Linkages for a new fasciata gene
Święcicki W.K. and Inst. of Plant Gen.
Gawłowska M. Polish Acad. of Sci., Poznań, Poland
The fasciata phenotype is very useful in pea genetics and breeding; yet there remains a certain ambiguity regarding its genetic basis. In the international pea gene bank the line WL 6 was considered as the type line for two recessive genes, fa (linkage group [LG] IV) and fas (LG III), and the line WL 1143 is a tester line for LG IV with two markers fa and n, (v is not on LG IV) (2). Genetic analyses on fasciata resources in the collection at Wiatrowo resulted in the following conclusions (3):
1. The line WL 6 appeared to be the type line for fa, exclusively, implying that no type line for fas exists.
2. The gene fa in the tester line WL 1143 appeared to have very poor penetrance.
3. Stem fasciation in most of lines is controlled by the gene fa on linkage group IV.
4. The dichotomous branching mutation [type line Wt 10 785 (Gottshalk 37B)] is caused by an allele at Fa with the following dominance (Fa-fabif-fa).
5. The line Wt 12 185 has a fasciated phenotype that does not display allelism with fa. The objective of this study was to determine if Wt 12 185 could contain the gene fas.
As a type line for fas is not available for an identity test, a mapping approach was used. Presumably, if fasciation in Wt 12 185 was produced by fas, the phenotype should demonstrate linkage with markers on LG III. Several tester lines with markers were involved for the linkage tests.: Wt 11 288 (st, b, M – LG III), Wt 10 357 (unitac, pet - LG III), Wt 15 237 (rms1 – LG III), Wt 12 371 (was, led – LG IV) and Wt 11 238 (i, d, A, s, k, wb, tl, gp, U).
The linkage analysis revealed that the locus controlling fasciation in Wt 12 185 segregated independently of each of the loci on LG III, as well as was, led, i, a, d, s, k, wb, r and tl (Table 1). However, significantly disturbed
Table 1. Distribution of phenotypes in F2 populations (Wt 12185 x testerlines) and the linkage test for the gene fa*
|
|
Phenotype |
|
|||||||
|
Testerline |
Pair of genes |
DD |
Dr |
rD |
rr |
Total |
Joint chi square |
Cr-O value+SE (percent |
Phase |
|
Wt 11 288 |
fa* - st |
44 |
14 |
16 |
2 |
76 |
1.71 |
037.0±9.7 |
R |
|
|
fa* – b |
38 |
9 |
11 |
2 |
60 |
0.00 |
046.3±10.1 |
R |
|
|
fa* – M |
33 |
10 |
10 |
2 |
55 |
0.58 |
055.8±10.8 |
C |
|
Wt 10 357 |
uni - fa* |
88 |
29 |
36 |
11 |
164 |
0.00 |
048.9±5.9 |
R |
|
|
pet - fa* |
95 |
33 |
29 |
7 |
164 |
0.76 |
044.9±6.2 |
R |
|
Wt 15 237 |
fa* – rms1 |
45 |
18 |
16 |
1 |
80 |
3.81 |
025.7±10.3 |
R |
|
Wt 12 371 |
fa* - was |
92 |
22 |
24 |
15 |
153 |
5.82 |
063.0±5.1 |
R |
|
|
Fa* – led |
84 |
29 |
37 |
2 |
152 |
7.53 |
025.7±7.5 |
R |
|
Wt 11 238 |
fa* – i |
96 |
32 |
25 |
4 |
157 |
2.10 |
039.7±6.6 |
R |
|
|
fa* – A |
105 |
28 |
22 |
7 |
162 |
0.25 |
047.5±5.7 |
C |
|
|
fa* - d |
81 |
23 |
16 |
6 |
126 |
0.31 |
053.9±6.4 |
R |
|
|
fa* - s |
93 |
31 |
20 |
7 |
151 |
0.00 |
050.7±6.0 |
R |
|
|
fa* – k |
93 |
40 |
21 |
8 |
162 |
0.20 |
048.3±6.0 |
R |
|
|
fa* – wb |
99 |
32 |
21 |
6 |
158 |
0.00 |
048.3±6.1 |
R |
|
|
fa* – r |
96 |
32 |
20 |
9 |
157 |
0.21 |
054.2±5.7 |
R |
|
|
fa* - tl |
102 |
31 |
22 |
7 |
162 |
0.00 |
050.6±5.8 |
R |
dihybrid segregations were found for the gene pairs fa* - gp and fa* – U (tables 2 and 3) with Cr-O values 17.6 and 21.4, respectively. Considering the above results one could conclude that the locus responsible for the fascinated phenotype at Wt 12 185 is localized between Gp and U on chromosome V. I suggest the gene symbol fa2 for this new mutation and revise fa to fa1 for the gene on LG IV). The symbol fas should remain reserved for the gene on LG III, although suitable germplasm needs to be located in order to confirm its localization .
Table 2. Monohybrid segregation for the investigated gene fasciata2 and gene markers in the linkage group V in F2 population of the linkage test cross K. 2749 (Wt 12 185 x Wt 11 238
|
|
Allele |
|
|
|
Locus |
Dom |
Rec |
Total |
c2 (3:1) |
Fa2 |
133 |
29 |
162 |
4.35 |
Gp |
119 |
48 |
167 |
1.24 |
A |
132 |
36 |
168 |
1.14 |
U |
88 |
41 |
129 |
3.16 |
Table 3. Distribution of phenotypes in F2 population (Wt 12 185 x Wt 11 238) and the linkage test for the gene fasciata2
|
|
Phenotype |
|
|
|
|
|||
|
Pair of genes |
DD |
Dr |
rD |
rr |
Total |
Joint c2 |
Cr-O value + SE (per cent) |
Phase |
|
fa2 - gp |
88 |
45 |
29 |
1 |
162 |
13.4 |
17.6 ± 7.6 |
R |
|
fa2 - U |
81 |
22 |
6 |
18 |
127 |
23.3 |
21.4 ± 4.2 |
C |
|
gp - U |
59 |
37 |
28 |
4 |
128 |
7.0 |
30.0 ± 7.9 |
R |
In segregating populations fasciata genes can show certain lack of recessives caused by a reduced penetrance (e.g. very strong in WL 1143). But some sources of fa1 (e.g. WL 6) give undisturbed 3:1 segregation what suggest the influence of a genotypic background. In most of populations of the linkage test presented above (excluding the cross in Table 2) the monohybrid segregation of fa2 did not deviate significantly from the expected 3:1 ratio.
Wt 12 185 x Wt 11 288: 59 Fa2:18 fa2, c2 = 0.11;
Wt 12 185 x Wt 10 357: 124:40, c2 = 0.03;
Wt 12 185 x Wt 15 237: 63:18, c2 = 0.33;
Wt 12 185 x Wt 12 371: 114:39, c2 = 0.02
1. Blixt, S. 1976. Agri Hort. Genet. 34: 83-87.
2. Lamprecht, H. 1974. Monographie der Gattung Pisum. Steiermärkische Landesdruckerei, Graz. p. 655.
3. Święcicki, W.K. 2001. Pisum Genet. 33: 19-20.