Date of Graduation

12-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Andy Pereira

Committee Member

Richard Esten Mason

Second Committee Member

Paul A. Counce

Third Committee Member

Lisa Wood

Fourth Committee Member

Ainong Shi

Keywords

Breeding, Drought, Genetics, Genomics, QTL, Rice

Abstract

Rice (Oryza sativa L.) is the staple food for a majority of the world’s population, and uses 30% of the global fresh water during its life cycle. Drought at the reproductive stage is the most important abiotic stress factor limiting grain yield. The United States is the third largest exporter of rice, and Arkansas is the top rice-producing state. The Arkansas rice-growing region in the Lower Mississippi belt is among the 10 areas with the highest risk of water scarcity. Adapted U.S. rice cultivars were screened for drought resistant (DR) traits to find sources for breeding U.S. rice cultivars for a water saving agricultural system. A recombinant inbred line (RIL) population, derived from varieties Kaybonnet (DR) and ZHE733 (drought sensitive), termed K/Z RILs was chosen for genetic analysis of DR traits. The objectives of this research were to 1) analyze the phenotypic and grain yield components of the K/Z RIL rice population for drought-resistance-related traits, 2) evaluate the Abscisic Acid (ABA) response of the K/Z RIL rice population on root architectural traits in relation to drought stress resistance, 3) screen polymorphic molecular markers to identify genes linked to productivity traits of grain yield under drought stress, measured by number of filled grain per panicle using bulk segregant analysis (BSA), and 4) identify QTLs and candidate genes in the K/Z RIL population for drought resistance associated with vegetative morphological traits, grain yield components under drought stress and well-watered conditions, and root architectural traits related to ABA response. The RIL population was screened in the field at Fayetteville (AR) by controlled drought stress (DS) treatment at the reproductive stage, and the effect of DS quantified by measuring drought-related traits. ABA sensitivity was quantified by measuring root architectural traits at the V3 stage. Based on the filled grain per panicle number, 13.13% of K/Z RIL population and parent Kaybonnet were highly drought resistant, while 75.75% of RILs and parent ZHE733 were drought sensitive. Under ABA conditions, Kaybonnet and 48 drought resistant lines exhibit ABA sensitivity, implying regulation of osmotic stress tolerance via ABA-mediated cell signaling. Based on BSA screening, 13 polymorphic markers potentially linked to DR traits were identified. QTL analysis was performed with 4133 SNPs markers by using QTL IciMapping. A total of 213 QTLs and 628 candidate genes within the QTL regions were identified for drought-related traits. The RT-qPCR analysis of the candidate genes revealed that a high number of drought resistance genes were up-regulated in Kaybonnet as the drought-resistant parent. Information from this research will serve an important step towards improvement of adapted Arkansas rice cultivars for higher grain production under DS conditions.

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