Effect of BA, IBA and cutting type on transplants production from cuttings
GENETIC ANALYSIS TO FIND SUITABLE PARENTS
1. Egypt. J. Plant Breed. 19(1):55 – 70 (2014)
GENETIC ANALYSIS TO FIND SUITABLE PARENTS
FOR DEVELOPMENT OF CHERRY TOMATO HYBRIDS
UNDER GREEN HOUSE CONDITIONS
A.M.A. Mahmoud1
and A.A.S.A. El-Eslamboly2
1
Vegetable Crops Department, Faculty of Agriculture, Cairo University,
2
Horticulture Research Institute, Agriculture Research center, Cairo, Egypt.
ABSTRACT
Cherry tomato has the potential for improvement through heterosis breeding
which can further be utilized for development of desirable recombinants. A 7×7, half-
diallel mating design was used to determine heterosis over better parent, potence ratio,
combining ability and gene action for nine characters in cherry tomato. Preponderance
of additive gene action was evident for control of all characters studied except fruit
firmness and fruit ascorbic acid content for which both additive and non-additive gene
actions were evident. Generally, no particular cultivar or hybrid can be used to evaluate
all studied traits with equal efficiency. However, amongst the parental lines,
Solanumlycopersicum var. cerasiforme LYC 196/81 cv. Bubjekosoko (P1), PI 647522 cv.
Cal Red Cherry (P3) and PI 639207 cv. Black Cherry (P7) were the best general
combiners for fruit yield along with good quality traits and thus could be used in tomato
hybridization programs. Also, parent Solanum sp. PI 260402 cv. M-10 (P5) exhibited
highly significant general combining ability (GCA) effect in desired direction for fruit
contents of TSS, titratable acidity, ascorbic acid content, and lycopene. Some crosses
showing high significant specific combining ability (SCA) effects for fruit yield involved
parents showing high GCA for yield. The cross P1 × P7 exhibited highest significant
positive values of SCA of yield along with quality traits and this result incompatible with
those obtained in a performance evaluation trail of the produced hybrids with their
parents. The cross P6 (Solanum sp. PI 126915 cv. 125) × P7 exploited the best
combination for better quality traits.The general performances of the F1 hybrids reflected
the presence of various degrees of dominance effects; i.e., partial to overdominance for
the evaluated characters. Some produced F1 hybrids had significantly heterobeltiosisin
desired direction for the evaluated traits.
Keywords: Cherry tomato, Solanumlycopersicum var. cerasiforme, Heterobeltiosis,
Dominance, Gene action, Combining ability.
INTRODUCTION
Cherry tomato,Solanumlycopersicum var. cerasiforme (Alef.)Voss,
is a botanical variety of the cultivated tomato and it is thought to be the
originator of all cultivated tomato types.Cherry tomato is grown for its
edible fruits, which are generally round, red when ripe, small (less than 30g)
and longer than 1.5 cm, but less than 3 cm in diameter (Kalloo 1991
andRancet al 2008).Cherry tomatoes are largely used for fresh consumption
and their commercial importance is continuously increasing because of their
high nutritional value, antioxidant properties and good taste (Kavthaet al
2014,Premaet al 2011and Renukaet al 2014).
Cherry tomato varieties are generally characterized by higher dry
matter and soluble solids levels than normal-sized fresh market cultivars;
these differences are due to the higher content of sugars (fructose and
glucose) and organic acids (citric and malic), which, in turn, are major
2. 56
factors in determining the greater sweetness, sourness, and overall flavor
intensity of most cherry varieties (Causseet al 2003 andRenukaet al
2014).Cherry tomato is a rich source of antioxidants (mainly lycopene and
β-carotene), vitamin C, pro-vitamin A carotenoids, and minerals like Ca, P
and Fe in diet (Garcýa-Closaset al 2004,Lenucciet al 2006 andKavithaet al
2014), which are protective against infectious and degenerative diseases,
such ascardiovascular diseases (Marchioliet al 2001) or certain cancers
(Byers and Guerrero1995). For this reason, there is an emphasis on breeding
new tomato cultivars with nutraceutical value, but there has been less work
done with respect to quality improvement in cherry tomatoes. There has
been no breeding program targeted towards nutritive values in Egypt.
Many tomato breeding programs are directed toward the
development of superior Fl hybrids. Hybrids are preferred over pure line
varieties in tomato on account of their maturity earliness, more uniformity,
disease resistanceand superiority of marketable fruit yield and fruit quality
(Shankaraet al 2005). Thus, the cultivation of hybrid varieties is economical
and remunerative, and, therefore, the greater part of tomato crop is occupied
by hybrid varieties, especially in the greenhouse. Hybrid plants combine the
characters of the parent plants. Previous studies have suggested that
increasing genetic distances (variability) between parents, increases
heterosis, especially, heterobeltiosis (Melchinger 1999). The term heterosis
refers to the phenomenon in which the F1 population obtained by crossing
two genetically dissimilar individuals show increase or decrease in vigour
over the better parent (heterobeltiosis), over the average overall parents
(mid-parents heterosis), or over the best standard variety (standard
heterosis). Heterosis in desirable direction (hybrid vigour) is the ultimate
aim of breeders. Hence, there is great significance in the improvement of
methods for heterosis breeding and hybrid seed production.
Heterosis in tomato was first observed by Hedrick and Booth (1907)
for higher yield and more number of fruits per plant. Stoner and Thompson
(1966) reported that all crosses of small × small fruited strains and some
small × large fruited strains of tomato showed heterosis in the F1 with the
mean exceeding the top parent. Further genetic analysis indicated that
epistasis or non-allelic interactions were primarily responsible for heterosis.
Heterosis manifestation in tomato is in the form of greater vigour, faster
growth and development, earliness in maturity, increased productivity,
higher levels of resistance to biotic and abiotic stresses (Yordanov 1983).
Since then a number of workers have reported heterosis in tomato
(Metwallyet al 2003, Shalaby 2008, 2012 and 2013, Singh and Asati 2011,
and Solieman et al 2013).Khereba et al (2011) found a positive standard
heterosis of yield components and quality traits among 55 cherry tomato
hybrids produced and evaluated with standard hybrid cv. Sweet Million.
3. 57
In any crop improvement program, the choice of the parents for
hybridization is one of the critical and the most difficult tasks for the
breeder. The fitness of cultivars and lines for use as partners in hybrid
combinations is determined not only by their economically valuable
characters but also by their ability to produce high heterosis effect in F1
crosses. This ability, called "combining ability", plays a great role in the
success of heterosis breeding. Therefore, test crosses for general and
specific combining ability must be primarilyachieved. GCA reveals the
existence of additive gene effects, while SCA reveals non-additive gene
effects and additive × dominance and dominance × dominance interactions.
Information about GCA effects are beneficial in choosing best combiner
parents and SCA effects information reveal best cross combinations for
further judgment. Judicious application of information relevant to standard
heterosis and SCA are fruitful for selecting best hybrids for desired traits
(Moore and Currence 1950).
The present study was carried out to identify the best combiner
parents of cherry tomato accessions and best cross combinations between
themfor developing promising hybrids for yield and quality traitsunder
greenhouse conditions using a half-diallel mating design, in addition to
estimating the extent of heterobeltiosis and potence ratio.
MATERIALS AND METHODS
This study was conducted at greenhouses of Kaha Vegetable
Reserch Farm, Horticulture Research Institute, Agriculture Research Center
(ARC), Kalubia Governorate, Egypt. Seventy eight accessions of cherry
tomatowere planted in greenhouse duringthe 2012 winter planting for
propagation by selfing. Five accessions of S. lycopersicum var. cerasiforme
and 2 accessions of Solanum sp. were selected based on their characters,
especially productivity and fruit quality (Table 1).A crossing program was
conducted among 7 cherry tomato accession in a half-daillel mating design
(Grriffing, 1956).
Seeds of the 28 genotypes (7 parents + 21 F1's) were sown in
speedling trays filled with mixture of peatmoss and vermiculate (1:1)
enriched with macro and micro elements on mid of August and transplanted
on mid of September 2012 and 2013. A randomized complete block design
(RCBD) with 3 replicates was used. The area of the greenhouse was divided
into 5 beds. Each bed was 1.2 m wide, plants were transplanted on both
sides of the bed. The in-row distance between plants was 50 cm. Each
experimental unit (EU) consisted of ten plants. All cultural practices
(fertilization, irrigation, and controlling weeds, diseases and insects) were
performed as recommended for commercial tomato production in
greenhouse.
4. 58
Table 1. Cherry tomatoaccessionsevaluated.
Parent Accession Cultivar name Country Characters
S. lycopersicum var. cerasiforme
P1 LYC 196/81 Bubjekosoko
Indeterminate, high set and yield,
red fruit
P2 PI 204981 126-1 US
Indeterminate, plant vigor, red
fruit
P3 PI 647522 Cal Red Cherry
US,
California
Indeterminate, high set and yield,
dark red fruit
P4 PI 647555 Siten Macedonia
Indeterminate, plant vigor, red
fruit
P7 PI 639207 Black Cherry
Indeterminate, high set and yield,
pink fruit
Solanum sp.
P5 PI 260402 M-10 Indeterminate, plant vigor, high
yield, sweetness, red fruitP6 PI 126915 125
z
Accession: The LYC was the courtesy of the InstitutfürPflanzengenetik und
Kulturpfianzenforschung,Genebank, Gatersleben, Germany and the PIs were kindly provided
by the USDA through Dr. Charles Block (Plant Introduction Station, Ames, Iowa).
Data were recorded on evaluated genotypes on early (EY – the first
three harvests) and total yield (TY – all the collected fruits) per plant, and
fruit quality characters, i.e., average fruit weight (AFW – average weight of
30 fruits of EU), pericarp thickness (FPT - means of 10 fruits of EU), fruit
firmness (FF), and fruit contents of total soluble solids (TSS), titratable
acidity (TAC), ascorbic acid (AAC) and lycopene (LC).
Fruit firmness was determined in 10 red-ripe fruits from each
genotype perEU using a food pressure tester (Force Gauge Model M4-200)
Mark-10 (Series 4). Three readings were taken for each fruit by pushing the
pentameter needle slowly at 3 different sites (near the shoulder, blossom end
and equatorial plane). Then, mean of the 3 readings was calculated. Samples
of 30 ripe fruits (from the third to six clusters) representing each EU were
picked for analysis of fruit analyses. An extract was obtained by blending
and filtering flesh of each fruit sample. TSS was determined using a hand
refractometer. TAC was ascertained using 0.1 N NaOH solution and
phenolphthalein as indicator (AOAC, 1990). AAC (vitamin C) was
measured using 2,6 dichlorophenol indophenol dye (AOAC, 1990).
Statistical analysis
Results of the two years were combined and statistically analyzed
using MSTAT-C v. 2.1 (Michigan State University, Michigan, USA) and
mean comparisons were based on the Duncan's multiple range test (Steel
and Torrie, 1981).
Estimation of heterobeltiosis
Heterobeltiosis (better-parent heterosis - BPH) for the different
studied characters were calculated using the following equation (Mather and
Jinks, 1971):
5. 59
BPH =
S.E=
Where, , mean value of hybrid, mean value of the better parent, S.E.
standard error, MSe mean square of error, and r number of replicates.
Estimation of potence ratio
Potence ratio (P)was used to determine the direction of dominance
according to Smith (1952) as follows:
Where, mean value of the hybrid, mean of the smaller parent,
mean of the larger parent, and MP mid-parent value.
The absence of dominance was assumed when the difference
between the parents was significant and ــــ MP was not significant.
Complete dominance was assumed when P equaled to or did not differ from
±1.0. Meanwhile, partial dominance was considered when P was between
+1.0 and -1.0, but was not equal to zero. Over dominance (Heterosis) was
assumed when P exceeded ± 1.0.
Analyses of combining abilities
When the F-test revealed significant differences among the
genotypes, combining ability analysis was followed. The values of general
combining ability (GCA) and specific combining ability (SCA) were
estimated according to Griffing'smodel 1 method 2 of diallel analysis (Singh
and Choudhary, 1979):
Yij = μ + gi + gj + sij + eijk
Where,Yij is the mean phenotypicvalue, μ is the general mean, gi is the
general combining ability (GCA) effect, sijis the specific combining ability
(SCA) effect and eijkis the error term.
Analysis of variance table for combining ability with expectation of
mean square was set up as follows:
Source d.f. M.S. E.M.S.
GCA p-1 Mg
SCA p(p-1)/2 Ms
Error (r-1)(p-1)
The additive and dominance genetic variances were estimated from the
combining ability components as follows:
Where
Where
6. 60
RESULTS AND DISCUSSION
The present investigation was undertaken to evaluate performance of
cherry tomato accessions, calculate potence ration and extent of
heterobeltiosis and to identify potential parental lines and cross
combinations on the basis of combining ability under greenhouse conditions
in cherry tomato. Twenty-one cross combinations (F1s) along with their 7
parents were evaluated and observations were recorded on fruit yield and
component and fruit quality traits during winter seasons of 2013 and 2014
under greenhouse conditions of Kaha Vegetable Reserch Farm, ARC,
Kalubia Governorate.
Variation and mean performance of parents and hybrids
Significant differences were found among the evaluated genotypes
(parents and their hybrids) under greenhouse conditions during 2013 and
2014 winter seasons for all studied characters (Table 2). For yield and its
components traits, LYC 196/81 cv. Bubjekosoko (P1) was the best parents,
as it gave the highest EY and TY (0.88 kg/plant and 6.64 kg/plant,
respectively), followed by PI 647522 cv. Cal Red Cherry (P3 - 0.52 kg/plant
and 4.93 kg/plant, respectively) and PI 639207 cv. Black Cherry (P7) for TY
(5.13 kg/plant). For AFW, P1 have the highest fruit weight followed by P3.
For fruit quality traits, PT was high in P1, P3 and P7. Fruits of PI 204981 cv.
126-1 (P2) and PI 647555 cv. Siten (P4) had more firmness compared with
other parents. Fruit TSS content was higher with PI 260402 cv. M-10 (P5)
and PI 126915 cv. 125 (P6). Parent P7 had the highest content of ascorbic
acid and lycopene. Parent P2 had the highest content of titratable acidity.
For hybrids, the cross P1 × P7 have the highest EY and TY (0.88
kg/plant and 7.61 kg/plant, respectively), while, the cross P1 × P3 have
highly TY, 7.87 kg/plant compared with all evaluated genotypes.Average
fruit weight was higher in hybrid P4 × P7 followed by P1 × P7 and P1 × P3
(22.92, 20.77 and 20.51 g, respectively). For fruit quality traits, some
crosses were superior for the following traits:PT (P3 × P7 and P1 × P3), FF
(P2 × P4), TSS content (P5 × P6, P5 × P7, P6 × P7, and P1 × P5),TAC (P2 × P4,
P2 × P5, P2 × P6, P1 × P2, P1 × P5, P5 × P6, and P4 × P5),AAC(P5 × P6, P4 ×
P7, and P1 × P5), and LC (P6 × P7 and P5 × P7).
Mode of gene action for different characters
The success of a breeding program depends upon the choice of
suitable parents and their utilization by adopting an appropriate breeding
method. The combining ability analysis has been used extensively to
identify potential parents either to be used in the development of hybrids or
recombinant breeding for getting elite pure parents. This analysis facilitates
7. 61
Table 2. Combined mean performance of seven cherry tomato cvs and their
twenty one F1s of various studied characters during the 2012 and
2013 winter plantings.
Populations
Earlyyield
(kg/plant)
Totalyield
(kg/plant)
Averagefruit
weight
(g)
Pericarp
thickness
(mm)
Fruitfirmness
(kg/cm2
)
TSS
(%)
Titratable
aciditycontent
(mgcitric
acid/100gfresh
fruit)
Ascorbicacid
content
(mg/100gfresh
fruit)
Lycopene
content
(mg/100gfruit)
Parents
P1 0.88 a 6.64 b 24.88 a 3.30 a-c 0.27 g-j 7.33 f-j 0.81 g-i 20.24 h 1.59 n
P2 0.22 g 2.84 k 8.95 mn 2.60 l 0.33 b 5.47 l 1.21 a 20.77 gh 2.01 g-i
P3 0.52 de 4.93 e-i 20.81 c 3.31 a-c 0.27 g-k 7.40 f-i 0.83 g-i 17.32 i 1.68 mn
P4 0.22 g 3.47 jk 6.94 o 2.89 g-k 0.32 bc 6.40 j-l 0.94 c-h 22.79 d-f 1.86 k
P5 0.24 g 4.00 ij 8.62 n 2.81 j-k 0.26 j-l 8.80 a-d 1.04 a-f 24.25 cd 2.05 fg
P6 0.25 g 4.61 e-i 8.50 n 2.85 h-k 0.25 kl 8.00 c-g 0.99 b-h 21.81 e-h 2.18 b-e
P7 0.26 g 5.13 e-g 15.52 e-h 3.39 ab 0.27 g-j 6.93 h-k 0.59 j 25.30 bc 2.30 a
F1 hybrids
P1 × P2 0.58 cd 5.13 e-g 15.01 f-h 2.95 f-j 0.24 l 7.47 f-i 1.10 a-c 20.78 gh 1.88 jk
P1 × P3 0.73 b 7.87 a 20.51 c 3.43 ab 0.26 j-l 7.53 f-i 0.89 d-h 19.98 h 1.74 lm
P1 × P4 0.59 cd 5.22 d-f 14.90 gh 3.01 e-h 0.26 j-l 7.53 f-i 0.99 b-h 21.13 f-h 1.82 kl
P1 × P5 0.64 c 6.06 b-d 15.73 e-g 2.93 f-j 0.22 m 8.73 a-e 1.01 a-g 26.44 ab 1.93 h-k
P1 × P6 0.73 b 6.24 bc 15.16 e-h 2.98 f-i 0.21 m 8.17 b-f 0.95 b-h 22.42 d-g 1.98 g-j
P1 × P7 0.88 a 7.61 a 20.77 c 3.27 b-d 0.30 c-e 7.63 f-i 0.79 hi 25.05 bc 2.09e-g
P2 × P3 0.48 e 4.26 e-j 19.08 d 2.89 g-k 0.25 j-l 6.20 kl 1.08 a-d 22.56 d-f 1.89 i-k
P2 × P4 0.26 g 4.15 h-j 9.60 lm 2.86 h-k 0.35 a 6.17 kl 1.16 ab 20.50 h 2.01 g-i
P2 × P5 0.23 g 3.40 jk 10.96 k 2.56 l 0.26 h-k 7.07 g-k 1.14 a-c 20.41 h 2.09 d-g
P2 × P6 0.36 f 4.36 f-j 11.95 ij 2.85 h-k 0.26 h-l 6.80 i-k 1.13 a-c 22.41 d-g 2.18 b-e
P2 × P7 0.45 e 4.34 f-j 14.57 h 3.01 e-h 0.31 b-d 6.10 kl 0.89 d-h 23.98 cd 2.20 b-d
P3 × P4 0.49 e 4.92 e-i 15.14 e-h 3.02 e-h 0.26 j-l 6.87 i-k 0.95 c-h 24.20 cd 1.92 h-k
P3 × P5 0.49 e 5.11 e-h 14.91 gh 3.00 e-h 0.27 g-k 7.37 f-j 0.68 ij 23.54 c-e 2.01 g-i
P3 × P6 0.44 e 5.50 c-e 16.12 e 3.18 c-e 0.30 c-f 7.73 f-i 0.85 f-i 23.17 de 1.99 g-j
P3 × P7 0.53 de 6.64 b 22.92 b 3.47 a 0.28 e-h 7.80 e-i 0.79 hi 20.31 h 2.07 e-g
P4 × P5 0.28 fg 4.01 ij 11.11 jk 2.73 kl 0.32bc 7.93 d-h 1.05 a-f 20.67 gh 2.03 gh
P4 × P6 0.24 g 4.19 g-j 10.17 kl 2.96 f-j 0.27 g-k 7.53 f-i 0.96 b-h 23.19 de 2.03 gh
P4 × P7 0.28 fg 5.14 e-g 12.73 i 3.11 d-f 0.29 d-g 7.20 f-j 0.82 g-i 26.69 ab 2.15 c-f
P5 × P6 0.36 f 4.59 e-i 10.95 k 2.79 jk 0.24 l 9.13 a 1.06 a-e 27.88 a 2.19 b-e
P5 × P7 0.34 f 4.71 e-i 12.68 i 3.02 e-h 0.26 j-l 9.10 ab 0.86 f-i 22.96 de 2.22 a-c
P6 × P7 0.58 cd 5.38 c-e 15.99 ef 3.06 e-g 0.28 f-i 8.93 a-c 0.83 g-i 20.76 gh 2.37 a
z
Values followed by a letter in common are not significantly different at the 0.05 level according
to Duncan's multiple range test.
y
S. lycopersium var. cerasiforme:P1,LYC 196/81cv. Bubjekosoko;P2,PI 204981 cv. 126-1;P3, PI
647522cv. Cal Red Cherry;P4,PI 647555cv. Siten;P7,PI 639207cv. Black Cherry (P7);
Solanumsp. P5, PI 260402 cv. M-10 and P6,PI 126915 cv. 125.
the partitioning of genotypic variation of crosses into variation due to GCA
and SCA. GCA effects are the measure of additive gene action which
represent the fixable components of genetic variance and are used to classify
the parents for the breeding behavior in hybrid combinations. On the other
hand, SCA effects are the measure of non-additive gene action which is
related to non-fixable component of genetic variance (Griffing
1956).Therefore, it is important to assess the general and specific combining
ability effects in the selection of the parents and the formulation of an
appropriate crossing plan. Among the various breeding methods, diallel mating
8. 62
design (method 2) excluding reciprocals (Griffing 1956) has been used in the
present study to evaluate 7 parents and their 21 crosses.
Mean squares for genotypes, parents, and hybrids were highly
significant (P ≤ 0.01) for all studied traits (Table 3).The parents versus
hybrids (P vs H) component were highly significant for all studied
characters except pericarp thickness and titratable acidity.
Table 3. Mean squares from analysis of variance of 7 × 7 half diallel crosses of
tomato for various characters.
Character
Mean squares
Rep.
df = 3
Genotype
df =27
Parent (P)
df = 6
Hybrid (H)
df = 20
P vs H
df = 1
Error
df = 54
Early yield 0.0009 0.1186**
0.1871**
0.0955**
0.1721**
0.0019
Total yield 5.1213 4.1519**
4.6127**
4.0098**
6.9285**
0.2489
Average fruit weight 0.9640 63.8377**
149.7887**
39.8100**
28.6871**
0.2910
Pericarp thickness 0.0009 0.1631**
0.2827**
0.1352**
0.0048ns
0.0089
Fruit firmness 0.0001 0.0031**
0.0025**
0.0033**
0.0022**
0.0001
TSS 0.2537 2.6493**
3.4863**
2.4164**
2.2857**
0.2721
Titratable acidity 0.0050 0.0663**
0.1153**
0.0540**
0.0185ns
0.0113
Ascorbic acid content 5.5753 17.0021**
21.4142**
15.6940**
16.6895**
0.9252
Lycopene content 0.0055 0.0977**
0.1970**
0.0672**
0.1138**
0.0037
**
highly significant (Ρ ≤ 0.01) and ns
non-significant.
The analyses of variance for combining ability exhibited highly
significant (P≤0.01) components of GCA and SCA mean squares for most
of the studied characters except PT and lycopene content characters which
were significant (P≤0.05) and also SCA mean square of TA which was non-
significant (Table 4).
Table 4. Analysis of variance for combining ability of a 7 × 7 half diallel
crosses for various characters in tomato.
Characters
Mean squares
δ2
g δ2
s δ2
e δ2
g : δ2
s δ2
A δ2
DGCA
df= 6
SCA
df= 21
Error
d = 54
Early yield 0.150**
0.008**
0.001 0.032 0.007 0.001 4.29 0.063 0.007
Total yield 5.291**
0.311**
0.083 1.107 0.228 0.083 4.86 2.214 0.228
Average fruit weight 85.634**
2.892**
0.097 18.387 2.795 0.097 6.58 36.774 2.795
Pericarp thickness 0.222**
0.006*
0.003 0.048 0.003 0.003 14.60 0.096 0.003
Fruit firmness 0.002**
0.001**
0.00005 0.00033 0.000660.00005 0.51 0.00067 0.00067
TSS 3.226**
0.214**
0.091 0.669 0.123 0.091 5.44 1.339 0.123
Titratable acidity 0.083**
0.005ns
0.004 0.0175 0.0008 0.004 21.26 0.035 0.0008
Ascorbic acid content8.139**
4.961**
0.308 0.706 4.653 0.706 0.15 1.413 4.653
Lycopene content 0.223**
0.006*
0.003 0.0482 0.0032 0.003 14.90 0.096 0.003
**
Highly significant (Ρ ≤ 0.01); *
significant (P≤0.05); ns
non-significant.
These results proved that both additive and non-additive gene effects
play an important role in operating the heredity of all studied traits except
TA. Higher values of variance due to GCA (δ2
g) than variance due to SCA
(δ2
s) and δ2
g/δ2
s ratio was more than one for all studied characters, except FF
and AAC, suggesting preponderance of additive gene action for these
9. 63
characters. Meanwhile, higher values of δ2
s than δ2
g and δ2
g/δ2
s ratio was
less than one for FF and AAC, indicating that non-additive variance
prevailed in genetic determination of these characters. These results,
accordingly, indicated that cherry tomato crosses can produce F1 hybrids
which may perform better, in one or more traits, than either of their parents
or other commercial cultivars.
Due to the predominance of additive gene action in inheritance of
most yield components and quality traits, recurrent selection, a breeding
method that increases the frequency of favorable alleles and identifies the
superior combinations by repeated crossing and selection could be the best
method to exploit the additive gene effects. The use of diallel selective
mating (Jensen 1970) or mass selection with concurrent random mating
(Redden and Jensen 1974) or restricted recurrent selection by mating the
most desirable segregants followed by selection (Shende et al 2012) might
be useful breeding strategies for the improvement of these traits governed
by both additive and non-additive types of gene action.
Considering the non-additive gene action for the control of FF and
fruit AAC traits, selection will slow genetic improvement. The successful
breeding methods will be those that accumulate the genes to form superior
gene constellations interacting in a favorable manner, such as heterosis
breeding, which is the best possible option for improving these traits in
cherry tomato (Kalloo 1991).
Muttappanavar et al (2014) reported that additive gene effects
appeared more important than non-additive gene effects for some traits of
cherry tomato, i.e., TY, AFW, and PT. Also, Garg et al (2007 and 2008),
Hannan (2007) and Andrade et al (2014) reported that additive gene effects
appeared more important than non-additive gene effects for AFW, EY, TY
and fruit TSS for large-sized tomato. Hosamani (2010) found that the
estimates ratio of GCA variance to SCA variance were higher for PT and
TSS. Meanwhile, the previously presented results concerning AAC
character are in agreement with those obtained by Joshi and Kohli (2006)
and Garg et al (2007 and 2008) who reported the importance of non-
additive gene action in the inheritance of this character in large-sized
tomato.
Heterobeltiosis and potence ratio estimations of F1 hybrids
The discovery of hybrid vigour by Shull (1908) opened a new era in
genetic improvement of crop plants which is now referred to as “heterosis
breeding”. Genetically diverse varieties are the main necessity to observe
heterosis in F1 hybrids (Mole et al 1962). It is an effective tool in improving
the yield and component and quality traits of different crop species.
The percent increase (+) or decrease (-) of a cross over the better
parent was calculated to determine heterotic effects for all traits. Data on
11. 65
The extent of BPH varied from -32.16 to 123.08 for early yield, -
24.53 to 29.43 for total yield, -40.11 to 33.52 for average fruit weight, -
12.70 to 4.04 for pericarp thickness, -26.92 to 7.69 for fruit firmness, -19.7
to 5.41 for fruit TSS, -34.34 to 10.67 for fruit titratable acidity content, -
19.73 to 14.94 for fruit ascorbic acid content, and -6.74 to 31.34 for fruit
lycopene content (Table 5).
The estimates of heterobeltiosis, relative to better parent values
(Table 5) reflected significant effects in desirable directions on 13 F1
hybrids for fruit lycopene content, 6 F1 for average fruit weight, 5 F1 for
early yield, 3 F1 for fruit ascorbic acid content, 2 F1 for total yield, and no
hybrid exhibited significant heterobeltiosis in desired direction over better
parent for pericarp thickness, fruit TSS, and fruit titratable acidity content.
Positive and significant heterosis over standard hybrid variety in
cherry tomato traits has been reported Khereba et al (2011) and also, in
large-sized tomato traits have been reported by many investigators
(Metwally et al 2003, Shalaby 2008, 2012 and 2013, Singh and Asati 2011,
Solieman et al 2013).
The values of dominance estimates illustrated in 21 F1 crosses are
presented in Table (5). Early yield per plant showed that potence ratios
ranged from -23.6 to 49, and they were more than ±1 for nine crosses and
between ±1 in 12 crosses indicating over-dominance and partial dominance,
respectively. Potence ratio of total yield per plant varied from -0.03 to
15.85, and they were more than ±1 for 9 crosses, indicating over-dominance
and between ±1 in 8 crosses, indicating partial dominance. Average fruit
weight expressed over dominance in 8 crosses and partial dominance in 13
crosses. In respect to pericarp thickness, potence ratio ranged from -2.85 to
39, and they were more than ±1 for 7 crosses (over dominance), between ±1
for 12 crosses (partial-dominance), +1 for one cross (complete dominance),
and 0 for one cross (no dominance). In case of fruit firmness, 15 crosses
expressed over dominance and 6 crosses expressed partial dominance.
Regarding fruit TSS content, 11 crosses exhibited over-dominance and 10
crosses exhibited partial dominance. In case of fruit titratable acidity, most
of crosses exhibited over-dominance, while 3 crosses exhibited only partial
dominance. Potence ratio of fruit ascorbic acid content expressed over-
dominance in 15 crosses except 6 crosses, where partial dominance was
noticed. Fruit lycopene content character expressed over dominance in 5
crosses, complete dominance in two crosses and partial dominance in 14
crosses.
In cherry tomato, mere breeding for enhanced yield is not important
unless it is qualified by the quality requirements desired by the consumers.
The positive values of heterobeltiosis and potence ratio for the characters
EY, TY, AFW, AAC, and LC reflected the presence of various degrees of
dominance; i.e., partial- to over-dominance which are involved in the
12. 66
inheritance of these characters. Both dominant and additive gene effects
were reported in regulating the inheritance of EY, TY, AFW, and LC with
prevalence of dominance gene effect (Hannanet al 2007). Garg et al (2007
and 2008) illustrated that additive gene effects were found to be more
important than non-additive gene effects in the inheritance of AFW, EY,
TY, FF, PT and TSS. Hence, hybrid breeding can be used efficiently to
improve yield together with quality in tomato (Hannanet al 2007).
Identification of good general and specific combiners
No single parent was found to be a good general combiner for all
studied characters. However, parent P7 exhibited significant GCA effects in
desired direction in most of the heterotic crosses for TY, AFW, PT, FF, fruit
AAC and LC, and was considered as a good general combiner (Table 6).
Next to P7, significant GCA effects in desired direction for EY, TY, AFW,
PT and fruit TSS was shown by P1 and P3. Therefore, three parents P7, P1,
and P3 could be picked up as potential donors for fruit yield per plant and
other important horticultural traits. Parent P5 exhibited highly significant
GCA effects in desired direction for fruit contents of TSS, TA, AAC and LC
traits. Therefore, this parent could be selected as potential donor for fruit
quality traits.
Table 6. General combining ability (GCA) effects of 7 parents for different
characters of cherry tomato in a 7 × 7 half diallel cross.
Parent
Early
yield
Total
yield
Average
fruit
weight
Pericarp
thicknes
s
Fruit
firmness
TSS
Titratable
acidity
Ascorbic
acid
content
Lycopene
content
P1 0.26**
1.25**
4.01**
0.12**
-0.02**
0.21**
-0.02ns
-0.46**
-0.17**
P2 -0.09**
-0.98**
-1.85**
-0.19**
0.02**
-1.01**
0.15**
-0.92**
0.02**
P3 0.07**
0.45**
3.84**
0.17**
-0.003ns
-0.17ns
-0.07**
-1.34**
-0.13**
P4 -0.11**
-0.62**
-3.14**
-0.07**
0.02**
-0.42**
0.03ns
0.17ns
-0.05**
P5 -0.09**
-0.47**
-2.47**
-0.16**
-0.01**
0.79**
0.04**
1.11**
0.05**
P6 -0.04**
-0.07ns
-2.05**
-0.06**
-0.01**
0.5**
0.03ns
0.33ns
0.11**
P7 -0.0004ns
0.44**
1.66**
0.18**
0.01**
0.09ns
-0.15**
1.10**
0.17**
S.E. (gi) ±0.008 ±0.089 ±0.096 ±0.017 ±0.002 ±0.093 ±0.019 ±0.171 ±0.011
S.E. (gi - gj) ±0.012 ±0.136 ±0.147 ±0.026 ±0.003 ±0.142 ±0.029 ±0.262 ±0.017
**
Highly significant (Ρ ≤ 0.01); *
significant (P≤0.05); ns
non-significant.
z
S. lycopersium var. cerasiforme: P1, LYC 196/81 cv. Bubjekosoko; P2, PI 204981 cv. 126-1; P3,
PI 647522 cv. Cal Red Cherry; P4, PI 647555 cv. Siten; P7, PI 639207 cv. Black Cherry;
Solanumsp. P5, PI 260402 cv. M-10 and P6, PI 126915 cv. 125.
SCA involves non-additive effects and additive × dominance and
dominance × dominance interactions, which are non-fixable or non-heritable
and are of significance in hybrid breeding only. So, SCA effects are useful
to predict the potential of a particular cross in exploiting heterosis (Moore
and Currence 1950). Similarly, no single cross was judged as good specific
combiner for all studied characters (Table 7). The cross P1 × P7 exhibited
highly significant SCA effects for EY, TY, AFW, FF, AAC and LY in
desired directions. Also, three crosses exhibited highly significant SCA
effects in desired direction of TY, in addition to PT and FF in cross P2 × P4;
13. 67
to AFW and PT in cross P3 × P7; and to PT in cross P1 × P3 (Table 7).
Moreover, the cross P6 × P7 exhibited significant SCA effects in desired
direction of EY, AFW, FF, TSS and LC. According to the performance of
the hybrid P1 × P7 it was found to be the highest for EY and TY per plant
and one the best genotypes for some quality traits (Table 2); therefore, it
could be identified as potential specific combiner for certain important
traits.
Table 7. Specific combining ability (SCA) effects for different
characters of tomato in 21 crosses.
Character
Early
yield
Total
yield
Average
fruit
weight
Pericarp
thickness
Fruit
firmness
TSS
Titratable
acidity
Ascorbic
acid
content
Lycopene
content
P1 × P2 -0.04*
-0.16 -1.62**
0.01 -0.03**
0.79**
0.02 -0.40 0.01
P1 × P3 -0.05*
1.15**
-1.81**
0.13**
0.005 0.01 0.04 -0.78 0.02
P1 × P4 -0.003 -0.44*
-0.44 -0.06 -0.02**
0.26 0.03 -1.13*
0.03
P1 × P5 0.02 0.26 -0.28 -0.04 -0.03**
0.25 0.05 3.24**
0.03
P1 × P6 0.07**
0.05 -1.27**
-0.09*
-0.03**
-0.02 0.01 -0.01 0.02
P1 × P7 0.17**
0.90**
0.63*
-0.05 0.04**
-0.15 0.02 1.85**
0.07*
P2 × P3 0.05*
-0.23 2.63**
-0.10*
-0.03**
-0.10 0.05 2.26**
-0.01
P2 × P4 0.01 0.73**
0.12 0.11*
0.04**
0.12 0.03 -1.31**
0.03
P2 × P5 -0.04*
-0.16 0.81**
-0.09*
-0.01*
-0.19 0.01 -2.34**
0.01
P2 × P6 0.04*
0.39 1.38**
0.09*
-0.01*
-0.17 0.01 0.44 0.04
P2 × P7 0.09**
-0.13 0.30 0.01 0.01*
-0.46*
-0.05 1.24**
-0.004
P3 × P4 0.08**
0.08 -0.03 -0.10*
-0.03**
-0.02 0.05 2.81**
0.08**
P3 × P5 0.06**
0.12 -0.93**
-0.02 0.01*
-0.73**
-0.23**
1.22**
0.07*
P3 × P6 -0.03 0.11 -0.14 0.06 0.04**
-0.07 -0.05 1.62**
-0.006
P3 × P7 0.01 0.74**
2.95**
0.10*
0.003 0.40 0.07 -2.01**
0.01
P4 × P5 0.03 0.08 2.25**
-0.06 0.03**
0.09 0.04 -3.16**
0.01
P4 × P6 -0.06**
-0.14 0.88**
0.08 -0.01*
-0.02 -0.04 0.14 -0.04
P4 × P7 -0.05*
0.30 -0.26 -0.01 -0.01*
0.05 0.003 2.87**
0.01
P5 × P6 0.04*
0.11 0.99**
0.001 -0.01*
0.37 0.06 3.88**
0.02
P5 × P7 -0.02 -0.27 -0.98**
-0.01 -0.01*
0.74**
0.03 -1.81**
-0.02
P6 × P7 0.18**
-0.004 1.91**
-0.07 0.01*
0.87**
0.01 -3.23**
0.07*
S.E. (sii) ±0.019 ±0.220 ±0.238 ±0.042 ±0.005 ±0.230 ±0.047 ±0.424 ±0.027
S.E. (sij–sik) ±0.033 ±0.384 ±0.415 ±0.073 ±0.009 ±0.402 ±0.082 ±0.740 ±0.047
S.E. (sij – skl) ±0.031 ±0.359 ±0.388 ±0.068 ±0.008 ±0.376 ±0.077 ±0.693 ±0.047
**
Highly significant (Ρ ≤ 0.01); *
significant (P≤0.05); non-significant.
z
S. lycopersium var. cerasiforme: P1, LYC 196/81 cv. Bubjekosoko; P2, PI 204981 cv.
126-1; P3, PI 647522 cv. Cal Red Cherry; P4, PI 647555 cv. Siten; P7, PI 639207 cv.
Black Cherry; Solanumsp. P5, PI 260402 cv. M-10 and P6, PI 126915 cv. 125.
CONCLUSION
Results indicated that cherry tomato varieties can be developed
through hybridization. Traits that presented additive gene effects such as
early and total yield per plant, average fruit weight, pericarp thickness and
fruit contents of TSS, titratable acidity and lycopene may be improved by
selection provided there is sufficient genetic variability in the germplasm.
Meanwhile, fruit firmness and ascorbic acid content traits may be improved
by heterosis breeding as these were predominantly governed by non-
additive gene action. No particular evaluated parental cultivar could be used
14. 68
to evaluate all studied traits with equal efficiencies. However, the results
indicated that the most promising combiners for fruit yield along with good
horticultural traits were found to be of P1 (LYC 196/81cv. Bubjekosoko), P3
(PI 647555 cv. Siten) and P7 (PI 639207 cv. Black Cherry), and they could
be used further in cherry tomato hybridization programs. The best hybrid
combination was found to be of P1 × P7for yield and fruit quality. Partial- to
over-dominance reactions for the inheritance of fruit yield and other
economic important traits have been realized.
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