FLOWERING AND SEED PRODUCTION OF CABBAGE FOR THE TROPICS

Abstract

This thesis presents experiments to determine if cabbage flowering and seed production can be achieved in tropical conditions by selection of genotype and by chemical and physical treatments applied to seeds and to plants. Part one determines whether cabbage seed produced under tropical temperatures (20o -30oC) is viable and selects suitable lines and methods for further investigations. There was an indication that cabbage can flower and produce viable and vigorous seeds in the cooler part of the tropics provided that green plants are vernalized. Chlorophyll fluorescence parameters, especially variable fluorescence (Fv) and the ratio between Fv and maximum fluorescence (Fm), were found to be a good method for screening cabbage for heat tolerance. It was also found that cabbage seed can be primed and vernalized at the same time without adversely affecting the viability and vigour. The second part of the work was to determine whether there are alternatives to plant vernalization that can induce flowering and lead to less expensive cabbage seed production in the tropics. Seed vernalization and gibberellic acid (GA3) promoted early flowering of lines ‘HRI 011446’ and ‘HRI 006556’. For line ‘HRI 006556’, not only did additional supply of N reduce days to flowering of plants raised from medium with elevated sucrose (3%) but also GA3 treatment could be substituted for in vitro cold treatment to promote early flowering. The combined effects of seed vernalization and GA3 induced flowering in cabbage plants of line ‘HRI 009617’ developed from seeds or ratoons and potential flowering plants were easily generated from flowering stalks through vegetative propagation methods.