Aj. Downer et al., Association of cellulytic enzyme activities in eucalyptus mulches with biological control of Phytophthora cinnamomi, PHYTOPATHOL, 91(9), 2001, pp. 847-855
A series of samples were taken from mulched and unmulched trees starting at
the surface of mulch or soil to a 15 cm soil depth, forming a vertical tra
nsect. Saprophytic fungi isolated from the soil samples on rose bengal medi
um and surveyed visually were most abundant in mulches and at the interface
of mulch and soil (P < 0.05). Microbial activity as assayed by the hydroly
sis of fluorescein diacetate was significantly greater in mulch layers than
in soils. Cellulase and laminarinase enzyme activities were greatest in up
per mulch layers and rapidly decreased in soil layers (P < 0.05). Enzyme ac
tivities against Phytophthora cinnamomi cell walls were significantly great
er in mulch than in soil layers. When Phytophthora cinnamomi was incubated
in situ at the various transect depths, it was most frequently lysed at the
interface between soil and mulch (P <less than> 0.001). Roots that grew in
mulch layers were significantly less infected with Phytophthora cinnamomi
than roots formed in soil layers. In mulched soil, roots were commonly form
ed at the mulch-soil interface where Phytophthora populations were reduced,
whereas roots in unmulched soil were numerous at the 7.5 cm depth where Ph
ytophthora cinnamomi was prevalent. Enzyme activities were significantly an
d positively correlated with each other, microbial activity, and saprophyti
c fungal populations, but significantly and negatively correlated with Phyt
ophthora recovery.