--Dai Jingrui, Chen Liufang and Han Yashan

It was found that one-fourth of the kernels on the ear of dent corn inbred Chao23 had wrinkling and a transparent phenotype and looked like sweet corn kernels (Fig. 1). The phenotype of the other three-fourths of the kernels on that ear was the same as normal Chao23. Those two types of kernels were planted in 1986. The results showed that the plants from variant seeds produced only variant kernels. On the other hand, the plants from normal seed were of two types. About 1/3 of them produced only normal kernels; the remaining 2/3 produced both normal and sweet kernels in the proportions of roughly 3/4 and 1/4 (Fig.2). These results indicated that the sweet corn mutant was controlled by one pair of recessive genes.

Figure 1. Two types of kernels from mutant plant.

Figure 2. Ears from sweet and normal kernels.

The cross test between pure mutant (Chao23S) and other inbreds with su1 su1 genotype and the sugar content test were made in 1987. The results of the cross test showed that only one phenotype of sweet kernels was observed from the F1 generation. So this sweet mutant is su1. The total sugar content of Chao23S was higher than those of other inbreds according to the average of six tests on different dates after pollination. The test results 27 days after pollination also demonstrated that Chao23S could maintain the highest level of the total sugar and sucrose contents for a longer period. This phenomenon is very similar to the characters of inbred Ill779 (su1 su1 se se) and significantly different from those of inbred T48S (su1 su1 Se Se). The dry matter weights in the different period also appeared less different between inbred Chao23S and Ill779 and significantly different between inbred Chao23S and T485 (su1 su1). It is deduced that Chao23S may have genotype su1 su1 se se according to the above results. But studies are still in progress to determine whether the characters of Chao23S are due to genotype su1 su1 se se or due to another genotype. Two possibilities may be as follows:

1. Inbred Chao23 originally contained recessive gene se, and mutation only from gene Su1 to gene su1 occurred in that plant observed.

2. The genotype of Chao23 in itself contains a gene which differs from se and also enhances the appearance of su1. Anyway the inbred Chao23S is good material for studies on genetics and biochemistry because Chao23 and Chao23S are isogenic lines. If Chao23 originally contained gene se, it will be interesting because gene se is seldom seen in normal corn. This will inspire corn breeders working with sweet corn breeding.

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