From Tony Keinath, Extension Vegetable Pathologist.
As part of a large USDA Specialty Crop Research Initiative grant, I have been working with Dr. Jonathan Schultheis, Horticulturist at NCSU, to evaluate seedless watermelon cultivars grown in plots naturally infested with the Fusarium wilt fungus. The South Carolina trials were done in my Fusarium-infested field at the Coastal REC, a field that has had Fusarium races 1 and 2 in it since 2005. Ten cultivars were tested in 2021, and 12 cultivars were tested in 2022; eight cultivars were tested both years.
The figure shows the relationship between marketable weight per acre and the percentage of wilted plants at the end of the season (10 weeks in 2021 and 11 weeks in 2022). It’s clear that the more diseased plants in a field, the lower the marketable yield. Based on this graph, Fusarium wilt was the main reason yields differed in this study. Fascination grafted onto Carolina Strongback citron rootstock (Fascination grafted) hit the “magic” yield of 40,000 pounds per acre and had no plants wilted (0 of 96 plants examined in the 2 years). On the other end, Shoreline had the lowest yields in both years and the highest percentage of wilted plants.
Disease ratings were similar for each cultivar in the two years, although disease was worse in 2022 than in 2021. For example, the final wilt percentage on Shoreline was 68% in 2021 and 94% in 2022. Fusarium wilt symptoms continued to appear in 2022 after harvest started, likely due to the extremely dry conditions in June and high temperatures. Yields also did not differ significantly between years.
Postharvest quality was measured, but, in general, there were few differences among the cultivars. Hollow heart was relatively low, and most fruit with hollow heart had small cracks. There were more seeds per fruit in 2021 than in 2022; however, in 2022, grafted Fascination had more seeds per fruit (an average of 0.9 seeds) than all other cultivars. In 2021, cultivars with more diseased plants had lower Brix, while Brix was relatively high for all cultivars in 2022, likely due to the dry weather. Flesh firmness differed among cultivars in both years; however, firmness varied each year. In general, Shoreline had the firmest fruit both years, while Tri-X 313 was among the cultivars with less firm fruit.
| 2021 | 2022 | |
| Avg. fruit weight (lb) | 12.4 to 17.0 | 13.0 to 18.9 |
| Hollow heart (% of fruit) | 11% | 13% |
| Hollow heart 3-4 | 2% | 4% |
| Seeds per fruit | 0.5 to 1.2 | 0 to 0.9* |
| Brix | 9.2-11.5* | 10.6 to 12.1 |
| Flesh firmness | 3.2 to 4.6* | 2.6 to 3.9* |
Conclusions:
- Growers can expect similar yields from these cultivars planted into their fields infested with Fusarium wilt because the results were similar between the two years in this study. The test field is heavily infested with Fusarium, so yields in growers’ fields not as heavily or uniformly infested may be better.
- Six of the eight cultivars performed similarly, including El Capitan, Tri-X-313, Fascination, Powerhouse, Embasy, and 7197HQ, because they have resistance to race 1 but no resistance to race 2.
- The Carolina Strongback rootstock used to graft Fascination is resistant to races 1 and 2, which explains why it did so well in this study.
- Shoreline is not recommended in any field with Fusarium wilt. If growers must grow this cultivar to satisfy buyers’ requests, they need to use integrated management practices to reduce the percentage of infected plants. See Land-Grant Press 1022: Integrated Management for Fusarium Wilt of Watermelon.
The South Carolina Grower 