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Title: Response of ornamental sunflower cultivars ‘Sunbeam’ and ‘Moonbright’ to irrigation with saline wastewaters

item Grieve, Catherine
item Poss, James

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2009
Publication Date: 1/8/2010
Citation: Grieve, C.M., Poss, J.A. 2010. Response of ornamental sunflower cultivars ‘Sunbeam’ and ‘Moonbright’ to irrigation with saline wastewaters. Journal of Plant Nutrition. 33(11):1579-1592.

Interpretive Summary: Competition between agricultural and urban users for high-quality water supplies has increased as the population has increased. One environmentally-sound approach to the conservation of these dwindling water resources is the reuse of degraded, often saline, wastewaters for crop production. Growers of high value cut flower crops have traditionally used high-quality waters in order to salinity-induced reduction in yield and quality, and the resultant economic losses, due to salinity. However, little quantitative information is available in the literature that would guide growers in the selection of cut flower species which could be produced with recycled, saline waters. This report describes the response of two commercially important sunflower cultivars to irrigation with saline waters differing in ion composition. Solutions were prepared to simulate saline drainage effluents commonly present in two inland valley regions of California, namely (1) the San Joaquin Valley of the Central Valley and (2) the southern Coachella and Imperial Valleys. Ion compositions of available irrigation waters in those areas are very different. ‘Sunbeam’ and ‘Moonbright’ sunflowers were grown in greenhouse sand tanks. Five salinity levels were imposed with electrical conductivities of 2, 5, 10, 15, and 20 dS m-1. Flower diameter was not reduced by salinity. Length of the flowering stems declined from about 5' to 3' as salinity increased. Since growth regulators are often used to control excessive stem length in sunflower, the application of salinity would reduce costs of sunflower production by avoiding the use of chemical growth inhibitors. Both cultivars proved to be moderately salt tolerant. The enhanced ability of sunflower to withstand the challenge of salt stress appeared to be associated with its ability to exclude potentially toxic concentrations of sodium from leaf tissue. From this greenhouse study, we conclude that moderately saline irrigation waters can be used in the production of marketable ornamental sunflowers, thus conserving significant quantities of high quality waters. This research will benefit growers, farmers and those interested in sunflower cultivars.

Technical 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 Na+ and SO42- and (2) Imperial and Coachella Valleys (ICV) where tailwaters are predominately Na+ and Cl-. Five salinity treatments of each water composition were imposed on 10-day-old seedlings each replicated three times. Electrical conductivities (EC) of the irrigation waters were 2, 5, 10, 15, and 20 dS m-1. Plant heights were determined weekly. 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. Stem length decreased significantly as salinity increased. Mineral ion concentrations in upper and lower stems, upper and lower leaves were determined. Even at salinities as high as 20 dS m-1, Na+ was effectively limited in the upper portions of the stem and preferentially partitioned to the lower leaf and stem tissue. Potassium-sodium selectivity coefficients were, as a result, unusually high. 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. Both ornamental sunflower cultivars proved to be good candidates for production of marketable flowering stems using moderately saline wastewaters