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Biological Aspects of Chinese Cabbage (Brassica Pekinensis Kurp.) Seed Production in the Tropics
Dissertation Abstract:
During the 1984 cold season, experiments on Chinese cabbage seed production of open-pollinated cultivars were conducted at two experiment stations in Chiangmai, Thailand. The effects of planting dates, varieties, nitrogen fertilizer, and plant growth regulators on seed yield and its components were studied at Fang Horticulture Experimental Station, which had medium elevation (509 m). In the same period, experiments on seed production of F1 hybrid using the Asian Vegetables Research and Development Center (AVRCD) inbreds E-9 and O-2 were performed at Ang Khang Experimental Station, a highland (1,300 m), to study the optimal planting dates, flowering synchronization, degree of self-incompatibility, and methods in maintenance of the inbred lines.
For open-pollinated seed production, planting on 20 November produced a significantly higher seed yield per plant and per plot than earlier plantings because of better growth during pre-anthesis and post-anthesis development. The cultivars 77M (2/3)-43 and 77M (2)-25 had high yielding ability. However, further varietal improvement for earlier flowering and uniform bolting was necessary. high incidence of soft rot at planting density of 66,700 plants per hectare caused no significant difference in seed yield compared with planting density of 33,300 plants per hectare. Nitrogen at 50 kg/ha, using split-thrice application, had significantly higher seed yield than the control. Spraying GA3 (gibberellic acid) at 200 ppm two weeks after transplanting increased seed yield.
In F1 hybrid seed production, the degree of self-incompatibility of an inbred was the same for both highland and medium elevation conditions.
Planting in November gave the highest yield of F1 hybrid, but a decline was observed with the later transplanting.
The inbred E-9 flowered 14 days earlier, while deheading O-2 advanced its flowering by seven days; therefore, flowering synchronization could be better achieved by adjusting planting dates of the parental inbreds. Seeds of F1 from this experiment showed heterosis in vegetable yield.
In maintenance and increase of inbred lines, selfing open flowers gave less seed set than bud-pollination owing to mechanical injury of the sigma. To increase an inbred population, flower-sucker cuttings were successfully rooted by soaking in IAA at 100 ppm. Propagation through tissue culture of axillary buds in Murashige and Skoog's medium involved shoot regeneration with 0.5 ppm BA (benzyl adenine) + 0 ppm NAA (napthalene acetic acid) as well as 0.5 ppm BA + 0.2 ppm NAA, shoot multiplication with 2.0 ppm BA + 0 ppm NAA as well as 2.0 ppm BA + 0.2 ppm NAA, and root formation with 0.2 ppm BA + 0.2 ppm NAA as well as 0.5 ppm BA + 0.2 ppm NAA.
