Feasibility of growing halophyte "agretti" (Salsola soda) as an alternative boron-tolerant food crop in unproductive boron-laden regions

Authors: ZHU, HUI - Chinese Academy Of Sciences; CHENG, RUI - Chinese Academy Of Sciences; Banuelos, Gary; CENTOFANTI, TIZIANA - Central European University

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2019
Publication Date: 10/17/2019
Citation: Zhu, H., Cheng, R., Banuelos, G.S., Centofanti, T. 2019. Feasibility of growing halophyte "agretti" (Salsola soda) as an alternative boron-tolerant food crop in unproductive boron-laden regions. Plant and Soil. 445:323-334. https://doi.org/10.1007/s11104-019-04280-x.
DOI: https://doi.org/10.1007/s11104-019-04280-x

Interpretive Summary: Alternative crops are needed to face current threats to irrigated agricultural production in central California where water scarcity, recurrent droughts, and decreases in soil quality with excessive boron (B) threaten productivity and food security. To maintain agricultural production under such conditions, new B-tolerant crops must be identified that can be grown with poor-quality waters high in B. One potential new crop is agretti, a halophyte originating from the Mediterranean basin, that grows in saline coastal regions of Italy. In these two greenhouse studies, the B tolerance of agretti was evaluated in soils irrigated with varied levels of B and in hydroponic solutions with increasing B. In both experiments, agretti tolerated the high range of B exposure. Boron toxicity symptoms, e.g., leaf necrosis, were not observed, nor were biomass yields decreased. For typical agronomic crops grown under such high B levels, survival rate would likely be nonexistent, especially by the high accumulation of B by plants with increasing B treatments. Generally, plants under stress respond by increasing their total phenolic production. In these studies, we observed inexplicable results in regards to total phenolic concentrations in agretti. The level increased when agretti was irrigated with B-laden waters and decreased when grown hydroponically in extremely high B solutions. In this regard, more research is needed to study the different responses observed with using total phenolics as a stress indicator in agretti production. We demonstrated, however, that agretti is a B-tolerant crop when irrigated with or grown in high-B waters. Our results suggest that field studies are needed to validate growing agretti under field conditions using the typical high B waters present in the west side of central California.

Technical Abstract: Over 200,000 ha of the western central California exhibit naturally high levels of salinity and boron (B). Due to the natural occurrence of salts and in conjunction with intensive irrigation practice on such poor-quality soils, drainage effluent originating from San Joaquin Valley (SJV) farmland contains high levels of soluble salts, i.e., salinity levels (EC) sometimes as high as 15.2 mS cm-1 and soluble B concentrations as high as 14.5 mg L-1. Excessive B can pose toxicity to many plant species, and consequently this B intolerance restricts planting of typical crops in boron-laden regions. In these greenhouse pot and hydroponic studies, we evaluated the B tolerance of an alternative crop, agretti (Salsola soda), irrigated with water containing the following B concentrations: 0.25 (control), 3.5, 7.0, 10.0, and 17 mg B L-1. In the hydroponic study, agretti transplants were grown in waters containing the designated B concentrations (i.e., 0.25 (control), 10, 20, 50, 100, and 200 mg B L-1). In addition to measuring the accumulation of B in plant tissues, total phenolics were analyzed to determine if the plants were excessively stressed, as indicated by excessive phenolic production. In the soil pot experiment, there were no significant differences in dry biomass of leaves, stems and roots among the five B irrigation treatments. Agretti exhibited no B toxicity symptoms for any of the five B irrigation treatments throughout the entire experiment. The highest B concentration observed in the pot experiment was 635.6±30.9 mg kg-1 in leaves from plants exposed to 17.0 mg B L-1 treatment. In the hydroponic study, the average leaf tissue B concentrations of S. soda ranged 1421±141 mg kg-1 and 2596±374 mg kg-1 on Day 7 and Day 14, respectively, with 200 mg B L-1 treatment. A complicated response of total phenolic content in S. soda to high B treatments was observed in this study. In the pot experiment, the total phenolic content generally increased in leaves with increasing B treatments, while our hydroponic study showed that increasing B treatments generally decreased the total phenolic content in leaves of S. soda on Day 7 in the hydroponic experiment, especially under highest B treatments (i.e., 50, 100 and 200 mg B L-1). This observation indicates that total phenolics are produced as a response to B stress only within a certain B level. When the B stress becomes too strong, then S. soda will apparently not contribute physiological energy related to the syntheses of total phenolics. More research is needed to evaluate the role of total phenolics as an indicator of boron-related stress in agretti. We demonstrated, however, that S. soda is a boron-tolerant crop under our test conditions, which means that the crop can be potentially grown as a viable alternative food crop for unproductive boron-laden areas within the western SJV of Central California.