PNL Volume 19 1987 RESEARCH REPORTS 41
ON THE GENES FOR RESISTANCE TO FUSARIUM WILT
Muehlbauer, F. J. USDA, ARS, Pullman, WA U.S.A.
Several races of the pea wilt fungus (Fusarium oxysporum f.
sp. pisi) cause economic losses in the pea growing regions of the
U. S. and other countries. Resistance to four races of the fungus
(races 1, 2, 5, and 6) is reportedly controlled in each case by
single dominant genes (1,2,3,4,6). Wade (6) was able to show that
resistance to race 1 was controlled by a single dominant gene (Fw)
linked by about 30 map units to Le on chromosome 4. Resistance to
race 2 or "near wilt" is controlled by a single dominant gene de-
signated as Fnw (7). The gene for resistance to race 2 (Fnw) was
reported by Wells e_t al. (7) to be about 40 map units from Fw;
however, his F3 data indicated independence of the two genes,
and no linkage of Fnw with Le was found. The chromosomal lo-
cations of the genes for resistance to races 5 and 6 of wilt are
unknown and no linkage studies have been reported.
For our study, we tentatively designated the gene for resis-
tance to race 5 as 'Fwf'. To determine the chromosomal locations
and linkage relationships of the genes for resistance to races 2,
5, and 6, we crossed known wilt-resistant material with genetic
stocks that were chosen for marker genes on the seven chromosomes.
Because the gene for resistance to race 1 (Fw) is reportedly on
chromosome 4, we initially concentrated our studies on that chro-
mosome and attempted to determine whether Fnw and Fwf were located
there as well. Our approach was to develop F2 populations that
were well characterized for the morphological markers and various
isozyme loci followed by scoring F3 families from individual
F2 plants for resistance or susceptibility to the races of wilt.

42
PNL Volume 19 1987 RESEARCH REPORTS
In F3 families from populations of F2 plants segregating
for morphological genes in chromosome 4 (v, le, Np, Td, fa, was,
and n), it appeared that Fwf is linked to Le (Table 1) with a
recombination fraction estimated at 29%. Fwf did not show lin-
kage with n; however, Fwf appeared to be loosely linked to v as
expected based on the apparent close linkage of v with Le. Fwf
and Le appeared to be linked in two other segregating families
(Tables 2 and 3) with recombination fractions of 34% and 39%.
respectively. The probabilities associated with the chi-squares
were 0.07, 0.09, and 0.08, respectively; however, the consistency
of results among populations indicate a likely linkage of Fwf with
Le. Fwf showed some linkage with lum, a gene tentatively placed
on chromosome 4. However, Fwf did not appear to be linked to fa,
n, or Np.
Table 1. Joint segregation (A285-283 to A285 286)
Pairs                 _F3 families

           of                                                                                                                       Prob-             Recomb.

genes                      n      +/+ +/- -/+  -/-     X2            ability   Fraction
n, 'Fwf'
51
21
18
7
5
0.07
0.78
0.47 .10
v, 'Fwf'
51
25
14
3
9
5.66
0.02
0.33 .12
le, 'Fwf'
51
20
21
8
2
3.16
0.07
0.29 .12
le, v
51
29
12
10
0
3.82
0.05
0.004 .14
le, n
51
32
9
7
3
0.29
0.59
0.44 .11
Table 2. Joint segregation (A285 280 to A285-282)
Pairs                    F3 families

           of                                                                                                                          Prob-            Recomb.

genes                          n      +/+ +/- -/+ -/-     X2      ability  Fraction
le, 'Fwf'
77
37
16
21
3
2.78
0.09
0.34 0.1
lum, 'Fwf'
77
41
12
14
10
2.93
0.09
0.37 +1.1
1e, 1um
77
42
13
16
6
0.11
0.74
0.47 .09

PNL Volume 19 1987 RESEARCH REPORTS
43
In populations segregating for Fwf, Td, and fa, it was
apparent that Fwf was not linked to Td as would be expected if Fwf
were located on chromosome 4 in proximity to Le (Table 4). Also,
Fwf, was very loosely linked to fa as would be expected based on
where fa is placed in that linkage group.
The genes for resistance to races 1 and 5 (Fw and Fwf,
respectively) both appear to be linked with Le and with similar
recombination fractions. The results indicate a probable close
linkage of Fw with Fwf. We are currently developing the lines
needed to test this apparent linkage. Fwf was also linked to v
and to lum indicating that chromosome.4 is the probable location
of Fwf. The lack of linkage with Td and other markers on
chromosome.4 may indicate that the gene is in a distal position to
Le; however, further information (5) indicates that Td may be
located elsewhere in the genome.
Acknowledgment:
Families A283-250 to A283-259, shown in Table 3, were pro-
vided by G. A. Marx.
1. Haglund, W. A. and J. M. Kraft. 1970. Phytopathology 60
1861-1862.
2. ' Haglund, W. A. and J. M. Kraft. 1979. Phytopathology 69
273-275.
3. Haglund, W. A. and J. M. Kraft. 1979. Phytopathology 69
818-820.
4. Hare, W. W., J. C. Walker and E. H. Delwiche. 1949. J.
Agric. Res. 78:239-250.
5. Marx, G. A. 1987. PNL 19:38.
6. Wade, B. L. 1929. Wise. Agric. Exp. Stn. Res. Bull. 97.
32 p.
7. Wells, D. G., J. C. Walker and W. W. Hare. 1949. Phyto-
pathology 11:907-912.

44 PNL Volume 19 1987 RESEARCH REPORTS
Table 3. Joint segregation of pairs of loc1 (A283-250 to A283-259)
Pairs _F3 families

            of                                                                                                                          Prob-           Recomb.

genes                      n      +/+  +/- -/+ -/-      X2           ability  Fraction
fa:le
117
79
24
13
1
1 .92
0.17
0.39 0.08
n: le
117
6/
21
25
4
1 .32
0.25
0.41 0.08
Np:le
117
76
8
16
17
24.80
0.00
0.23 0.08
Fwf:le
114
66
14
23
11
3.07
0.08
0.39 0.08
Fwf:fa
114
.71
9
29
5
0.26
0.61
0.49 0.07
Fwf: n
114
61
19
24
10
0.40
0.53
0.46 0.07
Fwf:Np
114
59
21
23
11
0.44
0.51
0.45 0.07
Table 4. Joint segregation of pairs of lod (W286-104, W286-89 and
W286-92 families
Pairs F3 families
Pairs                                     Prob-         Recomb.
of genes       +/+  +/- -/+  -/-    X2  ability  Fraction
Fw f:fa
66
36
10
17
3
0.40
0.53
0.43 0.10
Fwf:Td
26
13
6
5
2
0.02
0.88
0.48 0.15
Fwf:Td
50
10
15
13
12
0.72
0.39
0.44 0.07
*****