RESPONSE OF ORNAMENTAL SUNFLOWER CULTIVARS ‘SUNBEAM’ AND ‘MOONBRIGHT’ TO IRRIGATION WITH SALINE WASTEWATERS

Abstract

To explore the possibility that saline wastewaters may be used to grow commercially acceptable floriculture crops, a study was initiated to determine the effects of salinity on two pollen-free cultivars of ornamental sunflower (Helianthus annuus L.). ‘Moonbright’ and ‘Sunbeam’ were grown in greenhouse sand cultures irrigated with waters prepared to simulate wastewaters commonly present in two inland valley regions of California: 1) San Joaquin Valley (SJV) where saline-sodic drainage waters are dominated by sodium (Na⁺) and sulfate (SO ²⁻ ₄ ) and 2) Coachella Valley (CV) where major ions in tailwaters are Na⁺, chloride (Cl⁻), SO ²⁻ ₄ , magnesium (Mg²⁺), calcium (Ca²⁺), predominating in that order. Ten-day-old seedlings were subjected to five salinity treatments of each water composition, each replicated three times. Electrical conductivities (EC) of the irrigation waters were 2.5, 5, 10, 15, and 20 dS·m⁻¹. Flowering stems were harvested when about 75% of the ray flowers were nearly horizontal. Stem length and fresh weight, flower and stem diameter were measured. Mineral ion concentrations in upper and lower stems, upper and lower leaves were determined. Sodium was excluded from the young tissues in the upper portions of the shoot and retained in the basal stem tissue. Inasmuch as sunflower is also a strong potassium (K)-accumulator, K⁺/Na⁺ selectivity coefficients were unusually high in the younger shoot organs. Despite a five-fold increase in substrate Ca²⁺ in both solutions, shoot-Ca decreased as salinity increased and this cation was retained in the older leaves. A few of the lower leaves of plants irrigated with ICV waters at EC = 10 dS·m⁻¹ and higher, exhibited necrotic margins which were undoubtedly caused by high concentrations of Cl⁻ in the tissues. Flowering stems produced in all treatments met florist quality standards in terms of diameters for stems (0.5 to 1.5 cm) and blooms (8 to 15 cm). Across treatments, stem lengths ranged from 60 to 175 cm. Both ornamental sunflower cultivars proved to be good candidates for production of marketable flowering stems using moderately saline wastewaters.

Keywords:

• floriculture
• ion relations
• ion selectivity
• salinity
• sand cultures
• water reuse

ACKNOWLEDGMENTS

The authors are indebted to Phyllis Nash for statistical analyses and to Donald A. Layfield for mineral ion analyses. John Draper and Doug Diaz provided excellent technical assistance. We thank Sakata Seed America, Inc., Morgan Hill, CA for donating seed for the study. Mention of company names or products is for the benefit of the reader and does not imply endorsements, guarantee, or preferential treatment by the USDA or its agents.

This article not subject to US copyright law.

Notes

^†Irrigation water compositions prepared to simulate saline tailwaters commonly present in the Coachella Valley of California.

^‡Irrigation water compositions prepared to simulate saline drainage waters commonly present in the San Joaquin Valley of California.

^† Within columns and growth parameters, means followed by a different letter are significantly different at the 0.05 probability level according to Tukey's studentized range test. Values are the means of 30 observations.

^† Within columns and cultivars, means followed by a different letter are significantly different at the 0.05 probability level according to Turkey's studentized range test. Values are the means of three replications.

^†Within columns and solution type, means followed by a different letter are significantly different at the 0.05 probability level according to Tukey's studentized range test. Values are the means of 3 replications.

^†Within columns and solution type, means followed by a different letter are significantly different at the 0.05 probability level according to Tukey's studentized range test. Values are the means of three replications.