P. lacustris sp. nov. (formerly known as Phytophthora taxon Salixsoil) was first isolated in 1972 in the UK and then in many other European countries, including Poland. The aim of this work was a morphological, physiological, and genetic characterization of the P. lacustris isolates by means of the daily growth rate, mycelium morphology, and generative and vegetative structures, depending on the temperature of incubation and growth media. In addition, the ability to colonize willow shoots and leaves was estimated.
Out of 114 isolates of P. lacustris obtained from water habitats located near plant nurseries in central and southeastern Poland in 2007-10 that were identified on the basis of molecular tests which showed high diversity in colony growth patterns and daily growth rates, 10 groups were separated by means of Duncan’s test. Representatives of these 10 groups together with three reference isolates – P. lacustris P245 as the holotype, P. gonapodyides CBS 117380 as a specimen most closely related phenotypically to P. lacustris, and P. cactorum as a positive control of forest trees’ pathogen – were researched.
Great heterogeneity in the growth rates and morphology of mycelium, as well as in the structure of zoosporangia and hyphal swellings, were observed. Moreover, the isolates differed in their ability to colonize the willow leaves and shoots in the in vitro tests. Some correlation may be found between the daily growth rates and colonizing abilities, and between the daily growth rate and the dimension of the sporangia. Also, a large genotypic variation between the isolates based on the fingerprint patterns generated by molecular techniques (RAPD and ISSR) was obtained.