Water use, stomatal conductance, electron micro-
scopy, and histochemical analyses demonstrate that
foliar application of chitosan reduces transpiration of
pepper plants through partial or full closure of stomata.
Reduced water use was found under growth-chamber
as well as field conditions. Compared to the opti-
mal environmental conditions in the growth-chamber
study, the pepper plants in the field experiment were
exposed to more variable, and more realistic, meteo-
rological and soil conditions. The consistent findings
with respect to reduced water use and increased
biomass-to-water ratio through foliar chitosan appli-
cation are encouraging. The water conservation for
pepper plants was considerable, and of the same order
of magnitude reported for wheat, barley, and tomato
treated with ABA analogs (Rademacher et al., 1987;
Rademacher et al., 1989). Reduction in yield and
biomass from chitosan-induced closure of stomata
were not statistically significant.
Evapotranspiration modeled using the Penman-
Monteith equation showed good agreement between
measured and calculated evapotranspiration for con-
trol plants. For chitosan-treated plants, simulation
results indicate a three fold increase of stomatal resis-
tance as compared to control plants (
r
s
D
210s m
−
1
versus 70 s m
−
1
). A stomatal resistance of 210 s m
−
1
found by the evapotranspiration simulations corrobo-
rates the interpretation of partial closure of stomata;
for completely closed stomata the resistance would
be about 840 s m
−
1
(Allen et al., 1998).
Chitosan is commercially prepared as a waste
byproduct from the shells of shrimp, crab, and lobster
(Muzzarelli, 1977), and as such, its use as an anti-
transpirant in crop production seems economically
feasible. In view of the increasing demand for limited
resource water, the possibility to reduce crop transpi-
ration, particularly in irrigated agriculture, would be
advantageous.