For anyone working on Phytopthora
Dave
http://www.citrusresearch.com/publications.asp
Suppressive Soils
Much has been written about suppressive soils with respect to avocado
root rot (Borst, 1983; Broadbent and Baker, 1974;
Downer, 1998; Halsall, 1982, Ko and Shiroma, 1989; Pegg et al., 1982;
Turner and Menge, 1994). Avocado root rot
suppressive soils occur naturally. For example, natural rainforest
habitats were suppressive to avocado root rot and a
complex method called the Ashburner method was created to duplicate
the suppressive rainforest soils (Broadbent and
Baker, 1974). The Ashburner method consisted of cover cropping,
applications of manure, dolomite, and super-phosphate,
and the addition of organic matter. Today the method has been
modified to provide only the key ingredients,
which are organic mulches and gypsum. High populations of bacteria
and actinomycetes (Broadbent and Baker, 1974) or
cellulose and lignin degraders (Downer, 1998) are naturally
stimulated to create the suppressive soils. As we learn more
about the factors that create suppressive soils, this term will lose
its mystique and we will speak of specific suppressive
factors. Certain bacteria, such as some species of Pseudomonas and
Chromobacterium violaceum, are required to stimu-late
sporangial production of P. cinnamomi, while other bacteria are
inhibitory (Erwin and Ribeiro, 1996; Zentmyer,
1980). Specifically, microorganisms such as Myrothecium roridum,
Trichoderma harzianum, Epiccocum purpurascens,
Catenaria anguillae, Humicola fuscoatra, Anguillospora
pseudolongissma, Hypochytrium catenoides, Myrothecium ver-rucaria,
Streptomyces griseoalbus, Micromonospora carbonacea, Streptomyces
violascens, and Ceraceomyces tessulatus
have been shown to be inhibitory to P. cinnamomi via competition,
antibiosis, or parasitism (Downer, 1998, Erwin and
Ribeiro, 1996). The complex community structure of microorganisms
like these is undoubtedly responsible for the fact
that some soils are suppressive while others are not. Zentmyer (1980)
draws attention to the fact that populations of P.
cinnamomi usually drop off dramatically after the first wave of root
rot occurs. He feels this may occur as parasites of P.
cinnamomi and other antagonistic microorganisms invade and make the
soil more suppressive.
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Received on Mon Oct 20 2003 - 00:16:49 EDT