PhD

The present investigation was undertaken to develop an indeterminate
hotset tomato with bacterial wilt resistance through line × tester analysis. The
experiment was conducted at the Department of Vegetable Science, College of
Agriculture, Vellanikkara, Kerala Agricultural University, during the year 2018-
2020.
The first experiment was the performance evaluation of 35 tomato
genotypes for two seasons in the year 2018, summer evaluation from January
2018 and rainy season evaluation from July 2018, in two protected structures viz.,
polyhouse and rainshelter. Genotypes exhibited significant variation for
vegetative, flowering, fruit, yield and biochemical traits under both growing
structures across season. Under polyhouse during summer the genotypes EC-
164263, EC-620387, EC-620401, EC-620406, EC-620410, and EC-620417
performed better for hotset traits (flowers with exerted stigma, pollen viability
and fruit set per cent) and yield traits (average fruit weight, number of fruits per
plant and yield). In rainshelter, the genotypes EC-165395, EC-165690, EC-
538153, EC-620401, EC-620406, EC-620410 were superior. During rainy season,
EC-164263, EC-538153, EC-620401, EC-620406, EC-620410, EC-631369 were
superior under polyhouse, and EC-620395, EC-620401, EC-620406, EC-620410,
EC-631369 and EC-631379 inside rainshelter, for hotset traits and yield traits.
The pooled data of flowers with exerted stigma, pollen viability, fruit set per cent,
number of fruits per cluster, days to first fruit set, average fruit weight, pericarp
thickness, number of fruits per plant and yield per plant were subjected to
multivariate analysis for discrimination of genotypes into clusters. Under
polyhouse seven clusters and inside rainshelter five clusters were observed. The
selection index was also applied for ranking of genotypes based on the hotset
distinctions and yield attributes. The hotset genotypes with high yield potential,
identified suitable for protected cultivation were EC-164263, EC-538153, EC-
620387, EC-620389, EC-620401, EC-620406, EC-620410, EC-620417 and EC-631369. The genotypes EC-620401 (1), EC-620406 (2) and EC-620410 (3) were
selected as hotset line for the line × tester analysis.
In the second experiment the genotypes were tested for bacterial wilt
resistance. The 35 tomato genotypes were sown in 98 well pro-trays holding
sterilised soil medium. Another set of pro-trays holding the same medium were
drenched with bacterial suspension with OD adjusted 0.8 to 1.3 at 600 nm and
kept as the sick pro-trays. The twenty-one days old seedlings were used for
inoculation through root dip method. With the help of sterilized scissors the
tertiary roots of the seedlings were sectioned. The root clipped seedlings were
dipped in bacterial suspension for thirty minutes. The inoculated seedlings were
transplanted in the sick pro-trays. The entire experiment was conducted inside
rainshelter with three replications. Each replication had five plants per genotype.
Periodical observation on bacterial wilt symptom expression was taken from third
day onwards. The disease index has revealed EC-620382 (0.20) and Arka Abha
(0.20) as highly resistant. Nine genotypes viz: EC-165395 (0.24), EC-165700
(0.25), EC-521067 B (0.25), EC-620376 (0.30), EC-620378 (0.28), EC-620427
(0.21), EC-620429 (0.23), Akshay (0.21), Anagha (0.28) were resistant. From
these EC-620382 (4), EC-620427 (5), EC-620429 (6) and Arka Abha (7) were
selected as testers.
In the third experiment, the identified lines and testers were crossed and
seeds were collected for twelve cross combinations. The fourth experiment was
the evaluation of F 1 hybrids from third experiment during summer in two
protected structures viz., polyhouse and rainshelter. The cross combinations were
laid along with the parents and two checks viz., one check hybrid (Abhilash) and
one check variety (Akshaya). The mean performance, relative heterosis (RH),
heterobeltosis (HB), standard heterosis (SH) and combining ability studies were
conducted. For vegetative traits, the cross combination 3 × 7 exhibited superiority
in the mean performance with significant positive sca effects in both the
structures. For flowering traits, the cross 2 × 5 exhibited significant positive sca
effects for pollen viability and significant negative sca effects for flowers withexerted stigma with significant RH, HB and SH in both the structures. In the case
of fruit and yield traits, the cross combination 2 × 5 exhibited negative significant
sca effects for days to first fruit set and positive significant sca effects for pericarp
thickness, average fruit weight and yield per plant with significant RH, HB and
SH. Inside rainshelter, 3 × 5 and 3 × 7 noted significant sca effects and positive
significant heterosis for fruit and yield traits. For biochemical traits, the cross
combination 2 × 5 exhibited positive significant sca effects and positive
significant RH, HB and SH for TSS, ascorbic acid and acidity under polyhouse. In
the seedling stage, all cross combinations exhibited resistance reaction to bacterial
wilt in the challenge inoculation. Depending on the mean performance, heterosis
and sca effects, the cross combination 2 × 5 was recommended for polyhouse and
the crosses 3 × 5 and 3 × 7 were recommended for rainshelter.
None of the parents revealed significant and desirable gca effect for all
traits studied. The comprehensive assessment of the parents by considering gca
estimates revealed that among lines EC-620406 is a good general combiner for
vegetative, fruit and yield characters under polyhouse, and EC-620406 and EC-
620410 could be regarded as good general combiners for vegetative, reproductive,
fruit and yield, quality characters and shelf life inside rainshelter. In the case of
testers EC-620427 and Arka Abha were good combiners for vegetative,
reproductive, fruit characters and shelf life in both the growing structures.
Dominant gene action was observed predominantly for characters studied
under both the structures. Plant height at harvest, days to 50% flowering, days to
first fruit set, days to first fruit harvest, number of fruits per plant, average fruit
weight, yield per plant, yield per plot, lycopene, ascorbic acid, shelf life, flowers
with exerted stigma, pollen viability, number of flowers per cluster, number of
fruits per cluster and fruit set per cent exhibited dominant gene action under both
the structures. Pericarp thickness exhibited complete dominance inside rainshelter.In the fifth experiment, available SSR markers were validated for bacterial
wilt resistance. Two SSR markers, SLM6124 and SLM6-110, produced
polymorphism between resistant and susceptible genotypes, two distinct bands for
resistant genotypes and four bands (two distinct and two fainted) for susceptible
genotypes.
In conclusion, the work indicates the change in the behaviour of genotypes
under different protected structures in different seasons. Hence the selection of
genotype and structure depending on the season is important. The heterosis
breeding is effective in improving hotset traits in tomato. The hybridisation
involving one resistant parent can generate bacterial wilt resistant off-springs. The
application of molecular markers can effectively reduce the time and labour
intensive field evaluation.