Cucurbit Genetics Cooperative Report 3:39-40 (article 22) 1980
Inheritance of a Pale Seedling Character in Citrullus
lanatus
B. B. Rhodes
Edisto Experiment Station, Blackville,
SC 29817
The pale seedling character in watermelon was as described
previously (1). On first examination, the character appeared
to be associated with resistance to race 2 anthracnose (AR2).
In 1979 the inheritance of this character and its relationship
to AR2 resistance was investigated. One week old seedlings
of the P1 (pale characters), P2 (Allsweet), F1, F2,
and BC1 to P1 were transplanted to the field in peat pellets on April 1.
Totals for seedling color for F2 progeny were pooled from
greenhouse and field data. On April 30, plants in the field
were inoculated with 1250 spores/ml of an AR2 suspension.
On July 26, plants were evaluated for resistance.
The F2 segregation of pale seedlings
and green seedlings fit a 13:3 ratio (Table 1). In the backcross
of pale seedlings x F1 (pale seedlings x Allsweet), the
data are consistent with a 1:1 ratio. It is important that
seedlings be scored after the cotyledons are fully expanded
and before the second true leaf stage, since the pale condition
often disappears after that period. If the pale seedlings
character is assumed to be due to a recessive gene at one
locus interacting with a dominant gene at a second locus,
then a 13:3 ratio for the F2 and
a 1:1 ratio for the BC1 populations are compatible.
The defoliation ratings and fruit lesion counts did not
support an association between AR2 resistance and the pale
seedling character (Table 2), nor that resistance existed
in the line with the pale seedling character. However, it
should be noted that disease ratings were made two weeks
after inoculation in the first comparison (1) and well past
fruit maturity in this comparison.
Table 1. Segregation for the pale seedling character in
the F2 and backcross populations from a pale seedling by
green seedling cross.
|
Observed |
|
|
|
Population |
Green |
Pale |
Expected ratio |
Chi-square |
Probability |
F2 |
318 |
72 |
3:1 |
8.892 |
0.003 |
|
|
|
13:3 |
0.021 |
>0.95 |
Pale x F1 |
90 |
104 |
1:1 |
0.506 |
0.50 |
Table 2. Frequency distribution for anthracnose 2 defoliation
ratings and fruit lesion counts within pale seedling and
normal seedling classes.
|
|
Percentage defoliation |
Population |
Seedling color |
10 |
20 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
100 |
Pale seedling |
Pale green |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
2 |
Allsweet |
Green |
0 |
0 |
0 |
0 |
3 |
0 |
1 |
0 |
0 |
4 |
F1 |
Green |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
1 |
9 |
F2 |
Pale green |
0 |
0 |
1 |
2 |
1 |
2 |
1 |
0 |
5 |
19 |
|
|
Number of lesions/fruit |
Population |
Seedling color |
0 |
1-5 |
6-10 |
11-20 |
>20 |
Allsweet |
Green |
1 |
1 |
3 |
0 |
2 |
F1 |
Green |
1 |
2 |
3 |
0 |
2 |
F2 |
Green |
10 |
3 |
0 |
4 |
6 |
|
Pale green |
13 |
3 |
2 |
2 |
2 |
Literature Cited:
- Rhodes, B. B. 1978. Race 2 anthracnose resistance in
a watermelon line with a pale leaf character. Cucurbit
Genetics Coop. Rpt. 2:29-30.
