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.