Waterlogging Impairs Quality and Flower Longevity in Zinnia elegans Jacq. cv. ‘Dreamland’

Waterlogging may be imposed by intense rainfall, excessive irrigation, or poor drainage. In Iran, besides the northern parts of the country with high precipitation, waterlogging may occur due to over-irrigation, or inadequate drainage especially for landscape use of ornamentals. In this study, the joint effects of growth stage (four-leaf stage, full growth and start flowering), at which waterlogging is encountered, and the duration of the episode (0, 6, 12, and 24 h) on flowering induction, plant growth, and external quality were investigated in zinnia (Zinnia elegans Jacq.). Waterlogging generally downgraded visually-perceived quality (stem length, flower size, leaf coloration), increased the risk of buckling (lower stem strength) and shortened flower bud longevity. Waterlogging adversely affected biomass accumulation, through decreases in both light capture (leaf area), and photosynthesis. Besides disturbed water relations, waterlogged plants underwent oxidative damage as indicated by reduced chlorophyll content, and elevated lipid peroxidation level. Waterlogging was further associated with increased activity of antioxidant enzymes (ascorbate peroxidase, peroxidase). The waterlogging-induced effects were generally more prominent as waterlogging duration increased, and the growth stage of application was less advanced, so that the plants waterlogged in four-leaf stage for 24 h showed the most negative effects and their plant dry weight reduced to 75 percent of that in controls. In conclusion, the obtained results offer a quantitative analysis of how both growth stage and duration determine the waterlogging-induced injury in zinnia.