48th TWC, Tob. Work. Conf., 2018, abstr. 39

Spatial distribution of pythium and other fungal species in tobacco greenhouses with root rot problems

Virginia Tech, Blackstone VA USA

Pythium root rot is one of the most common diseases in hydroponic greenhouse systems for tobacco seedling production, significantly affecting tobacco seedling germination and often significantly reducing production of usable transplants. Few studies have been conducted to investigate the roles of Pythium species causing problems in tobacco greenhouses, although Pythium myriotylum was found to be the major pathogenic species in tobacco greenhouses in North Carolina and Zimbabwe. In the present study, 424 samples were collected from 8 potential contamination sites within 41 tobacco greenhouses in Georgia, Maryland, Pennsylvania and Virginia. A total of 636 oomycete isolates were obtained using oomycete selective media (PARP). Initial sequencing results identified 6 Pythium species (P. aristosporum, P. attrantheridium, P. coloratum, P. dissotocum, P. irregulare, P. myriotylum) from weed, water, root-rot-symptomatic and asymptomatic tobacco seedling samples. Two Pythium-resembling genera, Saprolegnia spp. and Mortierella spp. were also found from water and tobacco seedlings samples. In an initial pathogenicity test, it was observed that P. myriotylum was the most aggressive species, causing foliar chlorosis and growth stunting on newly-germinated healthy tobacco seedlings. Identification and virulence analysis of the remaining collected isolates is underway to characterize the distribution of Pythium species in tobacco greenhouses. Alternative water treatments (Ethaboxam and Copper Ethanolamine complex) were compared with a standard Pythium control (Etridiazole) and Oomycete fungicide Ridomil Gold (Mefenoxam) to control P. myriotylum in tobacco float water systems. Ethaboxam appeared to be a promising alternative, as it significantly increased root length and root weight while reducing oospore reproduction, compared with untreated control. (Reprinted with permission)