EFFECT OF TASSEL DAMAGE AT THE BEGINNING OF FEMALE FLOWERING ON THE YIELD AND QUALITY OF MAIZE (ZEA-MAYS L) SEED

The combined effects of mechanical stress (tassel removal) and heat or drought stress were examined over a three year period on the seed pro duction of Mv Exp 23 hybrid maize (Zea mays L.). In low stress years ( no heat or drought stress), partial damage to the tassels did not resu lt in a substantial yield loss. In moderate stress years, partial tass el removal resulted in yield losses of 25-50%, i.e. the quantity of us able seed was 1.0-1.5 tons/ha lower. In high stress years, the combine d effect of heat and drought stress and mechanical damage was dramatic . Under these conditions, even partial tassel damage resulted in total yield loss when undamaged treatments produced little more than 0.3-0. 5 tons/ha. Among tassel damage treatments, removal of tassel branches proved to be least serious, resulting in minimal losses in low stress years, since the undamaged lower parts of the tassel continued to shed pollen. Removal of the main tassel spike delayed the initiation of po llen shed while removal of side branches shortened the duration of ant hesis. Their effect on yield depends on flowering synchronization and on weather conditions during flowering. Damage may range from 10-60% d epending on the year. When 100% of the tassels were removed, less chan ce of fertilization due to the isolation distance occurred and yield l osses were as great as 90%. Reduced fertilization due to tassel damage reduces the value of the seed, increases the thousand kernel weight, and the percentage of the large-round seeds. Due to the poor fertiliza tion, the maturity of the kernels on the cob varied considerably thus impeding timely harvest and drying and resulting in reduced germinatio n and seed vigour. From a practical perspective, these results depend on the crossing combination and year, since the compatibility of the p arental lines, the flowering synchronization and the microclimatic eff ects during flowering may differ greatly after hail (storm damage).