Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2005
Publication Date: 10/1/2006
Citation: Smith, B.J. 2006. Phytophthora root rot and botryosphaeria stem blight: important diseases of southern highbush blueberries in southern united states. Acta Horticulturae. (ISHS) 715:473-480. 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 and Botryosphaeria stem blight. A series of studies are being conducted to determine the relative susceptibility of southern highbush cultivars to root rot by growing the cultivars in soil infested with the root rot pathogen. Several of the cultivars are consistently more vigorous whether grown in infested or in non-infested soil. Blueberry growers will benefit immediately from the knowledge of which cultivars are most vigorous. A laboratory assay was used to determine the susceptibility of 20 southern highbush blueberry cultivars to stem blight which is a destructive disease of blueberries in the southeastern U.S. There are no fungicides available for control of this disease; therefore, resistant cultivars and cultural practices offer the most promise for its control. Little is known of the susceptibility of new southern highbush blueberry cultivars to stem blight. Ten southern highbush highbush cultivars were identified as resistant. The results of these studies are important to southern blueberry growers as they choose which cultivar to plant and to blueberry breeders as they choose parents to use in their breeding programs.
Technical Abstract: The commercial blueberry industry in the southeastern United States traditionally has been based on rabbiteye cultivars developed from native Vaccinium ashei. Southern highbush cultivars, interspecific tetraploid hybrids between V. corymbosum and various blueberry species native to the southeastern U.S., are extending the range of commercial blueberry production further south. Southern highbush cultivars are desirable because of their low winter chill requirement, late spring bloom, and early fruit production; however, little is known about their susceptibility to diseases. The objective of these studies was to compare the susceptibility of southern highbush blueberry cultivars to two diseases common to the southern U. S., stem blight, caused by the fungus Botryosphaeria dothidea, and Phytophthora root rot caused by the fungus Phytophthora cinnamomi. The susceptibility of southern highbush cultivars to root rot was determined by growing the plants in soil infested with P. cinnamomi. Three separate trials were conducted. 'Star', 'Bluecrisp', 'O'Neal', 'Jewel', 'Jubilee', 'Southmoon', and 'Misty' were more vigorous than other cultivars in at least two of these trials. The susceptibility of 20 southern highbush blueberry cultivars to stem blight was evaluated using a detached stem assay shown previously to correlate with field results. Cultivars that developed lesions shorter than those on the susceptible rabbiteye, 'Tifblue', were classified as resistant and included 'Pearl River', 'Southmoon', 'Marimba', 'Star' 'Sebring', 'Ozarkblue', Georgiagem', 'Sapphire', 'Bluecrisp', 'Misty', and 'Emerald'. Those with lesions as long or longer than 'Tifblue' were classified as susceptible and included 'O'Neal', 'Legacy', 'Cooper', 'Bladen', 'Jubilee', 'Magnolia', 'Biloxi', 'Gulf Coast', and 'Reveille'.