Accuracy and precision of population estimates of Verticillium dahliae on growth media in quantitative soil assays

Abstract

Verticillium dahliae Kleb. is a serious pathogen of many plant species. Growth media used to measure population density of V. dahliae in soil were evaluated for high recovery of the pathogen, as well as accuracy and precision of population estimates from naturally and artificially infested sandy loam soil using the soil dilution method. Recovery of V. dahliae from naturally infested field soil was highest on soil pectate Tergitol agar (SPT), soil extract agar + sodium polypectate (SEAP), modified pectate agar (MPA), potato dextrose agar + streptomycin sulphate (PDAS), and Talboys' prune lactose agar (TPA); however, PDAS and TPA were overgrown with contaminating fungi, making enumeration difficult. Use of SPT medium resulted in the most precise population estimate with a standard error (SE) of 12.6% of the mean followed by use of pectate agar (PA) (SE = 14.8%) and SEAP (SE = 19.1%). Ethanol, biotin, and Dox salts enhanced recovery of V. dahliae from naturally infested soil, but combining Dox salts with ethanol and biotin significantly reduced population density. Soil extract had no significant effects on population density. Accuracy of V. dahliae population estimates from sterile artificially inoculated soil was highest on modified soil extract agar (MSEA) (64%) followed by SPT (58%). However, accuracy of V. dahliae population estimates from nonsterile artificially inoculated soil was highest on SPT (36%). Soil extract is not an essential ingredient and biotin may increase recovery of V. dahliae from soil.Key words: Verticillium dahliae, verticillium wilt, population density, recovery, accuracy, precision.