--T. M. Song and X. W. Lu

Crosses were made between os stock and 10 inbred lines, including 5 high oil and 5 normal. All the F1's were selfed and backcrossed to os plants. Data from F2 and by a single locus. Three other endosperm mutants, o2, wx, and su2, were crossed with os. F2 data showed no phenotypic interaction between the germ traits, but there existed a clear interaction between the endosperm traits. The endosperms of double recessive os os o2 o2 and os os wx wx were still opaque and waxy, but the top parts of these seeds were lighter in color and the basal parts duller, so they can be distinguished from the seeds of pure o2 and wx genotypes. On the endosperm of os os su2 su2 seeds, however, the os gene showed typical epistatic effect. The top part of os su2 seeds is opaque and light color and the basal part is translucent and dull color.

The oil content of os seeds was significantly reduced both in the whole kernel and in the germ (see Table 1). it suggests that os is probably one of the major genes controlling the biosynthesis of oil. The interaction of the os gene with polygenic oil genes can also be seen clearly in the table.

Table 1. Oil content of the germs and the whole kernels of Os and os seeds in F2 under high oil and low oil background.
 

			Oil content (%)
Kernel part	Cross type (F2)	Number of cross	Os	os
Germ	High oil line x os	2	56.8	47.9
	Low oil line x os	2	37.7	34.4
Whole kernel	High oil line x os	10	10.7	6.7
	Low oil line x os	10	6.4	4.1

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