Molecular diagnosis of the brown root rot disease a gent Phellinus noxius on trees and in soil b y rDNA ITS analysis.

Phellinus noxius (P. noxius) is an important pathogen that causes brown root rot of trees in tropical and sub-tropical areas and has led to severe damage to trees. A quick and accurate diagnostic technique is essential to the timely confirmation of the pathogen and possible treatment. In this study, a fast, sensitive and accurate approach of molecular technique was used to diagnose the brown root rot pathogen on trees and in soils of subtropical Hong Kong. Two pairs of specific PCR primers were used to amplify the target rDNA internal transcribed spacer (ITS) region through polymerase chain reaction (PCR) for both tree tissues and soil samples. The amplified ITS fragments were then sequenced and analyzed phylogenetically for the diagnostic identification of the pathogen P. noxius. The results showed that 13 of 38 suspected trees in Hong Kong were infected with P. noxius through molecular detection. The pathogen showed no specific preference to any particular tree species. Quantitative PCR was applied to soils grown with trees identified both positive and negative for P. noxius, but the soils with healthy trees were also found positive for P. noxius. For the first time, P. noxius was reported to infect a wide range of tree species in Hong Kong and widely presented in soils, probably serving as a reservoir for the pathogen. Through this study, it is proposed that P. noxius is a soil-borne pathogen, which increases its infectivity when trees start to grow in the soil as a means in addition to the previously proposed root-to-root contact.