Comparison of Media for Recovery of Verticillium dahliae from Soil

Abstract

Polygalacturonic acid (PGA) is an important constituent of Sorensen's NP-10 medium (NP-10) for estimating the population density of Verticillium dahliae in soil. Different types of PGA are available, but not all of them favor the growth of V. dahliae. Unavailability of PGA sodium salt from orange (P-1879) has created an unprecedented problem for the quantification of microscle-rotia (MS) of V. dahliae in soil. The PGA from orange (P-3889) that is now available does not support the growth of V. dahliae. Therefore, experiments were conducted to optimize the use of NP-10 prepared with P-3889 and various concentrations of NaOH. NP-10 with P-3889 amended with eight concentrations of NaOH were compared with NP-10 prepared from PGA sodium salt from orange (P-1879, now discontinued) and citrus (P-3850) along with cellophane and Na-pectate media for recovery of MS from soil and growth of V. dahliae on the media. Seven soils were assayed for MS, and eight isolates of V. dahliae were evaluated for growth and production of MS. Concentrations of NaOH >0.035N and <0.02N in NP-10 with P-3889 reduced mycelial growth, microsclerotial production, and recovery of MS from soils. Similarly, NP-10 with P-3850 alone, cellophane, and Na-pectate media had significantly reduced growth on media and recovery of V. dahliae from soils. The NP-10 with P-3889 and 0.025N NaOH consistently yielded numbers of V. dahliae MS from soil samples and supported the growth and production of MS similar to the NP-10 with P-1879. The medium developed in this study can serve as a direct replacement for the original NP-10 that was developed nearly three decades ago, an important component of which is no longer available.