Salt Tolerance and Growth of 13 Avocado Rootstocks Related Best to Chloride Uptake

in HortScience

Avocado (Persea americana Mill.) is one of the most salt-sensitive crops and one of the highest value crops per acre. In the United States, avocados are grown primarily in California, in regions experiencing both scarcity of freshwater and salinization of available water supplies. Thus, our objectives were to evaluate avocado rootstocks for salt tolerance and evaluate the relationship between leaf ion concentrations, trunk diameter, leaf burn, and fruit yield. Our field experiment evaluated the salt tolerance of the Hass scion grafted onto 13 different avocado rootstocks using the Brokaw clonal rootstock technique. The experiment consisted of 156 trees arranged in a randomized complete block design with six replications of each saline [electrical conductivity (EC) = 1.5 dS·m–1, Cl = 4.94 mmol·L–1] and nonsaline (EC= 0.65 dS·m–1, Cl = 0.73 mmol·L–1) irrigation water treatment. We collected soil samples and leaves, then analyzed them for major ions. The rootstocks R0.06, R0.07, PP14, and R0.17, which had high concentrations of Cl and Na in the leaves, were the least salt tolerant, with 100% mortality in the rows irrigated with saline water for 23 months. The rootstocks R0.05, PP40, R0.18, and Dusa, which had low concentrations of Cl ions in the fully expanded leaves, were least affected by salinity, and these rootstocks exhibited the greatest yields, largest trunk diameters, and greatest survival percentages in the saline treatment. Yield and growth parameters correlated well with leaf Cl concentration, but not Na, indicating that salt damage in avocado is primarily a result of Cl ion toxicity. Under arid inland environments, no variety performed satisfactorily when irrigated with an EC = 1.5 dS·m–1 water (Cl = 4.94 mmol·L–1). However, the more tolerant varieties survived at soil salinity levels that would apparently be fatal to varieties reported earlier in the literature.

Contributor Notes

We thank the California Avocado Commission and Agricultural Experiment Station for funding this project.

We acknowledge Westfalia Technological Services (WTS) for granting us testing rights to their propriety rootstock selections and Brokaw Nursery for providing us with the WTS test trees.

Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

Corresponding author. E-mail: Nydia.Celis@ars.usda.gov.

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Article Figures

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    Mean electrical conductivity of soil extracts (ECe) from samples collected (A) in Dec. 2013 before the initiation of the experiment and (B) in Aug. 2014. Error bars represent ±2σ. Each point represents five repetitions.

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    Leaf burn percentage for each rootstock in rows irrigated with an electrical conductivity (EC) of 0.65 dS·m–1 and an EC of 1.5 dS·m–1 in 2014. Uppercase letters designate differences among varieties in the saline treatment. There were no significant differences among varieties in the control. Rootstocks with different letters signify significant differences according to the Tukey-Kramer test at α = 0.05. As a result of differences in survival, the number of samples varied from five to nine in 2014.

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    Dusa leaves in (A) a control row with an electrical conductivity of irrigation water (ECw) = 0.65 dS·m–1 and in (B) a salt-treated row with ECw = 1.5 dS·m–1. R0.07 leaves in (C) a control row with ECw = 0.65 dS·m–1 and in (D)a salt-treated row with ECw = 1.5 dS·m–1 in 2015.

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    Avocado survival percentage by rootstock in saline treatment in 2015. After being irrigated with the saline water for 20 months, only seven varieties survived.

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    Average fruit yield per tree for each rootstock irrigated with an electrical conductivity (EC) of 0.65 dS·m–1 and an EC of 1.5 dS·m–1, harvested Feb. 2014. Uppercase letters designate differences among varieties in the saline treatment. There were no significant differences among varieties in the control. Rootstocks with different letters signify significant differences according to the Tukey-Kramer test at α = 0.05. As a result of differences in survival, the number of samples varied from five to nine in 2014.

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    Yield based on the average total fruit weight per tree for each rootstock in the control treatment irrigated with an electrical conductivity (EC) of 0.65 dS·m–1 and a saline treatment irrigated with an EC of 1.5 dS·m–1, harvested in (A) Feb. 2015 and (B) Feb. 2016. There were no significant differences among varieties in the saline treatment and among varieties in the control in 2015. In 2016, rootstocks with different letters signify significant differences among varieties in the control treatment according to the Tukey-Kramer test at α = 0.05. As a result of differences in survival, the number of samples varied from one to nine in 2015 and from zero to nine in 2016.

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    Relative yield is expressed as the ratio of the saline yield (1.5 dS·m–1) divided by the control yield (0.65 dS·m–1) for the harvest in (A) 2015 and in (B) 2016.

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    Average rootstock trunk diameter in 2015 in the control and saline treatments. Uppercase letters designate differences among varieties in the saline treatment; lowercase letters indicate differences among varieties in the control. Rootstocks with different letters signify significant differences according to the Tukey-Kramer test at α = 0.05.

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    Leaf ion concentrations for different avocado rootstocks collected in Oct. 2013. Average (A) Na concentration in the control [electrical conductivity of irrigation water (ECw) = 0.65 dS·m–1] in the leaves per rootstock and (B) Cl concentration in the control (ECw = 0.65·m–1) in leaves per rootstock. There were no significant differences among varieties in Na concentration in 2013. Rootstocks with different letters signify significant differences according to the Tukey-Kramer test at α = 0.05.

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    Average ion concentration in leaves of individual rootstocks collected in Oct. 2014 for (A) Na in the control, (B) Na in the saline treatment, (C) Cl in the control, and (D) Cl in the saline treatment. *Only one tree remained and was not used in the statistical analysis. The two lines indicate leaf Cl concentration above which there is expected to be visual leaf injury ranging from slight to severe. Uppercase letters designate differences among varieties in the saline treatment; lowercase letters indicate differences among varieties in the control. Rootstocks with different letters signify significant differences according to the Tukey-Kramer test at α = 0.05.

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    Average concentration in leaves per rootstock collected in Oct. 2015 for (A) Na and (B) Cl. Average root concentrations for rootstocks collected in Mar. 2016 for (C) Na and (D) Cl. *Only one tree remained and was not used in the statistical analysis. There were no significant differences in Na concentration among varieties in the saline treatment of the avocado roots in 2016. Rootstocks with different letters signify significant differences according to the Tukey-Kramer test at α = 0.05. Uppercase letters designate differences among varieties in the saline treatment; lowercase letters indicate differences among varieties in the control. The missing samples (saline treatment) are rootstocks with trees that died before we sampled in 2015.

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    Average avocado trunk diameter vs. Cl concentrations in leaves in 2015. Open circles denote those in the saline treatment; closed circles denote those in the control treatment

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    Average fruit number vs. leaf (A) Na concentration and (B) Cl concentration for varieties sampled in 2015. Open circles denote those in the saline treatment; closed circles denote those in the control treatment.

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