W. Zhang et al., COMPOST-INDUCED SYSTEMIC ACQUIRED-RESISTANCE IN CUCUMBER TO PYTHIUM ROOT-ROT AND ANTHRACNOSE, Phytopathology, 86(10), 1996, pp. 1066-1070
Pythium root and stem rots cause problems in production of greenhouse
and nursery crops. Composts, however, can provide biological control o
f these diseases. We planted and germinated cucumber (Cucumis sativus
'Straight Eight') seeds in compost-amended (spruce or pine bark compos
ts) or in highly decomposed sphagnum peat (H-4 on the von Post decompo
sition scale) mixes suppressive and conducive to Pythium root rot, res
pectively. Two-week-old seedlings were transplanted, using the split-r
oot technique, into the compost-amended mixes and the peat mix. Split-
root pairings were peat/compost, peat/peat, and compost/compost. Only
one side of the split roots was grown in potting mix infested with Pyt
hium ultimum and P. aphanidermatum. Root rot in the infested mix, aver
aged across all spit-root pairings, was significantly (P less than or
equal to 0.05) less severe and mean root dry weights were significantl
y (P less than or equal to 0.05) higher in plants germinated in the co
mpost-amended mixes than in the peat mix. Also, root rot in the infest
ed pear mix was significantly less severe on roots paired with the com
post-amended mixes than those paired with the peat mix. Plants grown f
rom seed in the compost-amended mixes or the peat mix also were tested
for resistance to anthracnose. Three weeks after planting, anthracnos
e on the second leaf of cucumber 'Straight Eight' inoculated with Coll
etotrichum orbiculare was significantly less severe (P less than or eq
ual to 0.05) on plants grown in the compost-amended mixes than in the
peat mix. Peroxidase activity, a putative marker of systemic acquired
resistance (SAR) in cucumber, was significantly (P less than or equal
to 0.05) enhanced in plants grown in the compost-amended mixes compare
d to the peat mix. However, the activity of a peroxidase isozyme in th
e second leaf of cucumber plants was greater when plants were grown in
compost as well as after prior inoculation with C. orbiculare than if
grown in peat and with or without prior inoculation. The interaction
of compost and the pathogen appeared critical for rapid activation of
SAR-associated gene expression in cucumber plants.