The disposal of dry olive-mill residue, the
waste product from olive oil production, is a serious
environmental issue. Dry olive-mill residue, being rich in
organic and inorganic nutrients, could be used as fertilizer;
however, it contains phenolic compounds that can inhibit
plant growth. In order to clarify whether bioremediation of
this waste could be a valuable strategy for its reuse, the
effect of aqueous extract of dry olive-mill residue,
untreated or bioremediated by the saprobe fungi
Coriolopsis
rigida
and
Penicillium chrysogenum
-10, has been
analyzed in relation to some physiological parameters of
tomato plants. The data show that aqueous dry olive-mill
residue significantly reduces the biomass of roots and
shoots. In particular, it causes a dramatic reduction in root
length, area, and volume as well as in the number of root
tips. At an early stage, aqueous dry olive-mill residue also
reduces the content of chlorophyll
a and
b and the efficiency
of PS II. The inhibition of growth seems to be due to
the increase in phenolic compounds that induce oxidative
stress. Interestingly, when plants are treated with aqueous
dry olive-mill residue bioremediated by saprobe fungi a
decrease in phenolic content and an alleviation of oxidative
stress occur. In conclusion, the results show that bioremediation
of aqueous dry olive-mill residue is a useful tool
to remove most of the inhibiting effects of this waste on
plant growth.
