ISHS Acta Horticulturae 172: Composts as Horticultural Substrates
EFFECT OF COMPOSTS IN CONTAINER MEDIA ON DISEASES CAUSED BY SOILBORNE PLANT PATHOGENS |
| Authors: | H. A.J. Hoitink, G.A. Kuter |
| Abstract:
Organic components used in container media affect the severity of soilborne plant diseases. Media with peat as the soil organic component usually are conducive to disease development ; addition of composts to peat media may render them suppressive. All tree barks, for example, release inhibitors of Phytophthora spp. which account for some of the disease control. However, most mature tree bark composts do not release these inhibitors. Mature composts may be recolonized after peak heating by specific antagonists of plant pathogens. However, those batches of compost that are not recolonized remain conductive to disease. This review discusses some specific effects of organic components in container media that affect the fate of soilborne plant diseases. During the past decade, a significant body of knowledge has been published on biological control of soilborne plant diseases with composts. This has impacted on procedures used by the ornamentals industry, particularly for production of containerized plants. Traditionally, plant growth media consisted of peat, sand and vermiculite or Perlite. Essentially all reports on media containing various types of peats indicate that they are conducive to disease development, particularly if steamed. Examples of diseases that are not suppressed in Sphagnum peat media are those caused by Phytophtora app. (Hoitink et al., 1977 ; Spring et al., 1980), Pythium spp. (Robertson, 1973), Rhizoctonia solani Kuhn (Nelson Hoitink, 1982 ; Stephens et al., 1981), Fusarium spp. (Chef et al., 1983), nematode diseases (Malek and Gartner, 1975) and others. Recent Finnish reports indicate, however, that some sources of Sphagnum peats are suppressive to several diseases (Tahvonen, 1982). This apparent contradiction may be related to differences in levels of decomposition of peat sources (Dickinson and Maggs, 1974). The surface layer known as "light peat" is less decomposed, high in cellulose, low in lignin and may contain some living plant parts at harvest time (Kavanagh and Herlihy, 1975 ; Puustjarvi, 1977). The deeper layer is more decomposed, low in cellulose and is classified as "dark peat". | |
Download Adobe Acrobat Reader (free software to read PDF files) | |
