Submitted to: Acta Horticulturae
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/9/2001
Publication Date: 4/1/2002
Citation: Smith, B.J. 2002. Susceptibility of southern highbush blueberry cultivars to Phytophthora root rot. Acta Horticulturae. 574:75-77 Interpretive Summary: Southern highbush blueberry cultivars are being widely planted in the southern United States. These cultivars are hybrids of the northern highbush blueberry and various blueberry species native to the south. Little is know about the susceptibility of these cultivars to important blueberry diseases such as Phytophthora root rot. One of seven southern highbush cultivars grown in soil infested with the root rot pathogen was determined to be as resistant to Phytophthora root rot as the two rabbiteye blueberry cultivars in the trial. The other six southern highbush cultivars were very susceptible with most of their plants dying by the end of the five year study. Traditional Phytophthora root rot control practices such as fungicide drenches and raised beds resulted in only marginal improvement over untreated plants. The finding that one southern highbush cultivar is resistant to Phytophthora root rot indicates that blueberry breeders should be screening their elite selections to identify other resistant lines. Blueberry growers will benefit immediately from the knowledge that a resistant cultivar is currently available. The lack of control by the traditional methods indicates that further research is needed in this area.
Technical Abstract: Phytophthora root rot is a serious disease of highbush blueberry (Vaccinium corymbosum L.) which is more susceptible than rabbiteye blueberry (V. ashei Reade). As acreage of southern highbush cultivars (hybrids between highbush and "southern" blueberry species) increases so does the potential importance of this disease. This study was initiated to compare the susceptibility of 7 southern highbush cultivars and 2 rabbiteye cultivars to P. cinnamomi and to evaluate the effect of bed height and fungicide treatments on disease severity. After 2 years root rot symptoms were evident on plants throughout the field, but there were no differences in disease severity or plant vigor due to bed height or fungicide treatment. There were differences among cultivars. The rabbiteye cultivars, Tifblue and Premier, were more vigorous than the southern highbush cultivars, Marimba, Pearl River, Misty, Magnolia and Cooper. After 5 years, 100% of Premier, 90% of Gulfcoast and 76% of Tifblue plants were still alive and vigorous compared to less than 25% of the other southern highbush cultivars. After 5 years growth in Phytophthora infested soil, 21% of plants drenched with metalaxyl twice a year for 3 years and 16% of plants grown on raised beds were very vigorous compared to 14% of plants grown in untreated soil and 9% of plants grown on flat beds. These results indicate that at least 1 southern highbush cultivar, Gulfcoast, has field resistance to Phytophthora root rot equivalent to rabbiteye blueberry cultivars.