Agriculture Reference
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healthy avocado feeder root
avocado feeder root
healthy tree
infected tree
mycelium
zoospores discharged
zoospores motile in water
and are attracted to roots
mycelium
sporangia form
chlamydospores
produced in roots
sporangium forms
from clamydospore
chlamydospores survive in soil
Fig 2.15 Disease cycle of Phytophthora cinnamomi in avocado.
Fig 2.16 Phytophthora-infected roots (left) and healthy roots.
In the soil, they are attracted to the root tips of plants by a
chemical stimulus (chemotaxis) as well as root-generated
electric fields (electrotaxis). Three to five days after infection
has occurred, the pathogen sporulates again, forming
sporangia on the surface of the roots, and which release
more zoospores.
Phytophthora species survive in infected roots by forming
another type of asexual spore called chlamydospores. They
can survive adverse conditions for several years. The sexual
Fig 2.17 A culture of Phytophthora, showing a typical growth pattern.
Inset: sporangium.
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