Plant Resistance to the Moth Tuta absoluta (Meyrick) (Lepidoptera:Gelechiidae) in Tomato Cultivars

Abstract

The resistance of 11 tomato cultivars (Ps-6515, Berlina, Poolad, Petoprid-5, Zaman, Matin, Golsar, Sandokan-F1, Golshan-616, Sadeen-95 and Sadeen-21) to the tomato moth, Tuta absoluta (Meyrick) (Lepidoptera:Gelechiidae) was investigated under field conditions. A randomized complete block design was used with three replications. Data analysis indicated that there were significant differences (P?<?0.05) among cultivars regarding leaflet damage, leaf damage, overall plant damage, number of mines per leaf, number of holes on the stem, and fruit. Our findings revealed that the cultivars Berlina, Golsar, Poolad, and Zaman were less suitable cultivars, suggesting that they are more resistant to the tomato moth than the other cultivars. The high density of leaf trichomes present in the cultivars Berlina, Zaman, and Golsar can be one of the possible causes of resistance to T. absoluta. Knowledge of the extent of susceptibility or resistance of cultivars to a pest on a crop is one of the fundamental components of integrated pest management (IPM) programs for any crop.

Full text

1 23
Neotropical Entomology
ISSN 1519-566X
Neotrop Entomol
DOI 10.1007/s13744-016-0441-7
Plant Resistance to the Moth Tuta absoluta
(Meyrick) (Lepidoptera:Gelechiidae) in
Tomato Cultivars
F Sohrabi, H R Nooryazdan, B Gharati &
Z Saeidi

1 23
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PEST MANAGEMENT
Plant Resistance to the Moth Tuta absoluta (Meyrick)
(Lepidoptera:Gelechiidae) in Tomato Cultivars
FSOHRABI
1
,HRNOORYAZDAN
1
,BGHARATI
1
,ZSAEIDI
2
1
Dept of Plant Breeding, Faculty of Agriculture, Persian Gulf Univ, Bushehr, Iran
2
Dept of Plant Protection, Agricultural and Natural Resources Research Center, Chaharmahal and Bakhtiari, Iran
AbstractKeywords
Tomato moth, integrated pest management,
plant susceptibility, trichomes
Correspondence
F Sohrabi, Dept of Plant Breeding, Faculty
of Agriculture, Persian Gulf Univ, Bushehr,
Iran; f.sohrabi1361@gmail.com;
fsohrabi@pgu.ac.ir
Edited by Rafael Major Pitta - Embrapa
Received 21 April 2016 and accepted 29
August 2016
*Sociedade Entomológica do Brasil 2016
The resistance of 11 tomato cultivars (Ps-6515, Berlina, Poolad, Petoprid-5,
Zaman, Matin, Golsar, Sandokan-F1, Golshan-616, Sadeen-95 and Sadeen-21)
to the tomato moth, Tuta absoluta (Meyrick) (Lepidoptera:Gelechiidae) was
investigated under field conditions. A randomized complete block design was
used with three replications. Data analysis indicated that there were signif-
icant differences (P< 0.05) among cultivars regarding leaflet damage, leaf
damage, overall plant damage, number of mines per leaf, number of holes
on the stem, and fruit. Our findings revealed that the cultivars Berlina,
Golsar, Poolad, and Zaman were less suitable cultivars, suggesting that they
are more resistant to the tomato moth than the other cultivars. The high
density of leaf trichomes present in the cultivars Berlina, Zaman, and Golsar
can be one of the possible causes of resistance to T. absoluta. Knowledge of
the extent of susceptibility or resistance of cultivars to a pest on a crop is one
of the fundamental components of integrated pest management (IPM) pro-
grams for any crop.
Introduction
The tomato moth, Tuta absoluta (Meyrick)
(Lepidoptera:Gelechiidae), is a devastating insect pest affect-
ing tomato production in Iran and many other countries
(Baniameri & Cheraghian 2011,Gharekhani&Salek-
Ebrahimi 2014). The larvae produce galleries in the leaves,
stems, terminal buds and fruits. The main damage is caused
through larvae feeding on the parenchyma between the epi-
dermal layers of the leaves, reducing the photosynthetic ca-
pacity of the plant with subsequent reduction of the yield
(Desneux et al 2010,2011). Under heavy infestation, the yield
loss between 80–100% is common (Gebremariamd 2015).
In many agronomic and vegetable cropping systems, the
primary strategy employed to control this pest involves the
use of chemical insecticides. However, it has serious prob-
lems such as destruction of natural enemy populations
(Campbell et al 1991), build-up of insecticide residues on to-
mato fruits (Walgenbach et al 1991) and in the environment,
and, especially, evolution of T. absoluta resistance to many
of the active ingredients available on the market (Siqueira
et al 2000a,b, Lietti et al 2005, Silva et al 2011, Campos
et al 2015,Roditakiset al 2015).
One of the important control methods for sustainable
management of T. absoluta to minimize development of
pesticide resistance is the use of resistant host plants. The
use of resistant plants can be a useful component of an
integrated pest management (IPM) system that could affect
pest population density, herbivore damage, and decrease
pesticide applications in agricultural ecosystems. In addition,
in many cases, even partial resistant cultivars are useful to
enhance the effects of beneficial natural enemies (Hare &
Andreadis 1983,Bonget al 1991, Cogni et al 2002,Kaplan
2007, Kaplan & Thaler 2010). Plant resistance to a pest can
be caused by antixenosis, a mechanism employed by the
host plants, deters the insects from oviposition, feeding,
seeking shelter, and colonization (Oyetunji et al 2014); anti-
biosis, which has a direct influence on the life history of a
pest (Ofomata et al 2000,Liet al 2004); and tolerance, the
plant’s capacity of keeping its production under attack for
Neotrop Entomol
DOI 10.1007/s13744-016-0441-7
Author's personal copy

herbivore insect (Vargas 1970, Stowe et al 2000, Stevens
et al 2008). Many researchers have investigated the resis-
tance of host plants to tomato moth (Gilardón et al 2001a,
Leite et al 2001,Suinagaet al 2004,Silva2009, Gharekhani &
Salek-Ebrahimi 2014). In this study, we present data on sus-
ceptibility of 11 tomato genotypes to T. absoluta.Thedata
obtained fromthese experiments are used to understand the
mechanism of population build-up of this pest on different
tomato genotypes to develop a comprehensive pest man-
agement program for tomato.
Material and Methods
The experiment was performed in a field in the Faculty of
Agriculture, Persian Gulf University, Bushehr province,
Borazjan region, Bondarooz (Southern Iran) (29°12′54.1″N,
51°13′57.1″E, and elev. 99 m) from February 2014 to
June 2015. Eleven cultivars of tomato were used in this study,
including five cultivars Ps-6515, Berlina, Poolad, Petoprid-5,
Zaman from FALAT Co., Iran; two cultivars Matin and Golsar
from GOLSAM Co., Iran; and four cultivars Sandokan-F1,
Golshan-616, Sadeen-95 and Sadeen-21 from BEHTA Co.,
Iran. The tomato seeds were planted in plastic transplant
trays containing peat moss soil and perlite on November
2014. With the appearance of the first true leaves, the seed-
lings were transplanted into the main field. The evaluation of
the resistance was performed in a randomized block design
with three replications. A total of 20 plants per cultivar were
planted in each replicate plot (plot area = 24 m
2
) in two 150-
cm spaced rows. The space between plants in each row was
50 cm, and the space between plots was 150 cm. The culti-
vars were exposed to the natural infestation by indigenous
population of tomato leaf miner in the field.
Leaflet damage, leaf damage, and overall plant damage
caused by the insect were evaluated at days 20, 40, and 60
after infestation. Five plants were randomly selected in each
plot and marked notes and the different characteristics on
these plants were measured. Leaflet and leaf damage was
evaluated based on the percentage of leaflet or leaf area
affected by T. absoluta. In this case, three leaves were se-
lected from the upper third ofeach of the five selected plants
and the damaged area of each whole leaf and its leaflets was
recorded. The overall plant damage estimates were also per-
formed for each of the five selected plants. In addition, the
number of mines per leaf, holes on the stem, and holes per
fruit were assessed at the last sampling date. The number of
mines per leaf was counted on three leaves selected from
the upper third of each of the five randomly selected plants.
The number of holes on the stem and the number of holes
on the fruit were evaluated by performing a direct counting
of these features throughout the stem and five fruits from
each of these five selected plants, respectively. In addition,
Table 1 The mean percent of leaflet damage, leaf damage, and overall plant damage in tomato cultivars submitted to infestation of Tuta absoluta in different evaluation periods.
Leaflet damage Leaf damage Overall plant damage
Sampling time Sampling time Sampling time
Cultivar 20 40 60 20 40 60 20 40 60
PS6515
Berlina
SandocanF1
Matin
Sadeen95
Zaman
Petopride5
Golsar
Golshan616
Poolad
Sadeen21
11.33 ± 3.36a
3.00 ± 1.73d
9.33±3.05ab
11.33 ± 3.36a
7.00 ± 2.64bc
5.67 ± 2.38 cd
10.67 ± 3.26a
3.67 ± 1.90d
9.33±3.05ab
5.00 ± 2.24 cd
8.00 ± 0.00abc
30.00 ± 5.47a
8.67 ± 2.94d
33.67 ± 5.80a
33.00 ± 5.74a
21.00 ± 4.58b
14.33±3.78c
34.00 ± 5.83a
10.67 ± 3.26 cd
24.33 ± 4.90b
13.00 ± 3.60 cd
20.67 ± 4.54b
53.67 ± 7.30b
14.33 ± 3.80f
58.33 ± 7.60ab
65.00 ± 8.00a
36.67 ± 6.00d
24.00 ± 4.90e
63.00 ± 7.90a
19.00 ± 4.30ef
45.00 ± 6.70c
22.00 ± 4.70ef
37.33 ± 6.10d
11.33 ± 3.40a
3.33 ± 1.80e
9.67 ± 3.10abc
12.33 ± 3.50a
6.67 ± 2.60bcde
6.00 ± 2.50bcde
10.33 ± 3.20ab
4.33 ± 2.10de
9.33 ± 3.00abc
5.67 ± 2.30cde
8.33 ± 2.90abcd
36.67 ± 6.00a
11.00 ± 3.30e
34.00 ± 5.80ab
33.67 ± 5.80ab
22.33 ± 4.70 cd
17.66 ± 4.20de
36.33±6.00a
15.00 ± 3.90e
27.33 ± 5.20bc
17.33±4.20de
24.33 ± 4.90 cd
63.67 ± 8.00bc
20.67 ± 4.50 g
67.00 ± 8.20abc
71.00 ± 8.40ab
43.67 ± 6.60de
35.67 ± 6.00ef
74.67 ± 8.60a
29.33±5.40 fg
58.00 ± 7.60c
30.33 ± 5.50f
46.67 ± 6.80d
12.67 ± 3.50a
7.33±2.70bcd
10.00 ± 3.20abc
12.33 ± 3.50ab
7.33±2.70bcd
5.33 ± 2.30 cd
9.00 ± 3.00abcd
4.67 ± 2.10d
10.67 ± 3.30ab
7.33±2.70bcd
8.00 ± 2.80abcd
36.00 ± 6.00a
15.67 ± 4.00bc
31.33±6.00ab
31.33±6.00ab
22.67 ± 4.70abc
13.67 ± 4.00c
30.67 ± 5.50ab
16.00 ± 4.00bc
23.33 ± 4.80abc
19.67 ± 4.40bc
16.67 ± 4.00bc
55.67 ± 7.40a
26.33±5.10c
48.00 ± 7.00ab
50.00 ± 7.00a
37.00 ± 6.00abc
25.67 ± 5.00c
49.67 ± 7.00a
27.00 ± 5.20c
37.67 ± 6.10abc
28.67 ± 5.30bc
28.67 ± 5.30bc
Means followed by the same letters in columns do not differ by the Duncan test (α=0.05).
Sohrabi et al
Author's personal copy

three leaves were selected from the upper third of each of
the five randomly selected plants for counting the density of
total trichomes and type VI glandular trichomes on the
leaves. Then, three leaflets separated from each leaf and
trichomes were counted using a stereomicroscope (×40) on
three 2-cm
2
regions of each leaflet. The total number of
trichomes and type VI glandular trichomes were also count-
ed on different 2-cm
2
sections of the stem.
The normality of data was assessed with Shapiro-Wilk’s
test (Proc Univariate, SAS Institute (2003), Cary, NC, USA).
Data which needed to be normalized were transformed be-
fore being analyzed. The percentage data were subjected to
arcsin square root transformation; however, no count data
transformation was performed before analysis because there
was no evidence of non-normality within these data. Analysis
of variance was performed using the general linear model
(GLM) procedure in the SAS software and means were com-
pared using Duncan’s multiple range test. Total damage in-
dex for each cultivar was presented as thesum of the indices
gained for different evaluated traits. Index for each trait was
calculated by dividing the lowest recorded number in a cer-
tain cultivar to the greatest recorded number for that trait in
all cultivars. Pearson’s correlations (5% significance) were
used to evaluate the relationships between traits. Data were
then subjected to stepwise regression with overall plant
damage at 60 day as the dependent variable. Cultivar com-
parison and selection was accomplished by cluster analysis
according to Ward’s method using SAS software.
Results and Discussion
According to data of leaflet damage and leaf damage, and
overall plant damage, we found that the cultivars Berlina,
Golsar, Poolad, and Zaman more effectively avoided damage
caused by T. absoluta in the three evaluation periods
(Table 1). In contrast, Matin, Petopride5, SandocanF1, and
PS6515 showed significantly greater damage rates than other
evaluated cultivars (Table 1). There were also significant dif-
ferences in the number of mines on the leaf (F= 3.33, df = 10,
Table 2 The mean number of
mines on the leaf, number of
holes on the stem, and number
of holes on the fruit of tomato
cultivars submitted to infestation
of Tuta absoluta.
Cultivar Number of mines
on the leaf
Number of holes
on the stem
Number of holes
on the fruit
PS6515
Berlina
SandocanF1
Matin
Sadeen95
Zaman
Petopride5
Golsar
Golshan616
Poolad
Sadeen21
6.47 ± 2.50a
3.27 ± 1.80b
5.20a ± 2.30b
5.73 ± 2.40a
4.60 ± 2.10ab
3.20 ± 1.80b
6.13 ± 2.50a
3.53 ± 1.80b
4.67 ± 2.10ab
3.47 ± 1.80b
3.47 ± 1.80b
3.67 ± 1.90a
1.33 ± 1.00c
2.80 ± 1.60abc
3.13±1.70ab
2.33 ± 1.50abc
1.33±1.10c
3.33±1.80ab
1.40 ± 1.10c
2.40 ± 1.50abc
1.40 ± 1.10c
1.90 ± 1.10c
11.67 ± 3.40ab
4.07 ± 2.00e
11.00 ± 3.30ab
9.67 ± 3.10bc
6.87 ± 2.60cde
5.53 ± 2.30de
13.00 ± 3.60a
5.20 ± 2.30de
7.67 ± 2.70 cd
7.00 ± 2.60cde
8.67 ± 2.90bc
Means followed by the same letters in columns do not differ by the Duncan test (α= 0.05).
Table 3 Estimates of damage indices for different plant parts at day 60 after infestation and total damage index for tomato cultivars submitted to
infestation of Tuta absoluta.
Cultivar Leaflet damage
index
Leaf damage
index
Plant damage
index
Number of holes
on the stem index
Number of mines
on the leaf index
Number of holes
on the fruit indx
Total damage
index
PS6515
Berlina
SandocanF1
Matin
Sadeen95
Zaman
Petopride5
Golsar
Golshan616
Poolad
Sadeen21
0.78
0.21
0.84
0.94
0.53
0.35
0.91
0.27
0.65
0.32
0.54
0.84
0.28
0.88
0.93
0.57
0.47
0.98
0.39
0.76
0.40
0.61
0.80
0.38
0.70
0.72
0.53
0.37
0.71
0.39
0.54
0.41
0.41
0.78
0.28
0.60
0.66
0.49
0.28
0.70
0.30
0.51
0.30
0.30
0.74
0.37
0.60
0.66
0.53
0.37
0.70
0.40
0.53
0.40
0.40
0.67
0.23
0.63
0.56
0.40
0.33
0.75
0.30
0.44
0.40
0.50
4.60
1.75
4.24
4.47
3.44
2.15
4.76
2.05
3.05
2.23
2.76
Resistance of Tomato Cultivars to the Moth Tuta absoluta (Meyrick)
Author's personal copy

20, P= 0.0107), number of holes on the stem (F=3.37,
df = 10, 20, P= 0.0110), and fruit (F=9.10, df=10, 20,
P< 0.0001) caused by T. absoluta among the tomato culti-
vars (Table 2). The lowest number of mines on the leaf and
holes on the stem were observed in the cultivars Berlina,
Zaman, Golsar, Poolad, and Sadeen21. The cultivars Berlina,
Zaman, Golsar, and Poolad also had the lowest number of
holes on the fruit (Table 2).
Total damage index for evaluated tomato cultivars has
been presented in Table 3. Based on the results, the cultivars
Berlina, Golsar, Zaman, Poolad, and Sadeen21 with the low-
est total damage index (1.75, 2.05, 2.15, 2.23, and 2.76, re-
spectively) were the most resistant cultivars against
T. absoluta. The greatest total damage index was obtained
for the cultivars Petopride5, PS6515, Matin, and SandocanF1
(4.76, 4.6, 4.47 and 4.24, respectively) sustained less dam-
age from pest (Table 3).
Genetic variability is one of the characteristics of the
germplasm bank subsamples that gives higher or lower sus-
ceptibility to pest insects (Fernandes et al 2012). So, observed
differences between the levels of damages caused by
T. absoluta on different tomato cultivars in the present study
may have occurred because of genetic variability among
them. Resende et al (2006), Gonçalves et al (2008),
Oliveira et al (2009), Gonçalves Neto et al.(2010), Maciel
et al (2011), and Gharekhani & Salek-Ebrahimi (2014)have
also observed resistance to T. absoluta as non-preference
and antibiosis in some evaluated tomato cultivars.
The genetic diversity of tomato cultivars may display in-
appropriate morphophysiological features to oviposition of
T. absoluta adults and/or restrict the larvae feeding (Sobreira
et al 2009). Trichome density is the most important structur-
al feature of plants known to confer resistance to insect pests
(Sharma et al 2009,Heet al 2011). In the present study,
Table 4 Average densities
(number/2 cm
2
)oftotal
trichomes and type VI glandular
trichomes on the leaf and stem
for the plants used in the
bioassay.
Cultivar Leaf Stem
Total
trichomes
Type VI glandular
trichomes
Total
trichomes
Type VI glandular
trichomes
PS6515
Berlina
SandocanF1
Matin
Sadeen95
Zaman
Petopride5
Golsar
Golshan616
Poolad
Sadeen21
38.27 ± 6.20 cd
55.33 ± 7.40ab
43.00 ± 6.50c
36.40 ± 6.00 cd
60.4 ± 7.70a
50.13 ± 7.00b
26.80 ± 5.10e
55.33 ± 7.40ab
42.27 ± 6.50c
34.33 ± 5.90d
38.20 ± 6.20 cd
28.67 ± 5.30c
34.70 ± 5.90b
29.33±5.40c
23.70 ± 4.80c
37.70 ± 6.10a
34.33 ± 5.80b
17.70 ± 4.20e
37.70 ± 6.10a
30.70 ± 5.50c
23.33 ± 4.80d
25.67 ± 5.00d
64.70 ± 8.00a
78.30 ± 8.80a
70.40 ± 8.40a
84.10 ± 9.20a
87.7 ± 9.30a
101.7 ± 10.00a
86.8 ± 9.30a
110.00 ± 10.40a
94.50 ± 9.70a
72.30 ± 8.50a
69.30 ± 8.30a
20.00 ± 4.47abc
18.00 ± 4.24 cd
19.70 ± 4.43bc
16.00 ± 4.00d
21.70 ± 4.65ab
21.33 ± 4.62ab
22.00 ± 4.69ab
22.33 ± 4.72a
20.00 ± 4.47abc
16.70 ± 4.08d
18.00 ± 4.24 cd
Means followed by the same letters in columns do not differ by the Duncan test (α= 0.05).
Table 5 Estimates of Pearson’s correlations among the evaluated characteristics in tomato cultivars submitted to infestation of Tuta absoluta.
(1) (2) (3) (4) (5) (6) (7) (8) (9)
(1) Total number of trichomes on the stem –––––––––
(2) Number of Type VI glandular trichomes on the stem 0.19 ––––––––
(3) Total number of trichomes on the leaf 0.32 0.30 –––––––
(4) Number of type VI glandular trichomes on the leaf 0.30 0.30 0.91* ––––––
(5) Number of mines on the leaf 0.04 0.09 −0.40* −0.40* –––––
(6) Number of holes on the stem 0.02 0.1 −0.40* −0.40* 0.10* ––––
(7) Number of holes on the fruit −0.10 −0.03 −0.63* −0.61* 0.75* 0.74* –––
(8) Leaflet damage −0.17 −0.02 −0.58* −0.58* 0.76* 0.76* 0.82* ––
(9) Leaf damage −0.14 0.04 −0.58* −0.56* 0.73* 0.73* 0.82* 0.97* –
(10) Overall plant damage −0.07 0.08 −0.42* −0.40* 0.10* 0.10* 0.73* 0.78* 0.76*
*Significant at 5% by the ttest.
Sohrabi et al
Author's personal copy

significant differences were observed in the total number of
trichomes on the leaf (F= 21.47, df= 10, 20, P<0.0001),num-
ber of type VI glandular trichomes on the leaf (F= 46.58,
df = 10, 20, P< 0.0001), and number of type VI glandular tri-
chomes on the stem (F= 7.54, df = 10, 20, P< 0.0001) among
the cultivars (Table 4). However, differences in the total
number of trichomes on the stem were not significant
(P˃0.05) (Table 4). The cultivars with more total trichome
density on the leaf were Sadeen95, Berlina, and Golsar. The
most density of type VI glandular trichomes on the leaf was
observed in Sadeen95 and Golsar (Table 4). Golsar,
Sadeen95, Zaman, Petopride5, PS6515, and Golshan616 had
the greatest number of type VI glandular trichomes on the
stem. The lowest total number of trichomes and also type VI
glandular trichomes on the leaf was observed in Petopride5.
The cultivars Matin, Poolad, Berlina, and Sadeen21 had the
lower number of type VI glandular trichomes on the stem
(Table 4).
Pearson’s correlations revealed that the total number of
trichomes on the leaf had negative and significant correla-
tions with the overall plant damage (r=−0.42), leaf damage
(r=−0.58), leaflet damage (r=−0.58), number of mines on
the leaf (r=−0.40), number of holes on the stem (r=−0.40),
and number of holes on the fruit (r=−0.63) (Table 5).
Person’s correlation estimates between type VI glandular
trichomes on the leaf with overall plant damage (r=−0.40),
leaf damage (r=−0.56), leaflet damage (r=−0.58), number of
mines on the leaf (r=−0.40), number of holes on the stem
(r=−0.40), and number of holes on the fruit (r=−0.61) were
also negative and significant (Table 5). These results suggest
trichomes may have direct negative influence on both larval
feeding and oviposition by insects (Handley et al 2005), re-
sult in the lowest number of larvae and consequently lower
damage to leaves and plants. Gilardón et al (2001a)and
Neves et al (2003) also reported significant positive correla-
tion between the density of trichomes on the leaves and
resistance to Tuta species, as well as its relation to
trichomes type VI. Thus, the high density of leaf trichomes
present in the cultivars Sadeen95, Berlina, and Golsar can be
one of the possible causes of resistanceto T. absoluta known
as the antixenosis mechanism. Oliveira et al (2009)alsoob-
served that the HGB 1497 subsample of Solanum
lycopersicum L. presented resistance by antixenosis to the
tomato plant miner T. absoluta. The high density of tri-
chomes on tomato leaves can be extremely important for a
cultivar to avoid the presence of T. absoluta. In addition,
different metabolites are secreted from trichomes on the
stems and leaves of the tomato plants, which cause different
resistance against T. absoluta (Gilardón et al 2001b).
Compounds such as tridecan-2-one and undecan-2-one, es-
pecially secreted by type VI glandular trichomes on the to-
mato leaves, perform as physical and chemical barriers for
Table 6 Results of stepwise
multiple regression analysis
between overall plant damage at
day 60 (y) and the evaluated
characteristics.
Variable Parameter estimate Model R-square C(p) Fvalue
Number of mines on the leaf 8.85 0.92 2.30 360.29*
Total number of trichomes on the stem −0.06 0.93 0.40 5.04*
*Significant at P ≤0.05.
Fig 1 Dendrogram of 11 tomato
cultivars for six studied variables
using hierarchical cluster analysis
(Ward’smethod).
Resistance of Tomato Cultivars to the Moth Tuta absoluta (Meyrick)
Author's personal copy

insects and pathogens (Farrar & Kennedy 1991,Eigenbrode&
Espelie 1995,Justuset al 2000, Picoaga et al 2003). Such
features can be used in plant breeding programs aimed at
resistance to pests with selections toward genes that express
a higher number of trichomes. An exception was Poolad with
a low number of trichomes on the leaf (Table 4), which
showed high resistance to T. absoluta (Tables 1,2and 3).
Also, Sadeen95 with the most density of its trichomes
(Table 4), showed partially resistance to the pest (Tables 1
and 3). This result can be explained by the presence and role
of other potential resistance factors such as allelochemicals
that confer resistance to T. absoluta as shown by Leite et al
(1999) and Suinaga et al (2004).
Person’s correlation estimates between leaf and leaflet
damage with the number of mines on the leaf, number of
holes on the stem, and fruit were positive and significant
(Table 5). Overall plant damage also had positive and signif-
icant estimates of correlation with leaf damage (r= 0.76),
leaflet damage (r= 0.78), number of mines on the leaf
(r= 0.10), num ber of holes on th e stem (r= 0.10), and number
of holes on the fruit (r=0.73) (Table5). The number of holes
on the fruit had positive and significant correlations with the
number of mines on the leaf (r= 0.75) and number of holes
on the stem (r= 0.74) (Table 5). The number of holes on the
stem had positive and significant correlation with the num-
ber of mines on the leaf (r=0.10) (Table5).
Stepwise regression is an automated tool used in the ex-
ploratory stages of model building to identify a useful subset
of predictors. The process systematically adds the most sig-
nificant variable or removes the least significant variable dur-
ing each step. In order to remove the effect of non-effective
characteristics in the regression model on grain yield, step-
wise regression was used. The results of the stepwise regres-
sion analysis are presented in Table 6. The number of mines
on the leaf (x
4
) was the variable that best explained overall
plant damage at day 60 after infestation (y) as shown by
stepwise regression (Table 6). The total number of trichomes
on the stem (x
1
) was the second variable that exerted influ-
ence on overall plant damage. Parameter estimates showed
that the number of mines on the leaf had positive significant
effect, while the number of trichomes on the stem negatively
affected overall plant damage at day 60 (Table 6).
The results of cluster analysis separated 11 evaluated tomato
cultivars in three distinctive categories including Petopride5,
Matin, SandokanF1, and PS6515 as susceptible; Golshan616,
Sadeen21, and Sadeen95 as partially resistant; and Berlina,
Zaman, Golsar, and Poolad as resistant cultivars (Fig 1).
Conclusions
Significant differences in relative resistance of the studied
tomato cultivars demonstrate that the ones have potential
for use in backcrosses in processing tomato breeding pro-
grams. However, our results are preliminary and require fu-
ture studies for identifying the other resistance factors, other
than trichome density, associated with these cultivars. Also,
additional analyses with molecular markers will be needed
for indicating the probable genetic variation between these
tomato cultivars.
Acknowledgments Financial support provided by the research deputy
of Persian Gulf University is gratefully acknowledged.
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