Preservação do inóculo de Plasmodiophora brassicae utilizando o método de congelamento

Abstract

The preservation of Plasmodiophora brassicae resistance structures under laboratory conditions is difficult since this is an obligate parasite. The freezing method using an ordinary household freezer was tested to ensure the pathogen's survival and the preservation of its infective traits. Roots of different brassica species naturally infected by P. brassicae, showing typical clubroot symptoms, sampled in the same farm, located in the Pardinho County, State of São Paulo, were collected during different seasons and were immediately frozen at approximately 20°C. The treatments were divided as follows: T1: clubroots frozen for 389 days (arugula); T2: clubroots frozen for 242 days (broccoli); T3: clubroots frozen for 21 days (Chinese cabbage), and T4: control (without inoculum). The pathogenicity tests were conducted under greenhouse conditions (25±2°C). Each plant of the susceptible variety of Chinese cabbage (Pak choi) was inoculated with 2mL of a spore suspension of each treatment at a concentration of 10 7 spores.mL -1. Each treatment consisted of six replicates distributed in random blocks. The roots of plants were washed and evaluated five weeks after inoculation. There were significant differences between treatments. The frozen materials preserved their infective traits over a period of 21 to 242 days, demonstrating that the freezing method could be an option to preserve the resistance structures of this pathogen.