Screening of several disinfectants to assess their efficacy in controlling mycelia growth, sporangia germination, and recovery of viable Phytophthora ramorum

Abstract

Phytophthora ramorum is the causal agent of sudden oak death, a very serious disease that causes dieback and death of several important forest species in the USA. It was recently associated with a destructive disease of larch in the United Kingdom. The pathogen has a wide host range including ornamentals such as Rhododendron and Viburnum, and has been recovered from nursery soil samples. Diligent use of effective disinfectants in nurseries can contribute to integrated management strategies for P. ramorum. Nine disinfectants, some at different concentrations and duration, were evaluated in vitro and in vivo for their efficacy in controlling the growth of P. ramorum mycelia and the germination of sporangia. Chemprocide® (1.35%), PerCept™ (diluted 1:16) and 15% bleach treatments were the most consistent in their effectiveness for inhibiting both mycelia growth and sporangia germination. Chemprocide® (1.35%) and 10% bleach treatments were effective also for preventing P. ramorum recovery from contaminated plastic plant saucers and metal surfaces. Isolates representing the three clonal lineages (EU1, NA1, and NA2) of P. ramorum were included in all studies. Interestingly, 10 min treatments of ethanol (70% or 95%) were effective in preventing colony forming unit (CFU) growth, but were not as effective for preventing mycelia growth. Ethanol treatments for 5 min were among the least effective, and in every case was not significantly different from the water-treated controls. Concentration and treatment time were critical factors influencing efficacy in these studies. Differences in CFU production were observed among the clonal lineages with a high of 18 ± 1.19 (n = 66) for EU1 isolates, and a low of 9.0 ± 0.89 (n = 74) for NA2 isolates.