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ARS Home » Pacific West Area » Riverside, California » Agricultural Water Efficiency and Salinity Research Unit » Research » Research Project #435766

Research Project: Linking Performance of Almond Rootstocks to Underlying Physiological and Genetic Determinants of Salinity Tolerance

Location: Agricultural Water Efficiency and Salinity Research Unit

Project Number: 2036-13210-012-04-T
Project Type: Trust Fund Cooperative Agreement

Start Date: Oct 1, 2018
End Date: Jul 31, 2019

Objective:
Objective 1. Evaluation of selected almond rootstocks for their effects on scion performance, under salinity stress and identification of underlying genetic components. Objective 2. Using priming as an alternate approach to mitigate salinity stress in almond rootstocks. Objective 3. Functional validation of almond genes involved in salt tolerance using model plants.

Approach:
Objective 1: We previously evaluated 16 ungrafted rootstocks and learned that Na+ and Cl- are critical for tissue toxicity. Based on biochemical and genetic analyses, we selected the 5 best salt-tolerant rootstocks. This year we will use grafted plants to evaluate if genetic control is similar in grafted and ungrafted plants. Additionally, in our 2-year experiments we noticed that tissue Zn concentration increases with salinity. Recently, Zn was shown to improve photosynthetic performance in almonds under salinity (Amiri, et al., 2016). Hence, this year we will add supplemental Zn to evaluate its effect on salinity tolerance in almonds. Plants of 5 selected rootstocks, grafted with Nonpareil and Monterey will be transplanted into pots in 3 replications, with 3 plants/ replication. Plants will be field evaluated under three irrigation waters: Control (EC 1.4), Saline (EC 3.5); Saline + 20mg Zn/kg of soil, with 270 total plants (5 rootstocks, 2 scions, 3 water types, 3 replications, 3 plants/ replication). Plants will be treated for 8 weeks and samples will be taken to determine leaf ion composition. Based on the results from Year 1 and Year 2, we selected 12 genes (8 for Na+ transport and 4 for Cl- transport) that play significant role in salinity tolerance. Expression analysis will be carried out for scion leaf tissue and for rootstock root tissue. This analysis will increase our understanding about possible interactions between rootstocks and scions under salinity stress. Objective 2: “Priming” (exposing plants to chemicals before applying stress) is one of the alternate approaches that succeeded in mitigating salinity in many crop, These chemicals include growth regulating hormones, signal molecules and other compounds . We will use the same rootstock/scion (5 rootstocks and 2 scions) combinations as mentioned in objective 1. We intend to use primers such as H2S, melatonin, and salicylic acid (SA). The plants will be primed through foliar application or irrigation water before salinity treatments, depending on the established protocol. Two different levels of salinity: control salinity (EC 1.4 dS m-1) and EC 3.5 dS m-1, will be used. We plan to have 5 rootstocks, 2 scions, 2 salinity treatments, 4 priming treatments, 3 replications, 3 plants/ replication totaling 720 plants. Plants will be allowed to grow for 4-8 weeks after salinity treatment before sampling tissues. Objective 3: Results from the first two years of genetic analyses identified almond genes important for salt tolerance. We selected the genes HKT1 and SOS1 for functional validation. The Arabidopsis mutants for these genes are commercially available. The respective almond gene will be expressed under the dual CaMV 35S promoter (2x-35S) and the native promoter of the gene in Arabidopsis mutants. Transgenic lines will be developed using Agrobacterium mediated floral dip transformation method, by dipping the mutant inflorescence in A. tumefaciens carrying the target gene. The developed transgenic lines will be used to study salt stress tolerance along with the mutants and wildtype Arabidopsis lines.