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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Research Project #434000

Research Project: Investigating the Role of Roots in Breeding for Drought Tolerance and Nutrient Efficiency in Lettuce

Location: Crop Improvement and Protection Research

Project Number: 2038-21530-002-15-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Nov 1, 2017
End Date: Apr 30, 2020

The project aims to understand differences in drought-sensitive and drought-tolerant cultivars of lettuce by describing differences in root morphology and investigating the effects of gross root morphology on water and nutrient access. The project aims to use cutting-edge next-generation sequencing technology to study gene expression in roots exposed to different water regimes and different nutrient regimes and to correlate expression patterns with physiological and marketable traits to understand how access to nutrients can affect drought resilience, and to develop markers for marker-assisted selection for drought-tolerant cultivars. The project also aims to screen recombinant inbred lines (RIL) of cultivated lettuce and its deep-rooted wild progenitor, Lactuca serriola, to identify lines with deep taproots to incorporate new traits into breeding lines to increase water-use efficiency in lettuce.

In the first year (11/2017 – 10/2018), RIL lines will be assessed for drought tolerance. Drought-sensitive cultivars, drought-tolerant cultivars, and RIL lines will then be grown in media from which roots can be easily extracted. Plants will be grown under different water/nutrient conditions. Photosynthetic traits such as carbon assimilation, stomatal conductance, and water use efficiency will be measured. Tissue samples will be taken, and total tissue nitrogen will be analyzed by outside contractors. Root length and mass will be recorded, and gross morphological comparisons will be made among cultivars and RIL lines (all work by Postdoc). Root tissue samples will also be used for transcriptome sequencing by outside contractors. During the first half of the second year (11/2018 – 4/2019), we will analyze the transcriptome data and correlate root morphological traits and physiological traits with expression data, and thus identify genes in the root that are responsive to drought and low nitrogen conditions. Testable hypotheses will be generated from the transcriptome dataset (all work by Postdoc). During the second year (11/2018 – 10/2019), expression patterns will be confirmed using digital droplet polymerase chain reaction (PCR) and hypotheses will be tested under growth chamber and greenhouse conditions. Genes that affect root response to drought and nutrient conditions will be identified, and these will be disseminated for use in marker-assisted selection to produce new breeding lines. Early testing for enhanced drought tolerance in RIL lines, and selection with identified markers for water-use and nutrient-use efficient breeding lines will take place in the second half of the second year, and the first half of the third year (5/2019 – 4/2020). Publication and dissemination of knowledge through journals and websites will be on-going.