VIEW ARTICLE

Ecology and Epidemiology

Pine Bark, Hardwood Bark Compost, and Peat Amendment Effects on Development of Phytophthora spp. and Lupine Root Rot. Suzanne Spencer, Former graduate student, Department of Plant Pathology, North Carolina State University, Raleigh 27650; D. M. Benson, associate professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 72:346-351. Accepted for publication 6 July 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-346.

The use of bark and peat media for suppressing Phytophthora root rot was evaluated in the greenhouse and laboratory. Development of root rot of Lupinus angustifolius (lupine), an assay plant highly susceptible to Phytophthora cinnamomi, was observed in media containing peat, hardwood bark compost (HBC), or pine bark (PB). With or without added sand, HBC was more effective in suppressing root rot of lupine than was PB. The development of disease was delayed and suppressed more in PB at pH 4.5 than in PB at pH 6.0. Sand and lime amendments to PB reduced the suppressive capacity to that of similarly treated peat. Mycelial growth and chlamydospore formation by P. citricola and P. cinnamomi was greater on cornmeal and/or water agar incorporated with water-soluble, filter-sterilized extracts of PB and peat at pH 6.5 than on agar incorporated with HBC extract. Sporangial production by P. cinnamomi at pH 6.0 was lower in sterile PB and HBC extracts amended with a stimulatory salt solution than in amended sterile water. Sporangial production by P. citricola was not similarly reduced. Sporangial production by both Phytophthora spp. was generally higher in nonsterile extracts than in sterile extracts. Sporangial production was generally lower in solutions at pH 4.0 than at pH 6.0 although nonsterile extract of PB from one source overcame this pH effect.