Further confirmation of the integrity of linkage group III

 

Tonguc, M.                                                                                            Dept. Horticultural Sciences

                                                                                            Cornell University, Geneva, NY  14456

Weeden, N.F.                                                                     Dept. Plant Sciences and Plant Pathology

                                                                              Montana State University, Bozeman, MT  59717

 

      Several recent studies (1, 2, 6) have reported the synteny of markers on what was earlier assumed to be the B–Chi6 end of linkage group (LG) III and markers on the linkage group identified as LG IVB in (8).  Here we provide additional evidence that LG IVB is actually one end of LG III.  We used the morphological marker bulf, originally described by Sharma (7) and mapped to a position near Chi6 by Marx and others (3, 4, 5).  Although bulf is not commonly used in mapping studies, its phenotype (burnt leaf) is clear, and the position of the locus (approximately 20 cM from B) makes it an excellent marker to use for testing the integrity of the redefined LG III. 

      We examined an F2 derived from the cross Marx 19051 (bulf, Lap1-s) x A98-38-5 (Td, Lap1-f).  The 25 F2 plants were grown in the greenhouse and scored for segregation at Lap1, Bulf and Td, the latter locus usually associated with the previous LG IVB.  Phenotypes were clearly expressed, and segregation for all three loci gave normal Mendelian ratios (Lap1= 7:13:5; Bulf =19:6; Td =19:6).  Joint segregation analysis is presented in Table 1.  The linkage and order of the loci are unambiguous.  Only one plant displayed recombination both between Lap1 and Bulf and between Bulf and Td.  The linkage value between Lap1 and Bulf (21 cM) agrees well with the value of 20 cM reported between B and Bulf (5).  The 33 cM recombination value between Lap1 and Td also compares satisfactorily with the 25 cM distance calculated between B and Np (6) (the latter locus known to be close to Td).

 

Table 1.  Joint segregation analysis of markers on linkage group III

Loci

a/a*

a/b

h/a

h/b

b/a

b/b

c2

% recomb.

Std. Er.

Lap1:Bulf

3

4

11

2

5

0

6.3

21

+09

Lap1:Td

4

3

10

3

5

0

2.8

33

+11

Bulf:Td

17

2

–

–

2

4

7.9

18

+19

*a=dominant or slow; h=heterozygous; b=recessive or fast

 

1.  Gilpin, B.J., McCallum, J.A., Frew, T.J. and Timmerman-Vaughan, G.M.  1997.  Theor. Appl. Genet. 95: 1289-1299.

2.  Laucou, V., Haurogne, K., Ellis, N. and Rameau, C.  1998.  Theor. Appl. Genet. 97: 905-915.

3.  Marx, G.A.  1980.  PNL 12: 47-48.

4.  Marx, G.A.  1981.  PNL 13: 29.

5.  Marx, G.A., Weeden, N.F. and Provvidenti, R.  1985.  PNL 17: 57-60.

6.  Murfet, I.C. and Ellis, T.H.N.  1998.  Pisum Genetics 30: 12-14.

7.  Sharma, B.  1973.  PNL 5: 46.

8.  Weeden, N.F., Swiecicki, W.K., Timmerman-Vaughan, G.M., Ellis, T.H.N. and Ambrose, M.  1996.  Pisum Genetics 28: 1-4.