Salinity and Alkaline pH in Irrigation Water Affect Marigold Plants: I. Growth and Shoot Dry Weight Partitioning

Abstract

Marigolds are one of the most popular annual ornamental plants; both, the short-stature cultivars ( Tagetes patula L.) and the taller cultivars ( T. erecta L.) are used as container plants in landscape and garden settings. Tagetes erecta varieties can also make excellent cut and dried flowers for the florists' market. The present study was conducted to evaluate the response of T. patula ‘French Vanilla’ and T. erecta ‘ Flagstaff’ and ‘Yellow Climax’ to irrigation with saline water with and without pH control. Marigold plugs were transplanted into greenhouse sand tanks and established for 1 week under nonsaline conditions. Ten treatments were then applied with electrical conductivities of irrigation water (EC w ) of 2, 4, 6, 8, and 10 dS·m −1 and pH levels of 6.4 and 7.8. Growth of all three cultivars decreased in response to irrigation with saline waters at pH 6.4. Compared with the nonsaline controls, ‘French Vanilla’ exhibited a 20% to 25% decrease in plant height, leaf dry weight (DW), and shoot DW when irrigated with 4 dS·m −1 water. However, the number of flowering shoots and the diameter and number of flowers were not significantly affected until the EC w exceeded 8 dS·m −1 . Growth of ‘Flagstaff’ and ‘Yellow Climax’ also decreased as EC w increased. Shoot DW of the tall cultivars decreased by 30% and 24%, respectively, in response to the 4 dS·m −1 treatment, but additional salt stress had no further effect on DW production. Marigolds were highly sensitive to high pH. Plants irrigated with nonsaline water with pH at 7.8 exhibited a 50%, 89%, and 84% reduction in shoot DW in ‘French Vanilla’, ‘Flagstaff’, and ‘Yellow Climax’, respectively, compared with plants irrigated with water with pH 6.4. Marigold cultivars were rated as moderately tolerant to salinity because growth was affected when water EC w exceeded 8 dS·m −1 . Salinity tended to reduce internode elongation, resulting in attractive plants. Compactness was not increased as a result of a decrease in DW, resulting in attractive plants, which show great promise as bedding or landscape plants in salt-affected sites provided that the pH of the soil solutions remains acidic. Under our experimental conditions in the sand tank system, the EC w was essentially equivalent to those of the sand soil solution; however, considering that the EC of the sand soil solution is ≈2.2 times the EC of the saturated soil extract (EC e ), our salinity treatments may be estimated as 0.91, 1.82. 2.73, 3.64, and 4.55 dS·m −1 . Thus, the threshold EC w at which marigold cultivars exhibited acceptable growth, 8 dS·m −1 , would be equivalent to EC e of 3.64 dS·m −1 .