PhD

The most dreaded disease affecting okra (A belmoschus esulcntus (L.)
Moench) is yellow vein mosaic (YVM), which affects at all stages of the
crop growth Being a viral one, the best way to tackle this disease is to use
resistant varieties Thus it is essential to identify the sources of YVI\1
resistance and study the inheritance of resistance to develop high yielding
YVM resistant varieties of okra. Hence an investigation was undertaken to
reveal the genetic variability and to identify the resistant genotypes in a .
collection of gerrnplasrn, to estimate the combining ability and heterosis by
line x tester analysis and to assess the inheritance pattern of YVM
resistance and yield using generation mean analysis in order to formulate an
appropriate breeding programme for improving the economic characters.
Okra germplasm consisting of 101 genotypes was evaluated
simultaneously for YVM resistance and yield traits as two parallel field
experiments in RBD with two replications during summer 2000. Screening
for YVM resistance was carried out at four crop stages vi:., 30 DAS, 50
DAS, 70 DAS and final harvest. ANOV A revealed significant variation
among genotypes during all the stages except at 30 DAS. Number of
susceptible genotypes as well as disease intensity increased gradually from
30 DAS to final harvest. Four genotypes exhibited high resistance to YVM
,
throughout the crop phase. All the genotypes were observed for vector
population of white fly and leaf hopper in the morning and evening at 30
DAS, 50 DAS and 70 DAS and they varied significantly for white fly
population during all the crop stages whereas for leaf hopper count only at
50 DAS. Morning and evening populations of both vectors at 30 DAS had
significant association with disease occurrence during 50 DAS to final
harvest.
During the evaluation of yield traits ANOV A revealed significant
variation among the genotypes for the traits vi :., days to first flower, leaf
axil bearing first flower, leaf area, pollen sterility, fruits planf', average

fruit weight. fruit weight planfl (yield), fruit length, fruit girth, ridges
fruit I, seeds fruit I, plant duration, crude fibre content, protein content.
mucilage content, fruit and shoot borer incidence, YVM incidence (except
at 30 DAS) Besides, colour and pubescence of fruits also were scored for
each genotype.
The maximum values of both phenotypic and genotypic coefficients
of variation were noticed for protein content and fruit yield. Most of the
traits possessed high heritability especially fruits plant". fruit yield and
ridges fruifl. High genetic advance (% mean) could be noticed for majority
of the traits, the highest being for protein content and fruit yield.
Correlation analysis indicated that most of the character
combinations had higher genotypic correlation coefficients than phenotypic,
though both had the same direction. Fruit yield displayed positive
genotypic association with leaf area, fruits plant", average fruit weight.
fruit length, fruit girth, seeds fruirl, plant duration and protein content and
negative correlation with days to first flower, pollen sterility and incidence
of fruit and shoot borer and YVM (except at 50 DAS).
Among the thirteen component traits which had high association
with fruit yield the maximum positive and negative direct effects were
exerted by plant duration and days to first flower respectively. Maximum
indirect effects were exerted by fruits planrl in positive direction and by
leaf axil bearing first flower in negative direction and both these were
through days to first flower.
Selection indices were computed utilising yield and its thirteen
components and eight genotypes were chosen. Among these, five high
yielding but YVM susceptible types viz, NBPGRI TCR-2020 (LI),
N BPGR/TCR-1498 (L2), NBPGR/TCR-20 19 (L1), MDU-I (L.j) and
NBPGR/TCR-985 (Le) were used as lines and NBPGRlTCR-2060 (T I),
Parbhani Kranti (T 2) and Varsha Uphar (T 1) were used as testers for
crossing programme.

During line x tester programme, high values of KCO and SClI effects
were noticed for fruit yield and leaf area. L~ was the most superior line
which excelled with respect to mean performance and general combining
ability for yield average weight and length of fruits and leaf axil bearing
first tlower along with low YVM incidence. Among the testers T 2 was the
best being superior for yield, number, average weight. girth and ridges of
fruits
Out of the fifteen hybrids, overall performance with respect to per
SI! performance, standard heterosis and sea effects was superior for L2 x T,
(NBPGR/TCR-1498 x NBPGR/TCR-2060) with respect to days to first
tlower, leaf area, pollen sterility, fruits plant", average fruit weight, fruit
weight plant ", fruit length, fruit girth, seeds fruit" and YVM resistance.
Other excellent hybrids were L5 x T2 (NBPGR/TCR-985 x Parbhani Kranti)
.J
L~ x T 2 (NBPGR/TCR-20 19 x Parbhani Kranti) and L, x T, (MDU-I x
Varsha Uphar)
These four selected crosses were utilised for generation mean
analysis in order to detect the gene action with regard to 22 traits including
incidence of leaf roller and leaf spot. Presence of epistasis was tested and
subsequently interaction effects vi :., additive x additive, additive x
dominance and dominance x dominance effects were computed Duplicate
epistasis was more prevalent than complementary in majority of the cases.
Predominance of additive and additive x dominance interaction in
cross L2 x T, for yield and average fruit weight suggests its suitability for
direct selection and recombination breeding. Cross L5 x T 2 could be utilised
for heterosis breeding and selection, directly or in segregating generations,
in order to improve yield, average fruit weight and YVM resistance owing
to the prevalence of dominance and additive x additive components. The
gene effects were absent, non-significant or undesirable in cross L, x
T 2YVM resistance in L, x T., could be improved through heterosis
breeding, direct selection and recombination breeding due to the presence
of negatively significant dominance and additive x additive components