MVSc

Yellow Vein Mosaic (YVM) is a devastating disease infecting okra (Abelmoschus esculentus (L.)Moench), which affects all stages of crop growth, causing 50 to 90 per cent crop loss. The best way to tackle this disease is the use of resistant varieties. Hence a study was undertaken in the Department of Olericulture, College of Horticulture, Kerala Agricultural University, Vellanikkara, Thrissur during 2007-2008 for the evaluation of the F4 and F5 generations of the cross between Abelmoschus caillei variety Susthira (a semi wild yellow vein mosaic resistant variety) and Abelmoschus esculentus variety Salkeerthi (a high yielding widely adapted, but Yellow Vein Mosaic Virus (YVMV) susceptible variety), obtained from the earlier studies with the objective of identifying high yielding and YVM disease resistant lines from the segregating generations.
Okra germplasm consisting of 14 F4 selections along with their parents was evaluated simultaneously for YVMV resistance and yield traits in RBD with two replications during April to September 2007. The F4 segregants were morphologically more similar to semi wild parent Abelmoschus caillei and were highly resistant to YVMV. However, seven F4 selections viz., F4-2, F4-5, F4-8, F4-13, F4-15, F4-16, and F4-20 having more fruit length and desirable number of ridges per fruit were selected. These selections also showed considerably good amount of pollen fertility. So these selections were further advanced to F5 generation and were also subjected to detailed testing programmes for reaction to YVMV and yield traits. The F5 generation plants in general exhibited high level of resistance to YVMV throughout the crop phase.
During the evaluation of yield traits in the F4 generation, significant variation among the genotypes was observed for the traits, plant height, petiole length, days to first flowering, days to first harvest, length of fruit, number of fruits per plant, crop duration, yield per plant and pollen sterility.
The maximum values for both PCV and GCV were noticed for pollen sterility, number of fruits per plant, length of fruits, internodal length and length and width of epicalyx segments.
Most of the traits possessed high heritability especially for days to first flowering, length of fruit, locules per pod and yield per plant. High genetic advance could be noticed for majority of the traits, the highest being for yield per plant and plant height.
Correlation analysis indicated that most of the character combinations had higher genotypic coefficients of correlation than phenotypic though both had the same direction. Fruit yield displayed positive genotypic association with length of fruit and number of fruits per plant. Among the 17 component traits which had high association with fruit yield the maximum positive and negative direct effects were exerted by number of fruits per plant and days to first flowering respectively.
During the evaluation of yield traits in the F5 generation, significant variation among the genotypes was observed for the traits plant height, petiole length, days to first flowering, days to first harvest, first fruiting node, length of fruit, number of fruits per plant, crop duration, yield per plant and pollen sterility.
The maximum values for both PCV and GCV were noticed for coefficient of infection of YVMV, pollen sterility, number of fruits per plant, length of fruits, internodal length and length and width of epicalyx segment.
Correlation analysis indicated that most of the character combinations had higher genotypic coefficients of correlation than phenotypic though both had the same direction. Fruit yield displayed positive genotypic association with length of fruit and number of fruits per plant.
Most of the traits possessed high heritability especially for coefficient of infection of YVMV, pollen sterility, crop duration and days to first flowering. High genetic advance could be noticed for majority of the traits, the highest being for CI of YVMV, crop duration, yield per plant and plant height. High variation noted for /YVMV disease incidence offers more scope for selection based on disease incidence, in the process of selection for high yielding disease resistant lines.
Some of the F5 segregants showed characters similar to the cultivated species A. esculentus variety Salkeerthi such as less number of ridges per pod, longer fruit length, reduced width of epicalyx segment etc. The segregants such as F5-1, F5-3, F5-7, F5-9, F5-20 and F5-26 were selected based on its promising fruit characters tending towards A.esculentus. These selections also showed considerably good amount of pollen fertility and high level of resistance to YVMV. So these selections can be further advanced to develop YVMV resistance varieties with desirable plant and fruit characters in the future.