Detection and prevalence of Rosellinia necatrix in South African avocado orchards

Abstract

Rosellinia necatrix is an ascomycete that causes white root rot (WRR) of several plant host species resulting in economic losses to affected agricultural and forestry industries in various regions. This study aimed to identify and monitor the prevalence of R. necatrix in avocado orchards in South Africa. We used both morphological and molecular methods to isolate and identify R. necatrix from diseased plant material and soil. Results showed that R. necatrix was present on avocado in the Limpopo, Mpumalanga and KwaZulu-Natal provinces. Additionally, a semi-selective medium, containing Rose Bengal, nystatin, cycloheximide, chlorothalonil and 2-phenylphenol, was developed to improve isolation of R. necatrix. We also tested an already established R. necatrix-specific TaqMan qPCR protocol to determine if it can reliably detect the pathogen isolates in planta in the South African samples. Based on our results the technique had a detection rate of 91.3% in artificially infected roots and 100% in artificially inoculated soil. We tested natural infected plant and soil samples and detected R. necatrix in 86% of the plant samples and in 70% of the soil samples. Using a selective medium or an in planta molecular detection method streamlines isolation and detection of R. necatrix, which will help prevent further spread of the pathogen. Moreover, additional information on the prevalence of WRR will create awareness among growers and provide a basis for management of the disease.