Genetic diversity and candidate gene selection for drought tolerance in perennial ryegrass
Abstract
Perennial ryegrass (Lolium perenne L.) is one of the most important cool-season grass species used for forage and turf industries in temperate regions. The improvement of drought tolerance will significantly benefit the sustainable production of perennial ryegrass. The objectives of this study were to: (1) determine the ploidy level and DNA content of global perennial ryegrass germplasm accessions using flow cytometry; (2) analyze genetic diversity in a globally distributed collection of perennial ryegrass accessions with 99 simple sequence repeat (SSR) markers; (3) examine the expression patterns of the candidate genes involved in drought tolerance and responses in both drought-tolerant and -susceptible accessions of perennial ryegrass. The DNA content and ploidy level of 194 accessions from the USDA National Plant Germplasm System (NPGS) (including the commercial cultivar, Affinity) and six commercial cultivars (Brightstar SLT, Catalina II, Divine, Inspire, Manhattan 4, and Silver Dollar) were determined. Among the 200 germplasm accessions, 194 diploids and 6 tetraploids were identified. The average DNA content was 5.60 pg/2C and 11.45 pg/2C for the diploid and tetraploid, respectively. A total of 99 simple sequence repeat (SSR) markers were used to examine genetic diversity of 190 germplasm accessions. The cluster analysis using the unweighted pair-group method arithmetic average (UPGMA) showed the genetic diversity of commercial cultivars was limited. The principal component analysis (PCA) indicated that the first two principal components were significant and explained 7.7% and 2.6% of the total variation, respectively. The transcript levels of HARDY, plasma membrane intrinsic protein (PIP1;4) and ion superoxide dismutase (FeSOD ) were generally higher in one or two drought-tolerant accessions than in the susceptible ones. These candidate genes could be used for marker-trait association mapping of drought tolerance in perennial ryegrass. Our long-term goal is to establish a natural diploid mapping population and to associate physiological traits with genes responsible for drought tolerance. These three parts of research provide a foundation to achieve the goal.
Degree
M.S.
Advisors
Jiang, Purdue University.
Subject Area
Agronomy
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