PhD

Parthenocarpy along with gynoecious sex expression is an asset for
protected cultivation of cucumber (Cucumis sativus L.). Cultivation of
parthenocarpic gynoecious hybrids is gaining attention of the growers as it is a
reliable and profitable venture. But still, the growers are left with the option of
choosing from the private sector hybrids which costs very high (Rs. 4 to 7 per
seed) or from very limited public sector hybrids which are yet to be tested at
various places. Realizing the need and challenge, the present work ‘Development
of parthenocarpic gynoecious hybrids in cucumber (Cucumis sativus L.) for
protected cultivation’ was carried out at Department of Olericulture, College of
Horticulture, Kerala Agricultural University, Vellanikkara, Thrissur during the
period of 2012 - 2017 to develop the parthenocarpic gynoecious lines and then F 1
hybrids for protected cultivation at Kerala.
For maintaining the germplasm, in vitro seed germination protocol of two
parthenocarpic (CS 130 and CS 131), one gynoecious (EC 709119) and one
monoecious (L-04) genotype was standardized. Maximum shoot initiation (100
%) from seedling excised cotyledonary leaf explants was obtained with the half
strength MS medium supplemented with 0.5 mg/l IAA and 2 mg/l BAP. Shoot
initiation from stem nodal explants was achieved in A 2 (Full MS + 1.5 mg/l IAA
+ 2 mg/l BAP) media whereas half strength MS media without any hormones
resulted in rooting. In vitro development of fertile male and female flowers was
also noticed in all genotypes. Field evaluation of regenerated plants was also
carried out and reduced expression of parthenocarpy was observed.
Silver thiosulphate (STS) solution varying from 150 to 600 ppm
concentrations was used for inducing male flowers in the gynoecious and
parthenocarpic lines. The STS spray (twice) at 300 ppm was found best for early
male flower induction and longer duration of male phase.
Development of inbreds and evaluation of genetic variation helps to
provide valuable information about improved and new sources of genes. Four
inbreds were developed by selfing and following single seed descent method for
up to I 5 generations. The four inbred lines (CS 130, CS 131, CS 132 and CS 133)
exhibited variation in ranges for all the selected characters across generations.
Parthenocarpic expression exhibited less variation in advanced generations. The I 4
and I 5 generation inbreds were evaluated under RBD with three replications for
12 quantitative and nine qualitative traits.
Cucumber germplasm exhibited presence of significant differences among
inbreds for majority of characters. On the basis of mean performance, the
genotypes CS 133 was found superior for majority of the preferred quantitative
and qualitative traits. High GCV and PCV estimates were observed for downy
mildew PDI (%) in all the seasons, and parthenocarpy in pooled over seasons.
High heritability with high genetic advance estimates were observed for downy
mildew PDI (%) and yield per plant (kg) in I 4 generation, downy mildew PDI (%)
in I 5 and pooled over generations. Based on the performance for quantitative and
qualitative traits in both the generations, three genotypes were selected for the
crossing programme. Gynoecious inbred (EC 709119) was also utilized for full
diallel mating programme (4 × 4) including reciprocals for combining ability and
heterosis studies.
Evaluation of 12 hybrid combinations developed through full diallel mating
design and their parents along with standard check ‘Hilton’ for 16 quantitative and
10 qualitative traits indicated presence of significant difference for GCA, SCA
and reciprocal effects. Among the parental genotypes, CS 133 exhibited
significantly high GCA effects for majority of the desirable traits followed by CS
130. The hybrids, CS 132 × CS 133 and CS 130 × CS 132 showed significant
SCA effects for desirable traits viz., days to first harvest, fruits per plant, yield per
plant (kg), downy mildew PDI (%) and parthenocarpy (%). CS 133 × CS 132, CS
130 × CS 132 and CS 132 × CS 133 were exhibiting significant standard heterosis
estimates for majority of the desirable quantitative traits.
CS 133 × CS 132 was the most promising hybrid based on SCA effects,
heterosis and per se performance for desirable quantitative and qualitative traits
(crispness/texture).