PhD

A study entitled" Heterosis breeding and in vitro mutagenesis in pineapple
(Ananas comosus [L] Merr.) was undertaken in the Department of Plant Breeding &
Genetics, College of Horticulture, Vellanikkara during 1998-2003. The main objective
of the study was to create wide genetic variability for selecting ideal pineapple
genotypes. The field studies were taken up at Pineapple Research Station, Vazhakulam.
The six parental genotypes, used for hybridization, differ significantly in thirty
four out of the thirty five growth, yield and quality characters studied. The genotypes
also differ in qualitative characters like colour of leaf and fruit, depth of eyes and spine
character. All the genotypes are having a few, not all, desirable characters.
The genotypes differ significantly in number of flowers opened per day and
number of flowers per inflorescence. The flowers of Mauritius, Kew, Selection-l and
Ripley Queen open during 4 am to 5 am and that of Pampakuda local and Kakkoor
local open during 5 am to 6 am. Flower opening and anther dehiscence coincides in all
the genotypes. In all the genotypes, stigma remained receptive from 3 am to 6 pm.
All the six genotypes were crossed in all possible combinations. The crosses K
x S-] and M x RQ and their reciprocals were incompatible. The other crosses differ in
the extend of cross compatibility. The genotype Mauritius expressed highest
compatibility as a pistillate parent with all other genotypes. Among all cross
combinations, Mauritius and PKDA are the most compatible parents. Out of the thirty
cross combinations, only sixteen cross combinations reached the final stage of
evaluation of the progenies. The highest survival of the seedlings was observed in
PKDA x S-I.
The hybrids in the sixteen cross combinations were evaluated individually for
thirty five growth and yield characters using the parameters mean, range) percentage of
variation of range over mean, mode, mean deviation from mode and coefficient of
dispersion. Further, multivariate analysis using five characters, viz., fruit weight

without crown, TSS, total sugar, juice weight % and pulp weight % was done by
estimating the determinant of the eo variance matrix, Principal Component Analysis and
Euclidean distance. All the characters expressed transgressive and independent
segregation. Thus each individual plant is unique due to the independent segregation of
each character.
Evaluation of all the hybrids in all the cross combinations based on five selected
characters, viz., fruit weight without crown, TSS, total sugar, pulp weight % and juice
weight % simultaneously for relative heterosis, heterobeltiosis and standard heterosis
resulted in identifying 13 hybrids with relative heterosis and 7 hybrids with standard,
heterosis. When all.the twenty hybrids were compared, the hybrid number 257 of the
cross M x K was having the highest heterosis in four out of the five characters.
Among the progenies, hybrids with several distinct or abnormal features were
observed. Albino seedlings were observed in 16 cross combinations. Hybrids with
dual feature, low chlorophyll content, piping character, segregation of colour of heart at
the time of initiation of inflorescence, creamy white heart, white flower, extra long and
cylindrical fruit and fruits that ripen uniformly were obtained from among various
crosses.
For in vitro mutagenesis, shoot tips of Mauritius variety were cultured in MS
medium supplemented with BAP and uniform masses of globular structures were
irradiated with gamma rays at seven doses and compared with control. Chlorophyll
,
mutants and chimera were observed among the in vitro plants. Observations on height
and number ofleaves at 30 days interval of growth up to 120 days from plant out stage
showed that radiation of in vitro culture at 30 Gy gave enhanced vigour in growth of
plantlets. The production of chlorophyll mutants, leaf chimera and variability in height
and number of leaves indicated that in vitro mutagenesis could be used as a tool for
creating genetic variability in pineapple.