Survey of Potential Root Pathogens in Softwood Cuttings Collected from Georgia Blueberry Nurseries

Abstract

Survey sampling of 16 blueberry nurseries propagating softwood cuttings was conducted in 2007 and 2008 to determine which soilborne plant pathogens were most prevalent in commercial blueberry propagation systems in southern Georgia. Samples were collected four times: June (early), September (mid), and October (late) in the 2007 growing season, with additional sampling of overwintered cuttings in April 2008. This survey revealed that Calonectria ilicicola (Cylindrocladium parasiticum), causing Cylindrocladium root rot, is a primary pathogen of blueberry cuttings in southern Georgia. The organism was isolated consistently during all four survey dates with a cutting-level incidence of 3.6, 10.2, 36.4, and 14.3% in the first through fourth samplings, respectively. Rhizoctonia spp. were recovered less frequently and were only present during the first (10.9% cutting-level incidence), third (4.6%), and fourth survey dates (3.6%), whereas the oomycetes Pythium and Phytophthora were detected only on the second survey date. Fusarium spp. were isolated commonly (29.1% incidence in the first, 12.2% in the second, 18.2% in the third, and 7.1% in the fourth sampling), but pathogenicity remains uncertain. Across all survey dates, Calonectria, Rhizoctonia, oomycetes, and Fusarium were recovered at least once from 43.8, 18.8, 12.5, and 87.5% of nurseries surveyed, respectively. When nursery-level data on pathogen presence or absence collected from this survey were analyzed in relation to a survey of production practices used by these same propagators, the practice of reusing growth media was found to be significantly associated with Calonectria presence.