MSc

ABSTRACT

Okra (Abelmoschus esculentus (L.) Moench) is an important vegetable crop which is widely grown in tropical, temperate and subtropical regions of the world. The present investigation on ‘Assessment of genetic variability for YVM resistance in okra (Abelmoschus esculentus (L.) Moench)’ was conducted at the Department of Plant Breeding and Genetics, College of Horticulture, Vellanikkara, Thrissur during November 2019 to February 2020. The experiment was laid out in augmented design using thirty four okra accessions including two resistant check varieties (Parbhani Kranti and Varsha Uphar) and two susceptible check varieties (Salkeerthi and Pusa Sawani) collected from NBPGR and KAU. Ten plants of each accession were sown on ridges in a row with 60 cm x 45 cm spacing and the crop was managed as per package of practices recommendations of KAU (2017). Observations on five qualitative characters and fifteen quantitative characters were recorded from five randomly selected plants for each accession, as per the NBPGR descriptors. Scoring for YVM disease incidence was done as per the rating scale given by Arumugam et al. (1975).
The genotypes were classified based on five qualitative characters viz., fruit colour (multimorphic), fruit pubescence and petal colour (trimorphic), petal base colour (dimorphic) and seed hairiness (monomorphic). ANOVA for fifteen quantitative characters showed significant variation for days to flowering, leaf blade length , leaf area), plant height, branches per plant, fruit length, fruit diameter, ridges per fruit, seeds per fruit, number of fruits per plant, fruit weight, fruit yield per plant, coefficient of YVM incidence and vector population on young leaves. This indicated high variability in the okra germplasm which can be utilised in breeding programmes.
Phenotypic and genotypic coefficients of variation (PCV and GCV) were very high for leaf area and coefficient of YVM infection and high for five characters viz., fruit yield per plant, branches per plant, plant height, fruits per plant and ridges per fruit. In general, GCV was slightly lower than PCV for most of the traits indicating a small environmental effect in their expression.
Broad sense heritability (H2) was very high in three traits (leaf area, seeds per fruit and ridges per fruit) while genetic advance as % of mean (GA) was very high in two traits (leaf area and coefficient of YVM Infection). High H2 and GA were noticed in most of the traits including number, length, diameter, weight and yield of fruits. Coefficient of YVM infection also exhibited high H2 as well as GA. This indicates that these characters can be improved to a great extent by selection.
Fruit yield per plant had highly significant positive correlation with leaf area and seeds per fruit and significant positive correlation with days to first flowering, leaf blade width and plant height. Positive and highly significant correlation was observed for coefficient of YVM infection with days to first flowering, leaf area and vector population.
In the high yielding YVM susceptible category, the six best okra genotypes selected were Salkeerthi, TCR- 1774, TCR-1797, TCR- 2631, TCR-2627 and TCR-2626. Salkeerthi (KAU variety) in spite of being susceptible to YVM, had the highest fruit yield per plant (294.22 g) among all the genotypes evaluated in the present study. Besides, it had superior yield components viz., fruitsper plant, fruit length, fruit diameter and fruit weight. All the other selected genotypes (collected from NBPGR) were also superior in fruit yield per plant and other major yield components. These selected NBPGR accessions may further be evaluated for confirming their superiority in yield and yield traits.
Three genotypes viz., TCR- 30, Varhsa Uphar and Parbhani Kranti showed high resistance during the present study. Varhsa Uphar and Parbhani Kranti (two resistant checks) exhibited superiority in fruit yield as well as yield components viz., fruit number/plant, fruit length, fruit diameter and fruit weight. Even though a low yielder, TCR- 30 exhibited consistent high resistance to YVM disease throughout the crop period with the lowest number of white flies emphasising its resistance mechanism. Hence it can be recommended as a donor for imparting YVM resistance in breeding programmes.