The hypoploid frequency of progeny from crossing B-A translocations in four inbred backgrounds --M. Katsuta and E.H. Coe B-A translocations are a powerful tool to produce plants that have a chromosome arm deficiency. When a heterozygous B-A translocation pollinates a normal female, 25% hypoploid embryos with hyperploid endosperm and another 25% hyperploid embryos with hypoploid endosperms can be expected theoretically. However, Roman (1948) found that the frequency of hypoploid progeny shows a difference between endosperm and embryo, which he explained as due to preferential fertilization. Also, Carlson(1969) reported that the tendency for preferential fertilization depended on genetic constitution of the female-parent testers.

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.


Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors

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