Timing of salicylic acid application affects the response of maize (Zea mays L.) hybrids to salinity stress
The effect of genotype and timing of salicylic acid (SA) application on response of
maize to salinity stress has been investigated. Single and triple hybrids (SH and TH,
respectively) of maize were grown hydroponically and sprayed with 1 mM SA one
week either before or after application of 150 mM NaCl. The effect of salinity on
maize performance was stronger than that of SA regime or maize hybrid. The effect
of treatments was most evident on root biomass but least evident on number of
leaves. The genotypic difference in shoot biomass was vague in non-amended
plants but emerged, in favor of the SH, in SA-amended plants. The more
vigorous SH exhibited less pigment content (particularly the post-amended
plants) and less salt resistance, with preferential native allocation of plant
biomass to root compared with the TH. Salicylic acid, particularly the post
amendment under salinity stress, was stressful to maize foliage but beneficial to
roots. Salinity reduced root growth to a greater extent than shoot growth, with
the production of wider and shorter blades; but SA led to the opposite effect.
The effect of salinity on leaf chlorophyll a concentration was non-significant in
the SH, versus an increase (in the post-amended plants) or a decrease (in the
non-amended and pre-amended plants) of the TH. Sub-stomatal CO2
concentration (Ci) was higher in the SH than the TH, particularly in the post-
amended plants. Both salinity and SA induced stomatal closure, reduced rates of
transpiration and photosynthesis but increased Ci, with variable magnitudes in
the two hybrids. Salinity increased concentrations of soluble sugars, proline and
Naþ in the leaves, decreased Kþ and phenolics concentrations but marginally
affected protein concentration with limited effect of SA, which varied according
to time of application. The further stressing effect of SA post-amendment to ltstressed
maize can be related to reduced stomatal conductance and concentrations
of phenolics, proline and Kþ but increased Naþ concentration of the shoot,
particularly of the TH.