MSc

Yellow Vein Mosaic (YVM) is a devastating disease infecting okra (Abelmoschus esculentus (L.) Moench), at all stages of crop growth, causing 50 to 94 per cent crop loss. The best way to tackle this disease is the use of resistant varieties developed by interspecific hybridization. Hence a study was undertaken in the Department of Olericulture, College of Horticulture, Kerala Agricultural University, Vellanikkara during 2011-2012 for the evaluation of F9 selections of the cross between Abelmoschus caillei var. Susthira (YVMV resistant variety) and Abelmoschus esculentus var. Salkeerthi (high yielding, widely adapted but YVMV susceptible variety), with the objective of identifying promising lines having high level of resistance to YVMV.
Okra genotypes consisting of 12 F9 selections along with their parents and Arka Anamika were evaluated for qualitative, quantitative characters, pollenfertility and YVMV resistance in RBD with two replications. Variability, correlation and genetic divergence were also worked out. The screening for YVMV resistance was done by field evaluation creating artificial epiphytotic conditions, white fly transmission studies and graft transmission techniques. Four F9 generation selections (F9-5-5, F9-6-8, F9-8-14 and F9-9-23) exhibited high level of resistance to YVMV.
During the evaluation of quantitative characters in the F9 generation selections, significant variation among the genotypes was observed for the traits such as, plant height, petiole length, days to first flowering, days to first harvest, length of fruit, number of fruits per plant, crop duration and yield per plant.
The maximum values for both PCV and GCV were noticed for coefficient of infection of YVMV, pollen sterility and mucilage content. Most of the traits possessed high heritability especially for the coefficient of infection of YVMV and pollen sterility. High genetic advance could be noticed for coefficient of infection of YVMV and plant height. Correlation analysis indicated that fruit yield displayed positive genotypic association with length of fruit, number of fruits per plant and crop duration. The 15 genotypes were grouped into five clusters and no parallelism between geographical distribution and genetic diversity was observed.
Pollen fertility studies indicated that high level of pollen fertility was present in F9 generation lines also. Mucilage extraction analysis revealed that only low amount of mucilage was present in F9 generation lines compared to the wild parent A. caillei var. Susthira.
Four F9 selections showed characters such as lower number of ridges per pod, longer fruit length, reduced width of epicalyx segment and less mucilage content similar to the cultivated species A. esculentus var. Salkeerthi. Based on its promising fruit characters tending towards A. esculentus, selections such as F9-5-5, F9-6-8, F9-8-14 and F9-9-23 were identified. These selections expressed good amount of pollen fertility and high yield. Hence these selections can be further advanced to develop YVMV resistant varieties with desirable plant and fruit characters.