Cucurbit Genetics Cooperative Report 3:39-40 (article 22) 1980
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.