“Natuhusinari”, which has been bred in the Station in Kurume, produces female flowers at more than 80% of the nodes in spring and early summer sowings. Some lines of“Natuhusinari”, which segregate gynoecious plants, have been developed and are used as female in some commercial F1 hybrids and as breeding material.
This variety was found to be highly resistant to powdery mildew caused by Sphaerotheca fuliginea (SCHL.) POLLACCI. In order to study the inheritance of powdery mildew resistance, the F1, F2 and backcross plants between“Natuhusinari”and“Kurume-otiai No. 1”, a susceptible variety, were grown in the field in summer of 1958. Since heavy natural infection of powdery mildew occurred, it was easy to distinguish the resistant individuals from susceptible ones in the late stage of their growth.
The F1 plants as well as the susceptible parent were severely infected. The F2 and backcross data are presented in Table 1. It clearly show that the powdery mildew resistance is a recessive and monogenic factor.
The parents of the cross also differ in their fruit-Spine color:“Natuhusinari”has white spine, while “Kurume-otiai No. 1”has black spine. The F1 plants had black spine. The F2 and backcross data are given in Table 1.
The results show that a single gene difference exists between the parents for fruit-spine color, and further that there is no linkage between powdery mildew resistance and fruit-spine color.