Heterosis and Combining Ability of Pak-Choi (Brassica campestris L. ssp. chinensis Jusl) under Different Cropping Seasons

n order to obtain the genetic information on some leaf characters in pak-choi (Brassica campestris L. ssp. chinensis Jusl), 36 pak-choi hybrids from diallel crosses of 9 inbreds were planted at experimental farm of Seoul seed company in 1998. Genetic analysis for quantitative characters related to the two cropping seasons, spring and fall at field, was conducted. Mean heterosis(%) of leaf length, leaf width, midrib length, midrib width and midrib thickness were highly expressed in all the cropping patterns. Estimated as a mean heterosis and a heterobeltiosis effects(%), an increase in fresh weight per plant was attributed to the increase of midrib thickness, midrib width, midrib length, leaf length and leaf width characters. The effect was changed by different cropping seasons. The ratio of general combining ability (GCA) to specific combining ability (SCA) for all characters increased in spring cropping pattern, but SCA in fall cropping showed higher ratio than that of the spring cropping pattern. There were significant correlations between fresh weight per plant and plant height, leaf width, midrib length, midrib thickness of parent plants, but the fresh weight per plant of F1 was correlated with plant height, leaf length, midrib length and midrib thickness in spring cropping. Plant height, leaf number, leaf width, midrib length, and midrib thickness of parent plants and the plant height, leaf length, leaf width, midrib length and midrib width of F1 lines also showed significantly positive correlation with the fresh weight per plant in fall cropping pattern.

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