MSc

Okra is one of the most important vegetable crops grown in India for its tender
green fruits. The cultivation of okra is constrained by various pests and diseases.
Among the diseases, Yellow Vein Mosaic Disease (YVMD) is the most dreadful
disease which affects both the quality of fruit and yield adversely. It is a viral disease
caused by Yellow Vein Mosaic Virus (YVMV) and is transmitted by whiteflies
(Bemisia tabaci). The only practical solution to this problem is development of resistant
or tolerant varieties. The resistant varieties released in the past became susceptible due
to the development of new strains of virus or due to the recombination in the virus
strain. In this background, the present study entitled “Breeding for Yellow Vein Mosaic
Virus (YVMV) resistance in okra [Abelmoschus esculentus (L.) Moench]” was
undertaken with the objective of evaluating and identifying resistant varieties/lines of
okra against YVMV for augmenting effective resistant breeding programme in okra.
The present study was carried out at Department of Vegetable Science, College
of Horticulture, Vellanikkara during the period of 2018-2020. The experimental
material consisted of 34 genotypes of okra which were sown in randomized block
design with two replications. Out of 34 genotypes, 30 were collected from NBPGR
Regional station, Akola. Remaining genotypes included Arka Anamika and KAU
varieties namely Aruna, Salkeerthi and Susthira.
The genotypes were evaluated for their qualitative and quantitative characters
and described based on the NBPGR Minimal Descriptor for Characterization and
Evaluation of Agri-Horticultural Crops (2000). All the 34 genotypes were evaluated
under natural conditions for the selection of resistant/tolerant ones. The disease reaction
of genotypes to Yellow Vein Mosaic Disease (YVMD) were evaluated based on the
parameters viz., percent disease incidence, percent disease severity and coefficient of
infection. Based on the values of coefficient of infection, the genotypes were classified
as resistant, susceptible and highly susceptible. The results revealed the presence of
highly resistant to highly susceptible genotypes in the present study. Six genotypes (EC
305645, EC 305651, EC 305674, IC 13995, IC 14845 and Arka Anamika) were
grouped as highly susceptible, 27 genotypes as susceptible and Susthira as highly
resistant. Among the genotypes evaluated, Susthira showed resistance to YVMD at all
stages of crop growth under field conditions. Resistance of Susthira was further
confirmed under protected conditions using vector transmission method. Hence,
Susthira can be used as a source of resistance for developing YVMD resistant/tolerant
varieties.
The extent of variability present in the germplasm were studied using the
parameters viz., phenotypic coefficient of variation (PCV), genotypic coefficient of
variation (GCV), heritability and genetic advance. High heritability and genetic
advance were observed for the characters viz., plant height, internodal length, number
of fruits per plant, number of seeds per fruit, crop duration, number of ridges per fruit,
100 seed weight, average fruit weight, number of harvest, days to first symptom
appearance, yield per plant and coefficient of infection of YVMD at 80 and 90 days
after sowing. The results of correlation and path coefficient analysis revealed that the
characters viz., plant height, average fruit weight, number of fruits per plant, crop
duration and number of harvest had positive correlation and positive direct effect on
yield. Hence, direct selection using these traits would enhance yield.
Organoleptic evaluation of all the 34 genotypes were also done. The results
revealed the superiority of genotypes IC 15027, IC 15540 and EC 305647 with respect
to sensory qualities.
The selection of superior genotypes were done based on the characters viz.,
number of fruits per plant, average fruit weight, fruit length, yield per plant and overall
acceptability of organoleptic evaluation. The genotypes viz., IC 15027, IC 15540, EC
305647, EC 305650 and EC 305642 were found superior for these characters even
though they were susceptible to the disease. Hence, these genotypes can be crossed with
Susthira for developing high yielding YVMD resistant varieties.