V. Orbovic et al., Foliar-applied surfactants and urea temporarily reduced carbon assimilation of grapefruit leaves, J AM S HORT, 126(4), 2001, pp. 486-490
Citations number
31
Categorie Soggetti
Plant Sciences
Journal title
JOURNAL OF THE AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE
Although urea can be an effective adjuvant to foliar sprays, we examined ef
fects of additional surfactants on urea penetration through leaf cuticles a
long with the effect of urea with and without surfactants on net gas exchan
ge of leaves of 'Marsh' grapefruit (Citrus paradisi Macf.) trees budded to
Carrizo citrange (C. sinensis IL. Osbeck x Poncirus trifoliata L.. Raf,) ro
otstock. various combinations of urea, a nonionic surfactant (X-77), and an
organosilicone surfactant (L-77), were applied to grapefruit leaves and al
so to isolated adaxial cuticles. When compared to X-77, L-77 exhibited supe
rior surfactant features with smaller contact angles of droplets deposited
on a teflon slide. Both L-77 and X-77 initially increased penetration rate
of urea through cuticles, but the effect of X-77 was sustained for a longer
period of time. The total amount of urea which penetrated within a 4-day p
eriod, however, was similar after addition of either surfactant, Solutions
of either urea, urea + L-77, urea + X-77, or L-77 alone decreased net assim
ilation of CO2 (A(CO2)) for 4 to 24 hours after spraying onto grapefruit le
aves, A solution of X-77 alone had no effect on A(CO2) over the 4-day perio
d. Although reductions in A,,, were similar following sprays of urea formul
ated with two different surfactants, the underlying mechanisms may not have
been the same. For the urea + X-77 treatment, X-77 increased the inhibitor
y effects of urea on A(CO2) indirectly by increasing penetration of urea in
to Leaves. For the urea + L-77 formulation, effects of L-77 on A(CO2) were
2-fold, direct by inhibiting A(CO2) and indirect by increasing urea penetra
tion, One hour after application, scanning electron microscopy (SEM) of lea
f surfaces treated with X-77 revealed that they were heavily coated with th
e residue of the surfactant, whereas leaves treated with L-77 looked simila
r to nontreated leaves with no apparent residues on their surfaces. The amo
unt of X-77 residue on the leaves was lower 24 hours after application than
after 1 hour as observed by SEM.