MSc

Okra is an important vegetable crop grown in India and abroad for its fresh
green pods. The leafhopper Amrasca biguttula biguttula is a major sucking pest of
okra causing high damage to plants. High frequency of fruit picking and repeated
application of chemical pesticides to tackle the hopper menace, often leaves toxic
residues in the fruits. So it is inevitable that pest resistant varieties should be
developed. Hence a study was undertaken to study the genetic variability, for
yield and its component characters as well leafhopper resistance indices in a
collection of okra genotypes, to estimate the combining ability and heterosis as
well as gene effects involved in the inheritance of these characters using line x
tester analysis.
Forty okra germplasms collected from vanous sources were evaluated
simultaneously for yield and leaf hopper resistance. ANOV A revealed that the
treatments varied significantly for leafhopper resistance and also there was
significant variation among treatments for yield and yield attributes viz., days to
first flowering, leaf axil bearing first flower, number of primary branches, number
of fruits per plant, length of fruit, girth of fruit, weight of fruit, yield per plant
duration. Six genotypes exhibited resistance to the leafhopper throughout the crop
duration.
High values for phenotypic and genotypic coefficients of variation was
recorded for number of primary branches followed by leafhopper population
count. High heritability was exhibited by yield per plant followed by duration.
Maximum genetic advance was observed for number of primary branches
followed by yield per plant.
Correlation analysis indicated that most character combinations had higher
genotypic correlation coefficient than phenotypic correlation coefficient. Yield
exhibited significant and positive correlation with number of fruits and average

fruit weight and negative significant association with leaf axil bearing first flower,
leafhopper population count and leafhopper injury score.
Path analysis was carried out for nine biometric as well as two leafhopper
injury indices which had high correlation with yield. Highest positive direct effect
was exhibited by number of fruits while the highest negative direct effect on yield
was recorded for leafhopper population count per plant.
Resistant as well as susceptible genotypes were selected based on leafhopper
population counts and leafhopper injury score. Five resistant lines (female parent)
viz., Nemom (T21), re 45792, Venjaramood (T23), AE 279 and Palappur (T20) and
three susceptible testers (male parent) viz., Venganoor (T1S), Aruna (T37) and
Kalliyur (T24) were selected as parents for L x T analysis. These were crossed in
a line x tester fashion to produce 15 hybrids.
During L x T programme highly significant sea as well as gea effects were
obtained for yield. Lt was the best line while T 2 was the best tester. Among
hybrids L3 x T 2 was the best considering leafhopper resistance as well as yield and
yield attributes. Negative and significant sea effects were observed for days to
first flowering and leafhopper population count. It possessed all the desirable
characters like high yield, greater weight and girth of fruits and number of fruits.
It is also an early flowering type.
The ratio of additive to dominance variance was less than one for most of
the traits studied including leafhopper population counts and leafhopper injury
,
scores, indicates the predominance of non-additive gene action.
Since there is preponderance of non additive gene effects for characters such
as yield and its components as well as leafhopper resistance parameters,
exploitation of hybrid vigour is an appropriate breeding approach where yield and
leafhopper resistance are considered.