Temporal and Host Related Variation of Pythium and Globisporangium Species in Floricultural Crops

Abstract

Several species of Pythium and Globisporangium cause damping off of seedlings, seed rot, stem lesions, and root rot in greenhouse ornamental crops. Two hundred seven isolates from three greenhouses located in Long Island, New York, were collected from chrysanthemum plants in 2014 to identify the diversity of species present at these locations. Analysis of DNA sequences based on ITS region identified fifteen species of Globisporangium (n=4) and Pythium (n=11). Globisporangium irregulare, G. cryptoirregulare and P. aphanidermatum were the most common species found at the studied facilities. The G. irregulare s.l. complex (G. irregulare, G. cryptoirregulare) was the most prevalent species in 2014, which agrees with results of a previous study that analyzed samples collected over an eleven year period (2002 - 2013) from geranium and other spring season crops. The 2014 results showed the same predominant species in each greenhouse. Moderate to high genetic structure was found between greenhouse populations for each species of the G. irregulare complex. Allelic frequencies and distribution suggest local sources of inoculum as well as common sources of inoculum for Pythium diseases of chrysanthemum in the floricultural greenhouse operations studied. When the genetic composition of G. irregulare s.l. populations associated with geranium over different seasons and years (2009-2013) were compared, closely related genotypes occurred in the same location over different years, suggesting inoculum may have survived in greenhouse populations from year to year