Effect of hot-water-soluble Thuja plicata heartwood extractives on the growth of Thuja and non-Thuja isolates of Poria weirii

Abstract

Isolates of Poria weirii Murr. cultured from various hosts may be divided into two groups on the basis of their ability to parasitize Thuja plicata Donn. Measurement of linear growth along wood microsections confirmed that substances inhibitory to one isolate group are hot-water-soluble T. plicata heartwood extractives. Isolates from T. plicata (Thuja) were more tolerant than isolates from Pseudotsuga menziesii (Mirb.) Franco (non-Thuja) to a hot-water extract of Thuja plicata heartwood and its steam-volatile and non-volatile fractions; steam-volatile components caused greatest response differences. With sufficient inoculum potential, non-Thuja isolates may overcome effects of inhibitory compounds in T. plicata heart-wood; however, the resulting infections of T. plicata roots were usually localized. Non-Thuja isolates failed to increase tolerance to steam-volatiles both in laboratory tests and under field conditions. The results have significance for control of Poria weirii.