Sex Behaviour of Triploid Intersexes in Humulus japonicus

Abstract

1. In the second generation of the colchicine induced polyploids in Humulus japonicus in all 36 plants have been obtained. The sex types in relation to chromosome numbers of these plants are as follows:
2. A study of karyotype analysis in some of these plants showed that the triploid females have 2n=XXX+21a and the intersexes 2n=XXYY+21a chromosomes (Fig. 1a-b). These constitutions may represent a triploid condition to that of the normal female and male sexes, which having 2n=XX+14a and 2n=XYY+14a respectively. Thus, the relation between sex types and chromosome constitutions in H. japonicas agrees with the cases in Rumex Acetosa (ONO 1935).
3. The sex expression in the triploid intersexes of H. japonicus is monoecious, i.e. the same plant bears both distinct male and female flowers or flower clusters. Each cluster, however, may be found on the same or separate branches of the plant (Fig. 2, 3a-c).
4. The modi of disposition of the male and female flower clusters on each intersexual plant were examined. As indicated in Fig. 4a-c, the female clusters appear generally on the lower, while the male on the upper branches of the stem.
5. The intersexes show a series of intergradations in sex behaviour. They can be classified into the following 3 main types: male (±_??_), intermediate (_??_), and female intersexes (±_??_).
6. The triploid intersexes in H. japonicus are protogynous. They start out as female and later show a reversal to the male condition.
7. The triploid intersexes in H. japonicus are male sterile, while in the female side more or less fertile. After open pollination they produced good seeds with the exception of the male intersexes.