pH near neutra

l

optimal nutrie

nt levels

no harmful chemicals,

low levels of salts

good tilthsurface structure

porous and stable

no subsoil layers

restricting roots

good aeration, water

storage, drainage

extensive biodiversity

plentiful beneficial organisms

low pest pressure

chemical propertie

s

physical properties

bio

log

ical

pro

per

ties

Healthy

Soil

Figure 8.1. Optimal chemical, biological, and physical properties promote healthy soils.

2

1

Plant increases extrafloral nectar flow as food for adult

beneficials

3

Plant gives off signals to attract beneficials that attack pests

Plant produces chemicals that slow pest feeding

Figure 8.2. Plants use a number of defense strategies following damage by feeding insects. Modified from unpublished slide of W.J. Lewis.

defense proteins

salicylic acid

The plant defense proteins provide resistance to a variety of plant

pathogens.

Disease organisms and nonpathogenic microbes stimulate the plant above- or

belowground to produce the hormone

salicylic acid.

An increase in the hormone salicylic acid

causes the plant to produce many types of

defense proteins.

Plant hormones jasmonate and

ethylene increase throughout the plant and induce resistance

to a wide variety of plant pathogens.

jasmonate

ethylene

Plant growth- promoting

rhizobacteria (PGPR) stimulate plants roots, causing production of

plant defense hormones

a) systemic acquired resistance (SAR) b) induced systemic resistance (ISR)

Figure 8.3. Types of induced resistance to plant diseases. Modified from Vallad and Goodman (2006) by Heather Darby.