The influence of selective fertilization on the percentage of hybrid seedlings in Chinese cabbage

Abstract

The influence of selective fertilization on the percentage of hybrid seedlings in the progeny was studied by repeated pollination of a self-compatible Chinese head cabbage ( Brassica campestris L. ssp. pekinensis (lour) Olsson) with its own pollen and with a red sprouting Chinese cabbage. The average numbers of seed per pod between treatments with time intervals (hours) of 0(self) + 0(red Chinese cabbage), 0+24, 0+48, 0+72 and 0+96 did not show significant differences, but the percentages of hybrid seedlings in progeny lines decreased significantly with the increase of time-intervals between 2 pollinations. The result of treatments with the styles cut off 3, 6, 9, 12, 24 or 48 h after pollination revealed that pollen tubes of own pollen grains grew much more slowly than those of red Chinese cabbage. While the pollen tubes required for normal seed set had nearly all penetrated the style base 6 h after cross-pollination, some pollen tubes lagged behind the style base even 12 h after self-pollination. The selectivity of fertilization was not only expressed in the different growth rates of pollen tubes, but was possibly also related to the time required for pollen tubes to penetrate the embryo sac and for the fusion of male and female nuclei. It is impracticable to use self-compatible lines as parental lines for hybrid seed production, because the average percentage of hybrid seedlings in the progeny under natural field conditions or artificial 0+0 mixed pollination seldom exceeded 90%. However, the result of 9 lines out of 45 self-compatible lines with over 70% hybrid seedlings in their progenies under 0+48 repeated pollination indicated the possibility of using selected slow self-fertilizing lines, i.e. self-compatible lines possessing the property of producing a high percentage of hybrid seeds when pollinated with own pollen grains mixed with foreign grains.