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

Marigolds are one of the most popular annual ornamental plants; both, the short-staturecultivars(TagetespatulaL.)andthetallercultivars(T.erectaL.)areusedas 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 (ECw )o f 2, 4, 6, 8, and 10 dSm -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 4d Sm -1 water. However, the number of flowering shoots and the diameter and number of flowers were not significantly affected until the ECw exceeded 8 dSm -1 . Growth of 'Flagstaff' and 'Yellow Climax' also decreased as ECw increased. Shoot DW of the tall cultivars decreased by 30% and 24%, respectively, in response to the 4 dSm -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 ECw exceeded 8 dSm -1 . Salinity tended to reduce internode elongation, resulting in attractive plants. Compactness was not increased as a result of a decrease in DW, resultingin attractive plants,whichshowgreat promiseasbeddingor landscapeplants in salt-affected sites provided that the pH of the soil solutions remains acidic. Under our experimental conditions in the sand tank system, the ECw 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 (ECe), our salinity treatments may be estimated as 0.91, 1.82. 2.73, 3.64, and 4.55 dSm -1 . Thus, the threshold ECw at which marigold cultivars exhibited acceptable growth, 8 dSm -1 , would be equivalent to ECe of 3.64 dSm -1 .