Cucurbit Genetics Cooperative Report 2:29-30 (article 18) 1979
B. B. Rhodes
Edisto Experiment Station, Blackville, SC 29817
Hadwiger and Hall (1) reported increased growth of Colletotrichum orbiculare on the dark green striped rind area of ‘Garrisonian’ watermelon fruits. No other report relating this disease to the pigmentation of the watermelon fruit or vine is known.
A pale leaf line, originally designated R143, was obtained from seed stocks at the U.S. Vegetable Laboratory at Charleston, SC. The pale leaf character is quite evident in the cotyledon stage. The cotyledons are almost yellow. However, pigmentation differences become less evident as the plant matures and is almost imperceptible in the older leaves. The character is not reported in the literature.
In the fall of 1976, the pale leaf line was inoculated with race 2 anthracnose (AR2) spores. Roughly one-half of the 2-week old seedlings survived inoculation with a solution of 20,000 spores/ml of AR2. Survival rate in other lines varied from 0-10%. A pale leaf survivor was crossed with the cultivar ‘Allsweet’. The F1 seed were planted in the field in the spring of 1977. Self-pollinated fruit were harvested from these plants and provided F2 seed. Ten hills of these F2 lines, as well as their parents, and other genetic material possessing the pale leaf variant were planted in the field in the spring of 1978 and were inoculated with AR2 (140,000 spores/ml). Plants showing superior resistance to AR2 were flagged two weeks after inoculation. Resistance ratings were based on percent defoliation (Table 1). Percent defoliation was estimated by dividing the length of a single vine into the segment of that vine with necrotic leaves. The amount of variability within a line is shown in Table 2. One F2 population from the previously mentioned cross was judged to be the most resistant of more than 50 lines.
The pale leaf character was not evident in any of the parental material or F2 progeny in the field in 1978, nor in the F1 progeny in the field in 1977. The pale leaf character was clearly evident in the greenhouse plants used as the male parent in the winter of 1976-1977 and in all parental material and progeny planted in the greenhouse in the winter of 1978-1979.
Investigations are continuing on the inheritance of this character and its relationship, if any, to AR2 resistance.
Table 1. Percent defoliation of watermelon genotypes infected with race 2 anthracnose.
Genotype |
% defoliation a |
No. plants sampled |
| ‘Allsweet’ (AS) | 25 | 32 |
| Yellow 1 (yel-1) | 30 | 2 |
| Yellow 2 | 20 | 2 |
| Yellow 3 | 23 | 2 |
| F1 (yel-l x AS) | 23 | 12 |
| F2 (yel-l x AS) | 14 | 16 |
| F2 (yel-l x AS) | 21 | 18 |
| F2 (yel-1 x AS) | 5 | – |
a Defoliation two weeks after inoculation with 140,000 spores/ml of race 2 anthracnose.
Table 2. Percent defoliation of individual hills of progeny from a cross between ‘Allsweet’ and a pale leaf line of watermelon (yel-l x AS).
Generation |
Hill number |
|||||||||
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
|
| F1 | 15 | – | – | 25 | 20 | 25 | 20 | – | 35 | – |
| F2 | 15 | – | 15 | 15 | – | 30 | 7.5 | 10 | 15 | 15 |
| F2 | 20 | 20 | 15 | 25 | 25 | 20 | 20 | – | – | 20 |
| F2 | 5 | 5 | 5 | – | 5 | 5 | 5 | 10 | 7.5 | – |
Literature Cited
- Hadwiger, Lee A. and Charles V. Hall. 1961. The relationship and free amino acid content with resistance to Colletotrichum lagenarium in watermelons. Plant Dis. Reptr. 45:373-374.