plot consisting of 30 plants. Root-knot nem-
atode inoculums (Juveniles) were prepared by extracting
nematode eggs from the roots of infested plants, and hatched
2.2. Sowing of Rootstock Seeds. ,e seeds were sown in trays into juveniles [32]. ,ese were then concentrated into the
containing oven-sterilized soil. Solanummacrocarpon and S. various RKN inoculum levels (0, 500, 1,000, and 5,000). ,e
aethiopicum were sown ten days earlier than the other plants (rootstocks) were then inoculated with the juveniles,
International Journal of Agronomy 3
by making a small hole or depression in the soil, at the base among the rootstocks for eggs/g of root, six weeks after
plants after which the required inoculum level was gently transplanting in both years; however, differences were ob-
poured into the hole and covered. served among the eggs numbers twelve weeks after trans-
planting in both years. ,e recovered number of eggs/g of
root ranged from 2 to 14,714 in Samrudhi F1 and S.
2.7. Nematode Analysis. Soil samples taken from each plot aethiopicum, six and twelve weeks after transplanting the
were used to determine the RKN populations, before rootstock seedlings for year 1. In year 2, however, eggs/g of
transplanting (initial nematode population Pi), six weeks root ranged from 20 to 11,280 in Samrudhi F1 and S.
after transplanting (P6), and after harvesting (Pf) in each aethiopicum, six and twelve weeks after transplanting the
trial. Six random soil samples per plot were taken with a soil rootstock seedlings. Nematode reproductive factors (Rfs) on
augur, and bulked together into a well-labeled plastic bag. A the various rootstocks also ranged from 0.07 to 1.57 for
subsample of 200 cubic centimeter (cc) was used in soil Mongal F1 and S. aethiopicum, 6 and 12 weeks after root-
extraction, through the sieving and sucrose centrifugation stock transplant, respectively, in year 1. In year 2, however,
method [33]. Reproductive factors (Rfs) for each treatment Rf ranged from 0.45 to 2.37 for Samrudhi F1 and S.
plot, which is a ratio of the final to initial population (Pf/Pi), aethiopicum six and twelve weeks after rootstock transplant,
were used to determine the rate of nematode multiplication respectively.
in the soil. Gall scoring and nematode egg extraction were Within the pot experiments, significant differences did
carried out 6 and 12 weeks after transplanting rootstocks, to not exist among the rootstocks in relation to the various
estimate RKN gall development and egg production on the RKN inocula levels (500, 1000, and 5000), for mean gall
host. Sampled roots were washed separately and air-dried for scores and egg counts six weeks after treatment application
5 minutes. Galls on each root system were scored on a scale (Table 2). However, significant differences were noted for
of 0–10 (no damage to severe damage), using the severity mean gall scores and egg counts, twelve weeks after treat-
rating chart by Bridge and Page [34]. Roots were then cut ment application. ,e RFs for all rootstocks were below 1.
into pieces, and nematode eggs extracted using 10% sodium ,ere were no significant differences among the various
hypochlorite (NaClO) [32]. Eggs obtained were counted plant growth parameters for weeks 6 and 12, among the
under the compound microscope (Exacta–OptechBiostar rootstocks for the four RKN inocula levels applied (Table 3).
B5P, Germany) (magnification x100) and recorded. ,e Generally, dry shoot and root weights were lower compared
mean gall scores (GSs), egg count per gram of root, and with the fresh shoot and root weights.
reproductive factors (Rfs) obtained from the two field trials
were used as the basis to evaluate the resistance status of the
rootstocks. Rootstocks were classified as resistant when their 3.2.MeanPlantHeight, PlantGirth, andChlorophyll Contents
root GS< 2 and Rf< 1, tolerant when GS< 2 and Rf≥ 1, or in Rootstocks to Root-Knot Infection Five, Seven, and Nine
susceptible when GS≥ 2 and Rf> 1 [35, 36]. Weeks after TransplantingRootstocks. Growth performances
varied greatly among the rootstocks and between the dry and
2.8. Statistical Analysis. Data collected on agronomic pa- wet season trials. Significant increases (P≤ 0.05) in plant
rameters (plant height and plant girth), chlorophyll content, height, girth, and chlorophyll contents were recorded for S.
yield parameters, and plant biomass content were subjected aethiopicum during the dry season (Figures 1(a1), 1(b1), and
to analysis of variance (ANOVA), using Genstat 12th edition 1(c1)). Conversely, the vegetative growth of the three tomato
software [37], and significant means separated, using least rootstocks were robust in the rainy season, relative to S.
significant difference (LSD) at 5%. Where necessary, data aethiopicum and S. macrocarpon, but began diminishing
were transformed using the equation Log (x+ 1), for during fruiting or after the seventh week (Figures 1(a2), 1(b2),
normality. and 1(c2)). Aside having the thickest stem, S. macrocarpon’s
chlorophyll content was also significantly increased (P≤ 0.05),
3. Results compared with the other rootstocks screened against RKNs
(Figure 1(c2)).
3.1. Root-Knot Nematode Gall Development, Egg Formation,
andReproductionamongSelectedRootstocksSixand12Weeks
after Transplanting Rootstocks. Four Solanum rootstocks 3.3. RKN Infestation on the Different Rootstocks Yield
were evaluated for resistance to RKNs in a naturally infested Parameters. Overall, S. macrocarpon and S. aethiopicum
field, in two consecutive trials (dry season of 2015 and rainy showed significantly (P≤ 0.05) increased number of fruits
season of 2016). Data on the RKN gall development and (10 and 12/plant) and high yield performances (227.50 g and
reproduction among the rootstocks for the two-year trial 147.61 g/plant, respectively) in the dry season (year 1).
were highly comparable. Six weeks after transplanting the Higher fruit yields were obtained for the three tomato
rootstocks, lower gall scores ranging from 0.33 to 0.67 were rootstocks in the rainy season (year 2). ,e number of
observed on S. macrocarpon, Samrudhi F1, and Mongal F1 fruits/plant increased significantly (P≤ 0.05), in both
(Table 1). In year 2, S. macrocarpon had the least root gall Mongal F1 (20) and S. aethiopicum (19). Fruit yield/plant for
score (0.00), with a slight increase for Samrudhi F1 (0.17) Mongal F1 (1236.60 g) greatly increased (P≤ 0.05) relative to
compared with the others (>0.50), six weeks after trans- other three rootstocks screened against RKNs. Furthermore,
planting the rootstocks. Significant differences were absent the weight of individual fruits/plant for Samrudhi F1
4 International Journal of Agronomy
Table 1: Initial and final nematode count, mean gall scores, egg count/g of root, and reproductive factors (RFs) of RKNs after 6 and 12 weeks
of transplanting rootstocks in 2015 (year 1) and 2016 (year 2) for field experiments.
Nematode
count/200 Mean gall
Egg count/gram
of root ReproductiveTreatment
cm3 of soil scores (0–10) (transformed)∗ factor (Pf/Pi) yReaction
Weeks Initial Six Twelve(Pi) (Pf) (Pf) Six Twelve Six Twelve Six Twelve
Year 1 (dry season)
Sam 133.00 85.33 48.67 0.50a∗ 0.33a 16.30 (1.06)a 54.33 (1.23)a 0.64 0.36 R
Mon 839.33 59.67 99.00 0.67a 3.00ab 14.30 (0.90)a 1047.67 (2.33)ab 0.07 0.12 T
S. M 197.67.00 46.67 24.00 0.33a 0.67a 2.00 (0.43)a 1438.33 (3.06)bc 0.24 0.12 T
S. A 255.33 112.67 400.00 1.67a 5.17b 17.00 (0.86)a 14714.00 (4.07)c 0.44 1.57 T
Year 2 (rainy season)
Sam 397.00 178.00 227.00 0.17 0.67 20.00a 900.00 (2.66)a 0.45 0.57 R
Mon 220.00 176.00 331.00 0.50 1.67 50.00a 5145.00 (3.68)b 0.80 1.50 T
S. M 472.00 244.00 515.00 0.00 1.33 33.00a 4267.00 (3.58)b 0.52 1.09 T
S. A 239.00 286.00 567.00 0.50 2.17 48.00a 11280.00 (3.91)c 1.20 2.37 T
Gall scores: 0�no knots on roots; 10� all roots severely knotted, plant usually dead; rootstocks: Sam� Samrudhi F1; Mon�Mongal F1; S. M� S. mac-
rocarpon; S. A� S. aethiopicum. yReaction of rootstocks derived from 6 to 12 weeks after transplanting rootstocks (R� resistance and T� tolerance). ∗Means
having different letters in a column differed significantly (P≤ 0.05). ∗Log (x+ 1) transformed.
Table 2: Response of four rootstocks to four RKN inoculum levels on gall scores, egg count per gram of root, and reproductive factors 6 and
12 weeks after inoculation in pot experiments.
Mean gall score Nematode countper 200 cc of soil Egg count per gram Reproductive factor
Rootstocks Initial inoculum (1–10) (Pf) of root (Pi/Pf) Reaction
6 weeks 12 weeks 6 weeks 12 weeks 6 weeks 12 weeks 6 weeks 12 weeks
Mon 500 0.51a∗ 0.00a 48.30 41.28 6.50a 5.94a 0.09 0.08 T
SA 500 0.22a 0.20ab 125.60 60.72 9.60a 5.11a 0.25 0.12 T
Sam 500 0.02a 0.10a 46.60 4.00 2.60a 5.44a 0.09 0.22 R
SM 500 0.38a 0.00a 107.90 108.56 9.60a 3.00a 0.22 0.01 T
Mon 1000 1.11a 0.10a 62.20 20.56 12.8a 3.89a 0.06 0.02 T
SA 1000 0.67a 0.00a 192.30 93.89 12.2a 8.56b 0.19 0.09 T
Sam 1000 0.50a 0.00a 124.30 2.16 7.00a 0.15c 0.09 0.11 R
SM 1000 0.44a 0.00a 86.10 108.44 15.3a 6.33a 0.12 0.00 T
Mon 5000 0.33a 0.70c 91.60 9.39 7.20a 4.33a 0.02 0.00 T
SA 5000 0.72a 0.20ab 158.40 90.33 11.9a 5.00a 0.03 0.02 T
Sam 5000 1.00a 0.10a 84.70 13.66 8.50a 6.33a 0.04 0.01 R
SM 5000 0.55a 0.00a 206.00 71.00 9.60a 1.15c 0.02 0.00 T
Sam� Solanum lycopersicum “Samrudhi F1,” Mon� Solanum lycopersicum “Mongal F1,” SM� Solanum macrocarpon, and SA� Solanum aethiopicum
(R� resistance and T� tolerance). ∗Means having different letters in a column differed significantly (P≤ 0.05).
(66.95 g) was on the average heavier compared with the highest dry weights (16.81 g and 19.43 g) for years 1 and 2,
other rootstocks (Table 4). respectively.
3.4. Effects of Root-Knot Nematode Infestation on Fresh and 4. Discussion
Dry Weights of Shoot and Roots of the Rootstocks. Twelve
weeks after transplanting, S. aethiopicum and S. macro- ,e reproductive factors (Rfs) of the various rootstocks
carpon accumulated significant (P≤ 0.05) amounts of plant together with their mean gall scores (GS) provided an es-
biomass, with respect to its fresh shoot (331.40 g and timate of host suitability, to support nematode reproduction
159.10 g), and root weight (39.72 g and 14.05 g), obtained in and were used to verify host resistance [38]. A rootstock’s
the dry season trial (Table 5). In the subsequent trial, reaction to RKN resulting to GS< 2 and Rf< 1, GS< 2 and
however, the tomato rootstocks picked up steadily the fresh Rf≥ 1, and GS≥ 2 and Rf> 1 was identified as resistant,
shoot weight of S. macrocarpon (357.39 g) and Mongal F1 tolerant, and susceptible, respectively [35].
(325.28 g), which were significantly increased (P≤ 0.05), ,ere is evidence to show that fecundity increases in
compared with the other rootstocks (Table 5). Significant more vulnerable plant hosts than in resistant or tolerant
differences also existed among the dry shoot and root hosts [39]. Sobczak et al. [40] also described a stalled re-
weights for both year trials, and S. aethiopicum produced the sponse of the tomato Hero-gene, against invading cyst
International Journal of Agronomy 5
Table 3: Fresh and dry shoot and root weights in four rootstocks to three RKN inocula levels (0, 500, 1000, and 5000) 6 and 12 weeks after
treatment application.
Fresh root Fresh root Dry root Dry root Fresh shoot Fresh shoot Dry shoot Dry shoot
Rootstocks Initial RKNinocula levels weight (g) weight (g) weight (g) weight (g) weight (g) weight (g) weight (g) weight (g)6 weeks 12 weeks 6 weeks 12 weeks 6 weeks 12 weeks 6 weeks 12 weeks
Mon 0 5.58a∗ 6.32a 1.11a 1.69a 50.10a 53.78a 5.05a 7.91a
SA 0 7.19a 6.06a 1.82a 2.34a 45.70a 55.69a 5.34a 7.69a
Sam 0 6.82a 6.40a 0.94a 3.91a 43.30a 42.30a 7.09a 8.69a
SM 0 13.70a 9.40a 4.57a 3.68a 40.60a 52.16a 11.09a 6.21a
Mon 500 8.12a 4.34a 2.13a 2.55a 48.80a 57.73a 6.16a 7.40a
SA 500 9.21a 8.62a 2.64a 2.26a 48.80a 55.99a 6.96a 7.05a
Sam 500 5.23a 5.36a 1.21a 4.17a 47.40a 34.62a 6.18a 6.82a
SM 500 12.20a 12.85a 4.38a 3.92a 62.00a 51.32a 6.73a 6.75a
Mon 1000 3.28a 7.13a 1.36a 1.94a 37.70a 42.94a 9.56a 9.12a
SA 1000 15.65a 13.21a 3.48a 2.78a 46.70a 45.62a 7.49a 4.91a
Sam 1000 3.08a 10.97a 0.73a 3.21a 26.20a 34.07a 10.29a 7.78a
SM 1000 15.19a 15.24a 5.13a 3.10a 36.80a 43.68a 7.18a 8.79a
Mon 5000 7.50a 10.08a 1.94a 2.43a 50.70a 38.73a 7.28a 7.81a
SA 5000 16.52a 15.70a 11.46a 4.47a 54.40a 52.32a 8.08a 7.14a
Sam 5000 8.68a 15.12a 1.31a 2.72a 49.20a 46.15a 4.54a 6.75a
SM 5000 12.60a 15.26a 6.56a 3.59a 45.70a 41.58a 8.71a 7.29a
∗Means having different letters in a column differed significantly (P≤ 0.05).
nematode, leading to the death of nematodes at the late J2 experiments. Similarly, Lopez-Perez et al. [45] documented
stage, rather than the average 12 hours postinfection re- a tolerant response in resistant Mi gene-bearing rootstock
sponse [26]. Beaufort, for supporting RKN reproduction, with higher
Wehner et al. [41] recounted 12 weeks postinoculation yields compared with a susceptible genotype (Blitz). In
nematode, counts as the best option for inferring the re- another test, where 33 tomato genotypes were assessed by
sponse of rootstocks, as compared with six weeks nematode Jaiteh et al. [29], Mongal T-11 and Mongal F1 number 5
counts. Nematodes cause severe damage depending on their emerged resistant (GS� 3.25 and Rf� 0.71) and susceptible
population densities, host species, temperature, and the (GS� 7.25 and Rf� 2.47), respectively. Tzortzakakis et al.
period of incubation, to allow significant differentiation [46] also reported S. macrocarpon’s susceptibility to RKNs.
between resistant and susceptible rootstocks. A remarkable However, in the current study, the observed tolerance in S.
increase in nematode damage, along with reproduction, was macrocarpon and Mongal F1 might be due to inactivation of
observed 12 weeks after transplanting in both trials in S. the Mi gene arising from mutation, if present in the ge-
aethiopicum. However, some rootstocks (Samrudhi F1, notypes [45], or the possession of other genes (horizontal
Mongal F1, and S. macrocarpon) suppressed nematode resistance) rather than Mi gene. Solanum macrocarpon’s
activities, indicating the existence of genetic variability hardy roots makes penetration relatively difficult for nem-
among the rootstocks tested. In a previous study, Rahman atodes compared with tomato roots. Alternatively, Mi gene
et al. [42] observed the response of S. torvum and S. sisy- dosage effect may account for increased nematode re-
mbriifolium as resistant to RKNs. Similarly, Dhivya et al. [28] production in tolerant Mi heterozygous individuals than in
described S. torvum and S. aethiopicum as poor hosts of homozygous individuals [47, 48].
RKNs, whereas the former was found tolerant by Ioannou Apart from reducing nematode damage, resistant root-
[25]. In our study, S. aethiopicum could be classified as stocks are cultivated to help improve plant fitness and yield.
tolerant to RKNs, although had high root gall development Consequently, growth and yield performance of the test
(GS� 2.17–5.17), with increased reproduction (Rf� 1.58– rootstocks was evaluated in the study in infected and con-
2.37), the severest symptoms were observed during the dry trolled environments, to various inocula levels of RKN in pot
season.,is response could probably be due to predominant experiments. ,e absence of significant differences in the
elevated soil temperatures, leading to the permanent rootstocks in relation to the growth parameters (fresh and dry
breakdown of nematode resistance Mi gene [43, 44]. shoot and root weights) shows the tolerance levels of the
Unlike the resistance found in Samrudhi F1 various rootstocks to the RKN, irrespective of the inocula level
(GS� 0.33–0.67 and Rf� 0.36–0.57), S. macrocarpon and in the pot trials. Within the field experiments, significant
Mongal F1 were found promising because of their potential differences in plant girth, height, and chlorophyll content
in reducing nematode damage (GS� 0.67–1.33 and 1.67– were obtained among the tested rootstocks. ,ese observed
3.00, respectively). Based on nematode reproduction on differences showed that although the rootstocks belonged to
a host, their response could best be described as tolerant the same Solanum genus, these had (3) different species
because population levels of nematodes recovered were still origins. Among the three tomato rootstocks, Mongal F1,
high (Rf> 1) in field experiments, but below 1 in pot however, presented a more robust growth after transplanting.
6 International Journal of Agronomy
100 100
LSD
90 90 LSD
80 80
70 70
60 60
50 50
40 40
30 30
20 20
10 10
5 7 9 5 7 9
Weeks aer transplanting rootstocks Weeks aer transplanting rootstocks
S. A Mon S. A Mon
S. M Sam S. M Sam
(a1) (a2)
20 20
18 LSD 18 LSD
16 16
14 14
12 12
10 10
8 8
6 6
4 4
2 2
5 7 9 5 7 9
Weeks aer transplanting rootstocks Weeks aer transplanting rootstocks
S. A Mon S. A Mon
S. M Sam S. M Sam
(b1) (b2)
80 80
75 75
70 LSD 70 LSD
65 65
60 60
55 55
50 50
45 45
40 40
35 35
30 30
25 25
20 20
15 15
10 10
5 5
5 7 9 5 7 9
Weeks aer transplanting rootstocks Weeks aer transplanting rootstocks
S. A Mon S. A Mon
S. M Sam S. M Sam
(c1) (c2)
Figure 1: Growth parameters of rootstocks to RKN infection at five, seven, and nine weeks after transplanting rootstocks. (a) ,e mean
plant height, (b) the mean plant girth (c) the mean chlorophyll content in 2015 (1) and 2016 (2). Rootstocks: Sam� Samrudhi F1;
Mon�Mongal F1; S. M� S. macrocarpon; S. A� S. aethiopicum. Data were analyzed with two-way ANOVA and significant means separated
with the least significant difference (LSD) test. LSD bars represent the least significant difference at P≤ 0.05.
Plant chlorophyll content Plant girth (mm) Plant height (cm)
Plant chlorophyll content Plant girth (mm) Plant height (cm)
International Journal of Agronomy 7
Table 4: Mean yield parameters of the rootstocks after RKN infestation in 2015 (year 1) and 2016 (year 2).
Treatment Days to 50% Number offlowering fruits/plant Fruit yield/plant (g)
Fruit yield Mean fruit
(kg/ha) weight/plant (g)
Year 1 (dry season)
Sam 28.00a 2.33a 23.70a 2961a 8.89a
Mon 27.00a 5.00ab 44.62a 5581a 7.43a
S. M 39.00b 10.33bc 227.50c 28442b 22.74b
S. A 51.00c 12.00c 147.61b 18448ab 12.30b
Year 2 (rainy season)
Sam 27.00b 13.00ab 870.30b 27196.87b 66.95c
Mon 29.00b 20.00b 1236.60c 38643.75c 61.82c
S. M 41.00c 9.00a 339.10a 10596.88a 37.68b
S. A 58.00d 19.00b 204.40a 6387.50a 10.75a
Means having different letters in a column differ significantly (P≤ 0.05). Rootstocks: Sam� Samrudhi F1; Mon�Mongal F1; S. M� S. macrocarpon; S. A� S.
aethiopicum.
Table 5: Mean fresh and dry weights of shoot and roots of rootstocks after 12 weeks of root-knot nematode infestation.
Treatment Fresh shoot weight (g) Dry shoot weight (g) Fresh root weight (g) Dry root weight (g)
Year 1 (dry season)
Sam 40.60a 8.74a 3.74a 0.96a
Mon 53.70a 11.13a 5.17ab 1.42ab
S. M 159.10ab 33.78ab 14.05b 5.20b
S. A 331.40b 76.73b 39.72c 16.81c
Year 2 (rainy season)
Sam 257.74a 47.74a 25.13a 10.65a
Mon 325.28ab 65.02a 27.09a 12.09a
S. M 357.39b 62.14a 24.74a 12.67a
S. A 255.44a 63.51a 32.31a 19.43b
Means having different letters in a column differ significantly (P≤ 0.05). Rootstocks: Sam� Samrudhi F1; Mon�Mongal F1; S. M� S. macrocarpon; S.A� S.
aethiopicum.
,e plants were tall with thick stems and appeared dark green. Data Availability
Compared with Samrudhi F1, the plants stood more erect
(even at flowering) with soft stem tissues that easily break ,e data used to support the findings of this study are in-
upon fruit bearing (weight). ,e resistant response of host cluded within the article.
crops to RKNs is well known to correspond to increased yield
[24, 42, 45]. ,e fruit yield of the tolerant rootstock (Mongal Conflicts of Interest
F1) was significantly increased, compared with the resistant
Samrudhi F1. ,is suggests Mongal F1’s efficiency in con- ,e authors declare that there are no conflicts of interest
verting resources into fitness and in bearing of fruit rather regarding the publication of this article.
than controlling nematodes. Restif and Koella [49] detected
the distribution of tolerant plant resources towards fitness,
unlike in resistant plants where this is aimed at reducing Acknowledgments
pathogen infection. Within Samrudhi F1 genotypes, appre- ,e authors are grateful to the University of Ghana Research
ciable yields would be obtained in addition to suppressed Fund (UGRF), with a grant to NA and STN in response to
nematode population, making it possible for the cultivation of the 7th call for proposals.
susceptible crops in subsequent years [50].
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