Effects of saline irrigation on phytoregulator-treated chrysanthemum plants

The effects of irrigation with saline water (1.5 dS/m and 5 dS/m) and plant growth regulators (paclobutrazol at 25 ppm; ethephon at 500 ppm; control [no phytoregulator]) applied as a spray on the development of potted native chrysanthemum (Chrysanthemum coronarium) were investigated. A two-way ANOVA was established to study the statistical significance of the two factors (salinity and phytoregulator) and their interaction. Our results indicate that C. coronarium was moderately tolerant to salinity, although the number of inflorescences was much reduced in the salt stressed plants. It seems that the plant developed salinity tolerance mechanisms which involved slowing the transport of Na+ and Cl- in the stem and including toxic ions in the cytoplasm. Salinity symptoms were more pronounced in the lower leaves (leaf burn and necrosis), which accumulated more salt ions. Paclobutrazol was effective in reducing growth and made plants more suitable for growing in pots. In contrast, ethephon had little effect as a growth regulator, reduced the leaf chlorophyll content and seriously damaged flowering. Salinity reduced the plant photosynthetic capacity to reduce the maximum quantum yield of PSII (Fv/Fm), and paclobutrazol improved salinity resistance, thus preventing a decrease in Fv/Fm. The PSII protection mechanism of paclobutrazol in salinated C. coronarium plants appears to be related to reducing the Na+ and Cl- contents in leaf and root, increasing the K+ content in middle leaves and preserving leaf chlorophyll levels.