In this study we attempted to evaluate the effect of genetic background of B-A translocations on the frequency of hypoploid progeny. We used 17 B-A translocations which were backcrossed up to five times with four inbred lines, A619, A632, Mo17 and B73. They were crossed on appropriate testers in 1989, and the hypoploid frequency of endosperm and embryo was determined from the recessive characters of kernels or of seedlings on sandbench tests. Materials are shown in Table 1.

Table 1. List of B-A translocations and testers.
 

	Times backcrossed by inbreds1				Marker gene of tester
B-A translocation	A619	A632	Mo17	B73	endosperm	embryo
TB-1La	BC5	BC5	BC5	BC5	bz2	bz2
TB-1Sb	BC5	BC5	BC5	BC5	vp5/ dek1	---
TB-3La	BC5	BC5	BC5	BC5	a1/sh2	---
TB-3Sb	BC5	BC5	BC5	BC5	cl	c l/d1
TB-4Lc	BC5	BC5	BC5	BC5	c2	c2
TB-4Sa	F1	BC5	BC5	BC5	su1	---
TB-5La	BC5	BC5	BC4	BC5	lw/pr	gl8
TB-5Sc	BC5	BC5	BC5	BC5	a2	a2
TB-6Lc	BC5	BC5	BC5	BC4	y1	l12
TB-7Lb	BC5	BC5	BC5	BC5	o5	gl1/o5
TB-7Sc	BC1	BC1	BC1	BC1	vp9/o2	v5
TB-8Lc	BC5	BC5	BC5	BC5	pro1	---
TB-9Lc	BC5	BC5	BC5	BC5	dek13	gl15/v1
TB-9Sd	BC5	BC5	BC5	BC5	bz1	bz1
TB-10L19	BC5	BC5	BC5	BC5	---	g1
TB-10Sc	BC5	BC5	BC5	BC5	---	y2

1Heterozygous B-A translocations were backcrossed by these inbreds and have been maintained.

For each ear 50 kernels were used to estimate the hypoploid frequency in progeny. Hypoploid frequency was calculated from the number of kernels or seedlings that showed recessive characters. As shown in Figures 1-4, hypoploid frequency varied depending on the background and the B-A translocation. We found a significantly lower hypoploid frequency for some B-A translocations with Mo17 background. It appears that the background of B-A translocations affects the transmission rate. Also, hy-poploid frequency varied for each TB significantly. However, the cause of the difference between TB's is not clear, since testers were different for each TB.

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Table 2. List of testers.
 

Tester No.	Genotype and background
1L1	bz2 R-r b pl [W22b1x W23]
1L2	bz2 R-r b pl [W23 x W22b]
3S1	[B73 x A632] x (d1 + / d1 cl1)
3S2	[Mo17 x A619] x (d1 + / d1 cl1)
3S3	[A632xMo17] x (d1 + / d1 cl1)
3S4	[B73 x A632] x (d1 + / d1 cl1)
4L1	c2 R-r b pl [K55 x W23}
4L2	c2 R-r b pl [W22b x K55]
4L3	c2 R-r b pl [W23 x W22b]
5S1	a2 R-r b pl [W22b x K55]
5S2	a2 R-r b pl [W23 x K55]
5S3	a2 R-r b pl [K55 x W23]
5S4	a2 R-r b pl [W22b x W23]
6L1	y1 l12 / y1 +
7L3	[B73 x A619] x o5 gl1
7L4	[Mo17] x o5 gl1
7S2	([B73xMo17] x (+/vp9)) selfed
7S3	[B73 x Mo17] x o2 v5
9S1	sh bz wx R-r/R-scm [W23 x W22b]
9S2	sh bz wx R-r/R-scm [W22b x W23]
9S3	bz R-r/R-scm [W23 x W22b]

1W22b (p-ww b y C R-scm2) is a modified version of W22.

Table 3. Endosperm and embryo classification of progeny from tester X TB
 

		Endosperm		Embryo
TB background	Tester	Number of crosses	Percent1 recessive	Number of crosses	Percent recessive
A619	3S1	2	13.0 ± 0.70	2	12.7 ± 3.07
	3S2	2	16.0 ± 5.65	2	12.5 ± 1.28
	4L1	2	26.4 ± 1.72	2	18.9 ± 0.74
	4L2	6	35.3 ± 1.53	6	11.8 ± 1.21**2
	5S2	3	24.0 ± 0.92	3	21.3 ± 2.72
	6L1	11	21.6 ± 1.35	9	9.6 ± 0.96
	7S2	4	2.3 ± 0.41	3	2.0 ± 0.46
A632	3S2	2	11.0 ± 3.53	2	11.4 ± 1.80
	4L2	3	30.0 ± 1.63	3	14.5 ± 1.74**
	5L1	2	18.3 ± 5.43	2	22.8 ± 7.45
	5S1	5	24.4 ± 2.61	5	30.7 ± 3.61
	5S2	5	27.6 ± 1.04	5	29.8 ± 2.50
	6L1	8	23.1 ± 2.39	8	12.1 ± 2.40
	7S2	4	10.0 ± 1.87	4	8.5 ± 3.89
	9S1	6	23.3 ± 1.67	6	25.3 ± 1.40
	9S2	5	23.2 ± 1.45	5	25.1 ± 3.70
Mo17	1L1	10	25.0 ± 1.18	10	19.8 ± 1.35**
	1L2	10	26.5 ± 2.70	10	19.8 ± 0.84*
	1S2	7	13.7 ± 1.68	7	9.5 ± 0.65*
	1S3	7	13.7 ± 1.87	6	13.1 ± 1.81
	3S3	5	10.2 ± 1.53	4	12.0 ± 2.16
	3S4	3	7.3 ± 1.44	3	6.3 ± 0.94
	4L2	7	30.0 ± 2.37	6	13.2 ± 1.28**
	4L3	6	28.1 ± 0.48	6	20.1 ± 2.63**
	5S3	6	22.0 ± 1.85	6	20.0 ± 2.09
	5S4	6	25.1 ± 2.20	6	22.0 ± 1.66
	6L1	10	11.8 ± 0.99	8	9.2 ± 1.42
	7L3	8	9.2 ± 1.26	8	7.6 ± 1.82
	7L4	5	8.4 ± 2.21	5	10.9 ± 1.4
	7S3	7	8.7 ± 0.67	10	7.4 ± 0.76
	9S1	10	21.7 ± 1.34	9	22.8 ± 1.98
	9S3	8	20.9 ± 2.30	7	23.2 ± 2.06
B73	1L1	10	29.5 ± 2.91	9	23.6 ± 1.99
	1L2	11	35.2 ± 2.92	9	25.2 ± 2.27**
	3S3	9	15.9 ± 1.08	9	13.7 ± 1.71
	3S4	10	14.9 ± 1.43	10	15.3 ± 1.44
	4L2	7	39.9 ± 2.94	7	25.5 ± 2.07**
	4L3	5	34.0 ± 1.45	5	27.1 ± 1.62**
	5S3	6	24.7 ± 3.17	5	15.7 ± 1.91*
	5S4	10	17.3 ± 2.69	7	10.2 ± 1.29*
	6L1	10	25.3 ± 2.86	9	12.4 ± 1.54
	7L3	5	12.5 ± 1.56	5	13.6 ± 1.56
	7L4	9	16.5 ± 2.16	9	13.1 ± 1.82
	7S3	9	12.6 ± 1.68	10	7.7 ± 1.12**
	9S1	6	29.0 ± 1.82	5	25.1 ± 1.27
	9S3	6	28.2 ± 1.84	6	27.7 ± 2.85

1Data are shown as means of recessive percentage with standard error.

2Recessive frequency between kernels and seedlings was examined by t-test. T-value for difference of recessive percent was significantly different at 0.05 level(*) or 0.01 level (**). Since the genotype of the tester for TB-6Lc consists of a homozygous endosperm marker and heterozygous seedling marker, percentages of recessive seedlings were doubled and examined by the t-value.
 
 

TB-7Sc with A619 background showed extremely low hypoploid frequency. However, this TB was backcrossed only once with inbred A619 and the others, so that it is difficult to determine the effect of inbred background.

For several of the TB's, the hypoploid frequency was determined for both kernel and seedling characters. Carlson (1969) reported that the occurrence of preferential fertilization is dependent on testers. To analyze the tendency for preferential fertilization, hypoploid frequency was examined for each tester. Information on testers is shown in Table 2, and data are given in Table 3.

With TB-4Lc, preferential fertilization occurred without regard to inbred background. Although Carlson (1969) found that some testers generate equal fertilization, all of our testers showed preferential fertilization for this chromosome. However, the difference in recessive frequency between endosperm and embryo seemed to be altered depending on the tester. This might be more clear after additional investigations.

Preferential fertilization also occurred with TB-1La in Mo17 and B73 background, except for 1L1 tester when it was pollinated by B73 background. This indicates the possibility that tester and TB background generate the preferential fertilization together.

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